Assessment of RANS models for Rayleigh-Taylor mixing using the Macroscopic Forcing Method

The Macroscopic Forcing Method (MFM) is a numerical tool for assessing Reynolds-averaged Navier-Stokes (RANS) closure operators (Mani & Park, 2021). It specifically can be used to assess nonlocality by measuring moments of the eddy diffusivity kernel of a turbulent flow. Previous work showed that nonlocality should not be neglected in RANS models for Rayleigh-Taylor (RT) mixing using MFM measurements for mean scalar transport in both 2D RT (Lavacot et al, in review) and 3D RT (Lavacot et al, 73^rd APS DFD Meeting, 2022). In this talk, the k-L-F model is presented, which incorporates nonlocality of the eddy diffusivity through the addition of an equation for the turbulent scalar flux to the k-L model (Dimonte & Tipton, 2006) based on MFM measurements. By applying MFM to the RANS model itself, this model is evaluated along with the standard k-L model and the BHR-4 model (Braun & Gore, 2021), both of which are used for predicting RT mixing. Assessments are made by comparing the MFM-measured eddy diffusivity moments from the RANS simulations against those from high-fidelity simulations.