Study On Structure Design And Heat Transfer Mechanism Of High Efficiency Tip Cooling For Gas Turbine

Gas turbines are widely used in aircraft,ships,power stations and other fields because of their stable operation,high power density,low noise and fast start-up.In order to break through the bottleneck technology,China is catching up in the field of civil and military aviation in recent years.There is an inevitable gap clearance between the gas turbine blade tip and the stationary casing.During operation,the high-temperature leakage gas continuously sweeps over the turbine blade tip,which is prone to lead to oxidation,thermal ablation and even fracture.In this context,this paper puts forward a variety of passive cooling measures for the turbine rotor blade from the perspectives of cooling-air side and hot-gas side,aiming at strengthening internal heat exchange and weakening external heat load,so as to provide reference for the new design of turbine blade tip.First of all,taking the typical two-pass internal cooling channel as the research object,this paper establishes the flow and heat transfer model,illustrates the evolution of vortices and heat transfer mechanism of the typical internal cooling channel by using the flow topology analysis method,and discusses the flow and heat transfer characteristics of the internal cooling channel with different turning clearance,divider wall thickness and aspect ratio.It is concluded that the impingement and shear flow and counter-rotating Dean vortices caused by turning effect contribute to the tip high heat transfer zone,and the accumulation of low-energy fluid cluster formed by the spiral separation of downstream flow inhibits the local heat transfer.Secondly,this work studied the principles of the tip extraction affecting the flow and heat transfer of the internal cooling channel,compares the changes of the internal flow field as the bleed hole size,flow rate and layout change,and summarizes the rules of the tip heat transfer enhancement.It is found that when the tip bleed holes are arranged in the middle of the tip,the tip heat transfer is obviously enhanced.The drag effect of the cooling air on the Dean Vortex and the acceleration effect on the surrounding fluid stimulate the near-wall flow turbulence intensity,weaken the thickness of the boundary layer,and enhance the tip heat transfer.Thirdly,this work proposed a new measure to strengthen the tip heat transfer using delta-winglet longitudinal vortex generator,explains the reason of heat transfer enhancement by using flow topology analysis,and demonstrates the tip heat transfer enhancement by experimental method.The effects of delta-winglet type,layout,position,angle of attack,spacing and other parameters on tip heat transfer are summarized,and the effectiveness of delta-wing vortex generator in real turbine blade tip is verified by numerical simulation.It is found that attention should be paid to the interaction relationship between the placement direction of delta wing and the mainstream in the design stage.The common-flow-down form of delta-winglet vortex generator pair is more conducive to the tip heat transfer.When it is arranged in the middle and downstream of the tip,it can stimulate the disturbance of the downstream low-energy fluid cluster without damaging the original strong heat transfer in the upstream impingement zone,so as to improve the overall heat transfer of the tip.In addition,the conical vortex generator proposed in this paper can effectively improve the temperature uniformity while improving the tip heat transfer.Compared with the conventional pin-finned tip,this method can obtain greater heat transfer performance with less pressure loss penalty.Finally,in view of the local high temperature zone and large temperature gradient of the traditional ribbed blade,a rim cooling approach of squealer tip is proposed in this paper.By effectively combining the rim with film cooling,the clearance leakage can be effectively restrained and the heat load on the blade top can be reduced.By analyzing the effects of injection geometry,injection position and injection flow rate on the blade tip,it is found that the rim slot cooling is better than that of rim hole cooling.This new design form can make the cold air mixed with high-temperature gas in advance and roll into vortex in the cavity.The increase of cavity depth will enhance the rotation and maintenance of vortex in the cavity and help to reduce the tip heat load.In addition,from the perspective of internal cooling,this chapter applies the delta-winglet longitudinal vortex generator to the tip of the blade internal cooling channel,and verifies the protective effect of the new enhanced heat transfer microstructure on the blade tip using three-dimensional conjugated heat transfer calculation.By designing tip delta-winglet vortex generators with different angles of attack and spacing,the optimization method of enhancing the heat transfer of turbine blade tip inner wall by delta winglet vortex generator is summarized,which provides a reference for the novel design of blade tip internal cooling channel.