The location of the aerodynamic center, with respect to the center of gravity, determines the longitudinal static stability of an aerial vehicle. While most studies in the past focused on high Reynolds number (Re) flows, we consider flows at low Re (100≤Re≤6000) past an end-to-end wing and a finite wing of various semi-aspect ratio (0.25≤sAR≤5). It is shown that two-dimensional computations, even for an end-to-end wing, are inadequate for accurate prediction of aerodynamic coefficients. The chordwise pressure distribution as well as the variation of aerodynamic coefficients with angle of attack (α) at low Re are significantly different from that at high Re. Beyond a certain α, the flow is associated with a large recirculation zone, resulting in a non-linear variation of the aerodynamic coefficients with α. The conventional definition of the aerodynamic center is too restrictive at low Re. Owing to the non-linear variation of the pitching moment with change in α, it is not possible to determine one single location where it is invariant over a large range of α. The aerodynamic center is, therefore, determined over various sub-regimes of α. It varies significantly over the sub-regimes. The wing-tip vortex significantly affects the vortex shedding, flow structures, and pressure distribution on a finite wing. The locations of the aerodynamic center and center of pressure move fore, toward the leading edge, with a decrease in aspect ratio compared to that for an end-to-end wing.

中文翻译：

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低雷诺数时机翼的空气动力中心

空气动力中心相对于重心的位置决定了飞行器的纵向静态稳定性。虽然过去大多数研究都集中在高雷诺数 (Re) 流动，但我们考虑低 Re (100≤Re≤6000) 流过端到端机翼和各种半展弦比 (0.25≤ sAR≤5）。结果表明，即使对于端到端机翼，二维计算也不足以准确预测空气动力学系数。低Re时弦向压力分布以及气动系数随攻角(α)的变化与高Re时有显着不同。超过某个特定的 α 时，流动与大的再循环区相关，导致空气动力系数随 α 的非线性变化。空气动力学中心的传统定义在低 Re 情况下过于严格。由于俯仰力矩随α变化的非线性变化，不可能确定在大范围α内保持不变的单个位置。因此，空气动力学中心是根据 α 的各个子区域确定的。各个子政权的情况差异很大。翼尖涡对有限机翼上的涡脱落、流动结构和压力分布有显着影响。空气动力学中心和压力中心的位置向前移动，朝向前缘，与端对端机翼相比，展弦比减小。