Investigation Of Turbine Cascade Tip Clearance Control Uising Blade Tip Winglets

Gas turbine as one of important powerplant and technology is widely used in electric power station, ship power, mechanical drive device, and so on. Advanced gas turbine technology is the focus of research fields of a nation's science. As the core component of gas turbine, high performance turbine is relevant with overall performance. Tip leakage flow in turbine rotor is one of the main sources of the flow losses. The mixing of the tip leakage flow with the mainstream affects both the flow structure and blade load distribution, thereby causing flow loss increased and the working capacity decreased. The tip winglets can effectively control the tip leakage flow to reduce the leakage loss, and then improve the structure of the flow field and turbine efficiency. There already are more in-depth researches on the blade tip winglet in foreign country, lacking in the study of it tip winglets in turbine in broad.A detailed experimental and numerical study has been conducted to investigate the influence of the blade tip winglets on the tip clearance flow control in a turbine cascade, and reveal the flow mechanism at different tip clearance sizes and incidence angles and the aerodynamic characteristics of the turbine cascade with the blade tip winglets.Firstly, the method of experimental measurements is used for the research on the original cascade and other 8 cascades with different widths and installation locations of the tip blade winglets. The mechanism of the tip leakage loss and the impact on tip leakage flow with various incidence angles is analyzed and discussed on a linear turbine cascade. The effect on the turbine tip leakage flow at different widths and installation locations of the blade tip winglets is studied. At the same time, numerical simulation method is introduced for some places which could not be measured in detail by experiments. Results show that the blade tip clearance could induce the tip leakage flow, which is strengthened and the scale of the tip leakage vortex is enlarged with the increase of the tip clearance, the tip leakage vortex interacts with the upper passage vortex which makes the upper passage vortex move away from the upper endwall to the middle part of the blade passage. With the increasing of the tip clearance, the leakage vortex is strengthened and its influence region also increases, meanwhile, the leakage vortex moves towards to the pressure side of the adjacent blade which makes the outlet flow field become more uniform and increase the total loss of the cascade.In the design condition, the different tip winglet strategies change the tip vortex trajectory toward to the pressure side, it is more obvious that the suction side winglet and combination winglets (blade to winglets fixed on both sides of the blade) can change the trajectory. The optimal tip winglet is the suction side winglet named SW1.2, which can minimize the tip leakage loss and the total loss of the cascade, the use of the suction side winglet reduce loss in the tip leakage vortex region, the tip leakage vortex moves toward the pressure side of the adjacent blade and interacts with the upper passage vortex, reduce the strength and influence region of the upper passage vortex, thus the total loss of the cascade is reduced. Optimal pressure-side winglet is PW0.3, the cascade performance of the combination winglets is better than the one of the pressure-side winglet but less than the one of the suction side winglet.Then, the flow field is measured of the linear turbine cascade characteristic at different tip clearances and incidences with the winglets on the suction-side and on the blade tip pressure-side with different widths. The results show that greater or lesser of the tip clearance, PW0.4 could have a better control effect on the tip leakage flow. At different tip clearances, the suction-side winglets can make the leakage flow weakened, thereby pushing forward the generating position of the leakage vortex backward, then decreasing the loss of the upper passage vortex and the deflection degree of the flow angle along the upper half height of the cascade. The static pressure distribution on the suction-side surface of the blade is similar to that at the wide height. The optimal width for the suction-side winglets at different tip clearance is the case of SW1.2, which effect is even better with the tip clearance increasing. The suction-side winglets reduce the sensibility of the turbine cascade to the variation of the tip clearance, which basically not affect the control effect of the suction-side winglets to the leakage flow. Combination winglets work best for improving the flow deflection angle and making the outlet flow field more uniform at a greater clearance and incidence.Finally, research on the turbine cascades with and without winglets at different incidences is carried out and the influence of winglets with different width and installation positions are also studied simultaneously. The results show that, for the cascade without winglets, as the incidence changes from negative to positive, the scale of the tip leakage vortex decreases and the tip leakage vortex moves towards the suction side of the blade, tip leakage loss decreases and the flow separation on the suction surface is intensified which strengthens the upper passage vortex of the cascade and increases the total loss of the cascade, the overturning of the outlet flow angle increases. With the increasing of incidence, the flow separation at the front part of the suction side is intensified, the static pressure on the front part of the suction surface of the blade tip region decreases. Meanwhile, as the scale of the tip leakage vortex on the middle and back part been reduced, the static pressure on the suction surface of the blade tip region increases. Winglets on the tip pressure-side can control the tip leakage flow better at different incidences. At design and smaller incidences, PW0.3 behaves a better effect. When the incidence becomes greater or smaller, the winglets on the blade tip pressure-side with greater width have a good performance. The winglets on the blade tip pressure-side have an active effect on improving the scale of favorable incidences of the turbine cascade. The turbine has better aerodynamic performance under different incidence conditions. From the view of the influence of the combine winglet on different flow field parameters, the suction side winglets play a major role, but its performance is no better than the one with only the suction side winglets.