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

The spanwise growth of a turbulent spot in plane Couette flow is exper imentally analysed by determining the flow field in the region between the spot and the undisturbed surrounding flow. Both the streamwise an d spanwise velocity components were measured, and show that the spot f orces fluid outward, giving rise to a spanwise velocity component. The resulting velocity profile has an inflectional character and the exis tence of spanwise travelling waves was verified. The wave velocity was determined and found to be in good agreement with numerical simulatio ns as well as now visualisation results, earlier reported in the liter ature.