ON THE LARGE-SCALE TURBULENT STRUCTURE IN THE SELF-PRESERVING REGION OF A PLANE JET : THE MULTI-POINT SIMULTANEOUS MEASUREMENT OF TWO-COMPONENT VELOCITIES AND SIMPLE COHERENT STRUCTURE MODEL(Plane Jet)

In order to clarify the large-scale coherent structure in a turbulent plane jet, the simultaneous measurement of the main streamwise and the cross-streamwise velocity at 9 points in the self-preserving region of a turbulent plane jet has been performed by an array of X-type hot-wire probes. From the time variation of the main streamwise fluctuating velocity field, it is found that there exists a pair of fluid lumps with the positive and negative fluctuating velocity on opposite sides of the jet centerline. On the other hand, the instantaneous cross-streamwise fluctuating velocity shows the same sign over the cross-section, i.e., the vertically-striped pattern is formed. On the basis of the result of the KL (Karhunen-Loeve) expansion, a new interpretation of coherent structure model in the self-preserving region of a turbulent plane jet has been given from the combination of the "flapping" and the "puffing".