Simulation is the only way to get an idea what exactly happens during the reentry phase of a space vehicle, because measuring is very limited and expensive. Due to the role of chemistry and chemical reactions near the hot surface of the space vehicle, even wind tunnel experiments are not comparable to the flows and reactions appearing during a real reentry. This is a Direct Simulation Monte Carlo Simulation that was developed to simulate granular matter.
Granular materials are ubiquitous in nature, industrial processing and everyday life.
Similarly broad are the physical phenomena controlling their behavior in transport, storage and processing. Often, large-scale computation is the only way to deepen our insight. The reason is that typical granular systems consist of million of particles and most phenomena are only visible after long time scales. This picture shows a granular system of 100.000 dissipative particles demonstrating the clustering instability. The cluster size is already close to the system size.