Radial fluid migration and endwall blockage in axial flow rotors

摘要

The article presents an analytical model for systematic investigation of the effects stimulating or retarding radial outward migration of fluid in the suction side (SS) boundary layer of the blades of axial flow rotors, contributing to increased near-tip loss and promoting tip stalling. With application of the model to an experimental case study, coupled with evaluation of detailed flow measurement data, it has been pointed out that the outward migration and near-tip accumulation of high-loss fluid are intensified by the controlled vortex design (CVD) style. This phenomenon is related to the SS outward flow associated with the vortices shed from the blade of spanwise changing circulation. It has been found that the outward migration, and consequently, the endwall blockage at the casing, becomes more pronounced as the intensity of shed vortices due to CVD increases. Based on experimental data, it has been pointed out that the increase in axial displacement thickness is approximately proportional to the radial gradient of blade circulation. Based on the purposeful use of the analytical model, forward blade sweep was found to be especially beneficial for the rotors of CVD, as a means for moderating outward migration along the suction surface.