The Research Of Tip Leakage Control And Tip Leakage Flow In An Axial Turbine

The leakage flow in a high performance turbine is very complex, almost 1/3 of the losses in a turbine stage can be associated with the tip clearance, and tip leakage flow has profound effects on the downstream vane. In order to improve the turbine performance, Nature of tip clearance flow and mechanisms of losses should be taken seriously, and then effective measures are taken to improve the leakage flow state, thereby achieving the purpose of controlling leakage losses.In this paper, the research has been implemented on the stage high-pressure turbine rotor blade of E3 engine. Firstly, take passive control methods, such as endwall contouring and shrouded structure.The results show that the arcing endwall contouring can weaken passage vortex and tip leakage vortex, improve the flow angle condition, reduce the mass flow of tip leakage flow, raise outlet total pressure and the efficiency of the turbine. The optimized arcing endwall contouring reduces the blade tip leakage flow by 0.27% and increase the turbine efficiency by 0.77% compared with original turbine. The optimized arcing endwall contouring provides the largest efficiency increase when the inlet flow direction incidence is at the design incidence. When incidence change becomes larger, the blade tip leakage flow becomes smaller. And straight, stepped and interlacing labyrinth seal can reduce the mass flow of tip leakage flow, raise efficiency of the turbine. And interlacing labyrinth seal gets the best results, reduces high total pressure loss area on exit section. Labyrinth height have no influent on the leakage flow, and pressure ratio across the blade row and radial tip clearance are the main factors on the aerodynamic performance. Labyrinth seal shrouded related losses are seal loss and mixing loss mainly, and for different types of labyrinth seal, allocation region of seal loss is not the same in the shroud.Then, take active control method, such as casing injection. Use axial position’s injections jet on the tip, blocking the leakage flow into the tip clearance. By joint control from endwall contouring and casing injection, the influence of different injection location, injection massflow rates, different gap height on vortex development and turbine aerodynamic performance would be researched carefully, and finally study on 1.5-stage high-pressure turbine, investigate effects on leakages and mixing between shroud leakage flow and main flow on the downstream vane in shrouded and unshrouded turbines, the results show in the casing injection can improve leakage flow exit flow angle, reducing the tip leakage flow enters rotor tip or shroud. The leakage flow loss mechanisms have been investigated, casing injection bring new mixing losses, but the reduced mixing between leakage flow and mainstream improves turbine stage isentropic efficiency.