Detection of secondary flow in a turbine cascade using a tracer gas technique

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Virginia Polytechnic Institute and State University


This thesis presents an investigation into the motions of the horseshoe vortices and the passage vortex, within a plane turbine blade cascade. Fluid motion was determined using a tracer gas technique. Ethylene was injected into the pressure-side and suction-side legs of the horseshoe vortex, near the leading edge of the cascade. Ethylene concentrations were determined at two downstream locations using a flame ionization detector.

It was found that the pressure-side leg of the horseshoe vortex moved toward the suction side of the passage, starting the formation of the passage vortex, and was distributed throughout the passage vortex. The suction-side leg of the horseshoe vortex convected once around the periphery of the passage vortex before passing the cascade trailing edge. Downstream of the trailing edge, most of the fluid from the suction-side leg diffused into the passage vortex. However, twice as much fluid from the suction-side leg, as opposed to the pressure-side leg, mixed within the blade wake. At a location 40% of the axial chord downstream of the trailing edge, the passage vortex (shown previously to account for 60% of the overall total pressure losses) contained over 65% of the fluids from both legs.