On the effect of a penetrating recirculation region on the bifurcations of the flow past a permeable sphere

2021 ◽  
Vol 33 (12) ◽  
pp. 124103
Author(s):  
M. Ciuti ◽  
G. A. Zampogna ◽  
F. Gallaire ◽  
S. Camarri ◽  
P. G. Ledda
Keyword(s):  
Recirculation Region ◽  
Flow Past ◽  
Permeable Sphere

Vortex Shedding From a Bluff Body Adjacent to a Plane Sliding Wall

1991 ◽  
Vol 113 (3) ◽  
pp. 384-398 ◽  
Author(s):  
M. P. Arnal ◽  
D. J. Goering ◽  
J. A. C. Humphrey
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Solid Wall ◽  
Reynolds Numbers ◽  
Careful Examination ◽  
Recirculation Region ◽  
Stream Velocity ◽  
Flow Past ◽  
Lower Reynolds Number

The characteristics of the flow around a bluff body of square cross-section in contact with a solid-wall boundary are investigated numerically using a finite difference procedure. Previous studies (Taneda, 1965; Kamemoto et al., 1984) have shown qualitatively the strong influence of solid-wall boundaries on the vortex-shedding process and the formation of the vortex street downstream. In the present study three cases are investigated which correspond to flow past a square rib in a freestream, flow past a rib on a fixed wall and flow past a rib on a sliding wall. Values of the Reynolds number studied ranged from 100 to 2000, where the Reynolds number is based on the rib height, H, and bulk stream velocity, Ub. Comparisons between the sliding-wall and fixed-wall cases show that the sliding wall has a significant destabilizing effect on the recirculation region behind the rib. Results show the onset of unsteadiness at a lower Reynolds number for the sliding-wall case (50 ≤ Recrit ≤100) than for the fixed-wall case (Recrit≥100). A careful examination of the vortex-shedding process reveals similarities between the sliding-wall case and both the freestream and fixed-wall cases. At moderate Reynolds numbers (Re≥250) the sliding-wall results show that the rib periodically sheds vortices of alternating circulation in much the same manner as the rib in a freestream; as in, for example, Davis and Moore [1982]. The vortices are distributed asymmetrically downstream of the rib and are not of equal strength as in the freestream case. However, the sliding-wall case shows no tendency to develop cycle-to-cycle variations at higher Reynolds numbers, as observed in the freestream and fixed-wall cases. Thus, while the moving wall causes the flow past the rib to become unsteady at a lower Reynolds number than in the fixed-wall case, it also acts to stabilize or “lock-in” the vortex-shedding frequency. This is attributed to the additional source of positive vorticity immediately downstream of the rib on the sliding wall.

Influence of slip on the flow past superhydrophobic circular cylinders

2011 ◽  
Vol 680 ◽  
pp. 459-476 ◽  
Author(s):  
PRANESH MURALIDHAR ◽  
NANGELIE FERRER ◽  
ROBERT DANIELLO ◽  
JONATHAN P. ROTHSTEIN
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Superhydrophobic Surfaces ◽  
Separation Point ◽  
Circular Cylinders ◽  
Recirculation Region ◽  
Small Scale ◽  
Flow Past ◽  
Shedding Frequency

Superhydrophobic surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large- and small-scale channels. In this paper, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from polydimethylsiloxane with well-defined micron-sized patterns of surface roughness. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction, the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. Thus, in this paper we demonstrate that vortex shedding dynamics is very sensitive to changes of feature spacing, size and orientation along superhydrophobic surfaces.

scholarly journals MHD Prandtl fluid flow past an isothermal permeable sphere with slip effects

2019 ◽  
Vol 14 ◽  
pp. 100447 ◽  
Author(s):  
C.H. Amanulla ◽  
S. Saleem ◽  
Abderrahim Wakif ◽  
M.M. AlQarni
Keyword(s):  
Fluid Flow ◽  
Flow Past ◽  
Slip Effects ◽  
Permeable Sphere

The starting flow down a step

1975 ◽  
Vol 69 (2) ◽  
pp. 229-240 ◽  
Author(s):  
H. Honji
Keyword(s):  
Flow Visualization ◽  
Reynolds Numbers ◽  
Step Height ◽  
Recirculation Region ◽  
Symmetric Model ◽  
Flow Development ◽  
Flow Past ◽  
Starting Flow ◽  
Visualization Techniques

The incompressible starting flow past a downstream-facing right-angled step was investigated at Reynolds numbers R (based on step height) less than 500 by means of flow-visualization techniques. The distance between the step and the point of reattachment on the downstream wall was found to increase linearly with time at intermediate stages of the flow development. The recirculation region formed behind the step was composed of three vortex domains at earlier stages of its development when R [gap ] 140. It was observed for R [gap ] 200 that once the starting vortices had been shed downstream a steady recirculation region was established. The evolution of filaments of tracer in the flow down the step was found to vary considerably with R. The filaments were observed to develop faster in the flow down the step than in that past a symmetric model without a downstream wall when R [gap ] 140.

Computational analysis of the flow field structure of a non-reacting hypersonic flow over forward-facing steps

2014 ◽  
Vol 763 ◽  
pp. 460-499 ◽  
Author(s):  
P. H. M. Leite ◽  
W. F. N. Santos
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Hypersonic Flow ◽  
Field Structure ◽  
Recirculation Region ◽  
Transition Flow ◽  
Face Surface ◽  
Face Height ◽  
Flow Past ◽  
Forward Facing Step

AbstractThis work is a computational study of a rarefied non-reacting hypersonic flow past a forward-facing step at zero-degree angle of attack in thermal non-equilibrium. Effects on the flow field structure and on the aerodynamic surface quantities due to changes in step frontal-face height are investigated by employing the direct simulation Monte Carlo method. The work focuses the attention of designers of hypersonic configurations on the fundamental parameter of surface discontinuity, which can have an important impact on even initial design. The results presented highlight the sensitivity of the primary flow field properties, velocity, density, pressure and temperature, to changes in the step frontal-face height. In addition, the behaviour of heat transfer, pressure and skin friction coefficients with variation of the step frontal-face height is detailed. The analysis shows that hypersonic flow past a forward-facing step in the transition flow regime is characterized by a strong compression ahead of the frontal face, which influences the aerodynamic surface properties upstream and adjacent to the frontal face. The analysis also shows that the extension of the upstream disturbance depends on the step frontal-face height. It was found that the recirculation region ahead of the step is also a function of the frontal-face height. A sequence of Moffatt eddies of decreasing size and intensity is observed in the concave step corner. Locally high heating and pressure loads were observed at three locations along the surface, i.e. on the lower surface, on the frontal face and on the upper surface. The results showed that both loads rely on the frontal-face height. The peak values for the heat transfer coefficient on the frontal-face surface were at least one order of magnitude larger than the maximum value observed for a smooth surface, i.e. a flat plate without a step. A comparison of the present simulation results with numerical and experimental data showed close agreement concerning the wall pressure acting on the step surface.

Laminar flow past a permeable sphere

1982 ◽  
Vol 60 (2) ◽  
pp. 202-211 ◽  
Author(s):  
K. Nandakumar ◽  
Jacob H. Masliyah
Keyword(s):  
Laminar Flow ◽  
Flow Past ◽  
Permeable Sphere

Steady planar straining flow past a rigid sphere at moderate Reynolds number

2002 ◽  
Vol 466 ◽  
pp. 365-407 ◽  
Author(s):  
P. BAGCHI ◽  
S. BALACHANDAR
Keyword(s):  
Reynolds Number ◽  
Potential Flow ◽  
Reynolds Numbers ◽  
Uniform Flow ◽  
Recirculation Region ◽  
Flow Past ◽  
Moderate Reynolds Number ◽  
Strain Magnitude ◽  
Low Reynolds ◽  
Planar Strain

This study focuses on the effect of spatial non-uniformity in the ambient flow on the forces acting on a spherical particle at moderate particle Reynolds numbers. A scaling analysis is performed to obtain conditions under which such effects are important. A direct numerical simulation, based on spectral methods, is used to compute the three-dimensional time-dependent flow past a stationary sphere subject to a uniform flow plus a planar straining flow. The particle Reynolds number, Re, in the range 10 to 300 covering different flow regimes, from unseparated flow to unsteady vortex shedding, is considered. A variety of strain magnitudes and orientations are investigated. A systematic comparison with the potential flow results and axisymmetric strain results is given. Under elongational strain, both the planar and axisymmetric cases are found to stabilize the sphere wake and delay the onset of unsteadiness, while compressional strain leads to instability. In terms of separation angles, length of the recirculation eddy and topology of the surface streamlines, planar and axisymmetric strains yield nearly the same results. The drag force appears to have a linear relation with strain magnitude in both cases, as predicted by the potential flow. However, contrary to the potential flow results, the drag in planar strain is higher than that in axisymmetric strain. The generation of higher drag is explained using the surface pressure and vorticity distributions. Planar strain oriented at an angle with the oncoming uniform flow is observed to break the symmetry of the wake and results in a lift or side force. The variation of the drag and lift forces may be quite complex, and unlike the potential flow results they may not be monotonic with strain magnitude. The direction of the lift force may be opposite to that predicted by the inviscid and low Reynolds number (Re [Lt ] 1) theories. This behaviour is dictated by the presence or absence of a recirculation eddy. In the absence of a recirculation region at low Reynolds numbers (Re < 20), or at a very high strain magnitude when the recirculation region is suppressed, the results follow somewhat the pattern observed in potential flow. However, with the presence of a recirculation region, results opposite to those predicted by the potential theory are observed.

scholarly journals Flow characteristics analysis for flow past the porous spheres: wake structures and drag force coefficients

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Likun Ma ◽  
Sina Kashanj ◽  
Shuliang Xu ◽  
Mao Ye ◽  
David Nobes
Keyword(s):  
Flow Characteristics ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Solid Sphere ◽  
Flow Fields ◽  
Stagnation Points ◽  
Flow Past ◽  
Characteristics Analysis ◽  
Permeable Sphere ◽  
Porous Spheres

Flow past a permeable sphere is different from that of a solid sphere due to the penetration of the fluid within porous structures, which can arise a change of flow fields. In this work, flow past porous spheres with Darcy numbers (Da) ranging from [0,10−3 ] were measured using planar Particle Image Velocimetry (PIV). The whole flow fields, including both leading edge and trailing edge, were captured at six different Reynolds numbers (Re) varying from 400 to 1400. Time-average flow fields were calculated based on instantaneous flow fields within fully-developed stages. Local minimum method was used to search for stagnation point positions. The results show positions of stagnation points are nearly proportional to the logarithm of Re. For most porous spheres, positions of stagnation points are extended to farther downstream positions than that of a solid sphere. However, at some certain Darcy numbers, ranging from 5 ∗ 10−6 to 2 ∗ 10−5, positions of stagnation points are closer to the sphere centers than that of an impermeable one.

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