In the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour fiel...In the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour field and velocity distribution function level. The comparison of the simulated results with the accurate numerical solutions of the B-G-K model equation shows that near equilibrium the BG-K equation with corrected collision frequency can give accurate result but as farther away from equilibrium the B-G-K equation is not accurate. This is for the first time that the error caused by the B-G-K model equation has been revealed.展开更多
对于高超声速飞行器在临近空间形成的连续与稀薄混合流场,DSMC(direct simulation of Monte Carlo)方法需要消耗巨大的计算资源,CFD(computational fluid dynamics)方法,无法对稀薄效应进行准确模拟。在对连续/稀薄耦合数值方法深入研...对于高超声速飞行器在临近空间形成的连续与稀薄混合流场,DSMC(direct simulation of Monte Carlo)方法需要消耗巨大的计算资源,CFD(computational fluid dynamics)方法,无法对稀薄效应进行准确模拟。在对连续/稀薄耦合数值方法深入研究的基础上,提出了一套非结构网格的CFD/DSMC耦合方法。该方法具有通用强、适应性良好的特点,进行耦合计算时对不规则复杂分界面无需进行光滑处理。对超声速圆柱绕流和钝锥体流场进行了模拟,数值结果表明:该方法对不规则分界面和复杂外形具有高度适用性,通过与重叠网格结果进行比较验证了该方法的有效性和计算效率,相较于传统的DSMC方法,计算效率分别提高了2.3倍和3.16倍,具有高效性。展开更多
针对近连续流过渡区多尺度绕流问题,学界发展了N-S(Navier-Stokes)/DSMC(direct simulation Monte Carlo)耦合方法,大多数此类求解器面临着耦合界面波动失稳的难题,因此对复杂外形和耦合界面的通用性值得重点研究。鉴于非结构网格面向...针对近连续流过渡区多尺度绕流问题,学界发展了N-S(Navier-Stokes)/DSMC(direct simulation Monte Carlo)耦合方法,大多数此类求解器面临着耦合界面波动失稳的难题,因此对复杂外形和耦合界面的通用性值得重点研究。鉴于非结构网格面向复杂外形高度的贴体性、优良适应性以及工程领域对过渡流区高效通用型计算方法的需求,提出并实现了一套三维复杂界面四面体非结构网格N-S/DSMC耦合方法用于模拟高超声速过渡流。该方法使用局部克努森数作为连续失效参数划分连续/稀薄区域,并生成三维复杂N-S/DSMC耦合界面,沿分界面两侧分别推进一层或多层界面信息传递单元,基于边界状态法进行信息耦合。该耦合方法无需对复杂不规则分界面作光滑和修型处理,具备对复杂过渡流区工程问题数值模拟的通用性。分别对三维高超声速圆球和钝锥绕流进行模拟,数值结果显示:与参考文献中的DSMC方法相比,激波处数值和壁面特征值基本一致,最大误差不超过8%,但计算效率分别提高了1.74倍和2.28倍,验证了该耦合方法的正确性和高效性。展开更多
This paper investigates the convergence proof of the Direct Simulation Monte Carlo(DSMC) method and the Gas-Kinetic Unified Algorithm in simulating the Boltzmann equation.It can be shown that the particle velocity dis...This paper investigates the convergence proof of the Direct Simulation Monte Carlo(DSMC) method and the Gas-Kinetic Unified Algorithm in simulating the Boltzmann equation.It can be shown that the particle velocity distribution function obtained by the DSMC method converges to a modified form of the Boltzmann equation,which is the equation of the gas-kinetic unified algorithm to directly solve the molecular velocity distribution function.Their convergence is derived through mathematical treatment.The collision frequency is presented using various molecular models and the local equilibrium distribution function is obtained by Enskog expansion using the converged equation of the DSMC method.These two expressions agree with those used in the unified algorithm.Numerical validation of the converging consistency between these two approaches is illustrated by simulating the pressure driven Poiseuille flow in the slip transition flow regime and the two-dimensional and three-dimensional flows around a circular cylinder and spherical-cone reentry body covering the whole flow regimes from low speed micro-channel flow to high speed non-equilibrium aerothermodynamics.展开更多
基金The project supported by the National Natural Science Foundation of China (19772059, 19889209)
文摘In the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour field and velocity distribution function level. The comparison of the simulated results with the accurate numerical solutions of the B-G-K model equation shows that near equilibrium the BG-K equation with corrected collision frequency can give accurate result but as farther away from equilibrium the B-G-K equation is not accurate. This is for the first time that the error caused by the B-G-K model equation has been revealed.
文摘采用分子动力学理论导出系统熵与熵产率的计算公式,识别高超声速稀薄流非平衡区域。根据熵产与非平衡现象的基本关系,确定了衡量气体非平衡态的判断方法。由于熵产率参数存在局限性,提出了一种熵产克努森数(Knudsen number)作为气体非平衡态衡量参数,与局部克努森数相结合作为非平衡态判据。基于两种非平衡判据相结合的策略,发展了一套高超声速流场非平衡区域识别与网格自适应重构的DSMC(direct simulation Monte Carlo)计算方法。对典型非平衡流场进行模拟,数值结果表明:所提出的识别参数能精准识别全流场中的非平衡效应,识别率达到了99%以上。在此基础上重构非平衡区域网格,计算得到的流场宏观量相对误差小于3%,壁面气动参数相对误差小于5%,证明了自适应重构方法的有效性。
文摘对于高超声速飞行器在临近空间形成的连续与稀薄混合流场,DSMC(direct simulation of Monte Carlo)方法需要消耗巨大的计算资源,CFD(computational fluid dynamics)方法,无法对稀薄效应进行准确模拟。在对连续/稀薄耦合数值方法深入研究的基础上,提出了一套非结构网格的CFD/DSMC耦合方法。该方法具有通用强、适应性良好的特点,进行耦合计算时对不规则复杂分界面无需进行光滑处理。对超声速圆柱绕流和钝锥体流场进行了模拟,数值结果表明:该方法对不规则分界面和复杂外形具有高度适用性,通过与重叠网格结果进行比较验证了该方法的有效性和计算效率,相较于传统的DSMC方法,计算效率分别提高了2.3倍和3.16倍,具有高效性。
文摘针对近连续流过渡区多尺度绕流问题,学界发展了N-S(Navier-Stokes)/DSMC(direct simulation Monte Carlo)耦合方法,大多数此类求解器面临着耦合界面波动失稳的难题,因此对复杂外形和耦合界面的通用性值得重点研究。鉴于非结构网格面向复杂外形高度的贴体性、优良适应性以及工程领域对过渡流区高效通用型计算方法的需求,提出并实现了一套三维复杂界面四面体非结构网格N-S/DSMC耦合方法用于模拟高超声速过渡流。该方法使用局部克努森数作为连续失效参数划分连续/稀薄区域,并生成三维复杂N-S/DSMC耦合界面,沿分界面两侧分别推进一层或多层界面信息传递单元,基于边界状态法进行信息耦合。该耦合方法无需对复杂不规则分界面作光滑和修型处理,具备对复杂过渡流区工程问题数值模拟的通用性。分别对三维高超声速圆球和钝锥绕流进行模拟,数值结果显示:与参考文献中的DSMC方法相比,激波处数值和壁面特征值基本一致,最大误差不超过8%,但计算效率分别提高了1.74倍和2.28倍,验证了该耦合方法的正确性和高效性。
基金supported by the National Natural Science Foundation of China (Grant Nos. 91016027 and 91130018)
文摘This paper investigates the convergence proof of the Direct Simulation Monte Carlo(DSMC) method and the Gas-Kinetic Unified Algorithm in simulating the Boltzmann equation.It can be shown that the particle velocity distribution function obtained by the DSMC method converges to a modified form of the Boltzmann equation,which is the equation of the gas-kinetic unified algorithm to directly solve the molecular velocity distribution function.Their convergence is derived through mathematical treatment.The collision frequency is presented using various molecular models and the local equilibrium distribution function is obtained by Enskog expansion using the converged equation of the DSMC method.These two expressions agree with those used in the unified algorithm.Numerical validation of the converging consistency between these two approaches is illustrated by simulating the pressure driven Poiseuille flow in the slip transition flow regime and the two-dimensional and three-dimensional flows around a circular cylinder and spherical-cone reentry body covering the whole flow regimes from low speed micro-channel flow to high speed non-equilibrium aerothermodynamics.
基金National Natural Science Foundation of China(51775096)Chinese Academy of Sciences WEGO Research Development Plan([2007]006)Fundamental Research Funds for the Central Universities,China(N2003009)。
