Experimental And Numerical Investigations On Tip Leakage Flow Control In Shrouded Turbine Cascade

As a kind of high power machinery, gas turbine has been widely used in energy, aviation, electric power, shipbuilding, and other areas of the national economy. With the rapid development of modern industry, the performance of gas turbine is required improving continuously. As a core part of the gas turbine, improving the aerodynamic performance of the turbine part plays a very important role. The design technology of modern gas turbine has been increasingly perfect, the conventional design method can make the turbine efficiency above93%, and it has a narrow space for continuing to improve. So, in order to reduce the loss of tip clearance leakage, an intensive study of the tip leakage flow and mixing mechanism has becoming the research priorities to further improve the performance of the turbine components in the future.In view of the tip leakage flow control, this paper has carried out an experiment research on low speed large scale rectangular tunnel. In order to reduce the tip leakage loss, methods of using shroud, grooved casing and tip jet were adopted and the aerodynamic performance was tested. First of all, the flow structure and performance of the unshrouded cascade was tested and researched with different clearance sizes and incidences. The research results show that the existence of the tip clearance enhanced cascade at the top of the secondary flow and deteriorate the flow at upper half part. With the increase of clearance size, the cascade total pressure loss and increases; with the increase of negative incidence, the cascade total loss increases.Secondly, on the basis of the unshrouded cascade research, the flow structure and performance ofthe shrouded cascade was tested and researched. The mechanism of the shroud structure to control the tip leakage and reduce the loss was analyzed. The results show that the blade tip shroud structure prevents air flowing across the blade tip, eliminates the clearance leakage vortex and greatly reduces the flowing loss. As the clearance size increases, the amount of fluid in the cavity increases, the mixing between leaking fluid and mainstream is aggravated, that leads to a large loss. Appropriate positive incidence can improve the aerodynamic performance of cascade with a large turning angle.Then, grooved casing was adopted to reduce upper cavity fluid leakage of the shrouded cascade and that will reduce mixing loss, improve the aerodynamic performance. The research results show that the grooved casing structure reduces the upper cavity fluid leakage, but increases radial kinetic energy of the cavity fluid at the upper cavity exitplane. Then the mixing between upper cavity fluid and mainstream is aggravated, and enhances the cavity leakage vortex, causes a higher loss in blade up region.Finally, this paper mainly studied the shrouded cascade with jet tip. The jet tip was adopted to reduce the upper cavity fluid to improve the shrouded turbine cascade performance. Research results show that the blade tip injection can increase the aerodynamic performance of mainstream area, but in blade tip region, a cavity leakage vortex is formed due to the mixing between the jet fluid and mainstream, that increases the aerodynamic loss in blade tip region. Numerical simulation results have a good agreement with the experiment.The comprehensive results of four cascades show that, the loss of shrouded cascade is minimal at tip region. Groove structure and tip injection will increase loss at the tip region. At the same time, the blade tip vortex and passage vortex occurs strong viscous friction and increases the loss in the passage vortex region.