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Streamwise vorticity in viscous, compressible, steady flow about aircraft is analysed on the basis of the steady Reynolds-averaged Navier-Stokes equations. It is shown, that Streamwise vorticity can develop in the presence of stre...
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Streamwise vorticity in viscous, compressible, steady flow about aircraft is analysed on the basis of the steady Reynolds-averaged Navier-Stokes equations. It is shown, that Streamwise vorticity can develop in the presence of stream-normal vorticity and can be non-negligible only inside e.g. boundary layers, shock layers, viscous (turbulent) wakes, jet exhausts and propeller slipstreams, but also along streamlines leaving such viscous and heat conduction dominated flow regions on their downstream side (e.g. downstream of shock layers). However, the actual development of Streamwise vorticity then still depends on such local flow characteristics as e.g. streamline curvature and streamline convergence or divergence. Two illustrative examples are discussed.
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Using a model of nonmagnetic impurity potential, we have examined the behavior of planar vortex solutions in the classical two-dimensional XY ferromagnets in the presence of a spin vacancy localized out of the vortex core. Our res...
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Using a model of nonmagnetic impurity potential, we have examined the behavior of planar vortex solutions in the classical two-dimensional XY ferromagnets in the presence of a spin vacancy localized out of the vortex core. Our results show that a spinless atom impurity gives rise to an effective potential that repels the vortex structure. [References: 17]
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A stability condition is provided for a class of vorticity boundary formulas used withthe second order finite-difference numerical scheme for the vorticity-stream function formulation ofthe unsteady incompressible Navier-Stokes eq...
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A stability condition is provided for a class of vorticity boundary formulas used withthe second order finite-difference numerical scheme for the vorticity-stream function formulation ofthe unsteady incompressible Navier-Stokes equations. These local vorticity boundary formulas arederived using the no-slip boundary condition for the velocity. A new form of these long-stencilformulas is needed to classify the stability property, in which local terms are controlled by globalquantities via discrete elliptic regularity for the stream functions.
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The stream function-vorticity formulation of the (Navier-)Stokes equations yields a coupled system of a parabolic equation for the vorticity and an elliptic equation for the stream function. The essential coupling between them occ...
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The stream function-vorticity formulation of the (Navier-)Stokes equations yields a coupled system of a parabolic equation for the vorticity and an elliptic equation for the stream function. The essential coupling between them occurs through the boundary conditions which in case of a Dirichlet boundary involve only the stream function. Therefore, the boundary condition for the vorticity must be derived from them and thus the vorticity equation must be coupled to the stream function equation via its boundary condition. In this paper we propose an unconditionally stable splitting scheme for the unsteady Stokes equations in a stream function vorticity formulation, that decouples the vorticity and stream function computations at each time step. The spatial discretization is based on a finite volume discretization on (generally) unstructured Delaunay grids and corresponding Voronoi finite volume cells. A generalization of the well-known Thom vorticity boundary condition is derived for such grids and the corresponding discrete problem is decoupled by a two-step splitting scheme which results in a decoupled discrete parabolic problem for the vorticity and an elliptic problem for the stream function. Furthermore, the scheme is extended to the unsteady Navier-Stokes equations. Finally, the stability and accuracy of the resulting schemes are demonstrated on numerical examples. (C) 2015 Elsevier B.V. All rights reserved.
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Computation of viscous fluid flow is an area of research where many authors have tried to present different numerical methods for solution of the Navier-Stokes equations. Each of these methods has its own advantages and weaknesses...
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Computation of viscous fluid flow is an area of research where many authors have tried to present different numerical methods for solution of the Navier-Stokes equations. Each of these methods has its own advantages and weaknesses. In the meantime, many researchers have attempted to develop coupled numerical algorithms in order to save storage for computational purposes and to save computational time. In this paper, a new coupled method is presented for the first time by combining FDM and DRBEM for solving the stream function-vorticity formulation of the Navier-Stokes equations. The vorticity transport equation is analyzed using a finite difference technique while the stream function Poisson's equation is solved using a dual reciprocity boundary element method. Finally, the robustness and accuracy of the coupled FDM-DRBEM model is proved using the benchmark problem of the flow in a driven square cavity.
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A linear and nonlinear analysis is presented of coupled ion-acoustic and drift waves in a plasma consisting of electrons and ions that is penetrated by a mono-energetic stream of ions of another kind. All the plasma species (elect...
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A linear and nonlinear analysis is presented of coupled ion-acoustic and drift waves in a plasma consisting of electrons and ions that is penetrated by a mono-energetic stream of ions of another kind. All the plasma species (electrons and two ion fluids) are allowed to have density gradients in the direction perpendicular to the external magnetic field lines. In the linear domain the standard streaming instability of the acoustic modes and their interaction with drift modes is demonstrated. The threshold values of the stream velocity and the parallel wave number are calculated and discussed. In the nonlinear limit stationary coherent solutions are found which can represent the saturated state of the linearly unstable modes. (C) 2004 Elsevier B.V. All rights reserved.
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Using the coarse-grain averaged hydrodynamic approach, we calculate the excitation spectrum of vortex lattices sustained in rotating Bose-Einstein condensates. The spectrum gives the frequencies of the common-mode longitudinal wav...
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Using the coarse-grain averaged hydrodynamic approach, we calculate the excitation spectrum of vortex lattices sustained in rotating Bose-Einstein condensates. The spectrum gives the frequencies of the common-mode longitudinal waves in the hydrodynamic regime, including those of the higher-order compressional modes. Reasonable agreement with the measurements taken in a recent experiment is found, suggesting that one of the longitudinal modes reported in the experiment is likely to be the n=2,m=0 mode. [References: 31]
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Natural convection in a rectangular cavity with a saturated porous layer on one of its vertical walls is studied numerically The governing equations using the Boussinesq approximation for the treatment of buoyancy term in the mome...
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Natural convection in a rectangular cavity with a saturated porous layer on one of its vertical walls is studied numerically The governing equations using the Boussinesq approximation for the treatment of buoyancy term in the momentum equation and the Darcy model are expressed using the vorticity-stream function approach These equations are discretized with the implicit finite-difference method. Thomas algorithm and Gauss-Seidel method are used to solve the resultant algebraic system equations. Results are presented in terms of streamlines, isotherms and isoconcentrations. The increase of the porous wall permeability leads to a more intensive buoyancy-driven flow through the porous wall and consequently an increase of heat and mass transfer occurs in the enclosure. Nusselt and Sherwood numbers are expressed as functions of dimensionless parameters as Darcy number, modified Grashof number and the geometric aspect ratio of the enclosure.
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A review emphasizing the quantitative studies of leading-edge vortices at supersonic speed is presented. While quantitative investigations of vortical flow over delta wings are extensive in the incompressible regime, and to a degr...
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A review emphasizing the quantitative studies of leading-edge vortices at supersonic speed is presented. While quantitative investigations of vortical flow over delta wings are extensive in the incompressible regime, and to a degree in transonic range, their measurements in supersonic freestream are very scarce. It is illustrated that the existing knowledge of leading-edge vortices in the supersonic regime is mainly qualitative, compiled from large amount of flow visualization experiments. A brief account of the flow visualization studies is first presented, followed by a comprehensive survey of the various measurement attempts to quantify these vortices. On the qualitative side, this survey reveals that in spite of the past efforts, the literature still lacks a unified topological description of the compressible leeward vortical Hows. In quantitative investigations, the experience with pressure probes and seed based optical measurement techniques is highlighted, and the associated results summarized. Amongst them, although there exists a topological similarity in the delta wing leeward flow at low- and high-speeds, available measurements suggest that leading-edge vortices in supersonic flow have a very different axial flow character. Additional salient features of leading-edge vortices in supersonic freestreams are also provided in the paper.
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In this paper we present a new method to solve the 2D generalized Stokes problem in terms of the stream function and the vorticity. Such problem results, for instance, from the discretization of the evolutionary Stokes system. The...
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In this paper we present a new method to solve the 2D generalized Stokes problem in terms of the stream function and the vorticity. Such problem results, for instance, from the discretization of the evolutionary Stokes system. The difficulty arising from the lack of the boundary conditions for the vorticity is overcome by means of a suitable technique for uncoupling both variables. In order to apply the above technique to the Navier-Stokes equations we linearize the advective term in the vorticity transport equation as described in the development of the paper. We illustrate the good performance of our approach by means of numerical results, obtained for benchmark driven cavity problem solved with classical piecewise linear finite element. (C) 2007 Elsevier B.V. All rights reserved.
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