Numerical and Experimental Study of the Performance Effects of Varying Vaneless Space and Vane Solidity in Radial Turbine Stators

An extensive experimental program has been carried out on a 135 mm tip diameter radial turbine using a variety of stator designs, in order to facilitate direct performance comparisons of varying stator vane solidity and the effect of varying the vaneless space. A baseline vaned stator was designed using commercial blade design software, having 15 vanes and a vane trailing edge to rotor leading edge radius ratio (R_te/r_le) of 1.13. Two additional series of stator vanes were designed and manufactured; one series having varying vane numbers of 12, 18, 24, and 30, and a further series with R_te/r_le ratios of 1.05, 1.175, 1.20, and 1.25. As part of the design process a series of CFD simulations were carried out in order to guide design iterations towards achieving a matched flow capacity for each stator. In this way the variations in the measured stage efficiency could be attributed to the stator passages only, thus allowing direct comparisons to be made. Interstage measurements were taken to capture the static pressure distribution at the rotor inlet and these measurements were then used to validate subsequent numerical models. The overall losses for different stators have been quantified and the variations in the measured and computed efficiency were used to recommend optimum values of vane solidity and R_te/r_le.