Better heat shields for dangerous phenomena
Spacecraft re-entering the Earth's atmosphere experience intense heat caused by friction with air molecules. Thermal protection systems (TPSs) protect the vehicles from over-heating. During the most critical phase of re-entry, the hypersonic flow of air (more than five times the speed of sound) over the surface of the spacecraft creates a sort of laminar boundary layer. Inside this layer, the majority of heat, momentum and mass transfer takes place. During a so-called hypersonic transition, the boundary layer flow goes from laminar to turbulent, causing the TPS at the same location to receive more than three times the incoming heat flux. European and Russian scientists initiated the EU-funded Transhyberian project to study hypersonic transition and propose local thermal control mechanisms at the boundary layer for future space missions. Investigators chose to study a sharp cone configuration at five experimental facilities in the EU and Russia. Experimental data is complemented by numerical simulations. During the first year of the project, investigators characterised the noise at each facility to explain possible differences in various measurements under seemingly comparable conditions. All numerical codes describing transition onset have been developed. Techniques include direct numerical simulation (DNS), stability algorithms, Reynolds-averaged Navier–Stokes (RANS) algorithms and correlation analysis. Scientists designed a common model experiment taking into account differences at the various facilities. Finally, a complete experimental and numerical (computational fluid dynamics (CFD)) campaign has been defined. Flexibility is built in to accommodate changes in response to problems or results during the second year. Transhyberian expects to enhance design for re-use of space vehicles on re-entry with protection against heat generated during hypersonic transition. The project will also strengthen Euro-Russian ties and cooperation in space research, thus strengthening the position of both space programmes.
