Experimental and numerical investigation on the development of surface shedding vortex caused by abnormal stagger angle in a compressor cascade

Abstract

To reveal the influence of abnormal adjustment of variable stator vanes on adjacent blade passages and to reduce the flutter and high period fatigue damage caused by strong blade vibrations due to unsteady aerodynamic fluctuation, an abnormal stagger angle scheme was hereby introduced in a high-aspect-ratio compressor cascade. The influence mechanism of the abnormal stagger angle scheme on the flow field in the cascade passage and the adjacent cascade passage was investigated using experimental and unsteady numerical methods. The results showed that deviations in blade stagger angle considerably impacted the boundary layer separation location on the blade, the frequency of vortex shedding, and the magnitude of unsteady aerodynamic disturbances at varying inlet attack angles. For attack angle of 0°, when the abnormal stagger angle was greater than 0°, the vortex shedding frequency was as high as 2056 Hz, and the maximum aerodynamic fluctuation value was 0.025. When the abnormal stagger angle was less than 0°, the vortex shedding frequency was as high as 1857 Hz, and the maximum relative aerodynamic fluctuation value is 0.075. Schemes utilizing larger negative attack angles exhibited superior performance. Compared with schemes involving a large positive attack angle, the boundary layer separation and unsteady aerodynamic fluctuation on the cascade surface were weakened, while the vortex shedding frequency on the blade surface was increased. Furthermore, adjusting the passage geometry between cascades with abnormal stagger angles and adjacent ones could alter vortex shedding patterns and structures on blade surfaces, and Proper Orthogonal Decomposition (POD) proved capable of elucidating the characteristics of both separation and shedding vortices. The abnormal stagger angle enhanced the flow field fluctuation of the adjacent blades and changed the energy proportion of the high-order POD modes, thereby altering the mixing and energy exchange between the main flow, the separation vortex, and the trailing edge shedding vortex.