Control of Large-Scale Structures in Spatially Developing Mixing Layers

Abstract

Direct numerical simulations of spatially developing mixing layers were conducted to clarify the effect of phase difference of inflow disturbances on the growth of mixing layers. The disturbances consist of the fundamental and subharmonic modes of the most unstable wave based on linear stability analysis, and the energy transfer between mean flow, fundamental and subharmonic modes was examined. The results show that it is possible to control the development of mixing layers by controling phase difference between two modes. The phase difference determines energy transfer in the regions downstream of the roll-up location where energy is transferred from fundamental to mean flow, and upstream of the pairing location where the energy is transferred from mean flow to subharmonic. This mechanism causes the enhancement and suppression of the growth rate of mixing layers. The phase difference which produces the slowest development of a mixing layer is about 11/16π.