Discrete Unified Gas Kinetics Scheme For Thermal Fluid And Numerical Simulation

Circulation in the atmosphere,heat dissipation of microelectronic devices,and the combustion of clean energy,the flow and heat transfer involved in natural and industrial survival fields can be regarded as incompressible heat flow.By studying incompressible heat flow,industrial production can be better guided.In order to systematically understand the characteristic of incompressible heat flow phenomenon,grasp the law of change between flow rate and heat transfer.In recent years,Guo proposed the Discrete Unified Gas Kinetics Scheme（DUGKS）,which provides a new method for computational fluid dynamics.DUGKS has no systematic research on incompressible heat fluids.Base on it,this paper takes the natural convection of the air in a square cavity as an example to study the change process of its flow and heat transfer through numerical simulation,aiming at a series of phenomena in the flow field from steady state to unsteady state under different Rayleigh numbers research.The main work is as follows:This article first introduces the result of numerical simulation in fluid mechanics in recent years and the current research status of natural convection.The common computational fluid dynamics methods and control equations are introduced,and a new mesoscopic method the discrete unified gas kinetics scheme is emphasized.In simulating continuous flow and rarefied flow problems,this method has good numerical accuracy and stability.Take the natural convection model in a two-dimensional closed square cavity as an example to study the flow and heat transfer process of incompressible heat fluid.With the other initial conditions unchanged,by changing the Raleigh number,the flow field gradually develops from laminar flow to turbulent flow.In the laminar flow stage,the difference in Raleigh number will affect the flow field and the temperature field eventually evolve to a stable state;in the turbulent flow stage,Raleigh number continues to increase,and the flow field and temperature field both show a chaotic state.In this paper,the Raleigh number is calculated as high as 10¹²,and it is found that the temperature gradient near the isothermal wall and the Raleigh number show a certain multiplication relationship.Under the simulation of high Rayleigh number,DUGKS has good numerical stability and high numerical accuracy.However,the structure of the algorithm is complex,and it still has large development space in computational efficiency.For the flow of incompressible thermal fluid,on the basis of the original algorithm,the trapezoidal rule is used instead of the midpoint rule to solve the convection term,a simplified DUGKS is proposed.Meanwhile,it is used for the numerical simulation of two-dimensional natural convection.Theoretical analysis and calculation results show that for the solution of two-dimensional natural convection,the simplified algorithm has the same stability and numerical accuracy as the original algorithm,and the calculation efficiency can be increased by 30%or so.