THE FLAPPING SHEAR-LAYER FORMED BY FLOW SEPARATION FROM THE FORWARD CORNER OF A SQUARE CYLINDER

The turbulent shear layer and the associated recirculation region on t he sidewall formed in flow separation from the forward comer of a squa re cylinder have been studied with one-component laser-Doppler velocim etry. Because of vortex shedding, the flow is approximately periodic, and is treated as a separated flow undergoing large-amplitude forcing at the shedding frequency. Phase (ensemble)-averaged velocities and tu rbulence intensities were obtained, and a close relationship in phase and amplitude between phase-averaged turbulence intensities and gradie nts of phase-averaged velocity is found in much of the flow region. Th e similarity behaviour of the phase-averaged profiles in the shear lay er as well as the streamwise growth of the shear layer are investigate d. While phase-averaged velocity profiles collapse well in similarity coordinates, normalized turbulence intensities exhibit systematic devi ations from similarity. Shear-layer growth also departs markedly from the linear growth law of unforced plane mixing layers. The effect of t he recirculation is suggested as a possible explanation for some of th ese deviations. Similarities to and differences from steady and forced mixing layers, steady separated flows with recirculation, and unstead y boundary layers are discussed.