Effect of geometry on secondary flows in blade rows

Hansen, A. G., Costello, G. R., Herzig, H. Z.

The influence of blade-row geometry on secondary flows in a two-dimensional cascade was investigated qualitatively by varying independently the stagger angle, aspect ratio, solidity, angle of attack, and by providing blade fillets. The influence of tip clearance and relative motion between blades and wall was also studied. Stagger angle and aspect ratio had no appreciable effect on this secondary flow, whereas solidity and angle of attack did affect the flow patterns indicating the turning as a major parameter. Blade-tip clearance induced a vortex produced by flow under the blade end which rotated opposite to the original secondary-flow passage vortex. The clearance vortex displaced but did not reduce the secondary-flow vortex. When the wall was moved relative to the blades, the blade leading surfaces "scraped" up entrained fluid near the wall and imparted a roll up motion to the air in this region. On the trailing surface the fluid was pulled off the blade onto the wall. The magnitude of the scraping effect was so large that it masked completely the secondary-flow and tip-clearance phenomena.

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