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通过对不同马赫数下(Ma=0.7、2.25、6)平板边界层进行直接数值模拟研究,提出比熵增的概念。比熵增表征单位机械能的耗散,并且在数值上表现出较好的单调性和马赫数无关性,因而能够可靠地表征边界层的范围。应用比熵增概念修正BL零方程湍流模型长度尺度,构造BL-entropy,同时采用原始的BL模型,SA一方程模型对后台阶(Ma=0.128)以及高超声速锥柱裙组合体(Ma=7.05)流动进行数值模拟,并与实验数据进行比较,结果表明BL-entropy能够准确地获取长度尺度进而得到均匀合理的涡粘性分布,极大地提升了原始BL模型模拟复杂流动的能力。
Through the direct numerical simulation of the slab boundary layer under different Mach numbers (Ma = 0.7, 2.25, 6), the concept of specific entropy increase is proposed. Specific entropy increases the dissipation of mechanical energy per unit, and shows good monotonicity and Mach-independence in terms of numbers, thus reliably characterizing the boundary layer. BL-entropy was constructed by using the concept of specific entropy increase, and BL-entropy was modified by using the original BL model. The SA-equation model was used to simulate the back step (Ma = 0.128) and hypersonic cone- ) Flow and compared with the experimental data. The results show that the BL-entropy can obtain the length scale accurately and obtain a uniform and reasonable eddy viscosity distribution, which greatly enhances the ability of the original BL model to simulate complex flow.