Investigation Of The Interaction Mechanism Between Rim Sealing Flow And Endwall Secondary Flow In A High-Pressure Turbine

In modern advanved gas-turbine engines,a large amount of cooling gas and sealing gas are required to ensure the safe operation of high pressure turbines.However,the rim sealing flow will interact with the mainstream in the blade passage while it ensures the normal operation of the engine,which will have a great impact on the turbine performance.The influence of the rim sealing flow on the mainstream flow characteristics and turbine performance has been an important issue that must be considered in the refined design of the turbine.In this paper,the influence of sealing flow on the structure of the endwall secondary flow and the interaction process between them were analyzed in detail.At the same time,the mechanism of the interaction between rim sealing flow and endwall secondary flow was revealed.The main contents of the paper are as follows:(1)The investigation of the interaction mechanism between rim sealing flow and endwall secondary flow under the simplified rim seal configurations was carried out.A typical high-pressure turbine blade was taken as the research object,and the effects of three different simplified rim seal configurations on the secondary flow in the endwall was studied by the combination of experiments and numerical simulations.The influence of the location of the sealing gap,the internal cavity of the seal and the change of the attack angle on the performance of the seal structure were focused on,and the study shows that the internal structure of the rim seal had a great influence on the sealing effectiveness.Complicated internal structure would improve the sealing effectiveness with the loss in rim seal increased,so it is necessary to weigh and consider the pros and cons.The structure of the rim seal outlet had a great influence on the total pressure loss in the blade passage,which determined the development of the leakage slot vortex and the passage vortex in the passage.At the same time,the leakage slot vortex would merge into the passage vortex when the leakage fraction was small.However,when the leakage fraction was high enough to make the pressure side leg of horse-shoe vortex be significantly suppressed and the leakage slot vortex be greatly strengthened,the leakage slot vortex and the passage vortex would not meet in the passage.At this time,the total pressure loss in the blade passage would decrease as the leakage fraction increased.(2)The investigation of the interaction mechanism between rim sealing flow and endwall secondary flow under real rim seal configurations was carried out.The influence of the rim sealing flow on the structure of the endwall secondary flow under real rim seal configurations and the interaction process between them were analyzed in detail.The numerical simulation method had been verified by experiment to guarantee the accuracy.The study shows that,on the one hand,the mainstream flow ingress occurred at the leading edge of the blade,which led to a recirculation zone at the outer part of the rim seal and a reverse vortex below it.The position and size of these two vortices influenced sealing effectiveness directly.On the other hand,the pressure side leg of horse-shoe vortex and the leakage slot vortex would get merged and developed into passage vortex in the blade passage later,which had the same sense of rotation in streamwise direction.The sealing configuration determined the outflow position of the leakage slot vortex,which affected the loss caused by sealing flow.At the same time,the Kelvin-Helmholtz instability phenomenon was observed to occur at the seal outlet,resulting from a certain circumferential velocity difference between the sealing flow and the mainstream flow with almost the same scale massflow at the interface of the seal outlet.With lots of low-energy boundary layer fluid ingested into the rim seal,the circumferential velocity of the sealing flow would decrease.The pressure side leg of horse-shoe vortex and the leakage slot vortex would subsequently get weakened,which contributed to reducing losses.