The impact of a vortex ring on a wall

Walker, James D.; Smith, C. R.; Cerra, A. W.; Doligalski, T. L.

doi:10.1017/s0022112087002027

Cited by 304 publications

(211 citation statements)

References 33 publications

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“…Moreover, the velocity profile within this region is not known, with previous studies being exclusive to a vortex ring interacting with solid (non-porous) surfaces, with axisymmetry assumed and for values of Re notably smaller than those considered here. 29,30 Hence, an analogous standard parameterisation was not possible and an alternative estimate for σ b was required, based on the available fluid velocity data. The following approach was adopted.…”

Section: Resultsmentioning

confidence: 99%

The interaction of a vortex ring with a sloped sediment layer: Critical criteria for incipient grain motion

Munro

2012

Physics of Fluids

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Experiments were performed to analyse the interaction between a vortex ring and a sloped sediment layer. Attention focussed on interactions under “critical” conditions, in which sediment motion was only just induced by the ring's flow field. Both hydraulically smooth and hydraulically rough bedforms were analysed, using near-spherical monodisperse sediments with relative densities of 1.2 and 2.5 and mean diameters (dp) ranging between 80 and 1087 μm. Measurements of the vortex-ring flow field were obtained, during the interaction, using two-dimensional particle imaging velocimetry. The threshold conditions for incipient sediment motion were analysed in terms of the critical Shields parameter (Nc), defined in terms of the peak tangential velocity measured adjacent to the bed surface. Bed-slope effects were investigated by tilting the sediment layer at various angles between the horizontal and the repose limit for the sediment. In all cases, the propagation axis of the vortex ring was aligned normal to the bed surface. The measured values of Nc were compared with a force-balance model based on the conditions for incipient grain motion on a sloping bed. For hydraulically smooth bedforms, where the bed roughness is small compared to the boundary-layer depth, the model was derived to account for how viscous stresses affect the drag and lift forces acting on the near surface sediment. For hydraulically rough bedforms, where this viscous-damping effect is not present, the model assumes the drag and lift forces scale with the square of the near-bed (inviscid) velocity scale. In both cases, the model predicts that bedforms become more mobile as the bed slope is increased. However, the damping effect of the viscous sublayer acts as a stabilizing influence for hydraulically smooth bedforms, to reduce the rate at which the bed mobility increases with bed slope. The measured values of Nc were in agreement with the trends predicted by this model, and exhibit a transition in behaviour between the smooth-bed and rough-bed cases when dp/δs ≈ 20 (where δs is the viscous-sublayer length scale).

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Section: Resultsmentioning

confidence: 99%

The interaction of a vortex ring with a sloped sediment layer: Critical criteria for incipient grain motion

Munro

2012

Physics of Fluids

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“…This vorticity separates and is ejected into the inviscid flow region above as a secondary vortex ring, which then interacts with the original ͑or primary͒ vortex ring. ͑This mechanism has been studied previously [17][18][19] for the case of a vortex ring interacting with a solid boundary.͒ The secondary ring, which is not dyed, is first seen in Fig. 2 deforming the outer streamlines of the primary ring at ͑t − t 1 ͒ / = 1.1.…”

Section: Resuspension Characteristicsmentioning

confidence: 94%

“…This is similar to the behavior observed when a vortex ring interacts with a solid boundary. 17 The sequence of white crosses included in Fig. 2͑i͒ shows the trajectory of the vortex core during the interaction.…”

Section: Resuspension Characteristicsmentioning

confidence: 99%

“…Moreover, the dynamics of vortex-ring interaction with solid boundaries is known from previous experimental studies 17 and numerical simulations. 18,19 Of course, this mechanism is notably different from the streamwise funnel vortices [7][8][9] found in turbulent channel flows, and is more readily associated with turbulence in the absence of a mean flow.…”

Section: Introductionmentioning

confidence: 99%

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Sediment resuspension and erosion by vortex rings

2009

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Particle resuspension and erosion induced by a vortex ring interacting with a sediment layer was investigated experimentally using flow visualization (particle image velocimetry), high-speed video, and a recently developed light attenuation method for measuring displacements in bed level. Near-spherical sediment particles were used throughout with relative densities of 1.2–7 and diameters (d) ranging between 90 and 1600 μm. Attention was focused on initially smooth, horizontal bedforms with the vortex ring aligned to approach the bed vertically. Interaction characteristics were investigated in terms of the dimensionless Shields parameter, defined using the vortex-ring propagation speed. The critical conditions for resuspension (whereby particles are only just resuspended) were determined as a function of particle Reynolds number (based on the particle settling velocity and d). The effects of viscous damping were found to be significant for d/δ<15, where δ denotes the viscous sublayer thickness. Measurements of bed deformation were obtained during the interaction period, for a range of impact conditions. The (azimuthal) mean crater profile is shown to be generally self-similar during the interaction period, except for the most energetic impacts and larger sediment types. Loss of similarity occurs when the local bed slope approaches the repose limit, leading to collapse. Erosion, deposition, and resuspension volumes are analyzed as a function interaction time, impact condition, and sediment size.

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“…It has been found that as a vortex approaches a wall perpendicular to its direction of motion, a region with opposite vorticity is formed between its core and the wall. See for instance Walker et al [28] and Allen and Chong [7] for experimental observations and Peace and Riley [30] for numerical calculations. In our simulations, this effect is present at the lower fixed wall for φ = 0 as can be seen from figure (16) where the vorticity field is plotted as a function of position for Re = 500, Y = 0.8.…”

Section: Case Re = 500mentioning

confidence: 99%

Vortex formation in a cavity with oscillating walls

et al. 2009

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The vortex formation in a two-dimensional Cartesian cavity, which their vertical walls move simultaneously with an oscillatory velocity and the horizontal walls are fixed pistons, is studied numerically.The governing equations were solved with a finite element method combined with an operator splitting scheme. We analyzed the behavior of vortical structures occurring inside a cavity with an aspect ratio of height to width of 1.5 for three different displacement amplitudes of the vertical oscillatory walls (amplitude/width= Y = 0.2, 0.4 and 0.8) and Reynolds numbers based on the cavity width of 50, 500 and 1000. Two vortex formation mechanisms are identified: a) the shear, oscillatory motion of the moving boundaries coupled with the fixed walls that provide a translational symmetry-breaking effect and b) the sharp changes in the flow motion when the flow meets the corners of the cavity. The vortices cores were identified using the Jeong-Hussain criterium and it is found that they occupy smaller areas as the Reynolds number increases. All flows studied are cyclic symmetric and for low Y and Re values they are also symmetric with respect to the vertical axis dividing the cavity in two sides. In asymmetric flows, the unbalance between the vortices on each side of the mid-vertical line generates a vortex that occupies the central part of the cavity. The breakdown of the axial symmetry was studied for a fixed value of the oscillation amplitude, Y = 0.8, taking Re as the bifurcation parameter. The results indicates that the symmetry is broken through a supercritical pitchfork bifurcation.

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The impact of a vortex ring on a wall

Cited by 304 publications

References 33 publications

The interaction of a vortex ring with a sloped sediment layer: Critical criteria for incipient grain motion

The interaction of a vortex ring with a sloped sediment layer: Critical criteria for incipient grain motion

Sediment resuspension and erosion by vortex rings

Vortex formation in a cavity with oscillating walls

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