INTERACTION OF A STREAMWISE VORTEX WITH A TURBULENT MIXING LAYER

An experimental study has been conducted on the interaction of a single streamwise vortex with a plane turbulent mixing layer. The vortex was generated by a half-delta wing mounted in the settling chamber of a blower-driven wind tunnel. The single-stream mixing layer originated from the top lip of the extended contraction exit, with a tripped initial boundary layer. Initially, the vortex rode below the mixing layer and its effect was to locally distort the mean velocity and Reynolds stress distributions in the lower (high-speed) side of the mixing layer. Once the vortex became embedded within the mixing layer, the distortion, which took the form of a wrinkle, spread through the whole width of the layer. The induced extra strain rates in the mixing layer resulted in the generation of additional, relatively large, Reynolds stresses in the regions around the vortex. In particular, the secondary shear stress ( u′w′̄) reached a maximum absolute value equivalent to about 40% of the maximum primary shear stress ( u′v′̄), thus indicating significantly increased three-dimensionality in the mixing layer. The position and behavior of u′w′̄ was found to be strongly correlated with that of the streamwise vorticity. The vortex appeared to decay rapidly once it was embedded in the mixing layer; the maximum mean streamwise vorticity was observed to decay as approximately 1/X2 in this region. By the last measurement station, almost all the effects in the mixing layer resulting from the vortex, and the identity of the vortex itself, had subsided. © 1990 American Institute of Physics.