Vortex/separated boundary-layer interactions at transonic Mach numbers

Abstract

An experimental study has been completed on the effect of a single longitudinal vortex on a separated, transonic, turbulent boundary layer. The vortex was generated by a half-delta wing mounted at the upstream end of an axisymmetric bump model. A flow visualization study was conducted using vapor screen and surface oilflow techniques. In addition surface pressures were measured and mean flow and turbulence data obtained using a two-component laser velocimeter. At precritical Mach numbers, the vortex delayed or eliminated boundary-layer separation on the downwash side and enhanced it on the upwash side, thus converting a nominally twodimensional separation into a three-dimensional one. At the postcritical Mach number, the effect of the vortex was to reduce the size and extent of the shock-induced boundary-layer separation throughout the region of interaction. The boundary-layer turbulence in both cases was found to reorganize accordingly, although in a rather complex manner. The onset of three-dimensi onality in the separation line produced by the vortex resulted in secondary vortices (foci), the sign and number being strongly dependent on the freestream Mach number.