Prediction of compressible flow pressure losses in 30-150 deg sharp-cornered bends

This paper considers the measurement and prediction of the additional total pressure losses of subsonic steady airflow in sharp-cornered bends, similar to those present in the secondary air cooling systems of gas turbine engines. The bends examined ranged between 30 to 150 in 30 deg increments and were circular in cross section. Experimental results covering a wide speed range up to choking are presented for five different bend geometries. An analytical flow model provided results in fairly good agreement with rite measurements obtained and equally compared favourably with the experimental findings of other researchers at low Mach numbers. The highest attainable upstream Mach number (M(U)) of the average upstream flow was 0.57 for the 30 deg bend The maximum possible values of M(U) represent a limiting condition dictated by downstream choking of the flow. The compressible flow coefficients, caused by the presence of the bends, can be expected to be between 10 to 20 percent higher than those for incompressible flow.