高超声速激波湍流边界层干扰直接数值模拟研究

高超声速激波与湍流边界层干扰会导致飞行器表面出现局部热流峰值,严重影响飞行器气动性能和飞行安全. 针对高马赫数激波干扰问题,以往数值研究多采用雷诺平均方法,而在直接数值模拟方面的相关工作较为少见. 开展高超声速激波与湍流边界层干扰的直接数值模拟研究,有助于进一步提升对其复杂流动机理认识和理解,同时也将为现有湍流模型和亚格子应力模型的改进提供理论依据. 采用直接数值模拟方法对来流马赫数6.0,34°压缩拐角内激波与湍流边界层的干扰问题进行了研究. 基于雷诺应力各向异性张量,分析了高超声速湍流边界层在压缩拐角内的演化特性. 通过对湍动能输运方程的逐项分析,系统地研究了可压缩效应对湍动能及其输运的影响机制. 采用动态模态分解方法,探讨了干扰流场的非定常运动历程. 研究结果表明,随着湍流边界层往下游发展,近壁湍流的雷诺应力状态由两组元轴对称状态逐渐演化为两组元状态,外层区域则由轴对称膨胀趋近于各向同性. 干扰流场内存在强内在压缩性效应(声效应),其对湍动能输运的影响主要体现在压力--膨胀项,而对膨胀--耗散项影响较小. 高超声速下压缩拐角内的非定常运动仍存在以分离泡膨胀/收缩为特征的低频振荡特性,其物理机制与分离泡剪切层密切相关. 

DIRECT NUMERICAL SIMULATION OF HYPERSONIC SHOCK WAVE AND TURBULENT BOUNDARY LAYER INTERACTIONS 1)

The peak of local thermal load might be severe due to the interactions of hypersonic shock wave and turbulent boundary layer. It has significant effect on the aerodynamic performance and flight safety of vehicle. Most previous studies on the interaction in hypersonic condition were based on the Reynolds-averaged methods, the corresponding direct numerical simulation is relatively scarce. The direct numerical analysis of hypersonic shock wave and turbulent boundary layer interaction are helpful to the understanding of the relevant mechanisms and the improvement of existing turbulent modes and sub-grid stress models. Numerical analysis of hypersonic shock wave and turbulent boundary layer interactions in a 34° compression ramp are carried out by means of direct numerical simulation for a free-stream Mach number M_{\mathbf{\infty }}=6.0. Based on the Reynolds stress anisotropy tensor, the evolution of turbulent boundary layer along the compression ramp is analyzed. The compressibility effects on turbulent kinetic energy and its transport mechanism are studied through item by item analysis of transport equation. Using dynamic mode decomposition method, the characteristic of unsteadiness in the interaction region is investigated. It is found that along the flow developing downstream, the turbulent state in the near wall region is gradually turned into two-component turbulence from two-component axisymmetric state. The turbulence in outer region approaches the isotropic state from axisymmetric expansion. The results exhibit that there exist significant compressibility effects in the interaction region. The pressure-dilation correlation in turbulent kinetic energy budgets is enhanced significantly. However, it has little effect on the dilatational dissipation. The low-frequency oscillation in hypersonic compression ramp is characterized by the breathing motion of separation bubble. According to the spatial structure of low frequency dynamic modes, the unsteadiness is strongly associated with the separated shear layer.