The Effect Of Tip Baffle And Tip Winglet On The Efficiency Of Turbine Rotor

The modern method of aerodynamic design and tests of gas turbine engine can improve thecomponent efficiency up to93%. But the users want the efficiency much higher, so how to reduce thetip leakage is discussed by scientists. When the hot gas flows into the tip clearance, it doesn’t outputthe power to blades, and the tip clearance vortex which is caused by the tip leakage can affect thecharacteristic of main passage flow. The aerodynamic losses that are contributed by tip clearanceleakage can range from20%~40%of an engine’s total losses. So the turbine blade tip clearance isthe main loss source of the engine. In order to reduce the loss of tip leakage, improve the efficiency ofturbine, and get higher performance of engines, it is necessary to study the characteristic of tipclearance leakage flow. Now there are two ways to control the tip leakage, one way is the passive flowcontrol method, the other one is the active flow control method. The feedback control system must befixed up to the engine, if the active flow control method is taken. So the structure of an enginebecomes more complex and the weight also gets much higher. In order to avoid these phenomenon,the treatments of blade tip are researched in this thesis——the tip baffle in rotor blade tip cavity, therotor blade pressure side winglet, and the combined forms of the two forms are all belong to thepassive flow control method. By using these treatments to change the tip leakage flow and reduce thetip clearance losses, we can achieve the efficiency improvement of the turbine rotor.Numerical calculations are performed to simulate the tip leakage flow of turbine rotor blade.Eighteen different kinds of blade tips of three categories are analyzed. Category A is on behalf of thenormal blade tip which contains the flat blade tip (model A1) and the blade tip recess (model A2).Category B means the tip recess with the baffle that contains one bending baffle (model A3), onestraight baffle (model A4), two straight baffles (model A5) and three straight baffles (model A6). Thecombined forms of category A or B with pressure side winglet belong to the category C. The length ofwinglet of model B1-B6is2millimeters, and the length of model C1~C6is3millimeters.By numerical simulation, the characteristic of tip leakage flow of different blade tip and thechanges of turbine rotor’s efficiency have been achieved. The simulation results show that thepressure drop ratio, output power and the improvement of efficiency of model A6, B4, C2are thelargest. The shapes of model B1and C3can improve the rotor efficiency, but the amplitude ofimprove are very low. Even though the pressure drop ratios of model A2and model A3are large, butthe aerodynamic losses of these two models are very large, so the output power and efficiency of rotordecrease. The pressure drop ratio, output power and efficiency of rotor of other different kinds ofblade tip are lower than model A1’s.