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1

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Experiments on the evolution of gravitational instability of an overturned, initially stably stratified fluid (1993)

Voropayev, S. I. ; Afanasyev, Y. D. ; van Heijst, G. J. F.

New York, NY : American Institute of Physics (AIP)

Physics of Fluids 5 (1993), S. 2461-2466

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: Unstable density stratifications were created in the laboratory by rapid overturning of a narrow tank containing an initially stable density structure. The experiments were carried out for two different initial density distributions: (i) a two-layer (steplike) and (ii) a linear stratification. For the former case the depth of the mixing layer was found to increase linearly with time. The number of convective elements (thermal-like flow structures) present at the front of the mixing layer was observed to decrease with time, through the mechanism of subsequent pairing. In the case of an initially linear stratification the flow evolution is characterized by a number of distinct stages: different modes of instability emerge subsequently through the entire fluid column, leading to the formation of horizontal layers, which finally break up into thermal-like convective flow structures.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.858759

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2

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Propagation of grid turbulence in homogeneous fluids (1996)

Voropayev, S. I. ; Fernando, H. J. S.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 8 (1996), S. 2435-2440

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: The purpose of this paper is to present the results of a laboratory experiment dealing with one-dimensional propagation of a turbulent front induced by an oscillating grid in a homogeneous fluid. The symmetrical quadrupolar mode of the flow, induced by the grid elements, was studied in the range KC=4–45, S=1–20 (KC is the Keulegan–Carpenter number, S is the Stokes number). It is shown that the depth H of the turbulent layer increases with time t as H∝t1/2. Experimental data for different grid parameters and oscillation amplitudes and frequencies are presented in the nondimensional form h=const τ1/2, using nondimensional depth h of the turbulent layer and nondimensional time τ. A semiempirical model is presented to explain this behavior. This model is based on the properties of a flow induced in a visous fluid by localized forcing of a line force dipole (force doublet). © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.869028

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3

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Starting and steady quadrupolar flow (1996)

Voropayev, S. I. ; Fernando, H. J. S. ; Wu, P. C.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 8 (1996), S. 384-396

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: Planar flow induced in a viscous fluid by a small cylinder oscillating in the direction normal to its axis is modeled theoretically and reproduced experimentally. In the model, a line force dipole (force doublet) was used as the source of motion. In an initially quiescent unbounded fluid this source produces zero net momentum and generates symmetrical quadrupolar flow consisting of two dipolar vorticity fronts propagating in opposite directions from the source. For starting flow at low Reynolds numbers, a second-order unsteady solution is obtained in terms of a power series of the Reynolds number, Re=Q/4πν2, where Q is the forcing amplitude and ν is the kinematic viscosity. This solution demonstrates that, as time t→∞, the flow in the vicinity of the source becomes steady and radial. To describe this steady asymptote, the Jeffery–Hamel nonlinear solution for radial flow is used. A particular solution is derived using the nondimensional intensity Re of the force dipole as a governing parameter. It is shown that the problem permits a similarity solution for all values of Re when a mass sink of prescribed intensity q=q(Re) is added to the flow. This steady asymptote is reproduced experimentally, using a vertical porous cylinder that oscillates horizontally in the shallow upper layer of a two-layer fluid and sucks fluid through its porous walls. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.868792

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4

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Dipolar eddies in a stratified shear flow (2001)

Voropayev, S. I. ; Smirnov, S. A.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 13 (2001), S. 3820-3823

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: The aim of this contribution is to present the results of experiments conducted to elucidate the conditions of formation and evolution of planar dipolar eddies in a stratified fluid in the presence of a vertical background shear. The flow regime diagram is derived and conditions under which the formation of dipolar eddies is possible are found and explained. The estimates for the dipole lifetime are given. Possible applications include oceanic mushroom-like currents, late stratified wakes and other cases when dipolar or quasi-dipolar eddies are observed in a stratified shear flow. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1416499

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5

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Symmetric interaction of developing horizontal jet in a stratified fluid with a vertical cylinder (1994)

Voropayev, S. I. ; Afanasyev, Ya. D.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 6 (1994), S. 2032-2037

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: A self-similar planar vortex dipole, arising at the front of developing horizontal jet in a stratified fluid, collides with a small vertical cylinder. The primary vortical flow interacts with the secondary vorticity generated at the boundary of the cylinder and finally a new dipole of reduced intensity forms. The estimates for the reduction of the flow momentum and alteration of the overall propagation velocity and length scales of the newly formed dipole are given. The evolution of the real flow is also explained mathematically.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.868210

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6

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Large vortex structures behind a maneuvering body in stratified fluids (1999)

Voropayev, S. I.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 11 (1999), S. 1682-1684

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: When a submerged self-propelled body makes a maneuver, e.g., accelerates, significant momentum is transported to the surrounding fluid. Our experiments show that in a stratified fluid this may lead to the formation of large vortex structures, much larger and different from those produced in the late wake during steady motion. Estimates also show that when an oceanic submerged vehicle changes its velocity by as little as 10% or its direction of motion by 5 degrees, large structures of the size of 1–2 km and with decay times of several days may be expected. Such effects may have potentially important applications and have not been studied previously. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.870030

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7

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Vortex quadrupoles and two-dimensional oscillating grid turbulence (1993)

Voropayev, S. I. ; Afanesyev, Ya. D.

Springer

Flow, turbulence and combustion 51 (1993), S. 475-480

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ISSN: 1573-1987

Keywords: planar flow ; turbulence ; coherent structure ; interactions

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The planar motions induced by a localized forcing of the type of a “point” force-dipole is reproduced using a vertical rod oscillating horizontally in a thin layer of fluid. This forcing gives rise to the formation of a vortex quadrupole. To model a chaotic vortical flow, a system of quadrupoles is generated using a linear grid of oscillating rods. As a result of quadrupole interactions, a turbulent layer with two sharp boundaries forms and propagates from the grid.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01082578

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