Tip Leakage Flow in a Radial Inflow Turbine with Varying Gap Height

Abstract

Tip leakage e ow in a radial ine ow turbineisinvestigated for two different uniform clearances of 0.6 and 1.2% of span. The clearances are typical of radial turbines for industrial applications. Measurements were also performed for increased axial clearances (6 and 7% of span ), while the radial clearance was kept constant. Static pressure and hot-wire measurements in the gap region cone rmed an earlier e nding by the authors that the tip leakage e ow behaviour in a radial turbine is interdependent with the scraping e ow. Changes in the nature of tip leakage e ow with increasing tip clearance height seem mainly to occur in regions where the scraping effect is important. The mass e ow over the tip of the present radial ine ow turbine was quantie ed for all four clearance cone gurations. The measurements revealed that the relative casing motion drags an approximately constant amount of scraping e uid from the suction side to the pressure side irrespective of the gap height, if the tip gap height to width ratio is above a critical value. The modeling of the effect of scraping in the inducer seems necessary if a successful prediction of the mass e ow and, hence, loss is attempted in the future.