EFFECT OF SURFACE ROUGHNESS ON LOSS BEHAVIOUR, AERODYNAMIC LOADING AND BOUNDARY LAYER DEVELOPMENT OF A LOW-PRESSURE GAS TURBINE AIRFOIL

摘要

Aerodynamic measurements on the linear low-pressure turbine cascade T106C were conducted in a high speed test facility, in order to investigate the effect of surface roughness on loss behaviour, aerodynamic loading, and boundary layer development. Three different roughnesses were investigated, with a ratio of the centerline average roughness to the profile chord of 0.8·10~(-5) 5·10~(-5) and 25·10~(-5). Tests were carried out under design outlet Mach number (Ma_(2th)=0.6), outlet Reynolds number ranging from Re_(2th)=5·10~4 to Re_(2th)=7·10~5 and inlet turbulence level Tu_1=3% and Tu_1=6%. The flow field downstream of the cascade and the loading distribution on the profiles were measured for each investigated operating point using five hole probes and surface static pressure taps. Additional measurements with a hot-wire probe in the suction surface (SS) boundary layer were also conducted, in order to investigate the differences in boundary layer development due to surface roughness. From loss and blade loading measurements it was found that roughness has no influence on the pressure distribution on the profile, although the highest investigated roughness produces a significant loss reduction at low Reynolds numbers. Hot-wire probe surveys show that at Re_(2th)=9·10~4 the boundary layer for the highest roughness immediately upstream of the flow separation point on the SS is substantially thinner than for the middle roughness and the smooth profile.