Final Report Summary - PHYS4ENTRY (Planetary Entry Integrated Models)
Executive Summary:
Executive Summary
Planetary Entry Integrated Models (Phys4Entry) is a scientific study aimed at improving the reliability and predictive capabilities of simulation tools for the design and analysis of the hypersonic entry phase of aerospace missions.
Precise and reliable estimation of the heat load to the vehicle during the very high speed entry into the atmosphere is a critical issue for planetary exploration missions and for missions with a planned re-entry to Earth.
The project gathered 13 partners from 6 european countries and from Russia, with a wide spectrum of scientific competencies, and studied the problem of high speed entry into the atmospheres of Earth, Mars and Jupiter from the fundamental physics of molecular collisions through the simulation of real-world aerospace vehicles' entry conditions.
Fundamental Molecular Dynamics (MD) studies have produced a wealth of accurate data for the description of the elementary processes (chemical reactions, radiative processes, gas-surface interactions) occurring in high temperature gas mixtures around high speed vehicles.
The fundamental nature of these studies, beyond being the basis for the development of physically sound simulation tools, will foster further studies in the aerospace community but also in such diverse fields as the edge plasmas relevant for magnetic confinement fusion, carbon dioxide chemistry of interest for environmental studies, gas jets and nonequilibrium plasmas for material processing and production.
In order to widen the outreach of this effort and to establish a shared source of accurate reference data, a digital database has been set up and made freely available to the scientific community.
With its focus on high temperature processes, this is the first ever attempt targeting the aerospace community and it will sustain the diffusion of physics based approaches to application-oriented engineering studies.
Detailed kinetic models have been produced that include all the new and accurate physical data. They have been validated against the scientific literature and shown to have a large impact on the simulation results while constraining further the sources of uncertainty, therefore improving on the reliability of the simulations themselves.
In addition, a great effort has been undertaken to develop fast and accurate reduced models to be used in feasibility or optimization studies.
The theoretical work has been complemented with a number of experimental campaigns aimed at the description of the phenomena occurring in high-temperature and/or high-speed gas flows.
Beyond serving as a validation benchmark for the new models, these data enrich the knowledge base and will foster new studies.
All this would however fall short of any measurable impact beyond the academic interest. It is therefore of the utmost importance that the accumulated knowledge be made available to industrial simulation codes. Computational Fluid Dynamics (CFD) specialists have therefore worked in close connection to theoreticians and have produced exciting new results for realistic problems.
Not only the results demonstrate that a more accurate, physics based, approach is viable; they also have shown that it can have a dramatic effect on the predictions of the simulations.
Overall, the project advanced the scientific knowledge, demonstrated the validity of a physics based approach and produced foregrounds that will foster new studies even in areas far apart from aerospace applications.
Project Context and Objectives:
Project context and objectives
One of the major technological challenges associated with the access to planetary surfaces is the entry of the space vehicle in the planetary atmospheres at superorbital speeds. The problem is the very large heat released to the vehicle surface by the surrounding gas either as convective heating or as radiation.
Optimization of the thermal shield design can have a profound impact on the overall mission mass, volume (and therefore energy and cost) budgets. However, a poor knowledge of the physics of hypersonic entry is the limiting factor. Uncertainties increase with the entry speed, in particular as radiation becomes a considerable contribution to the overall heat load.
Significant advance can only be achieved when the uncertainties in the physical modelling have been considerably reduced.
The main goal of this project is a thorough analysis of the physics describing space vehicle (re)entry into planetary atmospheres and an improvement of crucial elements of the modelling that allows reliable predictions of flight conditions.
In particular, the major role of nonequilibrium effects, already established in theoretical studies on model systems, will be quantified in realistic cases of engineering interest.
This study is therefore concerned with the development of advanced chemico-physical and plasma models of hypersonic entry flows. Advanced models mean the description of the non-equilibrium chemical kinetics of the high temperature medium on the basis of a state-to-state approach.
The state-to-state approach
The state-to-state approach decomposes any degree of freedom of the molecule in internal levels (vibrational, rotational, electronic). Each level is considered as an independent species described by an appropriate continuity equation and its own cross sections and rate coefficients. From the level distributions, the thermal properties of the gas and global rate coefficients can be calculated and they can be very different from those obtained by a thermal equilibrium or weak nonequilibrium (linear response) analysis.
When ionization is significant, new phenomena (energy exchange, chemical reactions) occur that involve the charged particles and that require plasma kinetic theory tools for their description.
It is then the interaction of the relevant species (molecules, atoms and ions) in the plasma with the vehicle surface that determines the heat flux on the surface and, to some extent, also the conditions in the gas phase.
The radiative heat flux on the vehicle surface becomes dominant at high entry speeds (e.g. speeds exceeding 10 km/s for Earth re-entry) that are likely to be achieved in future missions of planetary exploration. Predicting the radiative flux is a difficult task. It depends both on the nonequilibrium state of the plasma that results from the interplay of many elementary processes (chemical reactions, internal energy exchanges) and on the radiative transfer among different plasma regions. The study of the radiation transport requires the development of reliable spectroscopic databases for different radiation mechanisms.
Molecular Dynamics studies
The state-to-state approach, as described above, calls for a microscopic description of the elementary processes that play a role in the high temperature reactive gas mixtures surrounding the space vehicles during the entry phase. The first objective of the study is to assess the status of the cross section databases for use in hypersonics and to update, revise or complete it with the help of ab initio MD calculations. It is worth recalling at this stage that existing databases refer to processes involving ground state species. In this context instead, we are explicitly interested in processes involving excited (mainly vibrational and rotational) states. The processes considered include energy exchange and chemical reaction processes for:
Neutral-neutral and neutral-ion collisions
Electron-neutral collisions
Heterogeneous processes occurring on the vehicle surface.
Radiative processes
Since the complexity of the database increases with the number of active species, this objective will be pursued for each high temperature planetary atmosphere.
We select three planetary atmospheres (Earth, Mars and Jupiter) in order to explore several (re-)entry conditions for a wide screening of the model. The selection of Earth and Mars atmospheres are in line with the current European exploration plans. The Jupiter choice, although not considered as an high priority by European plans, gives us the possibility to study extreme speed entry conditions. In any case the relevant database for Jupiter will be of paramount importance for plasma physics (fusion) and industrial applications of plasma chemistry.
A critical review of the existing literature, together with the data collected from the above MD studies will lead to the development of a single comprehensive database of elementary processes occurring in high temperature gases that represents the physical basis for the development of the kinetic modelling.
Experiments
The predictive capabilities of the theoretical models will be assessed against well-defined experimental measurements. In the context of the present study, experiments will serve a double purpose. First, they will act as validation tests for the advanced models and provide feedback for the fine tuning of such theoretical models. To this end, the experiments must provide carefully controlled conditions and shall feature refined diagnostics able to access such elusive quantities as the energy distribution functions.
On the other hand, they will provide benchmark results to be compared against complete CFD rebuilding simulations. In the latter case, the measured quantities are those of direct interest for application: radiation signatures, aerodynamic coefficients, heat fluxes.
The following experiments have been conducted:
Spectroscopic measurements of nonequilibrium radiation from shock-heated gas mixtures (air, CO2-N2);
Spectroscopic measurements of nonequilibrium radiation from supersonic expansion of plasma jets in air;
Spectroscopic measurements of nonequilibrium radiation from subsonic expansion of plasma jets in CO2-N2;
Construction and characterization of a experimental facility for the study of shock waves propagating in weakly ionized gases.
CFD studies
The final step of the study is to assess the predictive capabilities of the theoretical models in realistic problems. These problems typically involve a great geometrical complexity and the coupling among different fundamental phenomena. In the flow around a re-entering body there is a shock-heated region, flow expansion in the body wake and interaction with the solid surface through the boundary layer. In ground experiments, additional complications may arise, due to the nonequilibrium character of the free (i.e. before interaction with the test object) portion of the flow. It is the case of arc-heated plasma wind tunnel, where accurate modelling of the flow is a prerequisite for the correct interpretation of the experimental measurements.
The advanced models and the simplified macroscopic models will therefore be implemented into robust CFD codes able to solve challenging 3D problems. This will, in the first place, assess the role of nonequilibrium effects in different flow configuration of interest. Conclusions shall be drawn on the degree of such nonequilibrium effects on various macroscopic observables that are of direct interest in technological applications (e.g.: TPS design). These are aerodynamic coefficients, heat loads (convective and radiative) on solid surfaces, radiation signatures.
Summary
The main objectives of the project can be summarized as:
(i) Molecular dynamics of elementary projects in gas phase and gas surface interaction. Construction of state-to-state (StS) cross sections databases for Earth, Jupiter and Mars atmospheres from calculated and existing results;
(ii) Advanced chemical physical and plasma models;
(iii) Experimental validation of crucial points of advanced models;
(iv) Implementation of advanced models in robust CFD (Computation Fluid Dynamics) codes for the simulation (rebuilding) of realistic problems (ground or flight tests).
Project Results:
Main results
The first part of the project has been dedicated to the application of quantum mechanics and semi-classical methods to the calculation of full sets of cross sections and rates of elementary processes describing the planetary atmosphere after the impact vehicle-atmosphere. During the impact the molecules of the atmosphere form atom and ions as well as electrons inducing in particular electron-molecule and atom-molecule collisions. The peculiarity of the project was to consider the dependence of the cross sections on the vibrational and rotational quantum numbers of molecule, a point practically absent in the current literature. Significant results have been obtained through the collaboration between IMIP-CNR and UCL on the resonant electron molecule cross sections either for the so-called eV (electron-vibration), dissociative attachment and resonant dissociation processes. For the first time cross sections and rate coefficients for e-M2(v,j) (M2 = H2, N2, O2, NO, CO2) processes have been obtained covering the whole vibrational ladder of diatomic molecules and presenting new data for the CO2 system. These cross sections after publication in International Journals [1-6] have been inserted in the database of cross sections developed by the collaboration between IMIP-CNR and SER&PS (see below). Concerning heavy particle-heavy particle collisions important results have been obtained by using the QCT (Quasi Classical Trajectory) approach on the VT (vibration-translation) energy transfer processes and dissociation processes involving M-M2(v,j) system (M2 = H2, N2, O2) (CNR-IMIP) and VV (vibration-vibration) and VT processes for the system CO2(v,j)+CO2(v,j)[7-9] (UniPg). In addition the IMIP-CNR dedicated a large effort in the characterization of Zeldovich reactions
N2(v,j) + O = NO(v’,j’) + N
N + O2(v,j) = NO(v’,j’) + O
Again the rate coefficients for all these processes have been inserted in the data base and are being published in International Journals. In the case of CO2(v,j)+CO2(v,j) a large effort has been also made on the construction of a suitable PES (Potential Energy Surface) used in the corresponding QCT calculations.
Other important results have been obtained by CNR-IMIP and UB for the characterization of typical gas surface interactions. The CNR-IMIP used a semiclassical method to characterize the interaction of atomic oxygen on a silica surface with particular emphasis of the formation of non-equilibrium ro-vibrational distributions during the recombination of atoms on the surface. The UB partner developed a DFT (Density Functional Theory) to characterize the hydrogen-silica processes.
All the results have been inserted in the Phys4Entry DB a web-access database (http://users.ba.cnr.it/imip/cscpal38/phys4entry/database.html) for state-selected dynamical information for elementary processes relevant to the state-to-state kinetic modelling of planetary-atmosphere entry conditions, a tool designed and implemented by the cooperative work of CNR-IMIP and SER&Practices. The DB is intended to the challenging goal of complementing the information in the existing databases, collecting and validating data of collisional dynamics of elementary processes involving ground and excited chemical species, with resolution on the electronic, vibrational degree of freedom. Three relevant classes of elementary processes are considered, i.e. electron-molecule collisions, atom/molecule-molecule collisions and atom/molecule surface interaction, constructing a taxonomy for process classification. Two DB interfaces have been created for different roles allowed to different actions: the contributor, uploading new processes, and the inquirer, submitting queries, to access the complete information about the records, through a graphical tool, displaying energy or ro-vibrational dependence of dynamical data, or through the export action to download ascii datafiles. In the construction of the database two aspects, that can be regarded as the most critical in affecting the reliability of results of the state-to-state kinetic modelling, have been considered: the accuracy of dynamical data and the data set completeness with respect to the vibrational manifold of molecular species, the treatment of rotational levels in kinetic codes requiring, even nowadays, approximations. Those aspects run oppositely, the former pushing the calculations towards sophisticated theoretical approaches and the latter imposing a balance between the level of approximation and the high computational load that characterize the calculation of complete sets. Assessing the accuracy of cross sections and rates is actually quite complex, in fact dealing with state-specific data a systematic comparison with experimental results cannot be performed for collision partners in all excited states, this being true for almost all systems. On the other hand comparing different theoretical results, the level of approximation in the adopted dynamic approach and the accuracy of the potential energy surface (PES), calculated ab initio or derived in the frame of a phenomenological approach, are to be considered as determining differences in different sets of results, neglecting the effects due to non-adiabatic coupling to other electronic states. In the Phys4EntryDB a great effort has been devoted to the systematic comparison of data with results available in literature, trying to give an index of reliability of the proposed kinetic model. Furthermore a posteriori the sensitivity of kinetic simulations to different data sets can be estimated or, in a more challenging perspective, the index of reliability established through the comparison of modelling results with experiments in the ground test facilities.
The DB is expected to have a significant impact on the modelling community working also in scientific fields different from the aerothermodynamics (i.e. fusion, environment, …), making practicable the state-to-state approach [10-12] and has been presented to the modelling community in different international Conferences [13-17]. On the other hand the complete sets of e-N2(v,j) cross sections have been used to obtain macroscopic relaxation times of eV processes [18] as well as to describe more accurately the kinetics of non-equilibrium nitrogen plasma kinetics [19,20]. Moreover the complete set of state selected cross sections for the H-H2(v,j) has been used to estimate the volume viscosities of molecular hydrogen in the trace limit [21].
The advanced chemical-physical and plasma models include a variety of actions carried out by different partners (CNRS-EM2C, IPMech, CNR-IMIP, UniBa) spanning from radiation transfer to the characterization of the planetary atmospheres flowing in the boundary layer of the vehicle, of the shock waves arising in the interaction of vehicle with the planetary atmosphere and in the expansion through nozzle. Important results have been obtained by CNRS-EM2C by developing a new database of emissivity properties of high temperature CO2 molecules [22-24], important for the Mars atmosphere. On the other hand IPMech has not only improved its database for the emissivity properties of high temperature air but also used this database in its CFD code to emphasize the role of radiation in the re-entry in the Earth atmosphere. Finally CNR-IMIP and UniBa have developed the radiative properties of the high temperature Jupiter (He-H2) atmosphere inserting a radiation transfer module into a complex kinetic plasma model, including the collisional radiative models of atomic hydrogen and atomic Helium, the vibrational master equation for H2 and a Boltzmann solver for the electron energy distribution function (eedf). The advanced plasma model has been introduced in an Euler solver to characterize the spatial evolution of the properties of Jupiter mixture during the shock and the expansion regimes. For the first time it has been shown the coupling between the radiative transfer and the eedf, in particular the re-absorption of radiation increases the concentration of electronically excited states, which in turn create important structures in eedf [25-27]. Important results have been also obtained by CNR-IMIP in the introduction of advanced models including the state-to-state Zeldovich of high temperature air in shock and boundary layer flows. A complete state-to-state vibrational kinetics considering coupled normal states of the CO2 vibrational ladder (about 8000 vibrational levels) has been implemented in the boundary code developed by CNR-IMIP coupled to a simplified dissociation kinetics [28]. The results represent the first example of the insertion of a complete vibrational ladder of CO2 in the boundary layer and show a satisfactory agreement on the heat transfer as compared with the macroscopic models inserted in a CFD code by the ISA partner. Macroscopic models based on state-to-state models have been developed by CNRS-EM2C obtaining very interesting results for nitrogen in the dissociation-recombination regime in nozzle expansion [29]. In particular the model is able to reproduce the long plateau appearing in the vibrational distribution of nitrogen due to the selective pumping of high-lying vibrational levels by the recombination process.
New experimental tests are reported explicitly designed to address the non-equilibrium character of plasmas generated in four different systems, including the post-shock air plasma in high-enthalpy shock tube, the shock wave generated by an acoustic shock tube, the subsonic nitrogen plasma jet produced by DC-Plasmatron facility and supersonic air plasma jets produced by Plasmatron facility.
The last objective of the project i.e. the introduction of the state-to-state kinetics in robust fluid dynamics codes has been achieved in the last year of the project. Due to the difficulty of this point it was decided during the third year meeting with the tutor and the referee of the EU project to dedicate the last year to this aim satisfying a road map able to reach the goal of the insertion of state to state models in CFD codes. This road map, developed by the partners ISA, CIRA, PoliTo, CNR-IMIP, UniBa and submitted to the EU project officer, included:
the insertion of state to state model of N2 in the dissociation-recombination regimes in a 2D, 3D Navier-Stokes code(CIRA, CNR-IMIP)
the insertion of the state-to-state complete kinetics of Jupiter atmosphere in 1D and 2D shock wave code (PoliTo, UniBa, CNR-IMIP)
the reduction of state-to-state to the macroscopic model for the Jupiter atmosphere to be inserted in the ISA CFD code(CNR-IMIP, UniBa, ISA).
These objectives have been realized; in particular the collaboration between CIRA and CNR-IMIP has shown for the first time the possibility of running a 2D and 3D CFD code with complete non equilibrium vibrational kinetics [30]. Moreover the corresponding collaboration between PoliTo and CNR-IMIP and UniBa has shown a real possibility to describe the Jupiter atmosphere including both dissociation-recombination, and ionization-recombination regimes by 1D, 2D CFD codes as well as to reduce state-to-state models to macroscopic ones [31].
Let us now examine the work made by the Consortium in the dissemination of the numerous results obtained in the framework of the Phys4Entry project. We have already anticipated the dissemination made of the Phys4Entry database. A part the dissemination made on International Journals we want to report two important actions made by the Consortium. We refer in particular to the organization of 53rd Course: Molecular Physics and Plasmas in Hypersonics (Erice September 8-15 2012, Directors M. Capitelli, D. Bruno, A. Laricchiuta), where all the partners of the project reported their mid-term results. In this occasion it was decided to publish a Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014) Guest Editors M. Capitelli, A. Laricchiuta on the main results obtained by the partners of the project [32-41].
To conclude we can say that the results of the Phys4Entry project offer a comprehensive view of the advances made in the investigation of different aspects connected to the predictive simulation of hypersonic flows in aerospace applications, emphasizing the role of non-equilibrium effects and the importance of StS approaches and representing a roadmap for the future of the research in this field. Moreover in the framework of this project a European network of Research Institutions has been created, able to be competitive in the future with the most important non-EU International Agencies in the aerospace domain.
References
1. V. Laporta, R. Celiberto and J. Tennyson, Dissociative electron attachment and electron-impact resonant dissociation of vibrationally excited O2 molecules", Physical Review Letters (2014) submitted
2. V. Laporta, D.A. Little, R. Celiberto and J. Tennyson, Electron-impact resonant vibrational excitation and dissociation processes involving vibrationally excited N2 molecules, Plasma Sources Sci. Technol. (2014) in press
3. R. Celiberto, R.K. Janev, V. Laporta, J. Tennyson and J.M. Wadehra, Electron-impact vibrational excitation of vibrationally excited H2 molecules involving the resonant 2g+ Rydberg-excited electronic state, Phys. Rev. A 88, 062701 (2013)
4. V. Laporta, R. Celiberto and J. Tennyson, Resonant vibrational-excitation cross sections and rate constants for low-energy electron scattering by molecular oxygen, Plasma Sources Sci. Technol. 22, 025001 (2013)
5. V. Laporta, R. Celiberto and J.M. Wadehra, Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N2 and NO molecules, Plasma Sources Sci. Technol. 21, 055018 (2012)
6. V. Laporta, C.M. Cassidy, J. Tennyson and R. Celiberto, Electron-impact resonant vibration excitation cross sections and rate coefficients for carbon monoxide, Plasma Sources Sci. Technol. 21, 045005 (2012)
7. A. Lombardi, N. Faginas-Lago, L. Pacifici, A. Costantini, Modeling of Energy Transfer From Vibrationally Excited CO2 Molecules: Cross Sections and Probabilities for Kinetic Modeling of Atmospheres, Flows, and Plasmas, Journal of Physical Chemistry A 117, 11430 (2013)
8. A. Lombardi, A. Laganà, F. Pirani, F. Palazzetti, N. Faginas Lago, Carbon Oxides in Gas Flows and Earth and Planetary Atmospheres: State-to-State Simulations of Energy Transfer and Dissociation Reactions, Lecture Notes in Computer Science 7972, 17 (2013)
9. M Bartolomei, F. Pirani, A. Laganà, A. Lombardi, A full dimensional grid empowered simulation of the CO2 + CO2 processes, Journal of Computational Chemistry 33, 1806 (2012)
10. M. Capitelli, I. Armenise, E. Bisceglie, D. Bruno, R. Celiberto, G. Colonna, G. D'Ammando, O. De Pascale, F. Esposito, C. Gorse, V. Laporta, A. Laricchiuta, Thermodynamics, transport and kinetics of equilibrium and non-equilibrium plasmas: a state-to-state approach, Plasma Chemistry and Plasma Processing 32, 427 (2012)
11. M Capitelli, R Celiberto, G Colonna, G D'Ammando, O De Pascale, P Diomede, F Esposito, C Gorse, A Laricchiuta, S Longo, L D Pietanza, F Taccogna, Plasma kinetics in molecular plasmas and modeling of reentry plasmas, Plasma Physics and Controlled Fusion 53, 124007 (2011)
12. G. Colonna, Problems and perspectives of state-to-state kinetics for high enthalpy plasma flows (invited), RGD29 29th International Symposium on Rarefied Gas Dynamics, Xi'an (China), July 13-18, 2014
13. A. Laricchiuta, Electron-impact excitation cross sections for air kinetics, Workshop Boris F. Gordiets: Air plasma chemistry, XXI Europhysics Conference on the Atomic and Molecular Physics of Ionized Gases, Viana do Castelo (Portugal), July 10-14 2012
14. A. Laricchiuta, The Phys4Entry database, 53rd Course dell'International School of Quantum Electronics del Centro Ettore Majorana "Molecular Physics and Plasmas in Hypersonics II", Directors M. Capitelli, D. Bruno and A. Laricchiuta, Erice (Italy), September 8-15, 2012
15. A. Laricchiuta, The Phys4Entry Database, Workshop on Plasma Data Exchange, organized by L. Pitchford and A. Laricchiuta, Special Session in 65th Gaseous Electronic Conference, University of Texas, Austin (TX), October 22-26, 2012
16. A. Laricchiuta Dynamical information for kinetic modelling and transport of He/H2 plasmas, 2nd IAEA Research Coordination Meeting on Atomic and Molecular Data for State-Resolved Modelling of Hydrogen and Helium and their Isotopes in Fusion Plasma, IAEA Vienna (Austria), July 3-5, 2013
17. A. Laricchiuta, I. Armenise, M. Cacciatore, R. Celiberto, F. Esposito, P. Gamallo, A. Laganà, V. Laporta, A. Lombardi, S. Orlandini, F. Pirani, M. Rutigliano, R. Sayós, J. Tennyson and M. Capitelli Phys4EntryDB: a Database for State-to-State Kinetics of Planetary Atmospheres, Special Session (382-FD-48) Reacting Flows, AIAA Science and Technology Forum and Exposition (SciTech2014), National Harbor, Maryland (USA), January 13-17, 2014
18. V. Laporta and D. Bruno, Electron-vibration energy exchange models in nitrogen-containing plasma flows, J. Chem. Phys. 138, 104319 (2013)
19. M. Capitelli, G. Colonna, G. D’Ammando, V. Laporta, A. Laricchiuta, The role of electron scattering with vibrationally excited molecules on non-equilibrium plasma kinetics, Physics of Plasmas 20, 101609 (2013)
20. M. Capitelli, G. Colonna, G. D’Ammando, V. Laporta, A. Laricchiuta, Non-equilibrium dissociation mechanisms in low temperature nitrogen and carbon monoxide plasmas, Chem. Phys. 438, 31 (2014)
21. D. Bruno, F. Esposito, V. Giovangigli, Relaxation of rotation and vibrational energy and volume viscosity in H-H2(v,j) mixtures, J. Chem. Phys. 138, 084302 (2014)
22. S. Depraz, M.Y. Perrin, A. Soufiani, Infrared emission spectroscopy of CO2 at high temperature. Part I: Experimental setup and source characterization, Journal of Quantitative Spectroscopy and Radiative Transfer 113, 1 (2012)
23. S. Depraz, M.Y. Perrin, Ph. Rivière, A. Soufiani, Infrared emission spectroscopy of CO2 at high temperature. Part II: Experimental results and comparisons with spectroscopic databases, Journal of Quantitative Spectroscopy and Radiative Transfer 113, 14 (2012)
24. A.S. Dikalyuk, S.T. Surzhikov, Equilibrium spectral radiation behind the shock wave front in a CO2-N2 gas mixture, High Temperature 52, 35 (2014)
25. M. Capitelli, G. Colonna, G. D’Ammando, R. Gaudiuso, D. Pietanza, Laser induced Breakdown Spectroscopy: Theory and Applications in Springer Chapter 2: Physical Processes in Optical Emission Spectroscopy (2014) (isbn 978-3-642-45084-6)
26. M. Capitelli, G. Colonna, L.D. Pietanza, G. D’ammando, Coupling of radiation, excited states and electron energy distribution function in non-equilibrium hydrogen plasmas, Spectrochimica Acta Part B 83-84, 1 (2013)
27. G. D’Ammando, M. Capitelli, F. Esposito, A. Laricchiuta, L.D. Pietanza, and G. Colonna, The role of radiative reabsorption on the electron energy distribution functions in nozzle plasma expansion (2014) submitted
28. I. Armenise, E. Kustova, State to state models for CO2 molecules: from the theory to an application to hypersonic boundary layers, Chem. Phys. 415, 269 (2013)
29. A Guy, A. Bourdon, M.Y. Perrin, Consistent multi-internal-temperatures models for nonequilibrium nozzle flows, Chemical Physics 420, 15 (2013)
30. L. Cutrone, M. Tuttafesta, M. Capitelli, A. Schettino, G. Pascazio, G. Colonna, 3D Nozzle Flow Simulations including State–to–State Kinetics Calculation, RGD29 29th International Symposium on Rarefied Gas Dynamics, Xi'an (China), July 13-18, 2014
31. G. Colonna, D. D’Ambrosio, L.D. Pietanza, G. D’Ammando, M.Capitelli Multi-temperature model derived from state-to-state kinetics for hypersonic entry in Jupiter atmosphere, RGD29 29th International Symposium on Rarefied Gas Dynamics, Xi'an (China), July 13-18, 2014
32. R. Celiberto, V. Laporta, A. Laricchiuta, J. Tennyson, J.M. Wadehra, Molecular Physics of Elementary Processes relevant to Hypersonics: electron-molecule collisions, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
33. A. Laganà, A. Lombardi, F. Pirani, P. Gamallo, R. Sayós, I. Armenise, M. Cacciatore, F. Esposito, M. Rutigliano, Molecular Physics of Elementary Processes relevant to Hypersonics: atom-molecule, molecule-molecule and atoms-surface processes, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
34. A. Bourdon, J. Annaloro, A. Bultel, M. Capitelli, G. Colonna, A. Guy, T.E. Magin, A. Munafó, M.Y. Perrin, L.D. Pietanza, Reduction of state-to-state to macroscopic models for hypersonics, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
35. E.V. Kustova, E.A. Nagnibeda, I. Armenise, Vibrational-Chemical Kinetics in Mars Entry Problems, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
36. D. Bruno, A. Panarese, S. Longo, F. Taccogna, P. Minelli, S.T. Surzhikov, A.S. Dikaljuk, P. De Palma, M.D. de Tullio, Particle methods for nonequilibrium hypersonic and plasma flows, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
37. G. Colonna, G. D'Ammando, A.S. Dikalyuk, M. Panesi, L.D. Pietanza, S.T. Surzhikov, Advanced Models in Shock-Waves, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
38. M.Y. Perrin, G. Colonna, G. D'Ammando, L.D. Pietanza, Ph. Riviere, A. Soufiani, S. Surzhikov, Radiation Models and Radiation Transfer in Hypersonics, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
39. S. Surzhikov, P. Reynier, G. Seller, F. Taccogna, Radiative aerothermodynamics of entering space vehicles: toward the use of state-to-state approach, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
40. Y. Babou, D. Lequang, O. Chazot, S.T. Surzhikov, A.S. Dikaljuk, A. Panarese, G. Cicala, S. Longo, J. Hoffman, Z. Szymanski, A. Kaminska, M. Dudeck, D. Vacher, Thermodynamic characterization of high-speed and high-enthalpy plasma flows, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
41. A. Schettino, D. D'Ambrosio, Different approximation levels in using CFD for the design of hypersonic vehicles, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014).
Potential Impact:
Potential impact
The project involved scientific research in a multidisciplinary framework. Efforts have been directed along the whole chain from the ab initio description of the elementary processes to the kinetic modelling and through CFD simulations of real-world aerospace vehicles's entry conditions.
The focus has been on gas mixtures representative of the atmospheres of Earth, Mars and Jupiter.
The results obtained are naturally instrumental to the achievement of the project's goals; but they also represent advance in scientific knowledge beneficial to other technological domains. In many cases, they have not been fully exploited within the project activities so that their scientific value is increased by the potential to solicit new studies.
Molecular Dynamics
Fundamental Molecular Dynamics (MD) studies have produced a wealth of accurate data for the description of the elementary processes (chemical reactions, radiative processes, gas-surface interactions) occurring in high temperature gas mixtures around high speed vehicles.
This is the basis for the development of physically sound simulation tools. With their focus on high temperature processes and on vibrational-selected resolution, the data obtained represent a clear advance with respect to the current knowledge.
In many cases, the production of accurate physical data, previously unavailable, lifts the need for phenomenological or ad hoc modeling thus improving the reliability of the simulation tools.
It is the case, for example, of the studies on collisional energy transfer in CO2. Being the first accurate data obtained for this problem, they will likely be useful for the carbon dioxide chemistry of interest for environmental studies.
Vibrational-specific collisional energy transfer in the Hydrogen molecule, instead, is of great interest in the magnetic confinement fusion community for its role in the neutral ion beam sources.
Results on gas-surface interactions are naturally of great interest for the design of the Thermal Protection System (TPS) of aerospace vehicles but they are also beneficial in material processing applications.
Establishment of a aerospace reference database
In order to widen the outreach of this effort and to establish a shared source of accurate reference data, a digital database has been set up and made freely available to the scientific community.
With its focus on high temperature processes, this is the first ever attempt targeting the aerospace community and it will sustain the diffusion of physics based approaches to application-oriented engineering studies.
Kinetic modelling
Detailed kinetic models have been produced that include all the new and accurate physical data. They have been validated against the scientific literature and shown to have a large impact on the simulation results while constraining further the sources of uncertainty, therefore improving on the reliability of the simulations themselves.
In addition, a great effort has been undertaken to develop fast and accurate reduced models to be used in feasibility or optimization studies.
Experiments
The theoretical work has been complemented with a number of experimental campaigns aimed at the description of the phenomena occurring in high-temperature and/or high-speed gas flows.
Beyond serving as a validation benchmark for the new models, these data enrich the knowledge base and will foster new studies.
Computational Fluid Dynamics
In order to make the accumulated knowledge available to real-world applications, the new models have been implemented in state-of-the-art, industrial-level, Computational Fluid Dynamics (CFD) simulation tools.
The results demonstrate that a more accurate, physics based, approach is viable thus urging the aerospace community to adopt the new paradigm.
In some cases, the new results clearly show the superiority of physics based modelling over phenomenological approaches. It is the case, for example, of the rebuilding of hypersonic flow tests with CO2 mixtures in the HYPULSE facility, where detailed modelling improved dramatically the agreement with experimental measurements; or the challenging problem of the very high speed Galileo entry into Jupiter atmosphere where the accuracy of fundamental physical data (transport properties, in this case) are shown to have a dramatic effect on the predicted convective heat flux.
Finally, in the frame of the project's lifetime, CFD studies did not explore the whole spectrum of possible applications, paving the way for additional studies.
Dissemination
The project activities and results have been made available to a wider audience via dissemination activities targeting the aerospace research community and the scientific community at large. In addition they have been presented at EU funded workshops aimed at increasing the general public's awareness on EU funded research activities.
Scientific community
The scientific results obtained have been published in international refereed journals and presented at specialised conferences. This resulted in 79 journal publications and 61 conference presentations (among which 17 are invited lectures).
In addition, the project objectives, activities and results have been discussed in few occasions:
1. The Discussion Group on Non-equilibrium flows, chaired by E. Josyula of the Air Force Research Laboratory holds its meetings during AIAA conferences. During the AIAA Science and Technology Forum and Exposition, held at National Harbor, Maryland (USA), 13-17 January 2014, a special session on reactive flows hosted two invited talks from the CNR partner (A. Laricchiuta and G. Colonna). (More details at: https://info.aiaa.org/tac/ASG/FDTC/DG/NEF.aspx)
2. During the 65th Gaseous Electronics Conference (Austin, TX, USA, October 22-26 2012), a special workshop on “Plasma Data Exchange Project” has been organised and chaired by A. Laricchiuta (CNR). During the workshop the project database has been presented. (More details at: http://meetings.aps.org/Meeting/GEC12/Session/GT2)
3. The “Ettore Majorana” Foundation and Centre for Scientific Culture, located in Erice, Italy, from 8 to 15 Sept 2012 hosted the 53rd course of the International School of Quantum Electronics dedicated to: “Molecular Physics and Plasmas in Hypersonics”. The course featured as directors and as invited speakers the project partners. (More details at: http://users.ba.cnr.it/imip/cscpal38/Erice2/)
FP7 project presentation workshops
“Let’s embrace space”, FP7 Space Conference 2011, Budapest, 12-13 May 2011.
European Corner supported by EU Commission, during the event “Notte dei Ricercatori”, held at the Politecnico of Bari (Italy) on September 23 2011.
FP7 Workshop: “Space – Space foundations”, Rome, 29 May 2012. Organised and sponsored by the Italian Space Agency.
List of Websites:
http://users.ba.cnr.it/imip/cscpal38/phys4entry/index.html
Executive Summary
Planetary Entry Integrated Models (Phys4Entry) is a scientific study aimed at improving the reliability and predictive capabilities of simulation tools for the design and analysis of the hypersonic entry phase of aerospace missions.
Precise and reliable estimation of the heat load to the vehicle during the very high speed entry into the atmosphere is a critical issue for planetary exploration missions and for missions with a planned re-entry to Earth.
The project gathered 13 partners from 6 european countries and from Russia, with a wide spectrum of scientific competencies, and studied the problem of high speed entry into the atmospheres of Earth, Mars and Jupiter from the fundamental physics of molecular collisions through the simulation of real-world aerospace vehicles' entry conditions.
Fundamental Molecular Dynamics (MD) studies have produced a wealth of accurate data for the description of the elementary processes (chemical reactions, radiative processes, gas-surface interactions) occurring in high temperature gas mixtures around high speed vehicles.
The fundamental nature of these studies, beyond being the basis for the development of physically sound simulation tools, will foster further studies in the aerospace community but also in such diverse fields as the edge plasmas relevant for magnetic confinement fusion, carbon dioxide chemistry of interest for environmental studies, gas jets and nonequilibrium plasmas for material processing and production.
In order to widen the outreach of this effort and to establish a shared source of accurate reference data, a digital database has been set up and made freely available to the scientific community.
With its focus on high temperature processes, this is the first ever attempt targeting the aerospace community and it will sustain the diffusion of physics based approaches to application-oriented engineering studies.
Detailed kinetic models have been produced that include all the new and accurate physical data. They have been validated against the scientific literature and shown to have a large impact on the simulation results while constraining further the sources of uncertainty, therefore improving on the reliability of the simulations themselves.
In addition, a great effort has been undertaken to develop fast and accurate reduced models to be used in feasibility or optimization studies.
The theoretical work has been complemented with a number of experimental campaigns aimed at the description of the phenomena occurring in high-temperature and/or high-speed gas flows.
Beyond serving as a validation benchmark for the new models, these data enrich the knowledge base and will foster new studies.
All this would however fall short of any measurable impact beyond the academic interest. It is therefore of the utmost importance that the accumulated knowledge be made available to industrial simulation codes. Computational Fluid Dynamics (CFD) specialists have therefore worked in close connection to theoreticians and have produced exciting new results for realistic problems.
Not only the results demonstrate that a more accurate, physics based, approach is viable; they also have shown that it can have a dramatic effect on the predictions of the simulations.
Overall, the project advanced the scientific knowledge, demonstrated the validity of a physics based approach and produced foregrounds that will foster new studies even in areas far apart from aerospace applications.
Project Context and Objectives:
Project context and objectives
One of the major technological challenges associated with the access to planetary surfaces is the entry of the space vehicle in the planetary atmospheres at superorbital speeds. The problem is the very large heat released to the vehicle surface by the surrounding gas either as convective heating or as radiation.
Optimization of the thermal shield design can have a profound impact on the overall mission mass, volume (and therefore energy and cost) budgets. However, a poor knowledge of the physics of hypersonic entry is the limiting factor. Uncertainties increase with the entry speed, in particular as radiation becomes a considerable contribution to the overall heat load.
Significant advance can only be achieved when the uncertainties in the physical modelling have been considerably reduced.
The main goal of this project is a thorough analysis of the physics describing space vehicle (re)entry into planetary atmospheres and an improvement of crucial elements of the modelling that allows reliable predictions of flight conditions.
In particular, the major role of nonequilibrium effects, already established in theoretical studies on model systems, will be quantified in realistic cases of engineering interest.
This study is therefore concerned with the development of advanced chemico-physical and plasma models of hypersonic entry flows. Advanced models mean the description of the non-equilibrium chemical kinetics of the high temperature medium on the basis of a state-to-state approach.
The state-to-state approach
The state-to-state approach decomposes any degree of freedom of the molecule in internal levels (vibrational, rotational, electronic). Each level is considered as an independent species described by an appropriate continuity equation and its own cross sections and rate coefficients. From the level distributions, the thermal properties of the gas and global rate coefficients can be calculated and they can be very different from those obtained by a thermal equilibrium or weak nonequilibrium (linear response) analysis.
When ionization is significant, new phenomena (energy exchange, chemical reactions) occur that involve the charged particles and that require plasma kinetic theory tools for their description.
It is then the interaction of the relevant species (molecules, atoms and ions) in the plasma with the vehicle surface that determines the heat flux on the surface and, to some extent, also the conditions in the gas phase.
The radiative heat flux on the vehicle surface becomes dominant at high entry speeds (e.g. speeds exceeding 10 km/s for Earth re-entry) that are likely to be achieved in future missions of planetary exploration. Predicting the radiative flux is a difficult task. It depends both on the nonequilibrium state of the plasma that results from the interplay of many elementary processes (chemical reactions, internal energy exchanges) and on the radiative transfer among different plasma regions. The study of the radiation transport requires the development of reliable spectroscopic databases for different radiation mechanisms.
Molecular Dynamics studies
The state-to-state approach, as described above, calls for a microscopic description of the elementary processes that play a role in the high temperature reactive gas mixtures surrounding the space vehicles during the entry phase. The first objective of the study is to assess the status of the cross section databases for use in hypersonics and to update, revise or complete it with the help of ab initio MD calculations. It is worth recalling at this stage that existing databases refer to processes involving ground state species. In this context instead, we are explicitly interested in processes involving excited (mainly vibrational and rotational) states. The processes considered include energy exchange and chemical reaction processes for:
Neutral-neutral and neutral-ion collisions
Electron-neutral collisions
Heterogeneous processes occurring on the vehicle surface.
Radiative processes
Since the complexity of the database increases with the number of active species, this objective will be pursued for each high temperature planetary atmosphere.
We select three planetary atmospheres (Earth, Mars and Jupiter) in order to explore several (re-)entry conditions for a wide screening of the model. The selection of Earth and Mars atmospheres are in line with the current European exploration plans. The Jupiter choice, although not considered as an high priority by European plans, gives us the possibility to study extreme speed entry conditions. In any case the relevant database for Jupiter will be of paramount importance for plasma physics (fusion) and industrial applications of plasma chemistry.
A critical review of the existing literature, together with the data collected from the above MD studies will lead to the development of a single comprehensive database of elementary processes occurring in high temperature gases that represents the physical basis for the development of the kinetic modelling.
Experiments
The predictive capabilities of the theoretical models will be assessed against well-defined experimental measurements. In the context of the present study, experiments will serve a double purpose. First, they will act as validation tests for the advanced models and provide feedback for the fine tuning of such theoretical models. To this end, the experiments must provide carefully controlled conditions and shall feature refined diagnostics able to access such elusive quantities as the energy distribution functions.
On the other hand, they will provide benchmark results to be compared against complete CFD rebuilding simulations. In the latter case, the measured quantities are those of direct interest for application: radiation signatures, aerodynamic coefficients, heat fluxes.
The following experiments have been conducted:
Spectroscopic measurements of nonequilibrium radiation from shock-heated gas mixtures (air, CO2-N2);
Spectroscopic measurements of nonequilibrium radiation from supersonic expansion of plasma jets in air;
Spectroscopic measurements of nonequilibrium radiation from subsonic expansion of plasma jets in CO2-N2;
Construction and characterization of a experimental facility for the study of shock waves propagating in weakly ionized gases.
CFD studies
The final step of the study is to assess the predictive capabilities of the theoretical models in realistic problems. These problems typically involve a great geometrical complexity and the coupling among different fundamental phenomena. In the flow around a re-entering body there is a shock-heated region, flow expansion in the body wake and interaction with the solid surface through the boundary layer. In ground experiments, additional complications may arise, due to the nonequilibrium character of the free (i.e. before interaction with the test object) portion of the flow. It is the case of arc-heated plasma wind tunnel, where accurate modelling of the flow is a prerequisite for the correct interpretation of the experimental measurements.
The advanced models and the simplified macroscopic models will therefore be implemented into robust CFD codes able to solve challenging 3D problems. This will, in the first place, assess the role of nonequilibrium effects in different flow configuration of interest. Conclusions shall be drawn on the degree of such nonequilibrium effects on various macroscopic observables that are of direct interest in technological applications (e.g.: TPS design). These are aerodynamic coefficients, heat loads (convective and radiative) on solid surfaces, radiation signatures.
Summary
The main objectives of the project can be summarized as:
(i) Molecular dynamics of elementary projects in gas phase and gas surface interaction. Construction of state-to-state (StS) cross sections databases for Earth, Jupiter and Mars atmospheres from calculated and existing results;
(ii) Advanced chemical physical and plasma models;
(iii) Experimental validation of crucial points of advanced models;
(iv) Implementation of advanced models in robust CFD (Computation Fluid Dynamics) codes for the simulation (rebuilding) of realistic problems (ground or flight tests).
Project Results:
Main results
The first part of the project has been dedicated to the application of quantum mechanics and semi-classical methods to the calculation of full sets of cross sections and rates of elementary processes describing the planetary atmosphere after the impact vehicle-atmosphere. During the impact the molecules of the atmosphere form atom and ions as well as electrons inducing in particular electron-molecule and atom-molecule collisions. The peculiarity of the project was to consider the dependence of the cross sections on the vibrational and rotational quantum numbers of molecule, a point practically absent in the current literature. Significant results have been obtained through the collaboration between IMIP-CNR and UCL on the resonant electron molecule cross sections either for the so-called eV (electron-vibration), dissociative attachment and resonant dissociation processes. For the first time cross sections and rate coefficients for e-M2(v,j) (M2 = H2, N2, O2, NO, CO2) processes have been obtained covering the whole vibrational ladder of diatomic molecules and presenting new data for the CO2 system. These cross sections after publication in International Journals [1-6] have been inserted in the database of cross sections developed by the collaboration between IMIP-CNR and SER&PS (see below). Concerning heavy particle-heavy particle collisions important results have been obtained by using the QCT (Quasi Classical Trajectory) approach on the VT (vibration-translation) energy transfer processes and dissociation processes involving M-M2(v,j) system (M2 = H2, N2, O2) (CNR-IMIP) and VV (vibration-vibration) and VT processes for the system CO2(v,j)+CO2(v,j)[7-9] (UniPg). In addition the IMIP-CNR dedicated a large effort in the characterization of Zeldovich reactions
N2(v,j) + O = NO(v’,j’) + N
N + O2(v,j) = NO(v’,j’) + O
Again the rate coefficients for all these processes have been inserted in the data base and are being published in International Journals. In the case of CO2(v,j)+CO2(v,j) a large effort has been also made on the construction of a suitable PES (Potential Energy Surface) used in the corresponding QCT calculations.
Other important results have been obtained by CNR-IMIP and UB for the characterization of typical gas surface interactions. The CNR-IMIP used a semiclassical method to characterize the interaction of atomic oxygen on a silica surface with particular emphasis of the formation of non-equilibrium ro-vibrational distributions during the recombination of atoms on the surface. The UB partner developed a DFT (Density Functional Theory) to characterize the hydrogen-silica processes.
All the results have been inserted in the Phys4Entry DB a web-access database (http://users.ba.cnr.it/imip/cscpal38/phys4entry/database.html) for state-selected dynamical information for elementary processes relevant to the state-to-state kinetic modelling of planetary-atmosphere entry conditions, a tool designed and implemented by the cooperative work of CNR-IMIP and SER&Practices. The DB is intended to the challenging goal of complementing the information in the existing databases, collecting and validating data of collisional dynamics of elementary processes involving ground and excited chemical species, with resolution on the electronic, vibrational degree of freedom. Three relevant classes of elementary processes are considered, i.e. electron-molecule collisions, atom/molecule-molecule collisions and atom/molecule surface interaction, constructing a taxonomy for process classification. Two DB interfaces have been created for different roles allowed to different actions: the contributor, uploading new processes, and the inquirer, submitting queries, to access the complete information about the records, through a graphical tool, displaying energy or ro-vibrational dependence of dynamical data, or through the export action to download ascii datafiles. In the construction of the database two aspects, that can be regarded as the most critical in affecting the reliability of results of the state-to-state kinetic modelling, have been considered: the accuracy of dynamical data and the data set completeness with respect to the vibrational manifold of molecular species, the treatment of rotational levels in kinetic codes requiring, even nowadays, approximations. Those aspects run oppositely, the former pushing the calculations towards sophisticated theoretical approaches and the latter imposing a balance between the level of approximation and the high computational load that characterize the calculation of complete sets. Assessing the accuracy of cross sections and rates is actually quite complex, in fact dealing with state-specific data a systematic comparison with experimental results cannot be performed for collision partners in all excited states, this being true for almost all systems. On the other hand comparing different theoretical results, the level of approximation in the adopted dynamic approach and the accuracy of the potential energy surface (PES), calculated ab initio or derived in the frame of a phenomenological approach, are to be considered as determining differences in different sets of results, neglecting the effects due to non-adiabatic coupling to other electronic states. In the Phys4EntryDB a great effort has been devoted to the systematic comparison of data with results available in literature, trying to give an index of reliability of the proposed kinetic model. Furthermore a posteriori the sensitivity of kinetic simulations to different data sets can be estimated or, in a more challenging perspective, the index of reliability established through the comparison of modelling results with experiments in the ground test facilities.
The DB is expected to have a significant impact on the modelling community working also in scientific fields different from the aerothermodynamics (i.e. fusion, environment, …), making practicable the state-to-state approach [10-12] and has been presented to the modelling community in different international Conferences [13-17]. On the other hand the complete sets of e-N2(v,j) cross sections have been used to obtain macroscopic relaxation times of eV processes [18] as well as to describe more accurately the kinetics of non-equilibrium nitrogen plasma kinetics [19,20]. Moreover the complete set of state selected cross sections for the H-H2(v,j) has been used to estimate the volume viscosities of molecular hydrogen in the trace limit [21].
The advanced chemical-physical and plasma models include a variety of actions carried out by different partners (CNRS-EM2C, IPMech, CNR-IMIP, UniBa) spanning from radiation transfer to the characterization of the planetary atmospheres flowing in the boundary layer of the vehicle, of the shock waves arising in the interaction of vehicle with the planetary atmosphere and in the expansion through nozzle. Important results have been obtained by CNRS-EM2C by developing a new database of emissivity properties of high temperature CO2 molecules [22-24], important for the Mars atmosphere. On the other hand IPMech has not only improved its database for the emissivity properties of high temperature air but also used this database in its CFD code to emphasize the role of radiation in the re-entry in the Earth atmosphere. Finally CNR-IMIP and UniBa have developed the radiative properties of the high temperature Jupiter (He-H2) atmosphere inserting a radiation transfer module into a complex kinetic plasma model, including the collisional radiative models of atomic hydrogen and atomic Helium, the vibrational master equation for H2 and a Boltzmann solver for the electron energy distribution function (eedf). The advanced plasma model has been introduced in an Euler solver to characterize the spatial evolution of the properties of Jupiter mixture during the shock and the expansion regimes. For the first time it has been shown the coupling between the radiative transfer and the eedf, in particular the re-absorption of radiation increases the concentration of electronically excited states, which in turn create important structures in eedf [25-27]. Important results have been also obtained by CNR-IMIP in the introduction of advanced models including the state-to-state Zeldovich of high temperature air in shock and boundary layer flows. A complete state-to-state vibrational kinetics considering coupled normal states of the CO2 vibrational ladder (about 8000 vibrational levels) has been implemented in the boundary code developed by CNR-IMIP coupled to a simplified dissociation kinetics [28]. The results represent the first example of the insertion of a complete vibrational ladder of CO2 in the boundary layer and show a satisfactory agreement on the heat transfer as compared with the macroscopic models inserted in a CFD code by the ISA partner. Macroscopic models based on state-to-state models have been developed by CNRS-EM2C obtaining very interesting results for nitrogen in the dissociation-recombination regime in nozzle expansion [29]. In particular the model is able to reproduce the long plateau appearing in the vibrational distribution of nitrogen due to the selective pumping of high-lying vibrational levels by the recombination process.
New experimental tests are reported explicitly designed to address the non-equilibrium character of plasmas generated in four different systems, including the post-shock air plasma in high-enthalpy shock tube, the shock wave generated by an acoustic shock tube, the subsonic nitrogen plasma jet produced by DC-Plasmatron facility and supersonic air plasma jets produced by Plasmatron facility.
The last objective of the project i.e. the introduction of the state-to-state kinetics in robust fluid dynamics codes has been achieved in the last year of the project. Due to the difficulty of this point it was decided during the third year meeting with the tutor and the referee of the EU project to dedicate the last year to this aim satisfying a road map able to reach the goal of the insertion of state to state models in CFD codes. This road map, developed by the partners ISA, CIRA, PoliTo, CNR-IMIP, UniBa and submitted to the EU project officer, included:
the insertion of state to state model of N2 in the dissociation-recombination regimes in a 2D, 3D Navier-Stokes code(CIRA, CNR-IMIP)
the insertion of the state-to-state complete kinetics of Jupiter atmosphere in 1D and 2D shock wave code (PoliTo, UniBa, CNR-IMIP)
the reduction of state-to-state to the macroscopic model for the Jupiter atmosphere to be inserted in the ISA CFD code(CNR-IMIP, UniBa, ISA).
These objectives have been realized; in particular the collaboration between CIRA and CNR-IMIP has shown for the first time the possibility of running a 2D and 3D CFD code with complete non equilibrium vibrational kinetics [30]. Moreover the corresponding collaboration between PoliTo and CNR-IMIP and UniBa has shown a real possibility to describe the Jupiter atmosphere including both dissociation-recombination, and ionization-recombination regimes by 1D, 2D CFD codes as well as to reduce state-to-state models to macroscopic ones [31].
Let us now examine the work made by the Consortium in the dissemination of the numerous results obtained in the framework of the Phys4Entry project. We have already anticipated the dissemination made of the Phys4Entry database. A part the dissemination made on International Journals we want to report two important actions made by the Consortium. We refer in particular to the organization of 53rd Course: Molecular Physics and Plasmas in Hypersonics (Erice September 8-15 2012, Directors M. Capitelli, D. Bruno, A. Laricchiuta), where all the partners of the project reported their mid-term results. In this occasion it was decided to publish a Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014) Guest Editors M. Capitelli, A. Laricchiuta on the main results obtained by the partners of the project [32-41].
To conclude we can say that the results of the Phys4Entry project offer a comprehensive view of the advances made in the investigation of different aspects connected to the predictive simulation of hypersonic flows in aerospace applications, emphasizing the role of non-equilibrium effects and the importance of StS approaches and representing a roadmap for the future of the research in this field. Moreover in the framework of this project a European network of Research Institutions has been created, able to be competitive in the future with the most important non-EU International Agencies in the aerospace domain.
References
1. V. Laporta, R. Celiberto and J. Tennyson, Dissociative electron attachment and electron-impact resonant dissociation of vibrationally excited O2 molecules", Physical Review Letters (2014) submitted
2. V. Laporta, D.A. Little, R. Celiberto and J. Tennyson, Electron-impact resonant vibrational excitation and dissociation processes involving vibrationally excited N2 molecules, Plasma Sources Sci. Technol. (2014) in press
3. R. Celiberto, R.K. Janev, V. Laporta, J. Tennyson and J.M. Wadehra, Electron-impact vibrational excitation of vibrationally excited H2 molecules involving the resonant 2g+ Rydberg-excited electronic state, Phys. Rev. A 88, 062701 (2013)
4. V. Laporta, R. Celiberto and J. Tennyson, Resonant vibrational-excitation cross sections and rate constants for low-energy electron scattering by molecular oxygen, Plasma Sources Sci. Technol. 22, 025001 (2013)
5. V. Laporta, R. Celiberto and J.M. Wadehra, Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N2 and NO molecules, Plasma Sources Sci. Technol. 21, 055018 (2012)
6. V. Laporta, C.M. Cassidy, J. Tennyson and R. Celiberto, Electron-impact resonant vibration excitation cross sections and rate coefficients for carbon monoxide, Plasma Sources Sci. Technol. 21, 045005 (2012)
7. A. Lombardi, N. Faginas-Lago, L. Pacifici, A. Costantini, Modeling of Energy Transfer From Vibrationally Excited CO2 Molecules: Cross Sections and Probabilities for Kinetic Modeling of Atmospheres, Flows, and Plasmas, Journal of Physical Chemistry A 117, 11430 (2013)
8. A. Lombardi, A. Laganà, F. Pirani, F. Palazzetti, N. Faginas Lago, Carbon Oxides in Gas Flows and Earth and Planetary Atmospheres: State-to-State Simulations of Energy Transfer and Dissociation Reactions, Lecture Notes in Computer Science 7972, 17 (2013)
9. M Bartolomei, F. Pirani, A. Laganà, A. Lombardi, A full dimensional grid empowered simulation of the CO2 + CO2 processes, Journal of Computational Chemistry 33, 1806 (2012)
10. M. Capitelli, I. Armenise, E. Bisceglie, D. Bruno, R. Celiberto, G. Colonna, G. D'Ammando, O. De Pascale, F. Esposito, C. Gorse, V. Laporta, A. Laricchiuta, Thermodynamics, transport and kinetics of equilibrium and non-equilibrium plasmas: a state-to-state approach, Plasma Chemistry and Plasma Processing 32, 427 (2012)
11. M Capitelli, R Celiberto, G Colonna, G D'Ammando, O De Pascale, P Diomede, F Esposito, C Gorse, A Laricchiuta, S Longo, L D Pietanza, F Taccogna, Plasma kinetics in molecular plasmas and modeling of reentry plasmas, Plasma Physics and Controlled Fusion 53, 124007 (2011)
12. G. Colonna, Problems and perspectives of state-to-state kinetics for high enthalpy plasma flows (invited), RGD29 29th International Symposium on Rarefied Gas Dynamics, Xi'an (China), July 13-18, 2014
13. A. Laricchiuta, Electron-impact excitation cross sections for air kinetics, Workshop Boris F. Gordiets: Air plasma chemistry, XXI Europhysics Conference on the Atomic and Molecular Physics of Ionized Gases, Viana do Castelo (Portugal), July 10-14 2012
14. A. Laricchiuta, The Phys4Entry database, 53rd Course dell'International School of Quantum Electronics del Centro Ettore Majorana "Molecular Physics and Plasmas in Hypersonics II", Directors M. Capitelli, D. Bruno and A. Laricchiuta, Erice (Italy), September 8-15, 2012
15. A. Laricchiuta, The Phys4Entry Database, Workshop on Plasma Data Exchange, organized by L. Pitchford and A. Laricchiuta, Special Session in 65th Gaseous Electronic Conference, University of Texas, Austin (TX), October 22-26, 2012
16. A. Laricchiuta Dynamical information for kinetic modelling and transport of He/H2 plasmas, 2nd IAEA Research Coordination Meeting on Atomic and Molecular Data for State-Resolved Modelling of Hydrogen and Helium and their Isotopes in Fusion Plasma, IAEA Vienna (Austria), July 3-5, 2013
17. A. Laricchiuta, I. Armenise, M. Cacciatore, R. Celiberto, F. Esposito, P. Gamallo, A. Laganà, V. Laporta, A. Lombardi, S. Orlandini, F. Pirani, M. Rutigliano, R. Sayós, J. Tennyson and M. Capitelli Phys4EntryDB: a Database for State-to-State Kinetics of Planetary Atmospheres, Special Session (382-FD-48) Reacting Flows, AIAA Science and Technology Forum and Exposition (SciTech2014), National Harbor, Maryland (USA), January 13-17, 2014
18. V. Laporta and D. Bruno, Electron-vibration energy exchange models in nitrogen-containing plasma flows, J. Chem. Phys. 138, 104319 (2013)
19. M. Capitelli, G. Colonna, G. D’Ammando, V. Laporta, A. Laricchiuta, The role of electron scattering with vibrationally excited molecules on non-equilibrium plasma kinetics, Physics of Plasmas 20, 101609 (2013)
20. M. Capitelli, G. Colonna, G. D’Ammando, V. Laporta, A. Laricchiuta, Non-equilibrium dissociation mechanisms in low temperature nitrogen and carbon monoxide plasmas, Chem. Phys. 438, 31 (2014)
21. D. Bruno, F. Esposito, V. Giovangigli, Relaxation of rotation and vibrational energy and volume viscosity in H-H2(v,j) mixtures, J. Chem. Phys. 138, 084302 (2014)
22. S. Depraz, M.Y. Perrin, A. Soufiani, Infrared emission spectroscopy of CO2 at high temperature. Part I: Experimental setup and source characterization, Journal of Quantitative Spectroscopy and Radiative Transfer 113, 1 (2012)
23. S. Depraz, M.Y. Perrin, Ph. Rivière, A. Soufiani, Infrared emission spectroscopy of CO2 at high temperature. Part II: Experimental results and comparisons with spectroscopic databases, Journal of Quantitative Spectroscopy and Radiative Transfer 113, 14 (2012)
24. A.S. Dikalyuk, S.T. Surzhikov, Equilibrium spectral radiation behind the shock wave front in a CO2-N2 gas mixture, High Temperature 52, 35 (2014)
25. M. Capitelli, G. Colonna, G. D’Ammando, R. Gaudiuso, D. Pietanza, Laser induced Breakdown Spectroscopy: Theory and Applications in Springer Chapter 2: Physical Processes in Optical Emission Spectroscopy (2014) (isbn 978-3-642-45084-6)
26. M. Capitelli, G. Colonna, L.D. Pietanza, G. D’ammando, Coupling of radiation, excited states and electron energy distribution function in non-equilibrium hydrogen plasmas, Spectrochimica Acta Part B 83-84, 1 (2013)
27. G. D’Ammando, M. Capitelli, F. Esposito, A. Laricchiuta, L.D. Pietanza, and G. Colonna, The role of radiative reabsorption on the electron energy distribution functions in nozzle plasma expansion (2014) submitted
28. I. Armenise, E. Kustova, State to state models for CO2 molecules: from the theory to an application to hypersonic boundary layers, Chem. Phys. 415, 269 (2013)
29. A Guy, A. Bourdon, M.Y. Perrin, Consistent multi-internal-temperatures models for nonequilibrium nozzle flows, Chemical Physics 420, 15 (2013)
30. L. Cutrone, M. Tuttafesta, M. Capitelli, A. Schettino, G. Pascazio, G. Colonna, 3D Nozzle Flow Simulations including State–to–State Kinetics Calculation, RGD29 29th International Symposium on Rarefied Gas Dynamics, Xi'an (China), July 13-18, 2014
31. G. Colonna, D. D’Ambrosio, L.D. Pietanza, G. D’Ammando, M.Capitelli Multi-temperature model derived from state-to-state kinetics for hypersonic entry in Jupiter atmosphere, RGD29 29th International Symposium on Rarefied Gas Dynamics, Xi'an (China), July 13-18, 2014
32. R. Celiberto, V. Laporta, A. Laricchiuta, J. Tennyson, J.M. Wadehra, Molecular Physics of Elementary Processes relevant to Hypersonics: electron-molecule collisions, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
33. A. Laganà, A. Lombardi, F. Pirani, P. Gamallo, R. Sayós, I. Armenise, M. Cacciatore, F. Esposito, M. Rutigliano, Molecular Physics of Elementary Processes relevant to Hypersonics: atom-molecule, molecule-molecule and atoms-surface processes, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
34. A. Bourdon, J. Annaloro, A. Bultel, M. Capitelli, G. Colonna, A. Guy, T.E. Magin, A. Munafó, M.Y. Perrin, L.D. Pietanza, Reduction of state-to-state to macroscopic models for hypersonics, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
35. E.V. Kustova, E.A. Nagnibeda, I. Armenise, Vibrational-Chemical Kinetics in Mars Entry Problems, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
36. D. Bruno, A. Panarese, S. Longo, F. Taccogna, P. Minelli, S.T. Surzhikov, A.S. Dikaljuk, P. De Palma, M.D. de Tullio, Particle methods for nonequilibrium hypersonic and plasma flows, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
37. G. Colonna, G. D'Ammando, A.S. Dikalyuk, M. Panesi, L.D. Pietanza, S.T. Surzhikov, Advanced Models in Shock-Waves, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
38. M.Y. Perrin, G. Colonna, G. D'Ammando, L.D. Pietanza, Ph. Riviere, A. Soufiani, S. Surzhikov, Radiation Models and Radiation Transfer in Hypersonics, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
39. S. Surzhikov, P. Reynier, G. Seller, F. Taccogna, Radiative aerothermodynamics of entering space vehicles: toward the use of state-to-state approach, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
40. Y. Babou, D. Lequang, O. Chazot, S.T. Surzhikov, A.S. Dikaljuk, A. Panarese, G. Cicala, S. Longo, J. Hoffman, Z. Szymanski, A. Kaminska, M. Dudeck, D. Vacher, Thermodynamic characterization of high-speed and high-enthalpy plasma flows, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014)
41. A. Schettino, D. D'Ambrosio, Different approximation levels in using CFD for the design of hypersonic vehicles, Special Issue of The Open Plasma Physics Journal Molecular Physics and Plasmas in Hypersonics vol. 7 (Suppl. 1:M1) (2014).
Potential Impact:
Potential impact
The project involved scientific research in a multidisciplinary framework. Efforts have been directed along the whole chain from the ab initio description of the elementary processes to the kinetic modelling and through CFD simulations of real-world aerospace vehicles's entry conditions.
The focus has been on gas mixtures representative of the atmospheres of Earth, Mars and Jupiter.
The results obtained are naturally instrumental to the achievement of the project's goals; but they also represent advance in scientific knowledge beneficial to other technological domains. In many cases, they have not been fully exploited within the project activities so that their scientific value is increased by the potential to solicit new studies.
Molecular Dynamics
Fundamental Molecular Dynamics (MD) studies have produced a wealth of accurate data for the description of the elementary processes (chemical reactions, radiative processes, gas-surface interactions) occurring in high temperature gas mixtures around high speed vehicles.
This is the basis for the development of physically sound simulation tools. With their focus on high temperature processes and on vibrational-selected resolution, the data obtained represent a clear advance with respect to the current knowledge.
In many cases, the production of accurate physical data, previously unavailable, lifts the need for phenomenological or ad hoc modeling thus improving the reliability of the simulation tools.
It is the case, for example, of the studies on collisional energy transfer in CO2. Being the first accurate data obtained for this problem, they will likely be useful for the carbon dioxide chemistry of interest for environmental studies.
Vibrational-specific collisional energy transfer in the Hydrogen molecule, instead, is of great interest in the magnetic confinement fusion community for its role in the neutral ion beam sources.
Results on gas-surface interactions are naturally of great interest for the design of the Thermal Protection System (TPS) of aerospace vehicles but they are also beneficial in material processing applications.
Establishment of a aerospace reference database
In order to widen the outreach of this effort and to establish a shared source of accurate reference data, a digital database has been set up and made freely available to the scientific community.
With its focus on high temperature processes, this is the first ever attempt targeting the aerospace community and it will sustain the diffusion of physics based approaches to application-oriented engineering studies.
Kinetic modelling
Detailed kinetic models have been produced that include all the new and accurate physical data. They have been validated against the scientific literature and shown to have a large impact on the simulation results while constraining further the sources of uncertainty, therefore improving on the reliability of the simulations themselves.
In addition, a great effort has been undertaken to develop fast and accurate reduced models to be used in feasibility or optimization studies.
Experiments
The theoretical work has been complemented with a number of experimental campaigns aimed at the description of the phenomena occurring in high-temperature and/or high-speed gas flows.
Beyond serving as a validation benchmark for the new models, these data enrich the knowledge base and will foster new studies.
Computational Fluid Dynamics
In order to make the accumulated knowledge available to real-world applications, the new models have been implemented in state-of-the-art, industrial-level, Computational Fluid Dynamics (CFD) simulation tools.
The results demonstrate that a more accurate, physics based, approach is viable thus urging the aerospace community to adopt the new paradigm.
In some cases, the new results clearly show the superiority of physics based modelling over phenomenological approaches. It is the case, for example, of the rebuilding of hypersonic flow tests with CO2 mixtures in the HYPULSE facility, where detailed modelling improved dramatically the agreement with experimental measurements; or the challenging problem of the very high speed Galileo entry into Jupiter atmosphere where the accuracy of fundamental physical data (transport properties, in this case) are shown to have a dramatic effect on the predicted convective heat flux.
Finally, in the frame of the project's lifetime, CFD studies did not explore the whole spectrum of possible applications, paving the way for additional studies.
Dissemination
The project activities and results have been made available to a wider audience via dissemination activities targeting the aerospace research community and the scientific community at large. In addition they have been presented at EU funded workshops aimed at increasing the general public's awareness on EU funded research activities.
Scientific community
The scientific results obtained have been published in international refereed journals and presented at specialised conferences. This resulted in 79 journal publications and 61 conference presentations (among which 17 are invited lectures).
In addition, the project objectives, activities and results have been discussed in few occasions:
1. The Discussion Group on Non-equilibrium flows, chaired by E. Josyula of the Air Force Research Laboratory holds its meetings during AIAA conferences. During the AIAA Science and Technology Forum and Exposition, held at National Harbor, Maryland (USA), 13-17 January 2014, a special session on reactive flows hosted two invited talks from the CNR partner (A. Laricchiuta and G. Colonna). (More details at: https://info.aiaa.org/tac/ASG/FDTC/DG/NEF.aspx)
2. During the 65th Gaseous Electronics Conference (Austin, TX, USA, October 22-26 2012), a special workshop on “Plasma Data Exchange Project” has been organised and chaired by A. Laricchiuta (CNR). During the workshop the project database has been presented. (More details at: http://meetings.aps.org/Meeting/GEC12/Session/GT2)
3. The “Ettore Majorana” Foundation and Centre for Scientific Culture, located in Erice, Italy, from 8 to 15 Sept 2012 hosted the 53rd course of the International School of Quantum Electronics dedicated to: “Molecular Physics and Plasmas in Hypersonics”. The course featured as directors and as invited speakers the project partners. (More details at: http://users.ba.cnr.it/imip/cscpal38/Erice2/)
FP7 project presentation workshops
“Let’s embrace space”, FP7 Space Conference 2011, Budapest, 12-13 May 2011.
European Corner supported by EU Commission, during the event “Notte dei Ricercatori”, held at the Politecnico of Bari (Italy) on September 23 2011.
FP7 Workshop: “Space – Space foundations”, Rome, 29 May 2012. Organised and sponsored by the Italian Space Agency.
List of Websites:
http://users.ba.cnr.it/imip/cscpal38/phys4entry/index.html