Numerical Simulation of Leakage Flow Inside Shroud and Its Interaction with Main Flow in an Axial Turbine

In a turbine, the leakage loss is an important source of turbine aerodynamic loss. In this paper, steady numerical simulations were performed to analyze the flow characteristics in the shroud of a 1.5-stage axial turbine and the interaction between the leakage flow and the mainstream. A spatial loss audit inside shroud was undertaken and the loss in the shroud was assessed. Based on the Liutex method, the vortices in the shroud were identified. The results show that the leakage flow in the shroud could be regarded as a jet process with several parts which are free jet and wall attached jet. The rest part of the shroud was occupied by the vortices and separated flows. There is both inflow and outflow on the interface of outlet cavity and mainstream, accompanied by a series of vortices in the outlet cavity. The loss in the inlet cavity is affected by the leakage flow intensity. The loss in the outlet cavity accounts for the largest part of the loss in the shroud.