A DNS Study on the Forcing of Three-Dimensional Instability Mechanisms of Laminar Planar Free-Shear Layers

Direct numerical simulations were performed of a free-shear layer developing downstream from a flat no-slip splitter plate. The simulation results show that 3D streaky perturbations developing in the boundary layer on the high-speed side of the splitter-plate are convected downstream from the trailing edge and influence the development of the planar free-shear layer. Several other simulations are performed in which a spanwise-wavy shape is introduced to the trailing edge of the splitter plate to force the downstream development of the free-shear layer. Introduction of the spanwise-waviness to the trailing edge results in significantly earlier smaller-scale breakdown of the free-shear layer. The effect of varying the spanwise wavelength and height of the waviness on the downstream development of the free-shear layer is characterized. The events leading to smaller-scale breakdown of the free-shear layer are studied in each of the forced cases, and a general mechanism for smaller-scale breakdown is identified.