XXVIII. The conditions at a sharp leading edge in supersonic flow

Summary Schlieren photographs have been taken to show the supersonic flow past a sharp wedge placed at an incidence large enough to give an expansion region on one side. In addition to the flow phenomena predicted by inviscid theory, the photographs show a weak shock wave immediately upstream of the expansion region. Various possible explanations of this are considered and it is shown that the shock wave is caused by the slight bluntness of the leading edge, although the thickness of the leading edge is only about 8 μ. It cannot be explained by considering the growth of the boundary layer, neither is there any evidence of boundary-layer separation.