Modelling Turbui~nt Mixing by Rayleigh-taylor Instability

Direct two-dimensional numerical simulation and experiments, in which small rocket motors accelerate a tank containing two fluids, have been used to investigate turbulent mixing by Rayleigh-Taylor instability at a wide range of density ratios. The experimental data obtained so far has been used to calibrate an empirical model of the mixing process which is needed to make predictions for complex applications. The model devised, which is a form of turbulence model, is based on the equations of multiphase flow. These equations describe velocity separation arising from the action of a pressure gradient on fluid fragments of different density. The dissipation arising from the drag between the fluid fragments is treated as a source of turbulence kinetic energy which is then used to define turbulent diffusion coefficients. Gradient diffusion processes are thereby included in the model.