Counter-rotating vortices embedded in a turbulent boundary layer with inclined jets

Counter-rotating vortex pairs in an otherwise flat-plate turbulent boundary layer were studied in a wind-tunnel model experiment. The vortices were produced with pairs of inclined round jets with nozzle exit flush with the plate surface. The skew angle and pitch angle of the nozzle were 45 deg. The Reynolds number based on the momentum thickness of the oncoming boundary layer was 3.8×10³. A velocity field survey was performed with a three-component laser Doppler anemometry system. The effects of jet speed on the streamwise development of the vortices were investigated. The flow had an upwash region in between the vortices that were embedded in the turbulent boundary layer. The upwash was produced by the vortices and the interaction between diametrically opposed secondary, near-wall flows. Velocity measurements indicated flow separation and entrainment behind the jet exit, and this was corroborated by surface flow observation. The vortex development was divided into two stages: a near-field stage where the wake of the jet plays an important role and a far-field stage where turbulent dissipation and diffusion are important.