A priori Validation of a Transition Model for Variable Density Flows

Numerous applications, including astrophysical and geophysical flows, as well as Inertial Confinement Fusion, require variable density models for stratified and sheared flows. Although existing models perform well in the fully turbulent regime, they are often unable to model the early stages of the disturbance growth. We assess a new transition model (Israel & Haas, 2023, APS DFD) using linear stability theory (LST) and direct numerical simulation (DNS). The model is an extension of the variable density BHR turbulence model developed by Besnard et al. Besides the conservation equations for mass and momentum, equations for the full Reynolds stress, the turbulence mass flux (a-equation) as well as the density-self-correlation (b-equation) are modified to ensure a physics-based approach to transition. LST and DNS are used to test the model for Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) dominated flows. Here we show the results of a priori tests using both LST and DNS results, considering balance equations to get insight into the contributions of various terms (e.g. production, dissipation, transport, etc.), and also to provide useful information for the design and validation of the transition model.