Lu Xingen

The Combined Effects of Surface Roughness with Upstream Wakes on the Boundary Layer Development of an Ultra-High-Lift LPT Blade

Abstract The combined effects of upstream wakes and surface roughness on boundary layer development have been investigated experimentally to improve the performance of ultra-high-lift low-pressure turbine (LPT) blades. The measurement was performed on a linear cascade with an ultra-high-lift LP turbine profile named IET-LPTA with a Zweifel loading coefficient of about 1.4. The wakes were simulated by the moving cylindrical bars upstream of the cascade. The surface roughness was achieved using sandpaper strips which were placed into the slot incised on the blades surfaces. Three types of slots combined with three types of roughness heights formed a large measurement matrix. The roughness with a height of 8.82 μm (1.05×10−4 chord length) covering 5.2 % suction surface reduced the profile loss in the whole tested Reynolds number range. The details of the boundary layer were measured with a boundary hot-wire probe. It was found that both the wake-induced transition and the nature transition between wakes were hastened due to the K-H instability expanded by the roughness of the S3-R3 surface. The nature transition process was more sensitive to surface roughness than the wake-induced transition.