New results on the structure of turbulence in a mixing layer with and without swirl

The near field of a 2.14 × 105 Reynolds number, low-Mach-number, cylindrical jet with and without swirl has been investigated by high-speed stereo PIV in a transverse plane, two diameters downstream of the jet exit. Using spatiotemporal correlations, we investigate the dynamics of streamwise vorticity in the shear layer, responsible for the mixing properties of the jet, and show how swirl affects this vorticity. A dynamical scenario is proposed, which explains how the mean shear and the azimuthal m = 0 vortices contribute to the spatial organization observed.