David Artt

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.

Experimental performance evaluation of a 99.0 mm radial inflow nozzled turbine with different stator throat areas

Abstract The performance of a single-stage, radial inflow turbine was measured with seven vaned stators of different throat areas. The turbine test facility is described and details of the turbine rotor and stator geometry are provided. Efficiency, mass flowrates and rotor static pressure ratios are presented for each turbine configuration at a range of speeds and pressure ratios. The experimental data clearly shows the turbine mass flowrate increasing approximately in proportion to the stator throat area, while the maximum attainable efficiency decreased as the stator throat area decreased.

An experimental assessment of incidence losses in a radial inflow turbine rotor.

Abstract The non-optimum angle of incidence at the rotor inlet is the primary cause of reduced efficiency at off-design operating conditions in a radial turbine. Prediction of the complete performance characteristic, rather than just the design point, is desirable when considering the radial turbine as part of a dynamic system, such as a gas turbine engine, air cycle refrigeration plant or a turbocharger. The existing, rather unsatisfactory, incidence loss models are summarized and any published experimental information about the effect of incidence angle is reviewed. Through the analysis of data obtained from experiments conducted by the authors and reported elsewhere, correlations are drawn between the magnitude of the rotor loss and the gas incidence angle at the rotor inlet. As a consequence of the analysis, a negative value for the optimum incidence angle is confirmed and consistent trends are presented for the effects of varying incidence angle at different rotor speeds.

Experimental performance evaluation of a 99.0 mm radial inflow nozzled turbine at larger stator/rotor throat area ratios.

Abstract Following on from experimental data already presented by Spence and Artt in 1997, further comprehensive performance tests were carried out on a 99.0 mm radial turbine with three larger vaned stators. The results have helped to confirm some of the trends noted in the earlier tests. Measurements of the efficiency, mass flowrate and rotor pressure ratio are presented together with the results of a simple loss analysis. For smaller stator sizes the turbine mass flowrate is shown to be proportional to the stator throat area. The significance of the stator-rotor throat area ratio is examined and its dependence on the stage pressure ratio is noted.

Experimental performance evaluation of a 99.0 mm radial inflow nozzled turbine with varying shroud profiles

Abstract In addition to the experimental data already presented by Spence, Doran and Art in 1999, further comprehensive performance tests were carried out on the same 99.0 mm radial turbine using four different shroud profiles with three nozzles of varying sizes. Efficiency maps are presented for each of 12 different turbine configurations tested. For the largest stator size giving the highest flowrate the turbine efficiency is shown to vary by over 3.5 per cent with different shroud profiles. An examination of the effect of shroud profile with respect to rotor incidence angle revealed that a larger radius of shroud curvature was better for positive incidence while a smaller shroud radius was most efficient for negative incidence.

Experimental and Numerical Investigation of Varying Stator Design Parameters for a Radial Turbine

The experimental and numerical investigations of five different vaned stators for a radial turbine are reported. Three different stator vane numbers and three different vane shapes were tested and modelled. The experimental tests were conducted at matched mass flow rates and pressure ratios, using the same 86 mm diameter turbine rotor, allowing direct comparison of the losses arising from each stator configuration. Stator vane number was found to have a small impact on measured stage efficiency (less than 1%), while vane shape was found to have a more significant effect (up to 4%). A commercial CFD code was used to construct a combination of full stage and single passage numerical models of the test turbine. Flow separation as a result of excessive incidence angle at stator inlet was shown to be a significant factor for some of the stators. Predicted pressure loss coefficients for the vaned stators were in the range 7–11%.Copyright