Abstract:

Numerical investigation is applied to a high endwall angle variable-geometry power turbine. The forming process of the variable vane endwall clearance leakage vortex is described. Then, the changes in the three-dimensional flow field and loss mechanisms of the variable turbine stage caused by the rotation of the variable vane are investigated. In addition, the effects of vane rotation on the overall performance of each power turbine stage are analyzed. The results show that, associated with turbine variable geometry, there are part clearances in the vane-end regions, which results in the existence of interaction zones of passage vortex and part clearance vortices. In addition, the core of the leakage vortex is made up of fluid that passes through the gap in the rear part of the rotating shaft. The rotation of the variable vane not only leads to the flow incidence to the vane self, but also results in a significant separated flow caused by high incidence near the downstream rotor leading edge. With the closing of the variable vane, the spiral upward movement of the separation bubble near the hub endwall induces the significant suction-side separated flow, showing strong three-dimensional flow characteristics, and it significantly deteriorates the variable geometry turbine performance. Besides, the rotation of the variable vane changes the vane throat area, redistributes the inter-stage enthalpy drop, and then affects each turbine stage performance to some extent. Overall, its effect on the variable geometry turbine stage is most obvious.

Key words: flow separation, high endwall angle, leakage flow, loss characteristics, variable geometry, power turbine