Swirl strength analysis of a turbulent round jet

Particle image velocimetry (PIV) measurements were conducted in the vertical (x-y) central plane of a round jet. From the instantaneous velocity fields, in-plane two-dimensional swirling strength evaluations are carried out and used to identify turbulent structures. Here, swirling strength is defined as the imaginary portion of the complex eigenvalue of the local velocity gradient tensor and it is unambiguous measure of rotation. From the swirling strength analysis, statistics of the vortex cores and their rotational sense is extracted. A vortex identification algorithm was employed to identify the size and distribution of the vortices.