A Numerical Study Of Unsteady Heat Transfer And Rotating Heat Transfer Of Dimple Vortex Generators

The overall efficiency of aero engine and gas turbine increases as inlet temperature of turbine increases.However,the augment of turbine inlet temperature depends on the development of blade cooling technology.Therefore,the design of heat transfer structure with higher efficiency is imperative to the development of gas turbine blade cooling technology.Compared with other heat transfer structures,dimple vortex generator is an attractive method for heat transfer enhancement with low pressure penalty and has aroused interests of researchers from all over the world.By far,the numerical simulation research of dimple is mainly concentrated on RANS simulation of stationary dimpled channel.Further research work on the unsteady turbulence characteristics and rotating effects of dimple channel is still needed.For this reason,the simulation analyses of transient SST k-? DES model on stationary channel and RANS model on rotating channel are done in this paper.Certified by the experiment results or literature data,the characteristics of turbulent flow and heat transfer in dimple channel are achieved to provide theoretical references for dimple application in turbine blade.The numerical simulation of transient SST k-? DES model on stationary channel with one dimpled surface at the condition of Re=50,500 has been achieved and the result shows that: the turbulent flow and heat transfer of dimple can be well captured by SST k-? DES model.The path of vortex structure induced by dimple can be divided into four processes,namely generation,rotation,reflux and broken in sequence.Rotating smooth channels and dimpled channels with aspect ratio of 4:1 are simulated by RANS model for Reynolds numbers of 10,000,30,000 and 50,500 and the rotation numbers of 0,0.07 and 0.119 respectively.For rotating dimpled channel,the leading and trailing surfaces are dimpled.The numerical simulation indicates that: compared with SST k–?and RNG k-? turbulent model,k-? model is the best model for rotating channel simulation.Stationary channel is not affected by the Coriolis force.And for rotating channel,there are two large symmetrical secondary vortexes with opposite directions formed at the cross section under the influence of Coriolis force.The vortex core is in the angular area formed by the leading surface and sidewall surfaces.The Coriolis force increases with the rotation number.Dimple complicates the flow pattern in rotating channel.The higher the Ro number is,the more the averaged heat transfer performance and the friction factor of rotating channel increase.Compared with stationary dimpled channel,rotating dimpled channel achieves 3%~6.5% heat transfer enhancement but 1.6-8.4 times friction factor at Reynold number of 30,000.Compared with rotating smooth channel,the rotating dimpled channel has higher heat transfer performance of 35%~40% enhancement and lower pressure loss of 5.4%~16% decrease.Therefore,the application of dimple in rotating channel has a promising prospect.