ORGANIZED VORTEX AND THERMAL STRUCTURES IN A FORCED CONVECTION REATTACHING SEPARATED FLOW.

A description of the time-dependent vortex and thermal structures in the separated and reattached flow around a rectangular cylinder is presented. Sound is applied to induce a perturbing velocity across the separating shear layers and to produce periodic vortex shedding. Results from three different types of investigation are presented: (1) numerical simulation of the flow and heat transfer process, (2) flow measurement by hot wire and laser doppler anemometry and (3) visualization of the instantaneous thermal gradient field using Schlieren photography. At moderate sound pressure levels, hot wire measurements of the velocity fluctuations induced by the passage of the vortex structures provide strong evidence of vortex pairing, in line with the predictions. The thermal gradient fields associated with the paired vortex structures are visualized using Schlieren photography. Autocorrelation and spanwise cross correlation using hot wire probes infer a regular spanwise structure to the flow as a result of the pairing process.