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The interaction of a short cylindrical vortex elongated along the transverse coordinate with a shear flow near a solid surface is considered. A cylindrical vortex with its ends lowered to the bottom of the channel is shown to turn...
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The interaction of a short cylindrical vortex elongated along the transverse coordinate with a shear flow near a solid surface is considered. A cylindrical vortex with its ends lowered to the bottom of the channel is shown to turn into a vortex ring. The obtained qualitative model is verified by experiment.
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It has been shown experimentally that an adverse pressure gradient leads to periodic deceleration of the boundary layer of a plane-parallel flow in an open channel. During the deceleration, the action of the reverse pressure gradi...
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It has been shown experimentally that an adverse pressure gradient leads to periodic deceleration of the boundary layer of a plane-parallel flow in an open channel. During the deceleration, the action of the reverse pressure gradient and friction force forms an instantaneous vertical velocity profile with a local minimum above the viscous layer between two inflection points. In a thin layer containing the upper inflection point, the plane-parallel flow is unstable, which has been confirmed experimentally: a cylindrical vortex is formed in this layer at a critical value of the reverse pressure gradient when the deceleration cycle terminates.
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The present experimental work is concerned with "twin jets in crossflow" (TJICF) concentrating upon the vorticity distribution and turbulent vorticity transport associated with the dominant vortical structure of the TJICF. The con...
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The present experimental work is concerned with "twin jets in crossflow" (TJICF) concentrating upon the vorticity distribution and turbulent vorticity transport associated with the dominant vortical structure of the TJICF. The configuration of the TJICF consists of a pair of identical jet nozzles and jet-flow conditions at the nozzle exits. The twin jets are issuing normally into a crossflow. The mean-flow velocity vector and associated turbulence statistics of the TJICF are determined using the standard crossed hot-wire anemometry technique. In the present contribution two geometrically symmetric TJICF arrangements, namely tandem and side-by-side arrangements (both with a nozzle centre-to-centre separation of 5D). are examined, focusing upon the dominant vortical structure rather similar to that of the ell-known contrarotating vortex pair of the single JICF. The formation and decay of this dominant cortical structure is closely associated with the turbulent vorticity transport. The two TJICF arrangements under consideration have their own specific vorticity transport features which are. firstly, visualized and interpreted in terms of turbulent vorticity fluxes. Secondly, the vorticity transport analysis shows the vortex-strength decay (i.e. circulation decay) as described by the corresponding integral decay-rate formula. The similarities and differences between the vorticity (distribution and transport) features associated with the two different TJICF arrangements. tandem and side-by-side, and the single-jet case are examined and discussed. The TJICF flow phenomenon represents an interaction of two single JICF and the gross qualitative features of the vortex formation process of the resulting (mean-flow) dominant vortical structure are described. (C) 2003 Elsevier Science Inc. All rights reserved. [References: 24]
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The effects of the forward inclination of a jet in crossflow on the jet fluid dispersion and upwind-side shear-layer characteristics were studied experimentally in an open-loop wind tunnel. The jet forward-inclination angle theta ...
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The effects of the forward inclination of a jet in crossflow on the jet fluid dispersion and upwind-side shear-layer characteristics were studied experimentally in an open-loop wind tunnel. The jet forward-inclination angle theta was varied from 0 degrees to 50% and the jet-to-crossflow momentum-flux ratio was adjusted between 1 and 2. Short- and long-exposure flow patterns were examined using the laser-assisted smoke flow visualization technique. The binary edge-detection technique was applied to the long-exposure flow images to obtain the jet penetration height. The instantaneous velocities in the upwind-side shear layer of the bent jet were captured by a hot-wire anemometer through a high-speed data acquisition system. The fast Fourier transform method was used to convert the instantaneous velocities from time to the frequency domain. Transverse dispersion of the jet fluids and jet trajectories described by the maximum jet-fluid concentrations were determined using the tracer-gas concentration detection method. The results revealed that at the same jet-to-crossflow momentum-flux ratio, a forward inclination did not significantly influence the flow characteristics and dispersion properties when the inclination angle was smaller than about 12 degrees. At moderate forward inclinations (about 12 degrees-42 degrees), the upstream-side coherent flow structures appeared periodically. The penetration height, transverse width, and dispersion of jet fluids were greater than those of the elevated transverse jet and the slightly forward-inclined transverse jet. At forward inclinations larger than about 42 degrees, the upstream-side coherent flow structures, penetration height, transverse width, and dispersion of jet fluids became the largest when compared with those of the elevated transverse jet as well as the slight and moderate inclination ranges. The jet trajectories in the moderate and large inclination ranges were located at transverse levels higher than those in the slight inclination range and elevated transverse jet due to the appearance of the large upwind-side shear-layer coherent flow structures. The effects of the forward inclinations on the time and length scales of the upwind-side coherent flow structures and the time and length scales of the turbulent eddies were presented and discussed.
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The flow and mixing characteristics of a forward-inclined stack-issued jet at various inclination angles (0) and jet-to-crossflow momentum flux ratios (R) were experimentally studied in an open-loop wind tunnel. Flow behaviors wer...
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The flow and mixing characteristics of a forward-inclined stack-issued jet at various inclination angles (0) and jet-to-crossflow momentum flux ratios (R) were experimentally studied in an open-loop wind tunnel. Flow behaviors were examined using the laser-assisted smoke flow visualization technique. The instantaneous velocities of the upwind-side shear-layer were digitized by a hot-wire anemometer using a high-speed data acquisition system. The instability frequencies in the upwind-side shear-layer vortices were obtained by the fast Fourier transform method. Long-exposure flow images were processed using the binary edge-detection technique to obtain the jet spread width. Transverse dispersion of jet fluids was determined using tracer gas concentration detection. The upwind-side shear-layer vortices revealed four characteristic flow modes: the High impingement-crossflow dominated mode (about θ < 15° and low R), the High impingement-jet flow dominated mode (about 9 < 25° and high R), the Low impingement-crossflow dominated mode (about θ > 15° and low R), and the Low impingement-jet flow dominated mode (about θ > 25° and high R). Increasing 9 in the crossflow dominated regimes eliminated the upwind-side shear-layer vortices, while increasing 9 in the jet flow dominated regimes emphasized the upwind-side shear-layer vortices. Increasing θ at a fixed value of R increased jet spread width in the far field in all modes. In the near field, at x/d < 5 in the High impingement-crossflow dominated regime, the jet spread width was greater than in the Low impingement-crossflow dominated regime. In the jet flow dominated regimes, higher 9 values led to greater jet spread width. Transverse dispersion of the jet fluids approached the jet spread width results. In the Low impingement-jet flow dominated regime, transverse dispersion of the jet fluids was significantly increased compared to the other regimes. In addition, the maximum tracer gas concentration was severely reduced at all axial stages, which implied better dispersion of the jet fluids in this regime.
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A mixed Lagrangian-Eulerian approach based on the vortex-in-cell method and the vorticity-velocity formulation is developed to solve the three-dimensional (3D), incompressible, inviscid spatially growing uniformly sheared fluid fl...
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A mixed Lagrangian-Eulerian approach based on the vortex-in-cell method and the vorticity-velocity formulation is developed to solve the three-dimensional (3D), incompressible, inviscid spatially growing uniformly sheared fluid flow. The Lagrangian vortex filaments are initially subjected to a 3D random perturbation in order to simulate an initial fluctuating velocity field with nearly isotropic conditions. Contour plots for the two orientation angles of the vortex filaments and the fluctuating vorticity vectors indicate the presence of preferred angles relative to the mean flow direction as the flow develops. A comparison with previously reported numerical simulation suggests that the prediction corresponds to the phase of early development where the non-dimensional time τ< 2. The downstream evolution of the component energy ratios K_(11), K_(22) and K_(33) are qualitatively in agreement with previous numerical simulations and experiments. Sensitivity of the contour plots for total and fluctuating vorticity vectors and vortex filaments, and component energy ratios to changes in numerical parameters is discussed.
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A vortex method is suggested for computing two-dimensional inviscid incompressible flows in a closed domain with a possible flow through it. An algorithm for searching for stable steady vortex configurations is described. The meth...
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A vortex method is suggested for computing two-dimensional inviscid incompressible flows in a closed domain with a possible flow through it. An algorithm for searching for stable steady vortex configurations is described. The method developed is used to study the dynamics of the Chaplygin-Lamb dipole in a rectangular channel in various flow regimes.
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The maximum height of a disturbance on the water surface, which occurs when a spatial (non-point) vortex departs from a viscous layer of a horizontal air flow that decelerates in the direction of motion, is estimated. The dependen...
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The maximum height of a disturbance on the water surface, which occurs when a spatial (non-point) vortex departs from a viscous layer of a horizontal air flow that decelerates in the direction of motion, is estimated. The dependence of the initial disturbance parameters on the air flow speed over the water surface is derived. It is shown that the height of the disturbance increases and its width decreases with an increase in the air flow speed. The suggested model is verified experimentally.
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All volcanic eruptions are accompanied by the degasification of the magma, which results in the growth of gas bubbles in the silicate melt. The number and growth rate of the bubbles determine the character of the eruption. When th...
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All volcanic eruptions are accompanied by the degasification of the magma, which results in the growth of gas bubbles in the silicate melt. The number and growth rate of the bubbles determine the character of the eruption. When the free-gas concentration is low, the eruption is weak and takes a short time. At high concentrations, the melt is fragmented and a gas-particle mixture is formed. This results in the catastrophic intensification of the eruption. In this study, for describing the magma flow in a volcano conduit with account for the mass transfer between the bubbles and the melt, we construct models in which the conduit magma flow is considered simultaneously with the dynamics of gas-bubble growth in the melt. The models describe the magma eruptions with equilibrium or weak growth of the bubbles and also with a moderate rate of bubble growth, which is more typical of volcanic systems. Using the models constructed, an intense steady-state eruption and the problem of the evolution of the eruption to the steady-state regime after the rupture of a plug near the top of the conduit are considered. The effect of gas diffusion on the intensity and duration of the eruption is indicated.
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Wake eddies are important to physical oceanographers because they tend to dominate current variability in the lee of islands. However, their generation and evolution has been difficult to study due to their intermittency. In this ...
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Wake eddies are important to physical oceanographers because they tend to dominate current variability in the lee of islands. However, their generation and evolution has been difficult to study due to their intermittency. In this study, 2 years of observations from Surface Velocity Program (SVP) drifters are used to calculate relative vorticity (ζ) and diffusivity (κ) in the wake generated by westward flow past the archipelago of Palau. Over 2 years, 19 clusters of five SVP drifters ~5 km in scale were released from the north end of the archipelago. Out of these, 15 were entrained in the wake. We compare estimates of ζ from both velocity spatial gradients (least squares fitting) and velocity time series (wavelet analysis). Drifters in the wake were entrained in either energetic submesoscale eddies with initial ζ up to 6f, or island-scale re-circulation and large-scale lateral shear with ζ ~ 0.1f. Here/is the local Coriolis frequency. Mean wake vorticity is initially 1.5f but decreases inversely with time (t), while mean cluster scale (L) increases as L ∝ t. Kinetic energy measured by the drifters is comparatively constant. This suggests £ is predominantly a function of scale, confirmed by binning enstrophy (ζ~2) by inverse scale. We find κ∝ L~(4/3) and upper and lower bounds for L(t) are given by t~(3/2) and t~(1/2), respectively. These trends are predicted by a model of dispersion due to lateral shear. We argue the observed time dependence of cluster scale and vorticity suggest island-scale shear controls eddy growth in the wake of Palau.
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