Advanced modelling reveals the secrets of complex fluid flows
The flow of liquids or gases, known as fluid dynamics, affects many aspects of daily life. Bodies are fluid mechanical laboratories, fluid mechanics drives engines and turbines, and weather patterns obey its laws. Fluid mechanics acts across scales, from microscopic aerosols, carrying viruses, to cosmological events such as supernovae. Shockwaves are a particular phenomenon in fluid mechanics, characterised by sudden changes in temperature and pressure. A well-known example is the ‘sonic boom’ of aircraft flying at supersonic speeds. Shockwaves can also be used to control fluid processes. The EU-supported NANOSHOCK project investigated the interactions of shockwaves with multi-material interfaces; liquid droplets, comprised of air and liquid, being interfaces of particular interest, especially regarding their shock-induced disintegration. “Understanding this offers promise for new microscopic drug delivery into individual cells, with cells temporarily perforated while a precise therapeutic dose of a compound is delivered into them,” explains the principal investigator Nikolaus Adams from the Technical University of Munich, the project host. A key NANOSHOCK result was the development of the numerical simulation environment ‘ALPACA’. “With 20 000 lines of code, ALPACA is one of the most advanced simulation environments for large-scale laboratory simulations of complex fluid flows,” according to project coordinator Stefan Adami. “We have developed groundbreaking numerical methods with unprecedented accuracy and efficiency, developing a virtual flow-physics laboratory.” ALPACA is open source and available to the scientific community. It is modular, so can be adapted and extended to integrate any flow-physics model based on continuum conservation equations. A range of postprocessing tools and data analysis instrumentation are also available.
Investigating realistic physical problems
A key concern of NANOSHOCK was to better understand the interaction between shockwaves and phase interfaces. At such interfaces, the liquid and gas phase of the same substance (e.g. liquid water and water vapour) or ‘multi-material’ fluids (e.g. oil and water) meet. The activity of these interfaces is key to chemical processes, including those of interest to biomedicine. ALPACA enabled the team to investigate many different shockwave and interface dynamics across various space and time scenarios in highly accurate detail. As such processes involve structures at the micrometre scale and at micro- to nanosecond timescales, experiments are not practical. “We discovered a previously unknown mechanism where shock breaks up a layered oil-shell capsule filled with a liquid drug, itself filled with a gas bubble. The shockwave causes the internal gas to deliver a highly focused and shielded micro-jet of the inner material, in a very precise quantity, through a cell-membrane surrogate. We are exploring this mechanism further, particularly with regards to targeted drug delivery,” adds Adams. The work was made possible by newly developed high-resolution numerical models for gas and liquid dynamics, and so-called level-set representations of the interfaces, using parallel computing for simulations on hundreds of thousands of supercomputer processing units.
More efficient applications
The ALPACA simulation environment can be used to investigate fundamental physical phenomena, optimise design parameters for a range of applications and support the discovery of new solutions. “Our models can be used as data generators to help detect hidden physical mechanisms and relations of flow phenomena,” says Adams. The project undertook collaborations with other research groups, which continue. One such collaboration involves the contribution of numerical data for experiments into nanoparticle manufacturing. In another, the team co-develops advanced tools for more accurate predictions of melt pool flows in metal additive manufacturing.
Keywords
NANOSHOCK, drug delivery, fluid dynamics, fluid mechanics, fluid, liquids, gases, shockwaves, droplets, cells, micrometre, nanosecond, simulation
