标题： 低雷诺数下通过翼型表面凹坑实现的稳定和力调制 显示英文标题

标题： Wake Stabilization and Force Modulation via Surface Dimples on an Airfoil at Low-Reynolds-Numbers

摘要： 本研究利用直接数值模拟，探讨了表面凹坑对基于弦长的雷诺数为$Re_c = 5300$和$10{,}000$的国家航空咨询委员会翼型（NACA0012）非定常空气动力学的影响。凹坑被放置在吸力面上，非维度弦向位置分别为$l_D/c = 0.035$和$0.35$，并在固定攻角$\alpha = 5^\circ$下研究了流动响应。 在$Re_c = 5300$处，位于$l_D/c = 0.35$的凹坑分别使升力和阻力波动减少了$26.5\%$和$33.3\%$，而平均力变化最小。 在$Re_c = 10{,}000$处，相同结构导致力波动增加了七倍，而平均值保持不变。 光滑翼型在此$Re_c$处表现出不规则、非周期的力信号，而凹坑情况则显示出高度周期性的行为，表明尾流得到了稳定。 流场可视化显示，凹坑在边界层内生成顺流向涡旋。 这些涡旋被发现对$Re_c = 5300$处的尾流动力学具有稳定作用，减少了涡旋破裂并增强了尾流结构的相干性。 谱本征正交分解（SPOD）表明，凹陷会根据雷诺数重新分配模态能量：在低$Re_c$时，它们减少宽带内容并抑制非定常性，而在高$Re_c$时，它们增强主导脱落模态并拓宽频谱能量分布。 这些结果表明，凹陷可以被动地调节流线型物体上的非定常力和尾流动力学，在不同的工况下，要么抑制要么增强流动不稳定性。 显示英文摘要

摘要： This study investigates the effect of surface dimples on the unsteady aerodynamics of a National Advisory Committee for Aeronautics airfoil (NACA0012) at a chord-based Reynolds numbers of $Re_c = 5300$ and $10{,}000$ using direct numerical simulations. Dimples were placed on the suction side at non-dimensional chordwise locations of $l_D/c = 0.035$ and $0.35$, and the flow response was studied at a fixed angle of attack $\alpha = 5^\circ$. At $Re_c = 5300$, dimples placed at $l_D/c = 0.35$ reduced lift and drag fluctuations by $26.5\%$ and $33.3\%$, respectively, with minimal change in mean forces. At $Re_c = 10{,}000$, the same configuration led to a seven-fold increase in force fluctuations, while the mean remained unchanged. The smooth airfoil exhibited irregular, aperiodic force signals at this $Re_c$, whereas the dimpled case showed highly periodic behavior, indicating wake stabilization. Flow visualizations revealed that dimples generate streamwise vortices within the boundary layer. These vortices are found to have a stabilizing effect on wake dynamics at $Re_c = 5300$, reducing vortex breakdown and enhancing the coherence of wake structures. Spectral Proper Orthogonal Decomposition (SPOD) showed that dimples redistribute modal energy depending on Reynolds number: at low $Re_c$, they reduce broadband content and suppress unsteadiness, while at high $Re_c$, they amplify dominant shedding modes and broaden the spectral energy distribution. These results demonstrate that dimples can passively modulate unsteady forces and wake dynamics for a flow over a streamlined body, either suppressing or enhancing flow instabilities depending on the regime.