Direct Numerical Simulation of Multicomponent-Species Transitional Mixing Layers

Abstract

A representation of multicomponent-liquid composition as a linear combination of two single Gamma probability distribution functions (PDFs) is used to describe a large number of multicomponent-liquid drops evaporating in a gas flow. The PDF, called the doubleGamma PDF, depends on the molar mass. Gas conservation equations for mass, momentum, species and energy are combined with differential conservation equations for the first four moments of the gas-composition PDF, all written in an Eulerian frame, and these equations are coupled to the perfect gas equation of state. Source terms in all conservation equations account for the gas/drop interaction. The drop governing equations, written in a Lagrangian frame, encompass differential conservation statements for position, mass, momentum, energy and four moments of the liquid-composition PDF. Direct Numerical Simulation (DNS) is performed for a three-dimensional mixing layer whose lower stream may initially be laden with drops colder than the surrounding gas. Simulations are performed for both gaseous and drop-laden mixing layers at high enough initial Reynolds number, so that transition is attained in all cases. The results from this transitional study are compared to previous single-component-liquid drop-laden mixing layers, and with previous pre-transitional DNS results obtained with the same multicomponent-liquid composition model. Of interest is the influence of the liquid composition on the development of the flow and the trends obtained with increasing free-stream gas temperature.