David Sumner
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
David Sumner has a total of 101 co-authors. Here are the top co-authors by number of shared publications:
- Donald John Bergstrom
Department of Mechanical Engineering, College of Engineering, University of Saskatchewan 1 , Engineering Building, 57 Campus Drive, Saskatoon, Saskatchewan SK S7N 5A9
15 shared publications D.J. Bergstrom
9 shared publicationsN. Rostamy
9 shared publications- Muyiwa Samuel Adaramola
Department of Energy Science and Technology, Faculty of Economics, Energy and Management Sciences Makerere University Business School
7 shared publications - Barbara L. da Silva
University of Saskatchewan
6 shared publications Donald J. Bergstrom
6 shared publications
Latest Publications
- 1 November 2024
- Published by AIP Publishing in Physics of Fluids
- Vol. 36 (11)
Wake interference effects for two surface-mounted cubes in tandem
Interference effects on the mean flow field, aerodynamic forces, and vortex shedding in the wakes of two cubes in tandem have been experimentally investigated, considering different boundary layer thicknesses of δ/D=0.8 and 1.3. The cubes had center-to-center longitudinal spacing ratios of L/D=1.5 to 5 and were exposed to an incoming flow with a Reynolds number of Re =7.5×104–9×104 based on the cubes' width D and the freestream velocity. For the thin boundary layer, the flow showed an intermittent regime with two Strouhal numbers for L/D2.25, and evidence of a cavity-locked regime around L/D=2.75. The intermittent regime featured flow reattachment but was not bistable, corresponding instead to unsynchronized shedding from both the upstream and downstream cubes. The mean drag force, normal force, and bending moment coefficients were examined across the regimes as functions of L/D and δ/D, showing greater variation for the downstream cube. Particle image velocimetry measurements revealed that the probability of reattachment on the downstream cube decreased, a second horseshoe vortex formed in the gap, and flow separated from the downstream cube's leading edges for high L/D. When increasing δ/D, vortex shedding from the upstream cube was delayed, leading to a high Strouhal number single-wake regime for L/D<2.5. The shorter formation region caused fluid to enter the gap, giving higher drag force coefficients for the downstream cube for small L/D, while the decreased probability of reattachment on the top of the cube led to a small increase in its normal force coefficient.
- 1 November 2024
- Published by AIP Publishing in Physics of Fluids
- Vol. 36 (11)
Wake interference effects for two surface-mounted cubes in tandem
Interference effects on the mean flow field, aerodynamic forces, and vortex shedding in the wakes of two cubes in tandem have been experimentally investigated, considering different boundary layer thicknesses of δ/D=0.8 and 1.3. The cubes had center-to-center longitudinal spacing ratios of L/D=1.5 to 5 and were exposed to an incoming flow with a Reynolds number of Re =7.5×104–9×104 based on the cubes' width D and the freestream velocity. For the thin boundary layer, the flow showed an intermittent regime with two Strouhal numbers for L/D2.25, and evidence of a cavity-locked regime around L/D=2.75. The intermittent regime featured flow reattachment but was not bistable, corresponding instead to unsynchronized shedding from both the upstream and downstream cubes. The mean drag force, normal force, and bending moment coefficients were examined across the regimes as functions of L/D and δ/D, showing greater variation for the downstream cube. Particle image velocimetry measurements revealed that the probability of reattachment on the downstream cube decreased, a second horseshoe vortex formed in the gap, and flow separated from the downstream cube's leading edges for high L/D. When increasing δ/D, vortex shedding from the upstream cube was delayed, leading to a high Strouhal number single-wake regime for L/D<2.5. The shorter formation region caused fluid to enter the gap, giving higher drag force coefficients for the downstream cube for small L/D, while the decreased probability of reattachment on the top of the cube led to a small increase in its normal force coefficient.
- 18 September 2024
- Published by Springer Nature
- p. 177-183
Flow Around Surface-Mounted Low-Aspect-Ratio Square Blocks
- 18 September 2024
- Published by Springer Nature
- p. 177-183
Flow Around Surface-Mounted Low-Aspect-Ratio Square Blocks
- Open Access
- 25 July 2024
- Published by Cambridge University Press (CUP) in Journal of Fluid Mechanics
- Vol. 991, A17
On the flow dynamics around a surface-mounted cube and boundary layer effects
Motivated by contradicting or insufficient information regarding the large-scale flow dynamics around surface-mounted finite-height square prisms of small aspect ratio, the present study investigates the dominant vortex shedding and low-frequency dynamics around a surface-mounted cube. These flow modes were obtained from the spectral proper orthogonal decomposition of large-eddy simulation results, at a Reynolds number of $\textit {Re}=1\times 10^4$ and two different types of boundary layer: a thin and laminar boundary layer with thickness $\delta /D=0.2$ and a thick and turbulent boundary layer with $\delta /D=0.8$ . The main antisymmetric mode pair revealed a new flow pattern with the alternate shedding of streamwise flow structures, indicating a transition from the half-loops of taller prisms to only streamwise strands (i.e. no vertical core) for smaller aspect ratio. The formation process of the streamwise structures is due to a reorientation of the vorticity of the arch vortex in the streamwise direction characteristic of the shed structures. The low-frequency drift mode affected the length of the recirculation region, the strength of vortex shedding, and the near-wall flow field and pressure distribution on the cube's faces, leading to low-frequency variations in the fluctuating drag and normal force coefficients. These large-scale flow dynamics were similar for both boundary layers, but minor differences were identified, related mostly to the occurrence of flow attachment and the formation of a headband vortex for the thicker boundary layer.- 25 July 2024
- Published by Cambridge University Press (CUP) in Journal of Fluid Mechanics
- Vol. 991, A17
Open AccessOn the flow dynamics around a surface-mounted cube and boundary layer effects
Motivated by contradicting or insufficient information regarding the large-scale flow dynamics around surface-mounted finite-height square prisms of small aspect ratio, the present study investigates the dominant vortex shedding and low-frequency dynamics around a surface-mounted cube. These flow modes were obtained from the spectral proper orthogonal decomposition of large-eddy simulation results, at a Reynolds number of $\textit {Re}=1\times 10^4$ and two different types of boundary layer: a thin and laminar boundary layer with thickness $\delta /D=0.2$ and a thick and turbulent boundary layer with $\delta /D=0.8$ . The main antisymmetric mode pair revealed a new flow pattern with the alternate shedding of streamwise flow structures, indicating a transition from the half-loops of taller prisms to only streamwise strands (i.e. no vertical core) for smaller aspect ratio. The formation process of the streamwise structures is due to a reorientation of the vorticity of the arch vortex in the streamwise direction characteristic of the shed structures. The low-frequency drift mode affected the length of the recirculation region, the strength of vortex shedding, and the near-wall flow field and pressure distribution on the cube's faces, leading to low-frequency variations in the fluctuating drag and normal force coefficients. These large-scale flow dynamics were similar for both boundary layers, but minor differences were identified, related mostly to the occurrence of flow attachment and the formation of a headband vortex for the thicker boundary layer. - 11 May 2023
- Published by Springer Nature
- p. 3-15
Dynamic Flow Structures in the Wake of a Surface-Mounted Finite-Height Square Prism
- 11 May 2023
- Published by Springer Nature
- p. 3-15
Dynamic Flow Structures in the Wake of a Surface-Mounted Finite-Height Square Prism
- 28 November 2022
- Published by Taylor & Francis in The Journal of the Textile Institute
- Vol. 114 (12) , 1909-1917
Measuring convection heat transfer coefficients and thermal resistance for protective fabrics using a heated cylinder in a wind tunnel
One tradeoff in design of protective clothing for firefighters and other workers is between thermal protection and thermal stress management. Standard methods for assessing thermal stress management of protective clothing include guarded hot plate and mannequin tests. In this study, a fabric-covered heated cylinder was used in a wind tunnel to measure convection heat transfer coefficients and thermal resistance at various air speeds. Measurements demonstrated the impact of air permeability and wind speed on these parameters. When the cylinder was covered with low permeability fabrics, convection heat transfer coefficients were similar to values predicted using a correlation for bare cylinders. Thermal resistance measurements generally ranked fabrics in the same order as guarded hot plate tests. This cylinder test is more representative of the body’s geometry than hot plate tests, but less expensive to conduct than mannequin tests, and could serve as a bridge between these two tests for design purposes.
- 28 November 2022
- Published by Taylor & Francis in The Journal of the Textile Institute
- Vol. 114 (12) , 1909-1917
Measuring convection heat transfer coefficients and thermal resistance for protective fabrics using a heated cylinder in a wind tunnel
One tradeoff in design of protective clothing for firefighters and other workers is between thermal protection and thermal stress management. Standard methods for assessing thermal stress management of protective clothing include guarded hot plate and mannequin tests. In this study, a fabric-covered heated cylinder was used in a wind tunnel to measure convection heat transfer coefficients and thermal resistance at various air speeds. Measurements demonstrated the impact of air permeability and wind speed on these parameters. When the cylinder was covered with low permeability fabrics, convection heat transfer coefficients were similar to values predicted using a correlation for bare cylinders. Thermal resistance measurements generally ranked fabrics in the same order as guarded hot plate tests. This cylinder test is more representative of the body’s geometry than hot plate tests, but less expensive to conduct than mannequin tests, and could serve as a bridge between these two tests for design purposes.
- 1 November 2022
- Published by AIP Publishing in Physics of Fluids
- Vol. 34 (11) , 115118
Mean wake and aerodynamic forces for surface-mounted finite-height square prisms of very small aspect ratio
The mean flow field, aerodynamic forces, bending moment and Strouhal number (St) were investigated for isolated surface-mounted finite-height square prisms of very small aspect ratio (AR). The Reynolds number was Re for the velocity measurements and for the force, bending moment and St measurements. Prisms with AR = 0.5, 0.7 and 1 were considered, under two different boundary layer thicknesses of –0.8 (thin) and (thick). For both boundary layers, the mean drag force coefficient showed a sharper increase with AR compared with taller prisms, and the mean normal force coefficient increased smoothly, with a lower magnitude than pressure-based normal force coefficients. An approximately constant point of action of the drag force was found for AR < 1. While the thick boundary layer caused the spectral peaks to weaken and St to decrease, some periodicity was still found for all AR. These features were connected to the changes in the mean wake of the prisms with AR and . A smaller AR and larger had similar effects, causing the wake to shorten, the probability and type of reattachment of the flow on the free end to change, and the mean wake structure to transition from a streamwise wake vorticity pattern to an inner vorticity pattern. The prism with AR = 1 showed a dipole wake structure similar to that of taller prisms, while the unique wake topology of prisms with AR < 1 was found to be responsible for the different force and St trends identified in this range of AR.- 1 November 2022
- Published by AIP Publishing in Physics of Fluids
- Vol. 34 (11) , 115118
Mean wake and aerodynamic forces for surface-mounted finite-height square prisms of very small aspect ratio
The mean flow field, aerodynamic forces, bending moment and Strouhal number (St) were investigated for isolated surface-mounted finite-height square prisms of very small aspect ratio (AR). The Reynolds number was Re for the velocity measurements and for the force, bending moment and St measurements. Prisms with AR = 0.5, 0.7 and 1 were considered, under two different boundary layer thicknesses of –0.8 (thin) and (thick). For both boundary layers, the mean drag force coefficient showed a sharper increase with AR compared with taller prisms, and the mean normal force coefficient increased smoothly, with a lower magnitude than pressure-based normal force coefficients. An approximately constant point of action of the drag force was found for AR < 1. While the thick boundary layer caused the spectral peaks to weaken and St to decrease, some periodicity was still found for all AR. These features were connected to the changes in the mean wake of the prisms with AR and . A smaller AR and larger had similar effects, causing the wake to shorten, the probability and type of reattachment of the flow on the free end to change, and the mean wake structure to transition from a streamwise wake vorticity pattern to an inner vorticity pattern. The prism with AR = 1 showed a dipole wake structure similar to that of taller prisms, while the unique wake topology of prisms with AR < 1 was found to be responsible for the different force and St trends identified in this range of AR.- 21 July 2021
- Published by ASME International in Journal of Fluids Engineering
- Vol. 144 (1)
Mean and Dynamic Aspects of the Wakes of a Surface-Mounted Cube and Block
The flow downstream of surface-mounted finite height square prisms with aspect ratio AR = 1 (cube) and 0.5 (block) was investigated experimentally in a low-speed wind tunnel, to determine the overall structure and dynamic behavior of the wake and the source of the streamwise vorticity. The Reynolds number based on the prisms' width D was Re and the boundary layer thickness at the location of the prisms was . A vortex shedding frequency was found in the wake of the cube, but no periodicity was found in the wake of the block. The mean wake of the cube showed features of prisms below the critical AR, but the wake of the block had a distinct behavior due to the dominant shear flow from the boundary layer. The shear changed the downwash and, consequently, the streamwise vorticity distribution in the wake, in addition to reducing the magnitude of the Reynolds stresses. The phase-average analysis for the cube revealed the alternate shedding of inclined structures related to the streamwise vorticity in the upper part of the wake. These vorticity regions were caused by the alternate bending and entrainment of the side flow, caused by the downwash. The periodic component of the total Reynolds stresses was, however, significantly smaller than the turbulence-related stresses. This study showed that the wake had a transitional behavior for the cube, but became fundamentally different for the block when compared with prisms of higher AR.- 21 July 2021
- Published by ASME International in Journal of Fluids Engineering
- Vol. 144 (1)
Mean and Dynamic Aspects of the Wakes of a Surface-Mounted Cube and Block
The flow downstream of surface-mounted finite height square prisms with aspect ratio AR = 1 (cube) and 0.5 (block) was investigated experimentally in a low-speed wind tunnel, to determine the overall structure and dynamic behavior of the wake and the source of the streamwise vorticity. The Reynolds number based on the prisms' width D was Re and the boundary layer thickness at the location of the prisms was . A vortex shedding frequency was found in the wake of the cube, but no periodicity was found in the wake of the block. The mean wake of the cube showed features of prisms below the critical AR, but the wake of the block had a distinct behavior due to the dominant shear flow from the boundary layer. The shear changed the downwash and, consequently, the streamwise vorticity distribution in the wake, in addition to reducing the magnitude of the Reynolds stresses. The phase-average analysis for the cube revealed the alternate shedding of inclined structures related to the streamwise vorticity in the upper part of the wake. These vorticity regions were caused by the alternate bending and entrainment of the side flow, caused by the downwash. The periodic component of the total Reynolds stresses was, however, significantly smaller than the turbulence-related stresses. This study showed that the wake had a transitional behavior for the cube, but became fundamentally different for the block when compared with prisms of higher AR.- 6 May 2021
- Published by Springer Nature
- p. 71-76
Free-End Mean Pressure Distribution for a Finite Cylinder: Effect of Aspect Ratio
- 6 May 2021
- Published by Springer Nature
- p. 71-76
Free-End Mean Pressure Distribution for a Finite Cylinder: Effect of Aspect Ratio