On separation of a divergent flow at moderate Reynolds numbers

Flow separation in a divergent channel was investigated in connection with problems of instability and oscillations in physiology at a Reynolds number range much smaller than that usually considered in engineering diffuser design. Experimental data on a divergent flow through a two-dimensional water tunnel in the Reynolds number range Re = 1000 to 6000 are presented. The quantities measured are flow rate, divergence angle, and mean pressure differential between two fixed points at the throat and downstream. In a lower range of divergence angle, flow separation is characterized by a sharp decrease in the mean pressure differential when the flow rate is increased continuously and gradually; whereas recovery from separation is signaled by a discontinuous increase in pressure when the flow rate is decreased again. The critical Reynolds numbers for separation and reattachment are detectably different.