Three-dimensional transition and force characteristics of low-Reynolds-number flows past a plunging airfoil
Three-dimensional transition and force characteristics of low-Reynolds-number flows past a plunging airfoil
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DOI：
10.1017/jfm.2023.735
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发表时间：
2023-10
影响因子：
3.7
通讯作者：
A. Gao;C. Cantwell;Onur Son;Spencer J. Sherwin
中科院分区：
文献类型：
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作者：
A. Gao;C. Cantwell;Onur Son;Spencer J. Sherwin
本文通过实验测量、数值模拟和线性稳定性分析，研究了在Strouhal数为0.10~1.0范围内，前缘涡的三维转捩和纵倾翼型的力特性，以了解展向不稳定性及其对力的影响。我们发现，LEV的相互作用模式，LEV从前一个周期（pLEV）和后缘涡（TEV）是影响的3-D过渡和相关的力特性的主要机制。对于$St_c\leq 0.16 $，3-D转变由LEV-TEV相互作用主导。对于$0.16 <St_c\leq 0.44 $，TEV位于LEV和pLEV的中间，因此它们之间的涡流相互作用相对较弱;因此，LEV在$St_c = 0.32 $时保持二维，直至相对较高的雷诺数$Re = 4000 $。当雷诺数较低时，pLEV和TEV形成顺时针涡对，有利于LEV的增升和稳定性。当St_c $为0.49时，pLEV和TEV趋于形成一个反涡对，这对升力和流动稳定性是不利的。在最后的$St_c $范围内，涉及LEV，TEV和pLEV的涡的相互作用导致不稳定的倍周期模式，其具有约两个弦长的波长和3-D过渡增强升力。
Abstract The three-dimensional (3-D) transition of the leading-edge vortex (LEV) and the force characteristics of the plunging airfoil are investigated in the chord-based Strouhal number $St_c$ range of 0.10 to 1.0 by means of experimental measurements, numerical simulations and linear stability analysis in order to understand the spanwise instabilities and the effects on the force. We find that the interaction pattern of the LEV, the LEV from a previous cycle (pLEV) and the trailing-edge vortex (TEV) is the primary mechanism that affects the 3-D transition and associated force characteristics. For $St_c \leq 0.16$, the 3-D transition is dominated by the LEV–TEV interaction. For $0.16 < St_c \leq 0.44$, the TEV lies in the middle of the LEV and the pLEV and therefore vortex interaction between them is relatively weak; as a result, the LEV remains two-dimensional up to a relatively high Reynolds number of $Re = 4000$ at $St_c = 0.32$. For $0.44 < St_{c} \leq 0.54$, and at relatively low Reynolds numbers, the pLEV and the TEV tend to form a clockwise vortex pair, which is beneficial for the high lift and stability of the LEV. For $0.49 \leq St_c$, the pLEV and TEV tend to form an anticlockwise vortex pair, which is detrimental to the lift and flow stability. In the last $St_c$ range, vortex interaction involving the LEV, the TEV and the pLEV results in an unstable period-doubling mode which has a wavelength of about two chord-lengths and the 3-D transition enhances the lift.