arXiv 2406.012322024-06-03physics.flu-dyn

大展长无限翼三维湍流跨声速抖振的高保真研究

High-fidelity study of three-dimensional turbulent transonic buffet on wide-span infinite wings

David J. Lusher, Andrea Sansica, Markus Zauner, Atsushi Hashimoto

AI总结：

本研究对NASA-CRM翼型在高达$AR=3$的展弦比下进行了高保真模拟，揭示了三维跨声速抖振的时空结构和分离泡特征，发现三维特性在低升力相位和广泛平均流动分离时最为显著。

摘要：

湍流跨声速抖振是一种气动不稳定性，会在航空航天应用中导致升力/阻力的周期性振荡。抖振涉及无粘与粘性效应之间的复杂耦合，其特征是激波振荡和流动分离/再附。先前的研究已识别出二维弦向激波振荡和三维抖振/失速单元模式。尽管二维不稳定性已被广泛研究，但对三维抖振的研究仅限于低保真模拟或实验。由于计算成本，迄今为止几乎所有的高保真研究都局限于约5%翼型弦长的窄展长范围内（展弦比，$AR = 0.05$），这不足以观察到大规模的三维特性。在这项工作中，对 $Re=5\times 10^{5}$ 下的无限无后掠 NASA-CRM 翼型进行了高达 $AR=3$ 的高保真模拟。在 $AR \geq 1$ 时，在抖振条件下观察到了间歇性的三维分离泡。尽管先前基于 RANS/稳定性的研究预测二维和三维抖振会同时发生，但本文在此识别出一种在展宽高达 $AR=2$ 时仍保持基本二维的抖振情况。最强的三维特性出现在抖振周期中流动分离最大的低升力相位附近，并在高升力相位期间恢复为基本二维的行为。当存在广泛的平均流动分离时，发现抖振变得具有三维特性。在 $AR \geq 2$ 时，形成了多个三维分离泡，波长范围为 $λ=\left[1c-1.5c\right]$。应用 SPOD 和互相关来分析三维抖振单元的时空结构。除了二维弦向激波振荡模式（Strouhal数 $St \approx 0.07-0.1$）外，在 $St \approx 0.002-0.004$ 的流动激波区域中还发现了三维模态结构。

英文摘要：

Turbulent transonic buffet is an aerodynamic instability causing periodic oscillations of lift/drag in aerospace applications. Involving complex coupling between inviscid and viscous effects, buffet is characterised by shock-wave oscillations and flow separation/reattachment. Previous studies have identified both 2D chordwise shock-oscillation and 3D buffet/stall-cell modes. While the 2D instability has been studied extensively, investigations of 3D buffet have been limited to only low-fidelity simulations or experiments. Due to computational costs, almost all high-fidelity studies to date have been limited to narrow span-widths around 5% of aerofoil chord length (aspect ratio, $AR = 0.05$), which is insufficiently wide to observe large-scale three-dimensionality. In this work, high-fidelity simulations are performed up to $AR=3$, on infinite unswept NASA-CRM wing profiles at $Re=5\times 10^{5}$. At $AR \geq 1$, intermittent 3D separation bubbles are observed at buffet conditions. While previous RANS/stability-based studies predict simultaneous onset of 2D- and 3D-buffet, a case with buffet that remains essentially-2D despite span-widths up to $AR=2$ is identified here. Strongest three-dimensionality was observed near the low-lift phases of the buffet cycle at maximum flow separation, reverting to essentially-2D behaviour during high-lift phases. Buffet was found to become three-dimensional when extensive mean flow separation was present. At $AR \geq 2$, multiple 3D separation bubbles form, in a wavelength range of $λ=\left[1c-1.5c\right]$. SPOD and cross-correlations were applied to analyse the spatio/temporal structure of 3D buffet-cells. In addition to the 2D chordwise shock-oscillation mode (Strouhal number $St \approx 0.07-0.1$), 3D modal structures were found in the shocked region of the flow at $St \approx 0.002-0.004$.

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