Bluff-body wakes and fluid-structure interactions

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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.