On the Development of Coherent Structure in a Plane Jet (Part 1, Characteristics of Two-Point Velocity Correlation and Analysis of Eigenmodes by the KL Expansion)

Abstract

The simultaneous measurement of the velocities at two points with X-type hot wire probes has been performed in three regions of a plane jet (i.e., the potential core region, the interaction region and the self-preserving region). The Karhunen Loeve (KL) expansion was applied to the velocity data, and the development of coherent structure was investigated by the eigenvalues and eigenfunctions as well as the spatial velocity correlations. It is found that in the potential core region the first and second modes are dominant in the kinetic energy with almost the same magnitude. The profiles of the eigenfunctions downstream of the interaction region show that the first mode of streamwise velocity u is asymmetrical about the jet centerline whereas that of cross-streamwise velocity v is symmetrical. These results are consistent with the feature of the two-point velocity correlation.