THE FLOW STRUCTURE AND STATISTICS OF A PASSIVE MIXING TAB

Water channel flow visualization and anemometry studies were conducted to examine the flow structure and velocity statistics in the wake of a passive mixing tab designed for enhancement of cross-stream mixing by generation of flow structures characteristic of turbulent boundary layers. Flow visualization reveals that the mixing tab generates a wake comprising a combination of counterrotating, streamwise vortices enveloped by distinct hairpin vortex structures. The counterrotating streamwise vortices are observed to stimulate a strong ejection of fluid along the symmetry plane, which results in very rapid cross-stream mixing. The hairpin vortices are found to undergo successive amalgamation and coalescence downstream of the device, which aids in the streamwise mixing and outward penetration of ejected fluid. After an initially intense mixing process, the mixing tab wake rapidly develops mean velocity, turbulence intensity, and boundary layer integral properties characteristic of a significantly thickened turbulent boundary layer.