Experimental test of a compressor cascade with non-axisymmetric end-wall contouring at off-design conditions

Abstract

End-wall losses in axial flow turbomachinery, particularly in compressors, constitute a significant challenge due to their adverse impact on overall efficiency. Pioneering works in this field have demonstrated the potential for end-wall loss reduction by improving end-wall profiles. However, many previous efforts have concentrated solely on design conditions, largely disregarding the behavior of these contoured end-walls under off-design conditions—where compressors often operate. This study investigates the adaptability of a non-axisymmetric end-wall contour, performing well under design conditions, to off-design scenarios, focusing particularly on the influence of Mach numbers on its ability to control corner separation effects. Experimental research was conducted using a combination of surface static pressure taps and aerodynamic probes to quantitatively and qualitatively analyze the effect of the non-axisymmetric end-wall contour on reducing losses. Quantitative outcomes demonstrate a notable decrease in overall losses in the blade cascade due to this end-wall contour. For all tested Mach numbers, the average loss reduces by 4% at 0 degrees of incidence, with a 0.9° decrease in deviation angle, and an 8% average loss reduction at 5 degrees of incidence, accompanied by a 1.5° decrease in deviation angle. Qualitative findings suggest that the mechanism by which the non-axisymmetric end-wall contour reduces blade cascade losses involves the enhancement of pitchwise pressure gradients. This enhancement redirects low-momentum fluid toward the blade's suction surface, diminishing its reach in the pitchwise direction. However, it also intensifies loss in the low-momentum fluid core. Additionally, the presence of a convex feature in the rear section of the blade passage mitigates pitchwise static-pressure gradients, effectively ameliorating secondary flows and preventing their further decline. Moreover, it was observed that the control effectiveness of the end-wall contour on corner separation increases with higher Mach numbers.