Effect of Leading Edge Roughness and Reynolds Number on Compressor Profile Loss

Abstract

An experimental investigation has been conducted to characterize the influence of leading edge roughness and Reynolds number on compressor cascade profile loss. Tests have been conducted in a low-speed linear compressor cascade at Reynolds numbers between 210,000 and 640,000. Blade loading and loss have been measured with pressure taps and pneumatic probes. In addition, a two-component laser-doppler velocimeter (LDV) has been used to measure the boundary layer velocity profiles and turbulence levels at various chordwise locations near the blade suction surface. The “smooth” blade has a centerline-averaged roughness (Ra) of 0.62 μm. The “rough” blade is roughened by covering the leading edge of the “smooth” blade, including 2% of the pressure side and 2% of the suction side, with a 100 μm-thick tape with a roughness Ra of 4.97 μm. At Reynolds numbers ranging from 210,000 to 380,000, the leading edge roughness decreases loss slightly. At Reynolds number of 210,000, the leading edge roughness reduces the size of the suction side laminar separation bubble and turbulence level in the turbulent boundary layer after reattachment. Thus, the leading edge roughness reduces displacement and momentum thicknesses as well as profile loss at Reynolds number of 210,000. However, the same leading edge roughness increases loss significantly for Re = 450,000 ∼ 640,000. At Reynolds number of 640,000, the leading edge roughness decreases the magnitude of the favorable pressure gradient for axial chordwise locations less than 0.41 and induces turbulent separation for axial chordwise locations greater than 0.63, drastically increasing loss. Thus, roughness limited to the leading edge still has a profound effect on the compressor flow field.