A Direct Performance Comparison of Vaned and Vaneless Stators for Radial Turbines

An extensive performance investigation has been conducted on a radial turbine with three different vaneless volutes and three corresponding vaned stators. Previously published comparisons have been based on turbines with unmatched flow rates, meaning that the impact of stator losses was not isolated from rotor and exit losses. Each vaned stator configuration tested in this investigation matched the flow rate of the corresponding vaneless volute to within 1%. The volutes and the vaned stators were all machined in order to achieve high quality and comparable surface finishes. At all operating conditions, the vaneless volutes were shown to deliver a significant efficiency advantage over the vaned stators. However, the vaneless volute turbines did not demonstrate any greater tolerance for off-design operating conditions than the vaned stator configurations. Full performance data are presented for the six different turbine configurations tested and a one-dimensional turbine performance model is evaluated as a means of predicting and extrapolating turbine performance.