Evolutional Fundamental Study on Active Control of Wall Turbulence

面对能源资源枯竭和环境恶化等全球性问题，越来越需要高度先进的湍流控制技术。湍流控制开辟了新的可能性，以实现更高的效率和最小的环境影响的各种热流体系统通过操纵和修改动量/热/质传递，噪音以及化学反应支持人类社会。在本研究中，我们集中研究了一种最典型的流动，即壁面湍流和相关的输运现象。我们特别致力于开发创新的预定控制，以大幅减少表面摩擦阻力并增强热/质传递。具体来说，我们引入了新的控制指标，如净节能率和控制增益，以评估现有控制策略的成本效益，以及新提出的行波式壁吹/吸。我们还将均匀吹吸应用于湍流边界层，以获得空间发展流动的一般控制策略。对于传热/质传递增强，我们重新检查了速度场和标量场的控制方程和边界条件，以澄清不同传热增强控制的可能情况。通过应用最优控制理论，证明了用简单的开环控制策略可以实现异类控制。

Facing the global issues such as depletion of energy resources and environmental deterioration, highly advanced technology of turbulence control is ever more needed. Turbulence control opens up new possibilities to achieve far greater efficiency and least environmental impact of various thermal-fluid systems supporting the human society through the manipulation and modification of momentum/heat/mass transfer, noise as well as chemical reaction. In the present study, we focused on one of the most canonical flows, i.e., wall turbulence and associated transport phenomena. We particularly aimed at developing innovative predetermined controls to drastically reduce skin friction drag and enhance heat/mass transfer. Specifically, we introduced new control indices such as the net energy saving rate and the control gain in order to evaluate cost effectiveness of existing control strategies and also a newly proposed traveling wave-like wall blowing/suction. We also applied uniform blowing/suction to a turbulent boundary layer to obtain general control strategies for spatially developing flows. For heat/mass transfer enhancement, we reexamined the governing equations and boundary conditions for the velocity and scalar fields in order to clarify possible scenarios for dissimilar heat transfer enhancement control. By applying the optimal control theory, we demonstrated that the dissimilar control is possible with a simple open-loop control strategy.