高速稀薄非平衡边界层输运分析与气动力热理论预测

Analysis of nonlinear transport in hypersonic rarefied nonequilibrium boundary layer and theoretical prediction of surface aerothermodynamics

  • 摘要: 准确快速预测壁面气动力热对飞行器设计至关重要。临近空间飞行器跨越大气层飞行时将受到稀薄气体效应的显著影响,导致传统Navier-Stokes(N-S)方程失效,给壁面气动力热的准确高效预测带来挑战。其中,准确描述飞行器近壁边界层的非线性输运特性尤为关键。对此,本文针对高速稀薄非平衡边界层,基于Grad 13矩方程和广义流体动力学方程进行理论分析,结合剪切流Boltzmann模型方程的正则解和直接蒙特卡罗(direct simulation Monte Carlo, DSMC)模拟结果,研究了边界层内的非平衡机理和非线性输运特性,给出了边界层主导输运关系式和非平衡效应表征参数,发展了壁面局部压力、摩阻和热流的关联预测公式,并在尖平板、钝平板、钝楔、钝锥及圆球绕流等不同外形下与DSMC模拟结果进行了对比验证。结果表明,边界层内各应力和热流分量的非线性输运函数均可表达为剪切非平衡参数Kσ和热力梯度非平衡参数Kq的显式函数;所建立的壁面气动力热关联公式可显著改进传统N-S计算结果,在连续流到早期过渡流区(Kσ ~1)范围内与DSMC模拟结果吻合良好。该公式仅需连续流N-S解(解析或数值)即可给出稀薄过渡流壁面气动力热的近似准确估计,无需求解矩方程或动理论方程,在近空间飞行器壁面气动力热快速预测方面具有很好的应用前景。

     

    Abstract: Accurate and rapid prediction of surface aerothermodynamics is critical for flying vehicle design. Near-space vehicles flying across the atmosphere are significantly affected by rarefied gas effects, which render the conventional Navier-Stokes (N-S) equations invalid and pose challenges to the accurate and 6efficient prediction of surface aerothermodynamics. In particular, the accurate description of nonlinear transport in the near-wall boundary layer is crucial for aerodynamic predictions. To address this, the present study conducted a theoretical analysis of hypersonic rarefied nonequilibrium boundary layers based on the Grad 13 moment equations (G13) and generalized hydrodynamic equations (GHE), in conjunction with the normal solutions of the Boltzmann model equation for shear flows and the simulation results from the direct simulation Monte Carlo (DSMC) method. The nonequilibrium mechanisms and nonlinear transport characteristics within the boundary layer were investigated, from which the leading transport relations and the parameters characterizing nonequilibrium effects were derived. A set of correlation formulae for local surface pressure, skin friction, and heat flux were developed, and were validated against DSMC simulations for various geometries, including flat plate, blunt plate, blunt wedge, blunt cone, and sphere. The results show that the nonlinear transport functions for each component of stress and heat flux in the boundary layer can be expressed as explicit functions of the shear nonequilibrium parameter Kσ and thermal gradient nonequilibrium parameter Kq. The established correlation formulae significantly improve the traditional N-S predictions and agree well with DSMC results from the continuum to early transitional regimes (Kσ ~1). Notably, these formulae can provide approximate yet accurate estimates of surface aerothermodynamics for the hypersonic transitional flows using only the continuum-based N-S solutions (either analytical or numerical), without solving moment or kinetic equations, thus showing promising prospects for rapid prediction of surface aerothermodynamics on near-space vehicles.

     

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