Dissimilarity between turbulent heat and momentum transfer induced by a streamwise travelling wave of wall blowing and suction
Dissimilarity between turbulent heat and momentum transfer induced by a streamwise travelling wave of wall blowing and suction
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DOI：
10.1017/jfm.2019.1045
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发表时间：
2020-01
影响因子：
3.7
通讯作者：
Arjun J. Kaithakkal;Y. Kametani;Y. Hasegawa
中科院分区：
文献类型：
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作者：
Arjun J. Kaithakkal;Y. Kametani;Y. Hasegawa
本文对充分发展的槽道湍流流动进行了一系列直接数值模拟，以阐明行波式壁面吹除和抽吸对不同传热强化的影响。当波形保持为正弦并且其幅度被设置为体积平均速度的5%时，行波的波长和相速度在宽的参数空间中系统地改变。其结果是，全局最优的参数集最大化的类比因子，这是定义为斯坦顿数和皮肤摩擦系数之间的比率，被确定。有趣的是，所获得的全局最优模式与Yamamoto等人（J. Fluid Mech.，第733卷，2013年，pp. 189-220）。瞬时速度场和温度场被分解为相干和随机分量，以评估每个分量对不同传热强化的贡献。通过对相干贡献和随机贡献的预算分析，解释了差异的详细机制。同时，通过流动显示，讨论了它们与应用控制所改变的近壁湍流结构之间的关系。据发现，随机分量作出了显着贡献的相异性，这可以解释通过修改的相干场的应用控制的间接效果。基于上述机制，我们提出了一个简单的非定常雷诺平均Navier-Stokes（URANS）的方法，其中的相平均速度和温度场直接解决，而随机分量的影响是由Boussinesq涡粘性和扩散假设建模。结果表明，目前的URANS可以捕捉不同的传热强化在一个很宽的参数范围内的整体趋势。本文的结果也解释了为什么最优控制理论与有限的时间范围内成功地预测全局最优控制模式。
A series of direct numerical simulations of a fully developed turbulent channel flow is conducted in order to clarify the effects of travelling wave-like wall blowing and suction on dissimilar heat transfer enhancement. While the wave form is kept sinusoidal and its amplitude is set to be 5 % of the bulk mean velocity, the wavelength and phase speed of the travelling wave are systematically changed in a wide parameter space. As a result, the global optimum of the parameter set for maximizing the analogy factor, which is defined as the ratio between the Stanton number and the skin-friction coefficient, is identified. Interestingly, the obtained globally optimal mode agrees well with that predicted from the optimal control theory taking into account the future dynamics within a limited time horizon by Yamamoto et al. (J. Fluid Mech., vol. 733, 2013, pp. 189–220). The instantaneous velocity and thermal fields are decomposed into coherent and random components in order to evaluate the contribution from each component to dissimilar heat transfer enhancement. The detailed mechanisms of dissimilarity are explained by the budget analyses of the coherent and random contributions. Also, their relationships with the near-wall turbulent structures modified by the applied control are discussed through flow visualization. It is found that the random component makes a dominant contribution to dissimilarity, and this can be explained by an indirect effect through the modification of the coherent field by the applied control. Based on the above mechanisms, we propose a simple unsteady Reynolds-averaged Navier–Stokes (URANS) approach, where the phase-averaged velocity and thermal fields are solved directly whereas the effects of the random component are modelled by the Boussinesq eddy viscosity and diffusivity hypothesis. It is shown that the present URANS can capture the overall trend of dissimilar heat transfer enhancement in a wide parameter range. The present results also explain why the optimal control theory with a limited time horizon succeeds in predicting the globally optimal control mode.