Research Of The Effect Of The Leakage From Turbine Inter-platform Gap On The Cascades Passage Flow Field

During the operation of the aero-engine,the guide vanes expand as they are exposed to high temperature environment.Thus,in practice,there exists inevitably a gap called“inter-platform gap”along the mating surfaces of the individual stator units.The cool gas in engine cavity could enter the turbine cascade passage through the gap changing the flow and even temperature characteristics.The present thesis studies the effect of the leakage on the cascade flow characteristics,especially the secondary flow,using the combined methods of Constant Temperature Anemometer(CTA)experiments and numerical simulations based on three dimensional Reynolds-Averaged Naiver-Stokes(RANS).The study can contribute to the reduction of the negative effect of the gap leakage and increase the cascade stage efficiency in both academic and engineering aspects.Firstly,for the low speed cascade consisting of the NASA C3X vanes,the thesis studies the leakage characteristics,i.e.cascades flow characteristics,secondary flow,and cascade loss,using the combined experimental and numerical methods.With increasing the leakage ratio M,the additional vortex is strengthened,and the horseshoe vortex is lifted and weakened.Accordingly,the area-averaged pressure loss?and the secondary kinetic energy also increase at the outlet.When the mainstream ratio~?is smaller than 1,the strength of the endwall-passage vortex reduces,so do the detached vortex and the attached vortex.With~?decreasing,the area-averaged pressure loss?generally decreases and it keeps almost constant later.Secondly,the thesis numerically studies the effect of the gap deflection angle?and the gap depthh.The results indicate that different deflection angle?plays an important role for the complex evolution of vortices in the cascades,i.e.passage vortex,detached vortex and attached vortex.When the deflection angle?is around 30°,the cascade pressure loss could be relatively smallest.It is also found that a proper gap depth can be benefit to reduce the pressure loss in the cascade.Finally,the paper studies the interaction of the turbine hot streak and inter-platform gap flow in a whole stage cascade under transonic condition.In stator passage,the leakage can effectively reduce the temperature at the stator endwall and the suction surface.In rotor passage,the upstream gap leakage can weaken the preferential migration of the hot gas towards the passage pressure side and reduce the temperature on the blade suction surface.