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

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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.