Simulating the Process of Turbulent Mixing, With Applications to Convection and Nucleosynthesis in Giant Stars and to the Laser-Driven Implosion of an Inertial Confinement Fusion Capsule
The process of fluid turbulence plays an important role in science and engineering in many different areas where fluid dynamics is involved. This research team has studied fluid turbulence for many years. Recent efforts are focused on the process of compressible turbulent mixing in inertial confinement fusion (ICF) and in late stages of stellar evolution. The recent development of many-core CPUs (and GPUs) is enabling these researchers to go beyond isolated simulations of tiny portions of problems of interest, such as turbulence in a box or convection in a tiny portion of the sun’s upper convection zone. They are now able to simulate the turbulent mixing processes of interest in their full and proper context. This is much more computationally demanding, but also much more scientifically rewarding. For giant stars, they simulate the entire convection zone above the helium burning shell, at a radius of about 10,000 km, up to the region at a height of about 30,000 km where hydrogen-rich material is entrained from the stably stratified layers above. Recently, they were able to simulate this entrainment process, and they are currently adding the nuclear reactions that drive the so-called hydrogen ingestion flash and that are responsible for nucleosynthesis of a range of heavy elements. In the ICF problem, they simulate the mixing of fluids with much larger density differences under the action of multiple fluid instabilities in a laser-driven compression. In both applications, statistical models for the turbulent mixing are sought to add into simulation codes. This requires highly resolved, first-principles simulations.