The flow past a downstream facing annular step was experimentally investigated in the Mach number range of 0.1 to 0.95. The approaching flow was steady and uniform. The boundary layer ahead of the step was turbulent. The upstream influence of the step and the variation of base pressure and recovery pressure with the reference Mach number are described. Results of hot-wire measurements in the shear layer and the locations of reattachment and secondary separation points are also reported
