Drawbacks on the application of nozzle vanes in turbocharger turbine under pulsating flow conditions

Abstract

It is commonly agreed that a turbocharger turbine behaves differently between steady and pulsating flow operations. This is due in no small part to the flow field distribution within the turbine stage. The use of nozzle vanes has significantly increased the three-dimensional complexity of the flow field, although some argue that the use of such stator could lead to improved overall turbine performance. This research investigates the drawbacks on the circumferential flow angle distributions due to existence of nozzle vanes particularly during pulsating flow conditions. In achieving this objective, a validated full stage unsteady CFD model was built to gain insight of the flow field behaviour. The results indicate that application of nozzle vanes has favourable effect on flow angle distribution at the rotor inlet during steady state operations for both design and off-design conditions. This is achieved in such a way that the existence of nozzle vanes has reduced the fluctuation of flow angle as compared to the flow upstream the vanes. On the other hand, during pulsating flow turbine operation, the fluctuation amplitude has spiked almost 400% the level of its counterpart under steady state operation at the rotor inlet. This behaviour could potentially have adverse effect on flow field distribution within the turbine passage and as such, reducing unsteady turbine efficiency.