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
逆向发动机常用于对飞行器进行减速或分离。为研究高空稀薄条件下逆向发动机喷流和自由来流的相互作用,构建了由两个逆向喷流和高超声速自由来流相互干扰形成的稀薄流场。通过直接模拟Monte Carlo(direct simulation Monte Carlo,DSMC)...逆向发动机常用于对飞行器进行减速或分离。为研究高空稀薄条件下逆向发动机喷流和自由来流的相互作用,构建了由两个逆向喷流和高超声速自由来流相互干扰形成的稀薄流场。通过直接模拟Monte Carlo(direct simulation Monte Carlo,DSMC)仿真发现在稀薄来流条件下会形成大面积相互干扰区,且该干扰区存在严重非定常流动现象。初步分析认为,该干扰区的范围和非定常演化过程与自由来流动能和逆向发动机喷流流量紧密相关。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
针对火星独特的CO_(2)稀薄气体环境以及探测器高超声速进入火星过程中的高温真实气体效应,研究了CO_(2)多振动模式的激发特性。采用非结构网格和直接模拟蒙特卡洛法(Direct Simulation Monte Carlo method, DSMC),基于非谐振子振动激发...针对火星独特的CO_(2)稀薄气体环境以及探测器高超声速进入火星过程中的高温真实气体效应,研究了CO_(2)多振动模式的激发特性。采用非结构网格和直接模拟蒙特卡洛法(Direct Simulation Monte Carlo method, DSMC),基于非谐振子振动激发模型,通过将CO_(2)离解能均分到4种振动模态,进而限制各模态最高振动能级,模拟了含CO_(2)的5组分17反应的高温稀薄真实气体化学反应模型。计算了“火星探路者”在火星大气环境65 km高度、进入速度为7 453 m/s、攻角为0°下的高温化学非平衡效应流场。结果表明:CO_(2)在激波后大量分解并消耗大量能量;迎风面激波中各组分占比与探测器物面特性等均与文献结果相符,证明了本文对于CO_(2)振动激发处理方法的可行性。在此基础上加入N_2组分,模拟火星大气8组分44基元化学反应流场,通过改变来流密度与马赫数分析了流场特性的变化。结果表明:随着来流密度减小,流场温度呈现先增加后减小的趋势,物面热流密度增大;来流马赫数增加使得流场温度和压力上升,物面热流密度提高但是热流密度系数变化幅度很小。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.
文摘逆向发动机常用于对飞行器进行减速或分离。为研究高空稀薄条件下逆向发动机喷流和自由来流的相互作用,构建了由两个逆向喷流和高超声速自由来流相互干扰形成的稀薄流场。通过直接模拟Monte Carlo(direct simulation Monte Carlo,DSMC)仿真发现在稀薄来流条件下会形成大面积相互干扰区,且该干扰区存在严重非定常流动现象。初步分析认为,该干扰区的范围和非定常演化过程与自由来流动能和逆向发动机喷流流量紧密相关。
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.
文摘针对火星独特的CO_(2)稀薄气体环境以及探测器高超声速进入火星过程中的高温真实气体效应,研究了CO_(2)多振动模式的激发特性。采用非结构网格和直接模拟蒙特卡洛法(Direct Simulation Monte Carlo method, DSMC),基于非谐振子振动激发模型,通过将CO_(2)离解能均分到4种振动模态,进而限制各模态最高振动能级,模拟了含CO_(2)的5组分17反应的高温稀薄真实气体化学反应模型。计算了“火星探路者”在火星大气环境65 km高度、进入速度为7 453 m/s、攻角为0°下的高温化学非平衡效应流场。结果表明:CO_(2)在激波后大量分解并消耗大量能量;迎风面激波中各组分占比与探测器物面特性等均与文献结果相符,证明了本文对于CO_(2)振动激发处理方法的可行性。在此基础上加入N_2组分,模拟火星大气8组分44基元化学反应流场,通过改变来流密度与马赫数分析了流场特性的变化。结果表明:随着来流密度减小,流场温度呈现先增加后减小的趋势,物面热流密度增大;来流马赫数增加使得流场温度和压力上升,物面热流密度提高但是热流密度系数变化幅度很小。
