Three- and Four-Equation RANS Modeling of a Small Atwood Number, Transitional Rayleigh–Taylor Mixing Experiment*

A priori calibrated three- and four-equation mechanical–scalar Reynolds-averaged Navier–Stokes models [O. Schilling and N. J. Mueschke, Physical Review E 96, 063111 (2017)] are applied to a small Atwood number, transitional Rayleigh–Taylor mixing experiment previously performed in a water channel facility and modeled using direct numerical simulation [N. J. Mueschke and O. Schilling, Physics of Fluids 21, 014106 (2009)]. It is shown that the use of time-dependent model coefficients and initial conditions closely corresponding to those in the experiment are needed to accurately capture transition to turbulence. Comparisons of the mixing layer width, molecular mixing parameter, mean and turbulent fields, and other quantities among the model predictions, experimental data, DNS data, and analytic self-similar solutions are presented are discussed.