Compressible Flow Pressure Losses in Wye-Junctions

Abstract

This paper considers the compressible flow pressure losses in sharp cornered wye-junctions with symmetrical branches under dividing and combining flow conditions. Determination of the additional total pressure losses occurring in flow through several three-leg junctions, using dry air as the working fluid, has been made experimentally. Results covering a wide speed range up to choking are presented for three different wye-junction geometries. Separate flow visualisation Schlieren tests detected the presence of normal shock waves, located at up to one duct diameter downstream of the junction, and therefore confirmed the choking of the flow at the vena contracta. The highest attainable Mach number (M3) of the averaged whole flow was 0.9 for one of the dividing flow geometries and 0.65 for several of the combining flow cases. These values of M3 were the maximum possible and hence represent a limiting condition dictated by choking. In general, the compressible flow loss coefficients, caused by the presence of the wye-junctions, can be expected to be higher for dividing flows and lower for combining flows than would be the case for incompressible flows because of the influence of Mach number (M3) on the magnitude of the denominator.