Research Interests

David Sumner, Ph.D., P.Eng., Professor

Department of Mechanical Engineering, University of Saskatchewan

 
Overview

My research program focuses on fundamental aspects of engineering fluid mechanics related to bluff-body aerodynamics, fluid-structure interactions, and unsteady flows.  My research falls within the broad field of experimental fluid mechanics with the use of wind tunnel testing and measurement instrumentation for aerodynamics forces and moments, vortex shedding frequencies, pressure, temperature, and velocity.


The overall objective of my research is to improve the current knowledge and fundamental physical understanding of the flow around surface-mounted finite-height bluff bodies (cylinders and prisms), primarily through wind tunnel experiments (to measure forces, pressures, and the turbulent velocity field) and the use of advanced measurement techniques (such as particle image velocimetry). Computational fluid dynamics simulations are also used to study the instantaneous flow field, vortex structures, and “modes” of fluid behaviour.

Specific interests of my researcg include (i) answering fundamental questions related to the effects of aspect ratio, body shape, body orientation, and the thickness of the boundary layer, primarily for isolated surface-mounted finite-height bluff bodies; (ii) identifying critical values of the various parameters, where there are marked changes in the flow patterns and the behaviour of the forces, moments, and vortex shedding frequencies; (iii) exploring the effects of wake and proximity interference for small groups of surface-mounted finite-height bluff bodies, including the effects of aspect ratio, boundary layer thickness, and the spacing of the bodies; (iv) understanding the effectiveness of passive flow control devices for these bodies, for suppression of vortex shedding and reduction of aerodynamic drag; and (v) discovering the effects of structural motion (as related to fluid-structure interactions and flow-induced vibration) on the wake flow patterns.

 

Petit, J.-C., 2004. Why do we need fundamental research? European Review 12, 191-207.

 
Bluff-Body Aerodynamics

A “bluff body” is an object or structure with a non-streamlined shape that significantly resists the motion of a moving fluid. This resistance causes bluff bodies to experience high aerodynamic drag forces or wind loading.  The complex flow around a bluff body is characterized by a large region of separated flow (where the flow does not follow the shape of the body), the development of vortices 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 downstream of the body. The phenomenon of “vortex shedding” occurs as vortices are released from the surface of the body, in a regular (periodic) fashion, into the wake. Under certain conditions, vortex shedding may cause unwanted structural motion known as “flow-induced vibration.”



Air and water flow around bluff bodies is encountered in many engineering applications, and at many different scales, including flow around buildings, chimney stacks, bridge pylons, offshore structures, trains, road vehicles, power transmission lines and towers, rooftop-mounted equipment, and electronic components on circuit boards. Study of bluff-body flows is motivated by practical industrial problems related to flow-induced vibration, turbulent buffeting, noise generation, erosion (or scour) of stream beds, mixing and dispersion of contaminants in the atmosphere and rivers, "downwash" from chimney stacks (where the plume is entrained into the wake of the stack rather than being dispersed upwards into the atmosphere), cooling of electronic components, and high wind loading caused by aerodynamic drag forces. 

The complex nature of these flows, however, poses significant challenges for field measurements, laboratory experiments, and computer simulations.
 
Wake and Proximity Interference
The flow around a bluff body becomes more complex when it is located in proximity to other bodies and structures. Groups of two or more bluff bodies immersed in air or water flows are found in a number of engineering applications, such as clusters of buildings and oil storage tanks, groups of chimney stacks, the risers of offshore oil drilling platforms, tube bundles in a heat exchanger, and arrays of closely packed electronic components on a circuit board. The wake and proximity interference effects encountered in the flow around small groups of bluff bodies lead to marked changes in the aerodynamic forces and moments, vortex shedding frequencies, and other characteristics of the flow field, compared to an isolated bluff body.
 
Surface-Mounted Finite-Height Bluff Bodies
Many of the engineering structures encountered in the aforementioned applications may be considered “surface-mounted", "finite-height” bluff bodies, where the local flow around the junction between the body and the surface, and the local flow over the “free end” of the body, strongly influence the aerodynamic forces and moments, the vortex shedding frequencies, the behaviour of the wake, and the tendency towards flow-induced vibration. The slenderness of the structure (the ratio of its height to its width, or “aspect ratio”), the thickness and character of the boundary layer on the surface (such as the atmospheric boundary layer encountered by buildings), the Reynolds number (which involves the fluid properties, the size of the body, and the wind speed), and the body's shape and orientation with respect to the oncoming flow, are several of the important influencing parameters. The effects of many of these parameters, however, are still not well understood.
 
Fluid-Structure Interactions
Prevention of flow-induced vibration (to reduce the oscillation of towers and flexible structures, for example), development of flow control strategies (to mitigate vortex shedding or avoid stack downwash, for instance), and reduction of aerodynamic drag (such as to improve the fuel efficiency of a transport truck), require a physical understanding of the “fluid-structure interactions” for the flow around isolated bluff bodies and groups of bluff bodies.
 

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Last updated: July 14, 2017