Simulations of spatially developing plane shear layers and jets

Abstract

A computational model has been developed for spatially evolving planar shear flows which captures the response of two-dimensional structures in planar shear layers and jets to external forcing. The simulations show that there is an initial increase in the energy transfer to the fluctuating quantities resulting in an increased growth of the layer. However, this increased growth is followed by a region with net transfer of energy from the fluctuating field back to the mean field resulting in a reduced growth of the layer. It appears that the far downstream (x/δ_ω>100) growth rate of the forced shear layer is only slightly different from the unforced case. The inhibition of pairing in the case of zero phase difference between subharmonic and fundamental that has been seen in temporal simulations was not observed in spatial simulations.

The shear layer growth in the initial region of weak planar jets was found to be sensitive to forcing. The varicose forcing used in this study was sufficient to inhibit the transition into a sinuous jet mode. The symmetry enforced by the varicose forcing lead to significant changes in the structure of the velocity fluctuations.