Structure of Turbulent Separating Flow in Two-Dimensional Diffusor

Summary

The structure of the turbulent wall layer developing into separation was studied. The experiments were performed in a two-dimensional asymmetric diffuser which was attached to a downstream end of a long straight channel to provide a fully developed turbulent inlet condition. The flow visualization revealed that the streaky structure in the wall layer of the approaching flow develops in its length scale under the action of the adverse pressure gradient and reaches to the local and instantaneous backflow, called incipient detachment. Further downstream, another lump of fluid comes running upstream with different spanwise scale and large transverse velocity, which characterizes the flow near the transitory detachment point.