Non-Oberbeck-Boussinesq effects in turbulent convection in cryogenic helium at high Rayleigh numbers

Non-Oberbeck-Boussinesq effects in turbulent convection in cryogenic helium at high Rayleigh numbers
Experiments on turbulent Rayleigh-Bénard convection (RBC) in cryogenic helium gas reach the highest possible Rayleigh numbers generating vigorous turbulence under controlled conditions that come close to those in real atmospheric flows and can thus provide insights into the turbulent transport mechanisms of heat and momentum in natural systems. However, the high Rayleigh numbers require to operate the working fluid close to the phase boundary or the critical point, which causes fluctuations of all material parameters, causing deviations from the Oberbeck-Boussinesq (OB) regime of thermal convection. In this project, we will focus on impacts of these deviations---the so-called non-Oberbeck-Boussinesq (NOB) effects---on the turbulent transport by systematically combining expertize in cryogenic RBC experiment (CZ) and massive numerical simulation (DE). We will implement accurate dependencies of cryogenic helium parameters on temperature and pressure into novel NOB numerical simulations, and directly compare with experiments as well as the idealized OB limit at the same Rayleigh numbers.