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<p>This study investigates the effects of spanwise wall oscillations (SWOs) on open channel flow at <i>Re</i><sub><i>τ</i></sub> = 85 using direct numerical simulations. The oscillation amplitude is fixed at <i>A</i><sup>+</sup> = 12, and the period <i>T</i><sup>+</sup> varies from 20 to 400. Results show that SWOs reduce drag, with the highest reduction of 31% at <i>T</i><sup>+</sup> = 70. The primary mechanisms include an elevated streamwise velocity profile, reduced Reynolds stress, and disruption of near-wall coherent structures. A novel vortex cluster structure emerges, weakening near-wall streaks and reducing skin friction drag. As <i>T</i><sup>+</sup> increases, the spanwise tilt of near-wall streaks becomes more pronounced, and turbulence recovers, leading to drag values closer to the uncontrolled flow. Beyond <i>T</i><sup>+</sup> = 70, the modulation effect on turbulence fluctuations saturates. SWOs mainly regulate Reynolds shear stress by controlling Q4 events, with shorter periods suppressing large-scale structures and longer periods enhancing velocity fluctuations.</p>

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Impact of wall oscillation on the drag and flow structure in an open channel at transitional Reynolds number

  • 期刊论文

  • 发表日期：

    2026年3月16日

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  • Bofu Wang,
  • Luyao Zhang,
  • Jianghua Li,
  • Quan Zhou

摘要

This study investigates the effects of spanwise wall oscillations (SWOs) on open channel flow at Reτ = 85 using direct numerical simulations. The oscillation amplitude is fixed at A+ = 12, and the period T+ varies from 20 to 400. Results show that SWOs reduce drag, with the highest reduction of 31% at T+ = 70. The primary mechanisms include an elevated streamwise velocity profile, reduced Reynolds stress, and disruption of near-wall coherent structures. A novel vortex cluster structure emerges, weakening near-wall streaks and reducing skin friction drag. As T+ increases, the spanwise tilt of near-wall streaks becomes more pronounced, and turbulence recovers, leading to drag values closer to the uncontrolled flow. Beyond T+ = 70, the modulation effect on turbulence fluctuations saturates. SWOs mainly regulate Reynolds shear stress by controlling Q4 events, with shorter periods suppressing large-scale structures and longer periods enhancing velocity fluctuations.