Investigation Of Scalloping Effects Of Radial Turbines With Computational Fluid Dynamics
Abstract: Turbochargers should both have high efficiency and rapid engine response. By removing material from the rotating parts in the turbocharger, decreases the inertia. Most suited is the turbine in the turbocharger, which has high density because of nickel-based alloys. The material is removed between the radial blades in a shape that looks like a scallop and therefore called scalloping. Volvo Powertrain AB has developed prototypes of non-scalloped turbines and now wants to evaluate if it is possible to design and investigate the performance of different scalloped rotors. This thesis presents a study on a mixed-flow prototype rotor. The rotor has been scalloped in five different models and covers a range where the inertia has been reduced by 35%. The models were simulated with the Computational Fluid Dynamics program STAR-CCM+ and a single blade passage geometry were designed with Creo Parametrics. Because of the time limit of this study, the simulations have been performed with steady state simulations compared to time-consuming transient simulations. Therefore, the exhaust pulse flow has been simplified as four different points covering the velocity ratios 0.51 to 0.77. A comparison between the scalloped and reference rotor have been made with the total to static efficiency. Also, a visualisation and evaluation of main stream flow through the rotors have been performed. The reference rotor was redesigned to be more comparable to the scalloped models with an outcome of increased efficiency. The results from the simulations show that a lightly scalloped rotor has similar efficiency as the new reference rotor but with a reduction in transient response time to 2.5%.
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