A comparison of mix models for the Rayleigh–Taylor instability

Four mix models, implemented into an Arbitrary Lagrangian–Eulerian (ALE) multi-physics code, are compared on simulations of the Rayleigh–Taylor instability. The specific models of interest are a mass diffusion model, the k – L turbulence model, the BHR turbulence model, and a multifluid interpenetration mix model. The bubble growth rates produced by the different models are compared to experimentally determined growth rates. The diffusion model reproduces the characteristic t 1 / 2 growth for diffusion processes and therefore does not reproduce instability growth rates, as expected. The k – L and BHR turbulence models reproduce the nominal instability growth rates at multiple Atwood numbers with a single set of model parameters. The multifluid interpenetration model exhibits diffusion-like behavior and therefore does not reproduce instability growth rates. All four models exhibit Cauchy-like convergence in the mixing layer width with decreasing mesh size, although the multifluid model exhibits both a larger error for a given mesh size and a slower convergence rate than the turbulence models. ► Four mix models have been compared on a Rayleigh–Taylor instability problem. ► The models span a range of physical processes from diffusion to turbulent mixing. ► The results suggest that multiple processes may drive mix in RT-unstable state.