Bluff-body wakes and fluid-structure interactions

“钝体”的非流线型形状使其承受高的空气动力阻力或风荷载。物体复杂的流场特征是流动分离(流动不跟随物体的形状)、从物体表面形成漩涡、剪切层之间的相互作用(流体速度在其上有较大变化的薄区域)以及物体后面的非定常低压尾迹。当旋涡周期性地从物体释放到尾流中时，就会出现“旋涡脱落”现象；在某些条件下，这可能会引起不必要的结构运动或“流致振动”(FIV)。钝体的例子包括建筑物、烟囱、桥塔、海上结构、火车、道路车辆、屋顶安装的设备和电路板上的电子元件。钝体流动的研究是由与FIV、流动诱导的噪声、污染物在大气中的扩散以及电子元件冷却相关的工业问题推动的。当钝体位于其他物体和结构附近时，例如在成群的建筑物、储油罐或堆栈中，以及当钝体是“表面安装”和“有限高度”时，钝体周围的流动变得更加复杂。在后一种情况下，物体表面和“自由端”上的局部流场对风荷载和FIV的趋势有很大影响。防止FIV，设计流动控制策略(例如，减轻涡流脱落)，以及实施减阻方法(例如，提高车辆的燃油效率)，都需要对钝体周围的流动有很好的物理理解。然而，这些流动的复杂性质给现场测量、实验室实验和计算机模拟带来了巨大的挑战。*研究计划的主要目标是提高对表面安装的有限高度钝体(如有限圆柱和棱柱)周围流动的基本物理理解，主要通过风洞实验，但辅之以计算流体力学。该计划将包括硕士、博士和本科生的培训。该研究计划的具体兴趣包括：(I)回答与高宽比、机身形状和方向以及表面边界层影响有关的基本问题；(Ii)确定流动模式和力发生显著变化的“关键”条件；(Iii)探索小群表面安装的有限高度钝体的尾流和邻近干扰效应；(Iv)了解被动流动控制装置对这些物体的有效性；以及(V)发现结构运动(与FSI和FIV相关)对尾流模式的影响。

The non-streamlined shape of a "bluff body" causes it to experience high aerodynamic drag forces or wind loading. The body's complex flow field is characterized by flow separation (where the flow does not follow the shape of the body), vortex formation from the body surface, interactions between shear layers (thin regions of fluid across which there are large changes in flow velocity), and an unsteady low-pressure wake behind the body. The phenomenon of "vortex shedding" occurs as vortices are released periodically from the body into the wake; under certain conditions, this may cause unwanted structural motion or "flow-induced vibration" (FIV).******Examples of bluff bodies include buildings, chimney stacks, bridge pylons, offshore structures, trains, road vehicles, rooftop-mounted equipment, and electronic components on circuit boards. The study of bluff-body flows is motivated by industrial problems related to FIV, flow-induced noise, dispersion of pollutants in the atmosphere, and cooling of electronic components. Flow around a bluff body becomes more complex when it is located near other bodies and structures, such as in groups of buildings, oil storage tanks, or stacks, and when the bluff body is "surface-mounted" and of "finite-height". In the latter case, the local flow fields at the surface and over the "free end" of the body strongly influence the wind loading and the tendency towards FIV. Preventing FIV, designing flow control strategies (to mitigate vortex shedding, for example), and implementing methods for drag reduction (to improve the fuel efficiency of a vehicle, for instance), require a good physical understanding of the "fluid-structure interactions" (FSI) for the flow around bluff bodies. The complex nature of these flows, however, poses significant challenges for field measurements, laboratory experiments, and computer simulations.******The main objective of the research program is to improve the fundamental physical understanding of the flow around surface-mounted finite-height bluff bodies (such as finite cylinders and prisms), primarily through wind tunnel experiments but secondarily with computational fluid dynamics. The program will involve the training of MSc, PhD, and undergraduate students. Specific interests of the research program include (i) answering fundamental questions related to the effects of aspect ratio, body shape and orientation, and the boundary layer on the surface; (ii) identifying "critical" conditions where there are marked changes in the flow patterns and forces; (iii) exploring wake and proximity interference effects for small groups of surface-mounted finite-height bluff bodies; (iv) understanding the effectiveness of passive flow control devices for these bodies; and (v) discovering the effects of structural motion (as related to FSI and FIV) on the wake flow patterns.