Effect of tip leakage vortex breakdown on losses in turbines

Numerical investigation is performed to simulate the tip leakage vortex (TLV) breakdown characteristics and its effect on leakage losses in the first-stage rotor blade of GE-E3 (Energy Efficient Engine) turbines at various tip clearances, by solving the Reynolds-averaged Navier-Stokes equations in conjunction with a standard k-ω two-equation turbulence model. The tip leakage vortex breakdown phenomenon and its dynamics are analyzed; so are the effects of tip clearance height on the tip leakage vortex structure and the vortex breakdown characteristics. Furthermore, the relationship between the tip leakage vortex breakdown and losses is investigated. Numerical results show that the turbine tip leakage vortex is unstable. When the tip leakage vortex has sufficient strength to overcome the entrainment of the tip passage vortex, and forms a complete vortex structure, the tip leakage vortex breakdown is initiated in the adverse-pressure region of the second half of the rotor blade, which leads to extra vortex breakdown losses. The tip clearance height has a great impact on the vortex breakdown location, and the tip leakage vortex tends to be relatively stable at large tip clearances. The tip mixing losses are divided into two stages marked by the tip leakage vortex breakdown. A lot of mixing losses occur after the tip leakage vortex breakdown, which is the main part of the tip mixing losses.