Some Effects of Non-Axisymmetric End Wall Profiling on Axial Flow Compressor Aerodynamics. Part I: Linear Cascade Investigation

Non-axisymmetric end wall profiling is now a well established design methodology in axial flow turbines, used principally to improve their aerodynamic efficiency by reducing secondary loss. However, profiled end walls (PEWS) have yet to find an in-service application in a gas turbine compressor. This two-part paper presents the results of a number of studies, both experimental and computational, into the potential aerodynamic benefits of applying PEWS in axial flow compressors. The first paper reports research carried out using a linear compressor stator cascade at Cambridge University. The datum geometry was based on previous research with this cascade. The PEW geometry was generated using a method that had been proven to reduce secondary loss in turbine blade rows. Data was taken on the datum and PEW geometries in the form of exit area traverses and surface static pressure measurements. The experiments demonstrated improvements to the exit flow field in terms of local reductions in the loss and under-turning in the secondary flow region due to the PEW. It was found that the original design method had over estimated the benefits of the PEW. The datum and PEW geometries were further analysed using state-of-the-art CFD (Computational Fluid Dynamics). The CFD is shown to achieve very good agreement with measurement at the design condition and a reasonable, qualitative match at off-design. It is concluded that the PEW geometry, though not optimum, effected predictable changes to the compressor stator flow field. The mechanisms for these effects are discussed and conclusions are drawn for taking the work forward. In particular, a mechanism is identified whereby the PEW enhances the cross-flow on the end wall and the subsequent radial migration of the secondary flow adjacent to the aerofoil suction surface. The control of corner stall by means of this flow mechanism is highlighted as a possible area for further investigation. This is followed up in the second paper, which presents a computational study of applying PEWS to a multi-stage HP compressor.