On the Development of Coherent Structure in a Planet Jet (Part2, Investigation of Spatio-Temporal Velocity Structure by the KL Expansion) On the Development of Coherent Structure in a Plane Jet : Part 2, Investigation of Spatio-Temporal Velocity Structure by the KL Expansion

The simultaneous measurement of the velocities at two points with X-type hot wire probes has been performed in three different downstream regions of a plane jet (the potential core region, the interaction region and the self-preserving region). By applying Karhunen-Loeve (KL) expansion in space and time, the structure development of the plane jet is investigated from a viewpoint of both space and frequency. From the downstream variation of the eigenfunctions, it is found that in the early stage of the interaction region the profiles of the first u (streamwise component of velocity fluctuation) and υ (cross-streamwise component of velocity fluctuation) mode in the low frequency range become self-similar, but in high frequency range these continue to change until the self-preserving region. The characteristics of coherent structure can be extracted efficiently by the two-point spatial velocity correlation reconstructed from the first mode of KL expansion.