On the Development of Coherent Structure in a Plane Jet: Part 4, The Multipoint Simultaneous Measurement of Two-Component Velocities and the Simple Coherent Structure Model

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 using 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., a vertically striped pattern is formed. On the basis of the result of the Karhunen-Loève (KL) expansion, a new interpretation of the coherent structure model in the self-preserving region of a turbulent plane jet has been given from the combination of “flapping” and “puffing”.