An Experimental Investigation By Using Curved Blade To Control Secondary Flow In Compressor Cascade

In this paper ,a detailed experimental investigation has been carried out in a low speed,large scale wind tunnel with five compressor cascades composed of conventional straight blades,positive leaned blades,positive curved blades,negative curved blades and S-type blades respectively. The blade surface, endwall static pressures and cascade exiting flow fields are measured with wall static pressure tappings,a small size five -hole probe at zero,positive and negative incidences and the flow visualizatons conducted at zero incidence. It is shown that the passage vortices are quite strong in the straight blade cascade. Due to the existence of concentreted shed vortices and corner vortices,the secondary loss at the two ends is much higher. On the acute side of the positive leaned blade cascade, the passage vortex is strengthened, the corner stall disappears and the secondary loss decrease. The topological structure on the suction surface of leaned blade acute side changes from the saddle/spiral node pattern separation to saddle /separation node pattern separation. On the obtuse side, the separation and the reverse flow become much stronger. And due to the migration and accumulation of low energy fluids the regions with high energy loss are enlarged . The beneficial effect on performance of reducing the secondary loss on the acute side is offset by an increase on the obtuse side ,while the total loss of the positive leaned blade cascade increases. Blade positive curving introduces the effect of positive lean on the two ends of the cascade, which enhances the passage vortices and makes the corner stall disappear. In this cascade, the "C" type static pressure distribution spanwise is established . The concentrated shed vortices move and converge towards the midspan and separate there. The secondary loss at the midspan increases. The total loss of the positive curved blade cascade does not decrease at zero and negative incidences compared with the straight blade cascade. Some gains in performance appear at positive incidences. In the cascade with negative curved blades,the passage vortices are weakened. Although the corner stall is somewhat intensified,the breakdown of the passage vortices and shed vortices disappears, and the concentrated shed vortices are weakened to be trailing edge shed vortices . Therefore ,the secondary loss...