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首页> 外文期刊>International Journal of Heat and Fluid Flow >On the friction drag reduction mechanism of streamwise wall fluctuations
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On the friction drag reduction mechanism of streamwise wall fluctuations

机译：关于流墙波动的摩擦减阻机制

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摘要

Understanding how to decrease the friction drag exerted by a fluid on a solid surface is becoming increasingly important to address key societal challenges, such as decreasing the carbon footprint of transport. Well-established techniques are not yet available for friction drag reduction. Direct numerical simulation results obtained by Jozsa et al. (2019) previously indicated that a passive compliant wall can decrease friction drag by sustaining the drag reduction mechanism of an active control strategy. The proposed compliant wall is driven by wall shear stress fluctuations and responds with streamwise wall velocity fluctuations. The present study aims to clarify the underlying physical mechanism enabling the drag reduction of these active and passive control techniques. Analysis of turbulence statistics and flow fields reveals that both compliant wall and active control amplify streamwise velocity streaks in the viscous sublayer. By doing so, these control methods counteract dominant spanwise vorticity fluctuations in the near-wall region. The lowered vorticity fluctuations lead to an overall weakening of vortical structures which then mitigates momentum transfer and results in lower friction drag. These results might underpin the further development and practical implementation of these control strategies.
机译：了解如何减少由固体表面上的液体施加的摩擦拖延越来越重要，以解决关键的社会挑战，例如降低运输的碳足迹。既定的技术尚未用于减少摩擦减阻。 Jozsa等人获得的直接数值模拟结果。 （2019）之前表明，通过维持主动控制策略的阻力减少机制，可以减少无源柔性壁可以减少摩擦阻力。所提出的柔性壁由壁剪切应力波动驱动并用流动壁速度波动响应。本研究旨在阐明潜在的物理机制，从而降低这些主动和被动控制技术的减阻。湍流统计和流场的分析表明，柔顺壁和主动控制均在粘性子层中放大流动速度条纹。通过这样做，这些控制方法抵消了近壁区域中的主干血管涡流波动。降低的涡流波动导致涡流结构的总体削弱，然后减轻动量转移并导致较低的摩擦阻力。这些结果可能支持这些控制策略的进一步发展和实际实施。

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