Physics and Engineering Science, Coastal Carolina University, Conway, SC, United States of America.
Mechanical and Aerospace Engineering, George Washington University, Washington, DC, United States of America.
Bioinspir Biomim. 2023 Sep 12;18(6). doi: 10.1088/1748-3190/acf540.
We studied the effects of leading-edge serrations on the flow dynamics developed over an owl wing model. Owls are predatory birds. Most owl species are nocturnal, with some active during the day. The nocturnal ones feature stealth capabilities that are partially attributed to their wing microfeatures. One of these microfeatures is small rigid combs (i.e. serrations) aligned at an angle with respect to the incoming flow located at the wings' leading-edge region of the primaries. These serrations are essentially passive flow control devices that enhance some of the owls' flight characteristics, such as aeroacoustics and, potentially, aerodynamics. We performed a comparative study between serrated and non-serrated owl wing models and investigated how the boundary layer over these wings changes in the presence of serrations over a range of angles of attack. Using particle image velocimetry, we measured the mean and turbulent flow characteristics and analyzed the flow patterns within the boundary layer region. Our experimental study suggests that leading-edge serrations modify the boundary layer over the wing at all angles of attack, but not in a similar manner. At low angles of attack (<20°), the serrations amplified the turbulence activity over the wing planform without causing any significant change in the mean flow. At 20° angle of attack, the serrations act to suppress existing turbulence conditions, presumably by causing an earlier separation closer to the leading-edge region, thus enabling the flow to reattach prior to shedding downstream into the wake. Following the pressure Hessian equation, turbulence suppression reduces the pressure fluctuations gradients. This reduction over the wing would weaken, to some extent, the scattering of aerodynamic noise in the near wake region.
我们研究了前缘锯齿对猫头鹰翼模型上发展的流动动力学的影响。猫头鹰是肉食性鸟类。大多数猫头鹰物种是夜间活动的，有些则在白天活动。夜间活动的猫头鹰具有部分归因于其翼微特征的隐身能力。这些微特征之一是小的刚性梳（即锯齿）以相对于来流的角度与初级翼的前缘区域对齐。这些锯齿基本上是被动的流动控制装置，可增强猫头鹰的一些飞行特性，例如空气声学，并且可能还有空气动力学特性。我们对锯齿状和非锯齿状猫头鹰翼模型进行了比较研究，并研究了在一定攻角范围内，锯齿对这些机翼上边界层的变化。我们使用粒子图像测速法测量了平均和湍流流动特性，并分析了边界层区域内的流动模式。我们的实验研究表明，前缘锯齿在所有攻角下都会改变机翼上的边界层，但方式不同。在低攻角（<20°）下，锯齿会放大机翼平面上的湍流活动，而不会对平均流动产生任何重大影响。在 20°攻角下，锯齿的作用是抑制现有湍流条件，可能是通过导致在靠近前缘的区域更早地分离，从而使流动在下游进入尾流之前重新附着。根据压力 Hessian 方程，湍流抑制会降低压力波动梯度。这会在一定程度上削弱近尾流区域中空气动力噪声的散射。
