Research On Flow And Heat Transfer Mechanism Of Inner Cooling Turbulator In Turbine Blade Based On Large Eddy Simulation

Gas turbines are the prime mover and widely applied in some critical indusries.Based on the purpose of improving efficiency and power output,the turbine intlet temperatures are far above the permissible metal temperatures.Therefore cooling system was applied to ensure safe operation of high pressure turbines.Internal cooling plays a significant role,where turbulators enhance the turbulence intensity and the uniformity of heat transfer in span direction and weaken the thermal gradient around the wall.Research on the mechanism of the flow and heat transfer of turbulators contributed to the design of the high-performance cooling system.Now numerical method is widely used to research turbine relevant research.The flow in Internal cooling channel is dominated by unsteady features,so it is important that Choosing reliable CFD procedures and evaluating the flow and heat transfer,accurately.RANS and LES approaches were adopted to analyze blade internal cooling structure related problems,like typical rib turbulators and new dimpled depression.Comparison of the performance about flow prediction and heat transfer evaluation between RANS method and LES method was conducted.Combining with the result of LES,the mechanism of the flow and heat transfer were explained from different point of view.Firstly,combined with experimental data,the periodic case and spatial case of widely studied were investigated in numerical method.Results show that RANS models used show poor prediction performance in acceleration zone upon rib and recirculation zone,near the wall.About turbulence intensity,both RANS and LES method succeed in predicting the maximum position.And in contrast to RANS method,LES method succeeds reproducing the change rule of the maximum value of the turbulence intensity,but a little lower than experimental data.In aspect of heat transfer,result by LES approach show agreement with experimental data on the plane between ribs and front plane of the rib,while on the up of the rib,SSG model have the best performance.The process of the vortex's generation and separation upon the rib is captured by LES approach.Results point out that Vortex shed,develop and mix with fliud around,while it's intensity waken,which is consistent with the regular of turbulence intensity.Also the secondary flow caused by Separated flow at upstream of the rib and the topological structure of streamline on the ribbed wall are revealed.By the way,correlations between the Nu and local turbulent kinetic energy is showed in this paper.On the basis of conclusion above,the RANS method and LES method are used to study the new turbulent structures.Results show the evolution process of the instantaneous large-scale vortex structure in the dimples,and point out the generation of the leading vortex structure and the process of bending of vortex axis along the main streamwise and shedding from the trailing edge.The turbulent flow from the upstream dimple and the fluctuating velocity and shear stress caused by the turbulent vortex in the staggered dimples will affect the flow field distribution of the downstream dimples.It is pointed out that the high turbulence kinetic energy and the Reynolds stress region have smaller space and the location closing to the wall is the reason for smaller loss of the channel.The comparative analysis shows that there are different forms of streamlines and topology,and the wall heat transfer coefficient is closely related to the spatial flow structure.