Numerical simulations of compressible and reacting temporal mixing layers and implications for modeling

Numerical simulations of temporally evolving compressible inert and reacting mixing layers are performed. The results are examined in terms of modeling techniques for transport and reaction in compressible, turbulent mixing layers. In particular, the calculations are analyzed with respect to a recently proposed compressible algebraic stress turbulent transport model (ASM). This new model accounts for variations in the anisotropy of the normal stresses through modification of the pressure-strain terms of the Reynolds stress transport equations. Results from the simulations are consistent with recent detailed compressible mixing layer data and further support the compressibility modification to the pressure-strain modeling. It is shown that incompressible pressure-strain modeling overestimates the contribution of these terms under compressible conditions. Reacting mixing layer results are also presented. Consistent with previous simulations, the mixing layer structure is relatively unaffected by slow reactions. The growth rate, however, is slowed. As the reaction rate increases relative to the convective large-eddy roll-over time scale, the structure is changed considerably. In the slower reaction case, the heat release takes place in a more distributed fashion at the mixed vortex core and results in controlled expansion of the eddy. For faster reactions, a larger fraction of the reaction/heat release takes place in the strained interface between the fuel and oxidizer layers within the vortices. This localized heat release greatly distorts the eddy structure.