scholarly journals Теневая визуализация турбулентного обмена между вихревым кольцом и окружающей средой при различных плотностях жидкостей в вихре и вне его

2019 ◽  
Vol 45 (7) ◽  
pp. 8
Author(s):  
В.В. Никулин
Keyword(s):  
Reynolds Number ◽  
Vortex Ring ◽  
Turbulent Exchange ◽  
Characteristic Distance ◽  
Vortex Velocity

AbstractThe turbulent exchange between a vortex ring and the environment was observed using shadowgraph imaging of the process when the density of the fluid inside and outside of the vortex is different. The characteristic distance of turbulent exchange traversed by the vortex is determined, and the dependence of this distance on the vortex velocity and the related Reynolds number is established.

Initial motion of a viscous vortex ring

1994 ◽  
Vol 446 (1928) ◽  
pp. 589-599 ◽  
Keyword(s):  
Reynolds Number ◽  
Asymptotic Analysis ◽  
Vortex Ring ◽  
Kinematic Viscosity ◽  
Reynolds Numbers ◽  
Initial Radius ◽  
Dimensionless Form ◽  
Ring Radius ◽  
Initial Motion ◽  
Matched Asymptotic Analysis

The behaviour of a viscous vortex ring is examined by a matched asymptotic analysis up to three orders. This study aims at investigating how much the location of maximum vorticity deviates from the centroid of the vortex ring, defined by P. G. Saffman (1970). All the results are presented in dimensionless form, as indicated in the following context. Let Γ be the initial circulation of the vortex ring, and R denote the ring radius normalized by its initial radius R i . For the asymptotic analysis, a small parameter ∊ = ( t / Re ) ½ is introduced, where t denotes time normalized by R 2 i / Γ , and Re = Γ/v is the Reynolds number defined with Γ and the kinematic viscosity v . Our analysis shows that the trajectory of maximum vorticity moves with the velocity (normalized by Γ/R i ) U m = – 1/4π R {ln 4 R /∊ + H m } + O (∊ ln ∊), where H m = H m ( Re, t ) depends on the Reynolds number Re and may change slightly with time t for the initial motion. For the centroid of the vortex ring, we obtain the velocity U c by merely replacing H m by H c , which is a constant –0.558 for all values of the Reynolds number. Only in the limit of Re → ∞, the values of H m and H c are found to coincide with each other, while the deviation of H m from the constant H c is getting significant with decreasing the Reynolds number. Also of interest is that the radial motion is shown to exist for the trajectory of maximum vorticity at finite Reynolds numbers. Furthermore, the present analysis clarifies the earlier discrepancy between Saffman’s result and that obtained by C. Tung and L. Ting (1967).

Numerical study of a vortex ring impacting a flat wall

2010 ◽  
Vol 660 ◽  
pp. 430-455 ◽  
Author(s):  
MING CHENG ◽  
JING LOU ◽  
LI-SHI LUO
Keyword(s):  
Reynolds Number ◽  
Vortex Ring ◽  
Three Dimensions ◽  
Angle Of Incidence ◽  
Secondary Vortex ◽  
Primary Ring ◽  
Flat Wall ◽  
Hydrodynamic Behaviour ◽  
Moderate Reynolds Number ◽  
Wall Interaction

We numerically study a vortex ring impacting a flat wall with an angle of incidence θ ≥ 0°) in three dimensions by using the lattice Boltzmann equation. The hydrodynamic behaviour of the ring–wall interacting flow is investigated by systematically varying the angle of incidence θ in the range of 0° ≤ θ ≤ 40° and the Reynolds number in the range of 100 ≤ Re ≤ 1000, where the Reynolds number Re is based on the translational speed and initial diameter of the vortex ring. We quantify the effects of θ and Re on the evolution of the vortex structure in three dimensions and other flow fields in two dimensions. We observe three distinctive flow regions in the θ–Re parameter space. First, in the low-Reynolds-number region, the ring–wall interaction dissipates the ring without generating any secondary rings. Second, with a moderate Reynolds number Re and a small angle of incidence θ, the ring–wall interaction generates a complete secondary vortex ring, and even a tertiary ring at higher Reynolds numbers. The secondary vortex ring is convected to the centre region of the primary ring and develops azimuthal instabilities, which eventually lead to the development of hairpin-like small vortices through ring–ring interaction. And finally, with a moderate Reynolds number and a sufficiently large angle of incidence θ, only a secondary vortex ring is generated. The secondary vortex wraps around the primary ring and propagates from the near end of the primary ring, which touches the wall first, to the far end, which touches the wall last. The rings develop a helical structure. Our results from the present study confirm some existing experimental observations made in the previous studies.

Laminar to Turbulent Buoyant Vortex Ring Regime in Terms of Reynolds Number, Bond Number, and Weber Number

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Xueying Yan ◽  
Rupp Carriveau ◽  
David S. K. Ting
Keyword(s):  
Reynolds Number ◽  
Vortex Ring ◽  
Weber Number ◽  
High Speed ◽  
Reynolds Numbers ◽  
Bond Number ◽  
Vortex Rings ◽  
Transition Regime ◽  
Turbulent Vortex ◽  
Buoyant Vortex Rings

When buoyant vortex rings form, azimuthal disturbances occur on their surface. When the magnitude of the disturbance is sufficiently high, the ring will become turbulent. This paper establishes conditions for categorization of a buoyant vortex ring as laminar, transitional, or turbulent. The transition regime of enclosed-air buoyant vortex rings rising in still water was examined experimentally via two high-speed cameras. Sequences of the recorded pictures were analyzed using matlab. Key observations were summarized as follows: for Reynolds number lower than 14,000, Bond number below 30, and Weber number below 50, the vortex ring could not be produced. A transition regime was observed for Reynolds numbers between 40,000 and 70,000, Bond numbers between 120 and 280, and Weber number between 400 and 800. Below this range, only laminar vortex rings were observed, and above, only turbulent vortex rings.

Formation of vortex rings from falling drops

1967 ◽  
Vol 29 (1) ◽  
pp. 177-185 ◽  
Author(s):  
David S. Chapman ◽  
P. R. Critchlow
Keyword(s):  
Reynolds Number ◽  
Vortex Ring ◽  
Liquid Drop ◽  
Prolate Spheroid ◽  
Ring Formation ◽  
Vortex Rings ◽  
Surface Tensions ◽  
Wide Range ◽  
The Moment

A study of the formation of vortex rings when a liquid drop falls into a stationary bath of the same liquid has been made. The investigation covered liquids with a wide range in surface tensions, densities and viscosities. The results confirm the reported existence of optimum dropping height from which the drop develops into a superior vortex ring. The optimum heights are analysed, by a photographic study, in terms of the liquid drop oscillation. It is found that vortex rings are formed best if the drop is spherical and changing from an oblate to a prolate spheroid at the moment of contact with the bath. A Reynolds number has been determined for vortex rings produced at optimum dropping heights; these numbers are approximately 1000. A possible mechanism for the ring formation is suggested.

scholarly journals Compressible starting jet: pinch-off and vortex ring–trailing jet interaction

2017 ◽  
Vol 817 ◽  
pp. 560-589 ◽  
Author(s):  
Juan José Peña Fernández ◽  
Jörn Sesterhenn
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Vortex Ring ◽  
Pressure Ratio ◽  
Reynolds Numbers ◽  
Chamber Pressure ◽  
Vortex Interaction ◽  
Dominant Feature ◽  
Chamber Temperature ◽  
Starting Jet

The dominant feature of the compressible starting jet is the interaction between the emerging vortex ring and the trailing jet. There are two types of interaction: the shock–shear layer–vortex interaction and the shear layer–vortex interaction. The former is clearly not present in the incompressible case, since there are no shocks. The shear layer–vortex interaction has been reported in the literature in the incompressible case and it was found that compressibility reduces the critical Reynolds number for the interaction. Four governing parameters describe the compressible starting jet: the non-dimensional mass supply, the Reynolds number, the reservoir to unbounded chamber temperature ratio and the reservoir to unbounded chamber pressure ratio. The latter parameter does not exist in the incompressible case. For large Reynolds numbers, the vortex pinch-off takes place in a multiple way. We studied the compressible starting jet numerically and found that the interaction strongly links the vortex ring and the trailing jet. The shear layer–vortex interaction leads to a rapid breakdown of the head vortex ring when the flow impacted by the Kelvin–Helmholtz instabilities is ingested into the head vortex ring. The shock–shear layer–vortex interaction is similar to the noise generation mechanism of broadband shock noise in a continuously blowing jet and results in similar sound pressure amplitudes in the far field.

scholarly journals Wall Confinement Effects for Spheres in the Reynolds Number Range of 30–2000

1984 ◽  
Vol 106 (1) ◽  
pp. 66-73 ◽  
Author(s):  
V. J. Modi ◽  
T. Akutsu
Keyword(s):  
Reynolds Number ◽  
Pressure Distribution ◽  
Vortex Ring ◽  
Time History ◽  
General Effect ◽  
Blockage Ratio ◽  
Number Range ◽  
Surface Pressure Distribution ◽  
Reynolds Number Range ◽  
Reynolds Number Dependency

The paper studies in detail the time history of formation, evolution, and instability of the vortex ring, associated with a family of spheres in the Reynolds number range of 30–2000 and with a blockage ratio of 3–30 percent. The flow visualization results are obtained using the classical dye injection procedure. Simultaneous measurements of pressure distribution on the surface of the sphere help establish correlation between the onset of instability of the vortex ring and the surface loading. The results suggest that the influence of the Reynolds number on the surface pressure distribution is primarily confined to the range Rn < 1000. However, for the model with the highest blockage ratio of 30.6 percent, the pressure continues to show Reynolds number dependency for Rn as high as 2300. In general, effect of the Reynolds number is to increase the minimum as well as the wake pressures. On the other hand, the effect of an increase in the blockage ratio is just the opposite. The wall confinement tends to increase the drag coefficient, however, the classical dependence of skin friction on the Reynolds number Cd,f ∝ R−1/2, is maintained. The paper also presents useful information concerning location of the separating shear layers as affected by the Reynolds number and blockage. For comparison, available analytical and experimental results by other investigators are also included. Results show that for a given blockage, separation points may move upstream by as much as 20 deg over a Reynolds number range of 100–600. In general, for a given Reynolds number, the wall confinement tends to move the separation position downstream.

Simulations of Asymmetric Flow Structures around a Moving Sphere at Moderate Reynolds Number

2015 ◽  
Vol 31 (6) ◽  
pp. 757-769
Author(s):  
D.-L. Young ◽  
C.-S. Wu ◽  
C. Wu ◽  
Y.-C. Lin
Keyword(s):  
Reynolds Number ◽  
Laboratory Experiment ◽  
Vortex Ring ◽  
Ring System ◽  
Wake Flow ◽  
Flow Structures ◽  
Leeward Side ◽  
Moderate Reynolds Number ◽  
Side Flow ◽  
Physical Instability

ABSTRACTThe evolution of asymmetric leeward-side flow structures around a moving sphere in the viscous flow is investigated. Simulations are carried out to investigate the variations of vortex-ring system at the moderate Reynolds number. A parallel laboratory experiment is undertaken in this study. The sphere travels a certain distance at constant speed and then stops to collide with a wall. The motion of moving sphere in fluid is described by the hybrid Cartesian immersed boundary method. Drag forces behind the moving sphere are extremely substantial as the solid body falls through viscous fluid for comprehending the formation of wake flow. The dynamic behavior consists of growth and breakup of the vortices which depend on two specific moderate Reynolds numbers. The onset of physical instability in the wake is obviously affected at the Reynolds number of 800. The generated vortex-ring system rolls upward to compact the primary vortex ring and interact with the secondary vortex. An asymmetric generation of the pairs of vortices is developed since the physical instability effect leads to shed in the wake with the increasing Reynolds number. The results from numerical simulations are also conducted to exhibit good comparison with those from the laboratory experiment.

Impact of a Vortex Ring on a Wall in High Reynolds Number Region

1996 ◽  
Vol 65 (4) ◽  
pp. 955-959 ◽  
Author(s):  
In-Sung Jang ◽  
Hiroyuki Chiba ◽  
Shinsuke Watanabe
Keyword(s):  
Reynolds Number ◽  
Vortex Ring ◽  
High Reynolds Number ◽  
High Reynolds
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