Abstract 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.

中文翻译：

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流向壁面波动的摩擦减阻机理研究

摘要 了解如何减少流体在固体表面上施加的摩擦阻力对于解决关键的社会挑战变得越来越重要，例如减少运输的碳足迹。还没有成熟的技术可用于减少摩擦阻力。Jozsa 等人获得的直接数值模拟结果。(2019) 先前指出，被动柔顺壁可以通过维持主动控制策略的减阻机制来减少摩擦阻力。建议的柔顺壁由壁剪切应力波动驱动，并响应流向壁速度波动。本研究旨在阐明能够减少这些主动和被动控制技术的阻力的潜在物理机制。湍流统计和流场分析表明，柔顺壁和主动控制都放大了粘性子层中的流向速度条纹。通过这样做，这些控制方法抵消了近壁区域的主要展向涡度波动。降低的涡度波动导致涡流结构的整体减弱，然后减轻动量传递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。降低的涡度波动导致涡流结构的整体减弱，然后减轻动量传递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。降低的涡度波动导致涡流结构的整体减弱，然后减轻动量传递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。