Effect of Actual Variable Nozzle Geometries on Radial Turbine Performance for Automotive Turbochargers

Abstract

For radial turbines used in automotive turbochargers, a variable flow capacity turbine becomes important to satisfy the demands of engine performance and emissions, recently. Especially, a variable nozzle turbine is an indispensable component not only for diesel but also gasoline engines to realize a high boosting from the low end to the rated engine condition.

On the other hands, since a variable nozzle turbine has several gaps and clearances around movable nozzle vanes to ensure the smooth operation under the hot gas condition, there is a possibility that these complicated geometries might lead additional loss and turbine efficiency decrement.

The author has conducted detail CFD calculations of a variable nozzle turbine in which considering nozzle vane clearance, strut pins, spindles and cavities and revealed these effects on a turbine performance when nozzle opening is varied from closed to full-opening condition.

CFD results show the effect of a nozzle vane clearance is dominant in nozzle closed condition. Hence, the effect of strut pins becomes relatively large at nozzle full-opening condition. Furthermore, compared with the actual turbocharger test result, it is confirmed that the predicted turbine efficiency agreed with the experimental result and CFD modelling in which considering above gaps and clearance is necessary for aerodynamic design of a variable nozzle turbine and its improvement.