AI 中文总结
研究自由流湍流对翼型上中等逆压梯度湍流边界层发展的影响，通过风洞实验，改变攻角调整压力梯度，用热线风速仪测量边界层特性，发现FST是控制参数，其影响随压力梯度放大，对相关流动研究有重要意义。
AI 中文摘要
在工业空气动力学应用中，承受逆压梯度（APG）的湍流边界层（TBL）很常见，但自由流湍流（FST）对中等APG下TBL发展的影响仍未得到充分理解。进行风洞实验研究FST对NACA 0015翼型上发展的TBL的影响。通过改变攻角（2°和4°）调整压力梯度，用热线风速仪测量不同弦向位置（$x/c$ = 0.400 - 0.625，$\beta = \delta^*/\tau_0 dP/dx$ = 0.2 - 1.5）的边界层特性。使用静态网格增加FST水平，范围从0.15%到6%。所有配置下基于弦长的雷诺数保持在约250,000不变。结果表明，增加FST会系统地改变APG边界层的平均流发展。更高的FST水平降低形状因子，部分抑制平均速度剖面中APG诱导的尾迹，同时使表面摩擦系数增加，更接近典型零压力梯度行为。流向速度方差在内区和外区都被放大，光谱分析表明这种增加与自由流湍流引入的高能大尺度运动有关，特征波长约为$\lambda_x/\delta \approx 13$。这些大尺度结构穿透到边界层并对近壁方差有贡献，随着逆压梯度增加影响更强。结果表明FST是翼型上发展的APG TBL的一个控制参数，其影响因压力梯度而放大。因此，在解释实际空气动力学环境中的平均流演化、湍流统计和尺度相互作用时必须考虑它。
英文摘要
Turbulent boundary layers (TBLs) subjected to adverse pressure gradients (APGs) are common to industrial aerodynamic applications, yet the effect of freestream turbulence (FST) on TBLs developing under moderate APGs remains insufficiently understood. Wind-tunnel experiments were conducted to investigate the effects of FST on a developing TBL over a NACA 0015 airfoil. Varying the angle of attack (2 and 4$^\circ$) adjusted the pressure gradient, and hotwire anemometry measured boundary layer properties at different chordwise positions ($x/c$ = 0.400--0.625, with $β= δ^*/τ_0 dP/dx$ = 0.2-1.5). The FST level was increased using static grids, resulting in levels ranging from 0.15 to 6$\%$. The chord-based Reynolds number was kept constant at around 250,000 for all configurations. The results show that increasing FST systematically modifies the mean-flow development of the APG boundary layer. Higher FST levels reduce the shape factor and partially suppress the APG-induced wake in the mean velocity profile, while increasing the skin-friction coefficient towards values closer to canonical ZPG behaviour. The streamwise velocity variance is amplified in both the inner and outer regions, and spectral analysis shows that this increase is associated with energetic large-scale motions introduced by the freestream turbulence, with characteristic wavelengths of order $λ_x/δ\approx 13$. These large scale structures penetrate into the boundary layer and contribute to the near-wall variance, with a stronger effect observed as the adverse pressure gradient increases. The results show that FST is a governing parameter in developing APG TBLs over airfoils and that its influence is amplified by the pressure gradient. It must therefore be considered when interpreting mean-flow evolution, turbulence statistics, and scale interactions in realistic aerodynamic environments.
