Control of Turbulent Transport: Less Friction and More Heat Transfer
Control of Turbulent Transport: Less Friction and More Heat Transfer
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湍流传输的控制：更少的摩擦和更多的热传递
DOI：
10.1115/1.4005151
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
K.
中科院分区：
文献类型：
--
作者：
Kasagi;N.,Hasegawa;Y.;Fukagata;K.& Iwamoto;K.
由于湍流传热的基础知识的重要性，进一步降低熵产生和提高效率，在各种热流体系统，我们重新审视一个经典的问题，是否可以提高传热与表面摩擦减少或至少不增加传热。许多先前的研究所提出的答案是相当悲观的，因为动量和热输运的类比概念在很宽的流动范围内都成立。然而，最近在分析湍流力学和设计湍流控制方面的进展为发展不同的动量和热量输运方案提供了机会。通过重新审视对流传热的控制方程和边界条件，在湍流中实现不同控制的基本策略通常分为两组，即，一个用于平均量，另一个用于波动湍流分量。因此，目前讨论两种不同的方法。首先，在三种典型的加热条件下，湍流输运对壁面摩擦和传热的贡献的数学公式，它表明，在如何在局部湍流动量和热量的输送贡献的摩擦和传热系数的差异是一个关键，回答了不同的控制是否是可行的。当导出的关系式中的应力和通量的权重分布不同时，这种控制很可能实现。其次，我们引入一个更一般的方法，即，最优控制理论Fréchet微分清楚地表明，速度场和标量场对给定控制输入的响应是完全不同的，这是由于速度是无发散矢量，而温度是保守标量。通过利用这种固有的差异，即使在平均动量和热输运方程具有相同形式的流动中，也可以实现不同的控制。
Because of the importance of fundamental knowledge on turbulent heat transfer for further decreasing entropy production and improving efficiency in various thermofluid systems, we revisit a classical issue whether enhancing heat transfer is possible with skin friction reduced or at least not increased as much as heat transfer. The answer that numerous previous studies suggest is quite pessimistic because the analogy concept of momentum and heat transport holds well in a wide range of flows. Nevertheless, the recent progress in analyzing turbulence mechanics and designing turbulence control offers a chance to develop a scheme for dissimilar momentum and heat transport. By reexamining the governing equations and boundary conditions for convective heat transfer, the basic strategies for achieving dissimilar control in turbulent flow are generally classified into two groups, i.e., one for the averaged quantities and the other for the fluctuating turbulent components. As a result, two different approaches are discussed presently. First, under three typical heating conditions, the contribution of turbulent transport to wall friction and heat transfer is mathematically formulated, and it is shown that the difference in how the local turbulent transport of momentum and that of heat contribute to the friction and heat transfer coefficients is a key to answer whether the dissimilar control is feasible. Such control is likely to be achieved when the weight distributions for the stress and flux in the derived relationships are different. Second, we introduce a more general methodology, i.e., the optimal control theory. The Fréchet differentials obtained clearly show that the responses of velocity and scalar fields to a given control input are quite different due to the fact that the velocity is a divergence-free vector, while the temperature is a conservative scalar. By exploiting this inherent difference, the dissimilar control can be achieved even in flows where the averaged momentum and heat transport equations have the same form.