Secondary Flows and Losses in a Turbine Cascade,
DURHAM UNIV (ENGLAND) DEPT OF ENGINEERING
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In designing axial flow turbines, one needs relatively simple prediction techniques for the angle variations and losses produced by secondary flows. To improve the physical basis of such techniques, an investigation was made of the flow in a cascade of large scale rotor blades of some 110 deg of turning. The aspect around 0.2 of the span. The flow was traversed in great detailed on ten planes using cobra-type probes with a computerised data recording and analysis system. Results are presented graphically using contour and vector plots on various planes through the flow field. The horse-show vortex and passage vortex development are clearly seen, with the upstream boundary layer being shed downstream as a loss core. Another region of high loss is related to a counter vortex in the corner between the sunction surface and the end wall. Results were also pitch averaged, and compared with predictions of angle and loss distribution. Some traversing was carried out using hot wire anemometry. Regions of high turbulence intensity and shear stress were identified, associated with the regions of high loss. Some indication is given of the mechanisms of loss production within the cascade.