Numerical Simulation of Two-Dimensional, Spatially Developing Mixing Layers

Numerical simulation of a forced, two-dimensional, spatially-developing mixing layer using a control-volume formulation is performed. Three classes of forcing functions are used at the inlet boundary which are; (i) steady boundary conditions, (ii) combinations of the fundamental, first subharmonic, and second subharmonic modes from linear inviscid stability theory, and (iii) a broad spectrum of modes whose velocity power spectrum and transverse turbulence intensity relationship is taken from experiment. The results show that shear layer rollup occurs for time-dependent inlet boundary conditions and that the resulting vortex dynamics are determined from the subharmonic content of the inlet boundary conditions. It is shown that the inlet boundary conditions play a major role in the development of time-averaged properties such as shear layer growth rate, time-averaged velocity profiles, and turbulence statistics. For low-Reynolds number computations (Re- 100), no explicit subgrid-scale (SGS) model is used, while for high-Reynolds number computations (Re -10000), the effect of unresolved scales is examined by using the Smagorinsky SGS model with a purely dissipative positive coefficient. A locally averaged spatially and temporally varying coefficient similar to the dynamic SGS model of Germano is explored.