Strong interaction effects on upstream wall pressure in a separated flow with a forward-facing wall jet

Results are presented for an experimental study of the effect of separation on the upstream wall pressure at large Reynolds number in the case of separation of an incompressible turbulent boundary layer on a flat surface. Interpretation of observed upstream wall pressure is facilitated by introducing the concept of reference and interaction flows. The interaction flow is found to be in the forward direction upstream of the separation point, and its magnitude ranges from 10 to 30% of the freestream velocity. A correlation which could be interpreted as a coordinate expansion for large distances is proposed. A discussion is presented of two interpretations of the observed wall pressure distribution for the separation of the boundary layer under favorable pressure gradient and for the separation of the wall jet under adverse pressure gradient