performance prediction of a nozzled and nozzleless mixed-flow turbine in steady conditions

this paper presents a meanline model to predict the performance parameters of a turbocharger turbine under steady state conditions. the turbine was developed at imperial college and the design was based on a commercial nozzleless unit that was modified into a variable geometry single-entry turbine. the wide range of tests data from the imperial college turbocharger group dynamometer enabled the evaluation of the model in the areas of the turbine map where currently no previous comparison had been made in the literature. this facility is designed to allow testing over a wide range of velocity ratios (0.3–1.1) previously unavailable with conventional test stands. the nozzleless turbine model was validated against experimental results spanning an equivalent speed range of 27.9 and 53.8 rev/s √k while for the nozzled case the model was validated against one single speed (43.0 rev/s √k) and three different vane angle settings (40°, 60° and 70°). the results of the model simulation showed that the performance can be predicted with excellent accuracy for different turbine speeds and vane angles. based on the model prediction, a breakdown aerodynamic loss was performed.