Flow and Pressure Characteristics Downstream of a Segmental Blockage in a Turbulent Pipe Flow

Abstract

Two mutually complementary sets of experiments were performed to study the flow and pressure fields created by the presence of a segmental orifice plate in a circular tube. In one set of experiments, axial and circumferential pressure distributions were measured, whereas in the second set the reattachment of the flow downstream of the blockage was studied by means of a visualization technique. Three degrees of flow blockage were employed and the Reynolds number ranged from 10,000 to 60,000. The pressure loss induced by the blockage, when normalized by the velocity head, is insensitive to the Reynolds number but increases markedly with the extent of the blockage; the values of the loss coefficient are comparable to literature values for a gate valve. The axial pressure distributions display a precipitous drop and a subsequent rapid recovery due to the acceleration—deceleration sequence experienced by the flow deflected by the blockage. Downstream of the blockage, beyond the reattachment and redevelopment regions, a fully developed flow is re-established. Relatively large circumferential pressure variations occur near the blockage but die away with increasing downstream distance; the high and low pressure regions of the circumferential distributions shift with distance along the pipe. Owing to the fluctuating nature of the separated flow, the reattachment point meanders within a zone of finite extent. The reattachment zone tends to shift downstream and to elongate with increasing blockage.