Surface Roughness Effects on Turbine Blade Aerodynamics

The aerodynamic performance of a turbine blade was evaluated via total pressure loss measurements on a linear cascade. The Reynolds number was varied from 600 000 to 1 200 000 to capture the operating regime for heavy-duty gas turbines. Four different types of surface roughness on the same profile were tested in the High Speed Cascade Wind Tunnel of the University of the German Armed Forces Munich and evaluated against a hydraulically smooth reference blade. The ratios of surface roughness to chord length for the test blade surfaces are in the range of $Ra∕c=7.6×10−06-7.9×10−05$⁠. The total pressure losses were evaluated from wake traverse measurements. The loss increase due to surface roughness was found to increase with increasing Reynolds number. For the maximum tested Reynolds number of $Re=1200000$ the increase in total pressure loss for the highest analysed surface roughness value of $Ra=11.8μm$ was found to be 40% compared to a hydraulically smooth surface. The results of the measurements were compared to a correlation from literature as well as to well-documented measurements in literature. Good agreement was found for high Reynolds numbers between the correlation and the test results presented in this paper and the data available from literature.