Showing papers on "Fluid parcel published in 2010"

On the role of the ambient fluid on gravitational granular flow dynamics

Abstract: The effects of the ambient fluid on granular flow dynamics are poorly understood and commonly ignored in analyses. In this article, we characterize and quantify these effects by combining theoretical and experimental analyses. Starting with the mixture theory, we derive a set of two-phase continuum equations for studying a compressible granular flow composed of homogenous solid particles and a Newtonian ambient fluid. The role of the ambient fluid is then investigated by studying the collapse and spreading of two-dimensional granular columns in air or water, for different solid particle sizes and column aspect (height to length) ratios, in which the front speed is used to describe the flow. The combined analysis of experimental measurements and numerical solutions shows that the dynamics of the solid phase cannot be explained if the hydrodynamic fluid pressure and the drag interactions are not included in the analysis. For instance, hydrodynamic fluid pressure can hold the reduced weight of the solids, thus inducing a transition from dense-compacted to dense-suspended granular flows, whereas drag forces counteract the solids movement, especially within the near-wall viscous layer. We conclude that in order to obtain a realistic representation of gravitational granular flow dynamics, the ambient fluid cannot be neglected.

EFFECTS OF f(R) DARK ENERGY ON DISSIPATIVE ANISOTROPIC COLLAPSING FLUID

Abstract: The purpose of this paper is to study the effects of dark energy on dynamics of the collapsing fluid within the framework of metric f(R) gravity. The fluid distribution is assumed to be locally anisotropic and undergoing dissipation in the form of heat flow, null radiations and shear viscosity. For this purpose, we take general spherical symmetric spacetime. Dynamical equations are obtained and also some special solutions are found by considering shearing expansion-free evolution of the fluid. It is found that dark energy affects the mass of the collapsing matter and rate of collapse but does not affect the hydrostatic equilibrium.

Mixing of a granular layer falling through a fluid.

Abstract: We analyze the granular Rayleigh-Taylor instability of densely packed grains immersed in a compressible or an incompressible fluid using numerical simulations and two types of experiments. The simulations are based on a two-dimensional (2D) molecular dynamics model and the experiments have been carried out in systems of grains immersed in water/glycerol (incompressible fluid) and in air (compressible fluid). The variation of the interstitial fluid is shown to generate different dynamical patterns and mixing properties of the granular systems. The results have been quantified using 2D autocorrelation functions, the power spectrum of the velocity field and velocity field histograms. Excellent agreement is found between the numerical simulations and the experiments.

Practical animation of compressible flow for shock waves and related phenomena

Abstract: We propose a practical approach to integrating shock wave dynamics into traditional smoke simulations. Previous methods either simplify away the compressible component of the flow and are unable to capture shock fronts or use a prohibitively expensive explicit method that limits the time step of the simulation long after the relevant shock waves and rarefactions have left the domain. Instead, we employ a semi-implicit formulation of Euler's equations, which allows us to take time steps on the order of the fluid velocity (ignoring the more stringent acoustic wave-speed restrictions) and avoids the expensive characteristic decomposition typically required of compressible flow solvers. We also propose an extension to Euler's equations to model combustion of fuel in explosions. The flow is two-way coupled with rigid and deformable solid bodies, treating the solid-fluid interface effects implicitly in a projection step by enforcing a velocity boundary condition on the fluid and integrating pressure forces along the solid surface. As we handle the acoustic fluid effects implicitly, we can artificially drive the sound speed c of the fluid to ∞ without going unstable or driving the time step to zero. This permits the fluid to transition from compressible flow to the far more tractable incompressible flow regime once the interesting compressible flow phenomena (such as shocks) have left the domain of interest, and allows the use of state-of-the-art smoke simulation techniques.

Fluid Mechanics for Engineers: A Graduate Textbook

Abstract: Vector and Tensor Analysis, Applications to Fluid Mechanics.- Kinematics of Fluid Motion.- Differential Balances in Fluid Mechanics.- Integral Balances in Fluid Mechanics.- Inviscid Potential Flows.- Viscous Laminar Flow.- Laminar-Turbulent Transition.- Turbulent Flow, Modeling.- Free Turbulent Flow.- Boundary Layer Theory.- Compressible Flow.

Research on the Air Stability of Limited Space

Abstract: Indoor air stability was defined as a type of characterstic or capability of indoor air to inhibit transverse motion of air parcel or particle, and it is categorized into three patterns, such as unstable, neutral, and stable patterns. Computational fluid dynamics (CFD) method was adopted, and the results show that if indoor air is unstable, turbulence flow is intensified and the pollution diffusion is reinforced along transverse direction that is perpendicular to the main flow direction, while turbulence flow is restrained when indoor air is stable. The paper presents a foundation theory for optimal design of indoor air distribution or limited space air distribution under the condition of low energy consumption, to control the contaminants effectively.

On modeling the response of the synovial fluid: Unsteady flow of a shear-thinning, chemically-reacting fluid mixture

Abstract: We study the flow of a shear-thinning, chemically-reacting fluid that could be used to model the flow of the synovial fluid The actual geometry where the flow of the synovial fluid takes place is very complicated, and therefore the governing equations are not amenable to simple mathematical analysis In order to understand the response of the model, we choose to study the flow in a simple geometry While the flow domain is not a geometry relevant to the flow of the synovial fluid in the human body it yet provides a flow which can be used to assess the efficacy of different models that have been proposed to describe synovial fluids We study the flow in the annular region between two cylinders, one of which is undergoing unsteady oscillations about their common axis, in order to understand the quintessential behavioral characteristics of the synovial fluid We use the three models given in Hron et al [J Hron, J Malek, P Pustejovska, KR Rajagopal, On the modeling of the synovial fluid, Adv in Tribol 2010 (2010) 12 pages, doi:101155/2010/104957 Article ID 104957] to study the problem, by appealing to a semi-inverse method The assumed structure for the velocity field automatically satisfies the constraint of incompressibility, and the balance of linear momentum is solved together with a convection-diffusion equation The results are compared to those associated with the Newtonian model We also study the case in which an external pressure gradient is applied along the axis of the cylindrical annulus

Environmental fluid dynamics-jet flow

Abstract: Jet flow is a very important research subject in both fundamental fluid dynamics and engineering applications. Jet flow has the essences of fluid dynamics, such as free and wall-bounded shear flows, turbulent flow, eddy and large vortical structures and their stability and control, and so forth. This article serves as an overview of our past and ongoing research activities on various types of jet flow, with particular reference to their application in the field of environmental fluid dynamics. The research objectives, approach, results and their engineering implications of each topic will be presented.

Generating inviscid and viscous fluid-flow simulations over an aircraft surface using a fluid-flow mesh

Abstract: Fluid-flow simulation over a computer-generated aircraft surface is generated using inviscid and viscous simulations. A fluid-flow mesh of fluid cells is obtained. At least one inviscid fluid property for the fluid cells is determined using an inviscid fluid simulation that does not simulate fluid viscous effects. A set of intersecting fluid cells that intersects the aircraft surface are identified. One surface mesh polygon of the surface mesh is identified for each intersecting fluid cell. A boundary-layer prediction point for each identified surface mesh polygon is determined. At least one boundary-layer fluid property for each boundary-layer prediction point is determined using the at least one inviscid fluid property of the corresponding intersecting fluid cell and a boundary-layer simulation that simulates fluid viscous effects. At least one updated fluid property for at least one fluid cell is determined using the at least one boundary-layer fluid property and the inviscid fluid simulation.

Simulation of particle/fluid flows in vertical circular pipes

Abstract: A two fluid continuum model is applied to the simulation of steady fully developed particle/fluid flow in a vertical circular pipe Both closed form and numerical solutions are obtained to the associated governing equations These solutions are compared to the predictions of another two fluid continuum model These comparisons are used to illustrate the differences in the predictions of two widely used models, even in the fundamental problem of steady flow in a circular pipe

Steady linked vortices with chaotic streamlines

Abstract: This paper contains background information for a fluid dynamics video submitted to the Gallery of Fluid Motion to be held along with the 63rd Annual Meeting of the American Physical Society's Division of Fluid Dynamics.

Peristaltic Flow of a Dusty Couple Stress Fluid in a Flexible Channel

Abstract: In this paper, we investigate the peristaltic two-phase fluid flow consisting of couple stress fluid and dusty fluid i n a flexible channel. The dusty flow equations are based on Saffmen model. The governing nonlinear equations are solved under the usual long wa velength approximation. The fluid and dust velocity components, the flux of the fluid across the channel are calculated for differe nt values of the

Motions of elastic solids in fluids under vibration

Abstract: Motion of a rigid or deformable solid in a viscous incompressible fluid and corresponding fluid–solid interactions are considered. Different cases of applying high frequency vibrations to the solid or to the surrounding fluid are treated. Simple formulas for the mean velocity of the solid are derived, under the assumption that the regime of the fluid flow induced by its motion is turbulent and the fluid resistance force is nonlinearly dependent on its velocity. It is shown that vibrations of a fluid’s volume slow down the motion of a submerged solid. This effect is much pronounced in the case of a deformable solid (i.e., gas bubble) exposed to near-resonant excitation. The results are relevant to the theory of gravitational enrichment of raw materials, and also contribute to the theory of controlled locomotion of a body with an internal oscillator in continuous deformable (solid or fluid) media.

Particle-based simulation and visualization of fluid flows through porous media

Abstract: We propose a method of fluid simulation where boundary conditions are designed in such a way that fluid flow through porous media, pipes, and chokes can be realistically simulated. Such flows are known to be low Reynolds number incompressible flows and occur in many real life situations. To obtain a high quality fluid surface, we include a scalar value in isofunction. The scalar value indicates the relative position of each particle with respect to the fluid surface.

Difference schemes on triangular and tetrahedral grids for Navier-Stokes equations of incompressible fluid

Abstract: New approximations of Navier-Stokes equations are proposed for incompressible fluid on triangular and tetrahedral grids in the predictor-corrector method. Estimates are presented for the unconditional stability of difference schemes, and calculation results for a two-dimensional problem about a fluid flow in a cavity with a floating top cover; and they are compared with the solutions of other authors. The problems of grid equations monotonization are discussed.

Fluid Structure Interactions for Tube Bundles: Physical Meaning of a Rayleigh Damping

Abstract: It is well known that a fluid may strongly influence the dynamic behaviour of a structure. Many different physical phenomena may take place, depending on the conditions: fluid flow, fluid at rest, small or high displacements of the structure. Inertial effects can take place, with lower vibration frequencies, dissipative effects also, with damping, instabilities due to the fluid flow (Fluid Induced Vibration). In this last case the structure is excited by the fluid. The paper deals with the vibration of tube bundles under a seismic excitation or an impact. In this case the structure moves under an external excitation, and the movement is influenced by the fluid. The main point in such system is that the geometry is complex, and could lead to very huge sizes for a numerical analysis. Important developments have been made in the last years to develop homogenization methods for the dynamic behaviour of tube bundles. The numerical size of the problem is reduced, and it is possible to make numerical simulations on large tube bundles with reasonable computer times. These methods consider that the fluid movement is governed by the Euler equations for the fluid. They are based on an analysis on an elementary cell, corresponding to one tube, and on an expression of the forces applied by the fluid to the structure. This force only depends on the fluid’s and tube’s acceleration. Only “inertial effects” will theoretically take place, with globally lower frequencies. A research program is under progress to take into account dissipative effects also, with a homogenization of the Navier-Stokes equations in the tube bundle. It is common, in numerical simulations, to add a damping for the structures by using a global Rayleigh damping. The paper deals with the physical meaning of this Rayleigh damping in the Euler homogenized equations. It can be demonstrated that this damping corresponds to a force applied by the fluid to the structure depending not only on the acceleration, but on the fluid and structure velocity also. This Rayleigh damping is a first step to take into account the dissipative effects for FSI in tube bundles.Copyright © 2010 by ASME

Spinnability simulation of viscoelastic fluid

Abstract: One of the most challenging issues of computer graphics is to represent the behavior of fluid. Visualizing the fluid behavior requires to solve Navier-Stokes equations, which take huge amount of time so that some researches use many super computers for the simulation, and others utilize the GPU performance. The common fluid is Newtonian that can be described by a single constant value of viscosity, and there are many researches related to Newtonian. On the other hand, there is another type of fluid called non-Newtonian that cannot be described easily, and one of non-Newtonians is viscoelactic fluid. Viscoelastic fluid has the characteristics of both viscosity of fluid and elasticity of solid, and it is difficult to represent the behavior of viscoelastic fluid. [Goktekin et al. 2004] represented the behavior of viscoelastic fluid. His technique is based on Eulerian methods and added elastic terms to Navier-stokes equations, which govern fluid behavior. [Clavet et al. 2005] used particle method for representing fluid behavior. Particle method can represent fine behavior of the fluid such as rain drops, fountains, clay manipulation. Their researches could visualize many types of behavior of viscoelastic fluid, however, they cannot represent the spinnability, which has three characteristics: 1) it stretches very thin as if it is a string, 2) the radius is getting smaller gradually from the both ends and the center part has the least radius, and 3) it shrinks rapidly as if it is a rubber.

A Compressible Fluid Model for Traffic Flow and Nonlinear Saturation of Perturbation Growth

Abstract: In this paper, we have proposed a new compressible fluid model for the one-dimensional traffic flow taking into account the reaction time of drivers, which is based on the actual measurements. This model is a generalization of Payne model by introducing a density-dependent function of reaction time. The linear stability analysis of this new model shows the instability of homogeneous flow around a critical density of vehicles. Moreover, the condition of the nonlinear saturation of density against small perturbation is derived from the analysis by using reduction perturbation method.

Method for determining local flow rates of e.g. air, involves spatially and temporarily limiting energy of external fluid in flowing fluid or refractive index of flowing fluid to generate density fluctuation in flowing fluid

Abstract: The method involves receiving captured images of fluid (3) flowing through a background object (10) i.e. stochastic dot pattern (11), simultaneously from different directions. The captured images are compared to spatial displacement of density fluctuation (8) in the fluid. Energy of external fluid in the flowing fluid or refractive index of the flowing fluid is spatially and temporarily limited for generating the density fluctuation in the flowing fluid, where the energy of the external fluid is time punctually brought into the flowing fluid. An independent claim is also included for a device for determining local flow rates of flowing fluid, comprising a camera.

Three‐Dimensional Shape Identification of a Body Located in Fluid Flow

Abstract: This study presents a numerical method of shape identification of the body located in viscous flow. The purpose of this study is to determine the shape of body located in a viscous flow, where the applied fluid force is minimized. In this study, the formulation to obtain the optimal shape is based on the optimal control theory. The finite element method is used for the calculation of fluid flow. In this study an optimal control is treated as fluid force minimization. Therefore, fluid forces are used in the performance function directly. The shape identification must be carried out satisfying the state equation. Therefore, the minimization with constraint condition is required. In this study, the Lagrange multipliers are introduced for the constraint minimization problem. In this study, an optimized shape of a body is obtained by computation. In the optimizing computation, a sphere is set into the computational domain as initial shape.

A Fluid Dynamics Study of a Modified Low-Reynolds-Number Flapping Motion

Abstract: The objective of the present study is to investigate the low Reynolds number (LRN) fluid dynamics of an elliptic airfoil performing a novel figure-eight-like motion. To this mean, the influence of phase angle between the pitching and translational (heaving and lagging) motions and the amplitude of translational motions on the fluid flow is simulated. Navier-Stokes (NS) equations with Finite Volume Method (FVM) are used and the instantaneous force coefficients and the fluid dynamics performance, as well as the corresponding vortical structures are analyzed. Both the phase angle and the amplitudes of horizontal and vertical motions are of great importance to the fluid dynamic characteristics of the model as they are shown to change the peaks of the fluid forces, fluid dynamic performance, and the vortical patterns around the model.Copyright © 2010 by ASME