Evolution of the Counter-Rotating Vortex Structure in a Crossflow Jet

The structure of counter-rotating vortex pair of round jet issuing normally into a crossflow was studied using a flow visualization technique and PIV measurements. Experiments were performed at a jet-to-crossflow velocity ratio of 3.3, and the Reynolds number of 1, 050, based on the crossflow velocity and jet diameter. Instantaneous velocity field was acquired using two frame cross correlation PIV technique. The angle of laser sheet beam was set to be perpendicular to the ensemble averaged trajectory of the crossflow jet. The mean velocity field was obtained by ensemble averaging over 300 realizations of instantaneous velocity fields for each plane. It was found that the counter-rotating vortex pair was initiated from the hanging vortices appearing at both sides of the jet colunm. The detailed characteristics of the velocity fields were discussed with the evolution of the counter-rotating vortex pair.