Flow-Induced Noise and Vibration Control in Engineering Structures via Geometric Modifications

拟议的研究计划将在两个主要工程问题的背景下，对不利流动效应的被动控制进行实验研究： 第一个问题是圆柱形结构（如海上平台）的流激振动控制。在结构表面采用某些突起装置（螺旋边条、交错分离线、环等）或对其外形进行微小的修改，在某些情况下可以成功地抑制流致结构振动。然而，在这一点上，这种控制技术的设计知识库仍然是不完整的。该计划的第一项研究活动旨在通过理解各种突出装置引起的流动控制来解决这一缺陷。重点将放在与结构载荷和振动有关的修正流动特性的探索上。试验将在UTIAS水洞中进行，试验对象为固定、受迫和自由振动的刚性圆柱体，圆柱体上安装有各种不同的突出装置。将使用速度测量（PIV、V3V和CTA）以及氢气泡可视化技术来解读流量操纵。通过同步测速和力测量，确定的流型也将与结构载荷联系起来。该计划将逐步建立一个知识库，通过该知识库可以设计有效的控制手段来抑制圆柱体上的流致振动。许多工程应用需要制定针对流致振动的控制措施的指南，这些应用将受益于该计划的成果。 另一个问题是与飞机起落架相关的流致噪声问题。由于对噪音政策的要求不断提高，这个问题已成为飞机制造商最近感兴趣的主题。在这一点上，起落架的噪声产生机制仍然没有得到很好的理解，因此很难制定有效的策略来减轻它们。起落架噪声是非定常流形成及其与飞机部件相互作用的结果。因此，建议的计划将通过全面了解在2轮和4轮起落架系统周围形成的相干非定常流结构来确定产生噪声的可能原因。利用这种理解，在可能的情况下，该计划将制定新的战略，旨在减少噪音。空气动力学测试将在UTIAS水洞中进行。虽然有几种飞机在进近和起飞过程中典型的马赫数都在不可压缩范围内，但以前从未使用过水设备来研究起落架流动。与传统风洞相比，水设施的优势在于水介质减缓了流动动力学，从而能够使用全局测速工具（PIV和V3V）对流动行为进行时间分辨捕获。在程序中，将首先研究起落架的简化模型。逐步地，测试模型将结合来自真实起落架的额外几何细节，以量化它们对气流的影响。积累的非定常流拓扑学知识将用于改进传统起落架以实现降噪。这些改进的有效性将在UTIAS消声风洞中通过声学试验进行评估。这项研究最终可能导致开发新的起落架设计，对与噪音有关的环境和健康问题敏感。加拿大航空业将从这一结果中受益匪浅。

The proposed research program will experimentally investigate the passive control of adverse flow effects in the context of two major engineering problems: The first problem is the control of flow-induced vibration in cylindrical structures, such as offshore risers. Adoption of certain protrusion devices (helical strakes, staggered separation wires, rings, etc) on the structures' surface or slight modifications in their external shape can, in some cases, succeed in suppressing the flow-induced structural vibrations. However, at this point, the knowledge base for the design of such control technologies is still incomplete. The first research campaign in the proposed program aims to address this deficiency by comprehending the flow control induced by various protrusion devices. The central emphasis will be on the exploration of the modified flow characteristics in relation to the structural loads and vibration. Tests will be conducted in the UTIAS water tunnel on stationary, forced- and free-vibrating rigid circular cylinders fitted with a variety of different protrusion devices. Velocimetry (PIV, V3V, and CTA) as well as hydrogen bubble visualization techniques will be used to decipher the flow manipulations. The identified flow patterns will also be linked to the structural loads through synchronized velocimetry and force measurements. This program will progressively build a knowledge base through which efficient control means can be designed to suppress flow-induced vibrations on cylindrical bodies. Many applications of engineering that are in need of guidelines for the development of control measures against flow-induced vibrations will benefit from the outcomes of this program. The other problem is the flow-induced noise issue associated with aircraft landing gears. Owing to the ever-increasing requirements in noise policies, this problem has become a recent subject of interest to aircraft manufacturers. At this point, noise-generation mechanisms for landing gears are still not well understood, and it is therefore difficult to develop efficient strategies to mitigate them. Landing gear noise is a consequence of the unsteady flow formations and their interactions with the aircraft components. For this reason, the proposed program will identify the possible causes of noise generation in 2- and 4-wheel landing gear systems by developing a comprehensive understanding of the coherent, unsteady flow structures forming around them. Using this understanding, where possible, the program will develop new strategies aiming noise reduction. Aerodynamic tests will be carried out in the UTIAS water tunnel. Although typical Mach numbers fall into the incompressible range during approach and takeoff for several airplane, a water facility has never been used before for the investigation of landing gear flows. The advantage of the water facility over traditional wind tunnels is that the water medium slows down the flow dynamics enabling time-resolved capture of the flow behavior using global velocimetry tools (PIV and V3V). In the program, simplified models of landing gears will be studied first. Step by step, test models will incorporate additional geometrical details from real-life landing gears to quantify their effects onto the flow. The accumulated knowledge of the unsteady flow topology will then be used to develop modifications on traditional landing gears to realize noise reduction. The effectiveness of those modifications will be assessed by acoustic tests in the UTIAS anechoic wind tunnel. This research can eventually lead to the development of novel landing gear designs, sensitive to environmental and health issues related to noise. Canada's aviation industry would greatly benefit from such an outcome.