Flow Characteristics in a Turbine Nozzle of Turbocharger

The clearance leakage flow has significant influence on the performances of variable nozzle turbine. In the other hand, the shock wave near the nozzle vane trailing edge can cause a forced response on the impeller, which can frequently lead to the impeller high-cycle fatigue failure. The interaction of the shock wave and the clearance leakage flow not only causes the loss of the flow, but also has significant influences on the reliability and lifetime of the turbine. The schlieren experiment and numerical simulations were carried out to describe the formation and developing processes of the clearance leakage flow and the shock wave under different clearance and expansion ratios in a linear turbine nozzle. Results indicate that the expansion ratio and clearance configurations have significant influences on the shock wave and the leakage flow. And the influence range of the clearance flow on the shock wave is increased with the increase of the expansion ratio or the clearance ratio. Furthermore, the shock wave is squeezed and bent in the opposite direction of the main flow in the interaction region. Results also show that with the increase of clearance ratio, the influence range of the clearance leakage flow is extended while the shock wave intensity near mid-span is increased.