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首页> 外文期刊>Journal of Fluids and Structures >Influence of self-adaptive hairy flaps on the stall delay of an airfoil in ramp-up motion
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Influence of self-adaptive hairy flaps on the stall delay of an airfoil in ramp-up motion

机译：自适应毛发襟翼对机翼加速运动中失速延迟的影响

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It is known in the case of some birds that the coverts on the upper side of their wings pop-up under critical flight conditions such as the landing approach, thus acting like a brake on the spread of flow separation. Taking experimental investigations as its basis, this paper deals with the influence of various configurations of self-adaptable hairy flaplets located on the lower half of the wing and with chord-length c (dense rows of slender elastomeric flaps, L=0.05c, 0.1c, 0.2c) on the flow around an NACA0020 airfoil at low Reynolds number flow (Re=77 × 10~3). Flow evolution along the airfoil when in ramp-up motion (α_0=0, α_s=20°, reduced frequency k=0.12) was measured with and without hairy flaps, with growth in the chord-normal thickness of the separation region above the airfoil investigated in order to determine stall onset time Ts. Whereas small flaps with L=0.05c do not change the overall stall process, it was possible to use configurations with L=0.1c (double-row, triple-row configuration) to delay stall onset Ts by a factor of around 2-4 when compared with the clean airfoil. The motion of the flaps and the flow field were measured simultaneously at high temporal resolution using high-speed PIV. Correlation between flap motion and velocity distribution showed that backflow induced by vortex structures is indeed prevented by the hairy flaps. A significant difference was identified in the shear-layer roll-up process, which was almost regular and locked with the fundamental frequency on the covered airfoil with no signs of non-linear growth over longer periods. By way of contrast, in the case of the clean airfoil the early merging of the shear-layer vortices and a rapid increase in the thickness of the separation region were observed. It is therefore concluded that mode locking is achieved between flap rows with an interspacing of 0.15c - 0.2c, while the fundamental shear-layer roll-up wavelength measured (λ_0 ≈ 0.15c - 0.2c) indicates the relevance of flap row arrangement at the specific Reynolds number. Furthermore, interaction between shear-layer vortices and flaps in the row furthest downstream leads to the beneficial modification of the trailing edge flow in a way which increases bound circulation.
机译：众所周知，在某些鸟类的情况下，机翼上侧的隐蔽物在诸如着陆进近等关键飞行条件下会突然弹出，因此对气流分离的扩散起着制动作用。以实验研究为基础，本文研究了位于机翼下半部且弦长为c（密集的细长弹性体襟翼，L = 0.05c，0.1）的各种形状的自适应毛状襟翼的影响。 c，0.2c）在低雷诺数流量（Re = 77×10〜3）时围绕NACA0020机翼的流动。在有和没有毛瓣的情况下，测量了在加速运动（α_0= 0，α_s= 20°，降低的频率k = 0.12）时沿着翼型的气流演变，翼型上方分离区域的弦法向厚度增加为了确定失速开始时间Ts，进行了研究。尽管L = 0.05c的小襟翼不会改变整个失速过程，但可以使用L = 0.1c的配置（双排，三排配置）将失速开始Ts延迟2-4倍与干净的机翼相比。使用高速PIV在高时间分辨率下同时测量襟翼的运动和流场。襟翼运动与速度分布之间的相关性表明，毛状襟翼的确阻止了涡旋结构引起的回流。在剪切层卷起过程中发现了显着差异，该差异几乎是规则的，并且被覆盖翼型上的基频锁定，并且在较长时期内没有非线性增长的迹象。相比之下，在干净的翼型的情况下，观察到剪切层涡旋的早期融合以及分离区域的厚度迅速增加。因此得出的结论是，襟翼行之间的锁模间隔为0.15c-0.2c，而测得的基本剪切层上卷波长（λ_0≈0.15c-0.2c）表示襟翼行布置在特定的雷诺数。此外，在最下游的排中，剪切层涡旋和襟翼之间的相互作用以增加束缚循环的方式导致后缘流的有益改变。

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