ON THE SPREADING MECHANISMS OF A TURBULENT SPOT IN PLANE COUETTE-FLOW

The spanwise growth of a turbulent spot in plane Couette flow is experimentally analysed by determining the flow field in the region between the spot and the undisturbed surrounding flow. Both the streamwise and spanwise velocity components were measured, and show that the spot forces fluid outward, giving rise to a spanwise velocity component. The resulting velocity profile has an inflectional character and the existence of spanwise travelling waves was verified. The wave velocity was determined and found to be in good agreement with numerical simulations as well as now visualisation results, earlier reported in the literature.