The article describes investigations on the influence of two possible endwall-penny concepts for variable stator vanes to secondary flow field development and the performance of high pressure compressors. Concept I uses a penny covering the whole vane chord with no radial clearances, whilst the concept II applies a piecewise flattened polygonal hub or casing to achieve constant radial gaps. Both approaches were converted to a linear cascade of modern stator profiles. Measurements were conducted with a 5-hole-probe in planes up- and downstream the cascade as well as with pressure tappings on the airfoil and the endwall. Additional 3D numerical calculations were carried out to gain information about the flow field inside the cascade. These analyses were performed at three stagger angles and two characteristic Reynolds numbers with a constant cascade turning to model the adjusting range of aircraft engines.
Compared to a reference case without endwall contour and no clearance the results indicate slightly increased efficiency due to smaller total pressure losses for both concepts. The penny edges as well as the polygonal endwall at the cascade inlet are responsible for a higher turbulence in the inlet boundary layer, which results in a smaller endwall separation that is detected with outlet loss distributions. Considering the cascade loading in terms of flow turning, a small overall benefit was achieved with both configurations caused by much higher overturning near the wall. These tendencies increase with the stagger angle at part-load conditions of the compressor. Furthermore, the results were compared with a part gap configuration of a variable vane with benefits concerning pressure losses and flow turning. For lower cascade loadings the concept I still reaches the highest overall flow turning. This benefit compared to the part gap configuration nearly disappears at the high stagger angle. Additionally, both concepts feature a much higher flow angle deviation along the blade height and significant increased losses.