An Experimental Investigation On Laminated Vane End-wall Cooling Characteristics

The improvement of the efficiency of modern gas turbine engines can be directly determined by an increasing in turbine inlet temperature,but which causes a higher thermal load to turbine component and a higher risk of the component damage thereby.The large area of the endwalls of first-stage turbine vanes is directly exposed to the severe thermal environment,and thus searching for more advanced cooling techniques has become imperative to prolong the service life of the endwalls.Film cooling on the hot side of the endwalls is one of the most common cooling techniques to protect vane endwall from the thermal damage.However,due to the undesirable effects of turbine cascade crossflow and secondary vortices,there are always some regions in the endwalls,it is difficult to form cooling air coverage,and ultimately to obtain a uniform wall temperature distribution.In this situation,laminated cooling is considered as one of the promising cooling methods for the next generation of high performance aero-engines.The laminated structure,which is a double-layer cooling structure that consists of a film-hole layer,impingement-hole layer and staggered arrays of pin-fins between the two layers,can cool the endwall from the frontside and backside.With the rapid development of precise manufacture technique,the application of complicated laminated structures in endwall cooling has become practicable in order to enhance the heat transfer,save coolant consumption,reduce the regions hard to be cooled and improve the uniformty of surface temperaute distribution.In this investigation,the laminated cooling endwall(LCE)is employed in the design of a first-stage turbine vane endwall cooling.The experimental investigation is carried out in the open-circuit hot wind tunnel system using infrared thermal image system.The low and close real engine temperature ratios of mainstream-to-coolant are considered respectively.The heat transfers coefficient of the endwall are messured and the cooling performance is compared with a traditional film cooling endwall(FCE).Morevoer,based on the experimental results,a modified layout of LCE is proposed.The dissertation focuses on three research contenets as follows.Firstly,LCE and FCE,which have the same thickness and film-holes layout,are designed and manufactured.The heat transfer and cooling characteristics of LCE are investigated under the undesirable conditions due to the three-dimensional flow in a turbine cascade.In comparison with FCE,it can be found that LCE can significantly reduce the endwall surface temeparture,obtain a uniform temperature distribution,and increase the durability of turbine endwalls in the hot environment,which can provide the useful reference to the endwall cooling design.Secondly,the effect of mainstream turbulence intensity(Tu)on the cooling characteristics of LCE is discussed.The results reveal that elevated Tu reduces the overall cooling effectiveness,enlarges the temperature gradient and leads to a poor uniformity of temperature distribution.Although the elevated Tu has the negative effect on the cooling performances of LCE,the benefit of LCE is still remarkable at the high Tu in comparison with FCE.The overall cooling effectiveness and surface temperature reduction can be significantly improved,the temperature gradient within the endwall c,an be reduced and a more uniform temperature distribution can be obtained due to the internal heat transfer contributed by pin-fins and impingements.Thirdly,to reduce the regions,which are difficult to be cooled,a modified LCE with new film-hole layout and internal cooling configuration is designed,based on the endwall temperature distribution measured by the heat transfer experiment.The modified LCE can not only reduce the endwall temperature,but also improve the uniformity of temperature distribution,and therefore it has a longer work lifespan.