Experimental And Numerical Research Of Leakage Control Over Tip-Jet Shrouded Turbine Cascade

Turbine blade leakage control has always been a heated problem in turbine research field. Tip leakage fluid has an effect over 70%-100% span, covering more than 30% loss of whole blade cascade. As to this fact, it is of high values to control tip leakage for boosting the efficiency of turbine machine.In this article, we have conducted the process of experiment measurement and validation of simulation. There are three types of blade tip structures in experiment testing section, including shrouded-jet blade,winglet shrouded-jet blade(WS-jet), winglet shroud-sealed-jet blade(WSS-jet).The testing section is operated in low speed rectangular wind tunnel, utilizing five-hole probe to obtain total pressure, static pressure, the distribution of velocity and flow angle. We also conducted the validation process through simulation with the aid of three-dimensional flow field software, getting the vortex patterns, leakage loss and total loss. Simulation results are adopted to verify the outcome from experiment.Firstly we focused on shrouded injection, Due to results of experiment, shrouded blade has an effective constraint over the development of leakage vortex, and meanwhile, tip jet plays a negatively induced role in the forming process of leakage vortex. Although the jet flow slightly enlarges the size of leakage vortex, it has a positive effect to the distribution of total pressure. The typical over tip leakage flow does not exist in this type of blade structure.Winglet shrouded-jet blade (WS-jet) is mainly discussed in the second part of this article. Based the aerodynamic performance of blade cascade and fluid condition in tip gap, we redesign a new structure of turbine blade. No-injection WS blade has already been discussed in other thesis, so our core concerns are about impact of injection, ignoring the structures comparison between shrouded blade and WS-jet blade. WS-jet can cause decrease in blade cascade loss to a certain degree, optimizing the flow mode in passage and the aerodynamic performance of the cascade. The jet mass flow is just small amount of all the fluid, so there is not apparent transformation in blade efficiency lifting.After we concluded the insightful results of WS-jet blade, we proceeded to investigate to another formation of blade tip. Winglet shrouded-sealed-jet(WSS-jet): adding seal structures inside the tip gap to get a contrastive research between WS-jet. The analysis reveals that seal structures can significantly minize the size of leakage vortex, enlarge passage vortex and tail vortex. Generally speaking, seal structure can decrease overall loss about 20%, and aerodynamic performance is no longer adapted to attack angle.