Loss reduction in the compressor corner region via blade cooling

With Reynolds number (Re) decreasing to a critical value (approximately 2.0 x 105), the laminar-to-turbulent transition on the blade/endwall surface accelerates the loss generation in the corner region of compressors. Thus, how to effectively control the three-dimensional turbulent mixing loss at a low Re is of great importance. In this study, the mechanism of loss variation in a high-speed compressor cascade as Re decreases from 5.6 x 105 to 1.5 x 105 is investigated by large eddy simulations (LESs). Then, an isothermal cooled wall condition with a constant temperature of 0.8T01 (T01 is the inlet total temperature) is specified on the blade surface to explore the potential of loss reduction via wall cooling at Re=1.5 x 105. At Re=5.6 x 105, the boundary layers on the blade suction surface strongly interact with the endwall boundary layers and multiple passage vortex structures near the spanwise location of x/H = 0.3, inducing a large-scale concentrated shedding vortex (CSV) and determining the loss generation rate in the corner region. With Re decreasing to 1.5 x 105, the blade boundary layers grow much thicker due to the delayed transition. Detailed loss classification result indicates that the stronger interaction between the thickened blade boundary layers and secondary flow accelerates the local generation of turbulent fluctuations, which is mainly responsible for the performance deterioration in the corner region at a low Re. As the blade surface is cooled, the growth of blade boundary layers and the migration of secondary flow in the blade passage can be controlled simultaneously. Thus, the interaction between the blade boundary layers and secondary flow near the spanwise location of x/H = 0.3 is weakened, leading to a reduction in the overall total pressure loss by 13.3%. The results hope to guide in controlling the loss in the corner region of compressors operating at a low Re.