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

An extensive experimental program has been carried out on a 135 mm tip diameter radial turbine using a variety of stator designs, so as to facilitate direct performance comparisons of varying stator vane solidity and the effect of varying the vane-less space. A baseline nozzle 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 sets were designed and manufactured; one set having varying vane numbers of 12, 18, 24 and 30, and a further set 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 measured stage efficiency could be attributed to the stator passages only, thus allowing direct comparisons to be made. Inter-stage measurements were taken to capture the static pressure distribution at rotor inlet, and these measurements then used to validate subsequent numerical models. The overall losses for different stators have been quantified, and the variations in measured and computed efficiency used to recommend optimum values of vane solidity and R_te/r_le.