Research On N-S/DSMC Hybrid Algorithm In The Transitional Domain

When hypersonic flight vehicles travel through higher atmospheric layer,where the condition of the gas is rarefied,complex flow structures would be encountered.During the process continuous/rarefied mixing flows,rarefied gas and thermochemistry nonequilibrium have remarkable effects on the flight of hypersonic vehicles.Meanwhile,the general and simple numerical simulation is greatly challenged by the flow phenomenon existing in continuum region,transitional region and particles region.Besides,due to the poor efficiency,great difficulty and impracticality of ground experiments,it has been great necessity to build effective models and adopt efficient numerical method to simulate continuous/rarefied mixing flows.Aiming to understand the aerodynamic characteristics of vehicles during the flying process and to improve the prediction accuracy of aerodynamic force and aerodynamic heat of vehicles,a mixing algorithm named hybrid algorithm of N-S equations and DSMC method is employed to simulate the issues,since the N-S equations and DSMC method work well in continuous region and rarefied flow regions,respectively.The present study is conducted to make investigations on the mutual hybrid algorithm of N-S equations/DSMC method,and the main contents are as follow:First,the theory of N-S equations and DSMC method is analyzed.The finite volume method of CFD and the N-S procedure applied in the present study are introduced.Meanwhile,the theory of rarefied gas dynamic and the operation steps of DSMC method are stated as well.By simulating typical flow models,the results of the hybrid algorithm are efficiently validated.In addition,the numerical simulation of simple chemical reaction of unsteady flows of rarefied gas dynamic is conducted,which is regarded as an important supplement for the DSMC algorithm.Then,the details of theory of hybrid algorithm and relative calculation modules are introduced.The key problems of hybrid algorithm,including continuum-rarefied interface location and information transmission pattern,are investigated intensively.The proper continuum breakdown parameters are confirmed by analyzing the literatures and testing the simulations.By comparatively analyze the advantages and disadvantages of different hybrid methods,the state-based hybrid method is chosen as the best one to transmit the information in the interface,and the calculation process of grid partitions is also presented.The grid partitions of two different hybrid algorithm are matched,and the global calculation process are also presented.Finally,based on the calculation process,the procedure is programmed,and the problem of 1D flow and two-dimensional cylinder in transitional region is studied by employing N-S/DSMC hybrid algorithm.The comparison of temperature in 1D flow and the distribution of the flow field of the model is obtained,and the feasibility and validation of the hybrid algorithm is confirmed by comparing the present results with those gained by utilizing the N-S equations and DSMC method.