An Experimental Study on the Development of Coherent Structure in a Plane Jet (1st Report, Distributions of Two-point Spatial Velocity Correlation and Analysis of Eigenmodes by the KL Expanision)

Abstract

To investigate the development of coherent structure in a turbulent plane jet, the simultaneous measurement of the velocities at two points with X type hot wire probes has been preformed in three regions of the plane jet (i.e. the potential core region, the interaction region and the self-presserving region). The KL expansion (POD) was applied to the velocity data, and the development of coherent structure was investigated with respect to the eigenvalues and eigenfunctions as well as the spacial velocity correaltions. From the distributions of the eigenvalues, it is found that the first and second mode in the potential core region are dominant in the kinetic energy and they show almost the same magnitude. The profiles of the eigenfunctions downstream of the interaction region show that the first mode of main streamwise velocity u is asymmetrical about the jet centeline whereas the one of cross streamwise velocity v is symmertical. These results are consistent with the feature of the correlation coefficient of the two velocity signals on opposite sides of the jet cenerline.