Controlling Secondary Flows in Highly-Loaded Compressor Cascades

Abstract

This thesis documents the experimental results of a research program investigating the effect of non-axisymmetric endwall contouring on the secondary flows and loss generation in a highly-loaded compressor cascade. The results are compared with the losses for the baseline flat endwall in order to evaluate the potential benefits.The compressor blade was designed by Pratt & Whitney Aircraft and is representative of an exit guide vane row in an aircraft engine. The experimental study was conducted in Carleton University's low speed linear cascade wind tunnel. The measurements were made at a constant Reynolds number of 150,000 (based on the axial chord and the inlet velocity) for two values of incidence, 0° (design incidence) and +7°.Quantitative results were obtained from static pressure measurements on the suction and pressure surfaces of the blade to evaluate the blade loadings and from measurements made by a seven-hole pressure probe downstream of the cascade to assess the blade row losses. Qualitative results were obtained from oil surface flow visualisation on the endwall and on the blade surfaces and were used to assist in the interpretation of the flow physics.The current research showed that the application of non-axisymmetric endwall contouring at design incidence modified the secondary flows near the endwall, mitigating the formation of the corner stall. The benefits from contouring were observed in terms of reductions in the secondary losses and in the underturning of the secondary flows compared to the flat endwall test case.However, these benefits were not observed at the off-design incidence studied. The application of endwall contouring generated higher secondary kinetic energy near the endwall, which penetrated deeper along the span and occupied a larger area, resulting in higher secondary and total losses as it dissipated moving downstream of the cascade.iii