Design Point Efficiency of Radial Turbines

Results are presented from CFD calculations on a large database of 3D, radially-stacked, radial turbine geometries. The database covers a comprehensive range of basic geometrical features allowing the most appropriate geometry to be selected for optimum efficiency over extensive ranges of blade-speed-ratio, flow coefficient and specific speed. Initial studies considered the wheel only and used 78 geometries for low Mach number applications and 102 geometries for high Mach number applications. Each was run over a range of blade-speed-ratios and inlet flow angles to generate preliminary results. Designs that did not contribute to the optimum efficiency trends were discarded. The remaining 17 low Mach number and 24 High Mach number wheels were recalculated with a range of nozzle guide vanes and back-face cavities to provide increased fidelity numerical solutions. The calculated optimum efficiency is presented on charts of blade-speed-ratio against flow coefficient, against specific speed and against non-dimensional mass-flow. The effect of exducer trim reduction, as often required for mechanical reasons, is demonstrated. The charts can be used for preliminary design of new applications.