超低轨航天器表面气固相互作用的分子动力学模拟

Molecular dynamics simulation of gas-solid interaction on the surface of ultra-low orbit spacecraft

  • 摘要: 为了准确模拟超低轨道上航天器的气动特性和优化气动布局,根据超低轨航天器所面临的高速来流气体与壁面相互作用的物理机制,采用分子动力学方法,分析了来流气体参数(气体温度、宏观来流气体速度大小、速度方向)和固体表面条件(壁面温度)对气体-表面相互作用过程中动量适应系数(momentum accommodation coefficient,MAC)和能量适应系数(energy accommodation coefficient,EAC)的影响规律及其作用机理。研究表明,精确计算动量和能量适应系数需要考虑气体的动力学参数和壁面条件的综合作用。在壁温150~450 K范围内,随着壁面温度的增高,切向动量适应系数(TMAC)几乎不变,法向动量适应系数(NMAC)和EAC降低,气体和壁面的切向动量交换对壁面温度的变化不敏感;在来流气体温度500~2000 K范围内,随着来流温度的增高,TMAC几乎不变,NMAC和EAC有所增大;在来流速度100~1100 m/s范围内,切向和法向速度对TMAC具有相反的影响效果,切向速度的增大使得TMAC减小,法向速度的增大使得TMAC增大,说明来流气体速度大小、方向对于适应系数具有耦合作用。

     

    Abstract: In order to accurately simulate the aerodynamic characteristics and optimize the aerodynamic layout of spacecraft in ultra-low orbit, based on the physical mechanism of high-speed incoming gas and wall interaction faced by ultra-low orbit spacecraft, molecular dynamics methods were used to analyze the influence and mechanism of incoming gas parameters (gas temperature, macroscopic incoming gas velocity, velocity direction) and solid surface conditions (wall temperature) on the momentum and energy accommodation coefficient in the gas-surface interaction process. Research has shown that accurate calculation of momentum and energy accommodation coefficients requires consideration of the combined effects of gas dynamic parameters and wall conditions. Within the wall temperature range of 150-450 K, as the wall temperature increases, the tangential momentum accommodation coefficient remains almost unchanged, while the normal momentum accommodation coefficient and energy accommodation coefficient decrease. The tangential momentum exchange between gas and wall is not sensitive to the change of wall temperature. In the range of macroscopic inflow gas temperature from 500 K to 2000 K, as the macroscopic inflow gas temperature increases, the tangential momentum accommodation coefficient remains almost unchanged, while the normal momentum accommodation coefficient and energy accommodation coefficient increase. The magnitude and direction of macroscopic incoming gas velocity have a coupling effect on the accommodation coefficient. Within the range of macroscopic incoming gas velocity from 100 m/s to 1100 m/s, tangential velocity and normal velocity have opposite effects on the tangential momentum accommodation coefficient. An increase in tangential velocity leads to a decrease in the tangential momentum accommodation coefficient, while an increase in normal velocity leads to an increase in the tangential momentum accommodation coefficient. Therefore, the accurate momentum and energy accommodation coefficients are the result of the combined action of gas parameters and solid surface conditions.

     

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