NS-DSMC(Navier Stokes-Direct Simulation Monte Carlo)耦合方法是计算连续-稀薄跨流域流动的主要方法,应用过程中如何确定连续流域和稀薄流域的界面是此方法的关键问题之一,界面位置通常通过连续失效参数来判定.为合理选择连续失效参...NS-DSMC(Navier Stokes-Direct Simulation Monte Carlo)耦合方法是计算连续-稀薄跨流域流动的主要方法,应用过程中如何确定连续流域和稀薄流域的界面是此方法的关键问题之一,界面位置通常通过连续失效参数来判定.为合理选择连续失效参数,对目前广泛使用的两种连续失效参数KnQ和B参数进行了理论上的分析和比较,表明虽然他们建立的出发点不同,但在数学形式上具有一定相似性.通过圆柱绕流问题的数值试验进一步验证了两种连续失效参数具有一定对应关系.KnQ和B两种连续失效参数在NS-DSMC耦合方法中应用效果相差不大,但KnQ的阈值0.05适用范围较广,而B参数的阈值对不同流动问题会有变化.展开更多
The low diffusion （LD） particle method, proposed by Burt and Boyd, is modified for the near-continuum two-phase flow simulations. The LD method has the advantages of easily coupling with the direct simulation Monte ...The low diffusion （LD） particle method, proposed by Burt and Boyd, is modified for the near-continuum two-phase flow simulations. The LD method has the advantages of easily coupling with the direct simulation Monte Carlo （DSMC） method for multi-scale flow simulations and dramatically reducing the numerical diffusion error and statistical scatter of the equilibrium particle methods. Liquidor solid-phase particles are introduced in the LD method. Their velocity and temperature updating are respectively, calculated from the motion equation and the temperature equation according to the local gas properties. Coupling effects from condensed phase to gas phase are modeled as momentum and energy sources, which are respectively, equal to the negative values of the total momentum and energy increase in liquid or solid phase. The modified method is compared with theoretical results for unsteady flows, and good agreements are obtained to indicate the reliability of the one-way gas-to-particle coupling models. Hybrid LD-DSMC algorithm is implemented and performed for nozzle discharging gas-liquid flow to show the prospect of the LD-DSMC scheme for multi-scale two-phase flow simulations.展开更多
Based on the first-order upwind and second-order central type of finite volume (UFV and CFV) scheme, upwind and central type of perturbation finite volume (UPFV and CPFV) schemes of the Navier-Stokes equations were de...Based on the first-order upwind and second-order central type of finite volume (UFV and CFV) scheme, upwind and central type of perturbation finite volume (UPFV and CPFV) schemes of the Navier-Stokes equations were developed. In PFV method, the mass fluxes of across the cell faces of the control volume (CV) were expanded into power series of the grid spacing and the coefficients of the power series were determined by means of the conservation equation itself. The UPFV and CPFV scheme respectively uses the same nodes and expressions as those of the normal first-order upwind and second-order central scheme, which is apt to programming. The results of numerical experiments about the flow in a lid-driven cavity and the problem of transport of a scalar quantity in a known velocity field show that compared to the first-order UFV and second-order CFV schemes, upwind PFV scheme is higher accuracy and resolution, especially better robustness. The numerical computation to flow in a lid-driven cavity shows that the under-relaxation factor can be arbitrarily selected ranging from (0.3) to (0.8) and convergence perform excellent with Reynolds number variation from 10~2 to 10~4.展开更多
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
文摘NS-DSMC(Navier Stokes-Direct Simulation Monte Carlo)耦合方法是计算连续-稀薄跨流域流动的主要方法,应用过程中如何确定连续流域和稀薄流域的界面是此方法的关键问题之一,界面位置通常通过连续失效参数来判定.为合理选择连续失效参数,对目前广泛使用的两种连续失效参数KnQ和B参数进行了理论上的分析和比较,表明虽然他们建立的出发点不同,但在数学形式上具有一定相似性.通过圆柱绕流问题的数值试验进一步验证了两种连续失效参数具有一定对应关系.KnQ和B两种连续失效参数在NS-DSMC耦合方法中应用效果相差不大,但KnQ的阈值0.05适用范围较广,而B参数的阈值对不同流动问题会有变化.
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)。
文摘The low diffusion （LD） particle method, proposed by Burt and Boyd, is modified for the near-continuum two-phase flow simulations. The LD method has the advantages of easily coupling with the direct simulation Monte Carlo （DSMC） method for multi-scale flow simulations and dramatically reducing the numerical diffusion error and statistical scatter of the equilibrium particle methods. Liquidor solid-phase particles are introduced in the LD method. Their velocity and temperature updating are respectively, calculated from the motion equation and the temperature equation according to the local gas properties. Coupling effects from condensed phase to gas phase are modeled as momentum and energy sources, which are respectively, equal to the negative values of the total momentum and energy increase in liquid or solid phase. The modified method is compared with theoretical results for unsteady flows, and good agreements are obtained to indicate the reliability of the one-way gas-to-particle coupling models. Hybrid LD-DSMC algorithm is implemented and performed for nozzle discharging gas-liquid flow to show the prospect of the LD-DSMC scheme for multi-scale two-phase flow simulations.
文摘Based on the first-order upwind and second-order central type of finite volume (UFV and CFV) scheme, upwind and central type of perturbation finite volume (UPFV and CPFV) schemes of the Navier-Stokes equations were developed. In PFV method, the mass fluxes of across the cell faces of the control volume (CV) were expanded into power series of the grid spacing and the coefficients of the power series were determined by means of the conservation equation itself. The UPFV and CPFV scheme respectively uses the same nodes and expressions as those of the normal first-order upwind and second-order central scheme, which is apt to programming. The results of numerical experiments about the flow in a lid-driven cavity and the problem of transport of a scalar quantity in a known velocity field show that compared to the first-order UFV and second-order CFV schemes, upwind PFV scheme is higher accuracy and resolution, especially better robustness. The numerical computation to flow in a lid-driven cavity shows that the under-relaxation factor can be arbitrarily selected ranging from (0.3) to (0.8) and convergence perform excellent with Reynolds number variation from 10~2 to 10~4.
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。
