Experimental Aspect Ratio and Tip Clearance Investigation on Small Turbines

This paper presents aerothermodynamic small turbine design considerations of four turbine flow paths, which were cold-flow tested to evaluate performance effects of span aspect ratio and tip clearance on turbine efficiency. Rotor blade heights were tested, complete performance maps were generated for the four configurations, and rotor tip clearance effects were evaluated at speeds over a range of pressure ratios. Results of the investigation suggest that predominance of high secondary losses allow a design with high aspect ratio blading and low wheel speeds to produce the same or better performance than low aspect ratio blading with high rim speeds.