Flow And Heat Transfer Control Of The Turbine Blades Trailing Edge Column Ribs Based On The Lattice Boltzmann Method

During the working process of the turbine engine,the turbine blades is directly affected by the impact of high-temperature and high-pressure airflow,the effective cooling of the turbine blades is a prerequisite for ensuring proper turbine power and improving overall engine performance.Therefore,a proper understanding of the mechanism of internal flow heat transfer in turbine blades is essential.With the development of computer technology,computational fluid dynamics(CFD)has become an important tool for exploring the mechanism of flow heat transfer.The lattice Boltzmann method(LBM)differs from traditional computational fluid dynamics methods in that it is a mediated simulation method between macroscopic continuous simulations and microscopic molecular dynamics simulations.Since its inception,LBM has gained the popularity of many scholars due to its clear physical background,easy parallel computing,and easy implementation of the program,etc.It has rapidly developed into a powerful numerical simulation method for computational fluid dynamics within a short time.LBM has been widely used in fluid mechanics,heat transfer,quantum mechanics and other fields of research,and has received more and more attention.In this paper,the basic theory of LBM is firstly clarified,and the Boltzmann model of thermal lattice with double distribution function based on multiple relaxation time(MRT)is introduced;on this basis,a diffusion coefficient offset method to improve the numerical stability of LBM calculations is proposed,and the numerical validation is performed by square cavity natural convection heat transfer.Finally,the cooling of the turbine blades column ribs of the turbine blades is simplified to the flow and heat transfer of a classic cylindrical winding.The flow heat transfer mechanism of a single,parallel double cylinder at rest and rotation is studied to provide a theoretical basis for the control of flow heat transfer at the trailing edge of the turbine blade.The main research content and results of this paper are as follows:(1)The diffusion coefficient counteracting method is used to improve the phenomenon that the traditional algorithm is easy to diverge when calculating low viscosity flow.The optimization method is that in the evolution equations of the double distribution functions,the additional viscosity coefficient and the additional thermal diffusion coefficient are artificially added,and then,the influence of the additional diffusion coefficient is eliminated by the introduced external force terms and source terms.The natural convection heat transfer of the square cavity is taken as an example,and the algorithm is verified by comparing the calculation results with the existing literature data.The results show that,with a small number of grids,the computational accuracy can still be guaranteed,and numerical stability is improved while computational costs are reduced.However,the additional diffusion coefficient should not be greater than three times of the actual diffusion coefficient,otherwise the error will increase.(2)The reliability of the computational algorithm used to solve the heat transfer problem of the flow around the cylinder was verified,by comparing the mean drag coefficient and St number with the experimental data in the existing literature.The flow and heat transfer around a single cylinder at different Reynolds numbers is calculated.As the number of Re increases,the flow field changes from constant to non-constant flow,Carmen vortices are generated after the cylinder,and the temperature field distribution is no longer continuous due to the perturbation of vortices.(3)Based on the results of single cylinder simulation,four typical spacing ratios(G/D=1.2,1.7,2.5,4.0)were selected in this paper to study the flow characteristics of the fluid in the stationary and rotating states of the parallel cylinders,respectively.The simulation results show that three typical tail flow patterns exist with different spacing ratios:single vortex flow,partial flow,and synchronous symmetric flow.As the spacing ratios increases,the average coefficient of drag decreases by 19%and the average coefficient of lift decreases by 70%.(4)Further study of the effect of the cylindrical rotation mode on the tail current structure.It was found that the rotation of the cylinder effectively inhibits the formation and dislodgement of the vortex.And when the rotating ratio reaches a critical rotating ratio the vortex street disappears.The four spacing ratios correspond to a critical rotating ratio|?_c|of1.2,1.2,1.3 and 1.7,respectively.At the same time,the absolute value of the cylindrical mean time lift coefficient increases with the increase of the rotating ratio,while the mean time resistance coefficient decreases with the increase of the rotating ratio.This suggests that the rotation of parallel double cylinder can effectively improve the flow stability of the flow field.(5)The heat transfer characteristics of the flow around a cylinder are investigated by introducing a thermal lattice model.The results show that the vortex structure is closely related to the temperature field distribution,and the disturbance of the vortex can enhance the heat transfer effect of the cylinder.For parallel double cylinders,too small or too large a spacing is not conducive to enhanced heat transfer.When the spacing ratio is less than 1.2,the heat transfer between the cylinder and the fluid cannot be conducted sufficiently,and while the spacing ratio is greater than 4,the interference effect of the cylinder is weakened,the cylinders can be considered independent of each other.For the parallel rotating double cylinders,although the interference of the vortex street can be eliminated,the intensity of convective heat transfer on the surface of the cylinders are also reduced.Compared to the stationary state,where the spacing ratio is 1.2,the mean Nu number for a single cylinder at the maximum rotating ratio is reduced by 33%;and the mean Nu number corresponding to the critical rotating ratio is reduced by about 10%at the spacing ratio is 2.5.When the flow and heat transfer characteristics were considered together,it was found that the critical rotating ratio can avoid the blockage of the flow channel while ensuring the convective heat transfer capacity between the column rib and the fluid as much as possible.