Showing papers on "Fluid parcel published in 2003"

On the steady flow of compressible viscous fluid and its stability with respect to initial disturbance

Abstract: We consider a compressible viscous fluid effected by general form external force in R3. In part 1, an analysis of the linearized problem based on the weighted- L2 method implies a condition on the external force for the existence and some regularities of the steady flow. In part 2, we study the stability of the steady flow with respect to the initial disturbance. What we proved is: if H3-norm of the initial disturbance is small enough, then the solution to the non-stationary problem exists uniquely and globally in time.

A Modeling of Compressible Droplets in a Fluid

Abstract: In this work, we are interested in a complex fluid-kinetic model that aims to take into account the compressibility of the droplets of the spray. The ambient fluid is described by Euler-like equations, in which the transfer of momentum and energy form the droplets is taken into account, while the spray is represented by a probability density function satisfying a Vlasov-like equation. Implicit terms crop up because of the compressibility of the droplets. After having derived the model, we prove that golbal conservations are satisfied. Then we present two numerical tests. The first one enables us to validate the numerical code, while the second one is performed in a physically realistic situation.

Limitations of using an equilibrium approximation in an aerosol activation parameterization

Abstract: [1] Because of its complex nature, attempts have been made to parameterize the process of cloud droplet formation and growth. The parameterization developed by Abdul-Razzak et al. [1998] and Abdul-Razzak and Ghan [2000], henceforth referred to as the ARG parameterization, is based on the adiabatic ascent of an air parcel, assuming that each particle is in equilibrium with its environment. Some of the limitations of the equilibrium assumption are evaluated here through direct comparison of a kinetic parcel model with the ARG parameterization. Conditions are described in which the supersaturation and the cloud droplet number concentration are underpredicted by the parameterization. The underprediction happens because of an overestimation of the condensation rate of water onto the larger particles. The effect is significant for conditions of lower updraft velocities (V 500 cm−3). The parameterization behaves well for higher updraft velocities and lower aerosol number concentrations. The impact of this effect on the activation of sulfate aerosols in the presence of sea salt aerosol is also investigated. Using the ARG parameterization to diagnose Nd in the presence of sea salt aerosol leads to a greater reduction in the number of activated sulfate particles in lower updraft conditions than does using the kinetic parcel model. The relative contribution of sulfate particles to total Nd is also significantly lower for the ARG parameterization than it is for the parcel model in low to moderate updrafts. The error in the first indirect radiative forcing introduced by the equilibrium assumption is estimated to be 6 to 15 W m−2 for typical marine clouds, depending on the updraft velocity.

The Shape of Moving Boundary of Fluid Flow in Sandstone: Video Microscopic Investigation and Stochastic Modeling Approach

Abstract: Many engineering problems such as exploitation of petroleum and gas, deposition of nuclear waste, and groundwater contamination by organic liquids are closely related to the movement of fluid in rocks. In this paper, a video microscope is employed to investigate the shape of moving front boundary of fluid flow in sandstone. The experimental results show that the fronts of the moving boundary display a fractal behavior. Based on the experimental results, a stochastic differential equation is proposed to describe the moving boundary. By decomposing the velocity of a given point into a drift term and a fluctuation term, the effect of the mesoscope structure of porous media on fluid flow is taken into account. The stochastic approach is in agreement with the experimental results. The analysis shows that the front of the moving boundary of fluid flow in rocks is a comprehensive result caused by the average tendency of fluid flow, which can be described by the classical Darcys Law, and the fluctuation tendency of fluid flow, which is closely related to the mesoscope structure of rocks.

Simulation, Modelling and Rendering of Incompressible Fluids in Real Time

Abstract: In this paper we present techniques for the real-time simulation and rendering of liquids. Appropriate approximations to a full 3D simulation are applied to reduce the numerical complexity. Fluid flow is described by the 2D Navier-Stokes equations; wave effects are represented according to the wave equation for shallow water waves on a height-field. A novel mechanism for coupling flow and wave behaviour is introduced to efficiently handle transport along a fluid flow and accurate wave propagation on the fluid surface. An additional noise-based animation of detailed fluid structures further improves the realistic appearance. Rendering makes use of fragment operations on consumer-level GPUs to allow for a physically guided representation of reflection, refraction and Fresnel blending of light.

Choice and Limits of a Fluid Model for the Numerical Study in Dynamic Fluid Structure Interaction Problems

Abstract: This paper is related to the study of a nuclear propulsion reactor prototype for the French Navy. This prototype is built on ground and is to be dimensioned toward seismic loading. The dynamic analysis takes the coupled fluid structure analysis into account. The basic fluid models used by design engineers are inviscid incompressible or compressible. The fluid can be described in a bidimensional by slice or a three-dimensional approach. A numerical study is carried out on a generic problem for the linear FSI dynamic problem. The results of this study are presented and discussed. As a conclusion, the three-dimensional inviscid incompressible fluid appears to be the best compromise between the description of physical phenomena and the cost of modeling. The geometry of the reactor is such that large displacements of the structure in the fluid can occur. Therefore, the linearity hypothesis might not be longer valid. The case of large amplitude imposed oscillating motion of a cylinder in a confined fluid is numerically studied. A CFD code is used to investigate the fluid behavior solving the NAVIER -STOKES equations. The forces induced on the cylinder by the fluid are computed and compared to the linear solution. The limit of the linear model can then be exhibited.Copyright © 2003 by ASME

Equilibrium temperature of moist air parcel due to competitive growth of cloud droplet on cloud condensation nuclei

Abstract: Taking account of the variation of the water vapor content and the temperature in the air parcel, a new model for the estimation of the cloud droplet size, the temperature and the saturation ratio has been developed by modifying traditional Kohler model for the equilibrium state. The modification of Kohler model is based on the mass and the heat conservation laws for the water (vapor and liquid) in the air parcel. Variations of size, temperature and saturation ratio with number density of CCN are simulated numerically. The results of simulations show that the temperature variation of the cloud droplet and air parcel is so small to change the values of physical properties but large enough to make the air parcel unstable (or convective) in the atmosphere.

Air parcel random walk and droplet spectra broadening in clouds.

Abstract: We study the effect of turbulent flow on the droplet growth in a cloud during the condensation phase. Using the air parcel model, we describe analytically how the size distribution of droplets evolves at the different stages of parcel movement. We show that turbulent random walk superimposed on an accelerated ascent of the parcel makes the relative width of droplet distribution to grow initially as ${t}^{1/2}$ and then decay as ${t}^{\ensuremath{-}3/2}.$

Ghost Fluid Method and Computation of Compressible Two-fluid Flows

Abstract: Compressible two\|fluid inviscid flow is computed by the Ghost Fluid method with Isobaric fix.The method can avoid numerical oscillation and smearing as is encountered with a shock\|capturing scheme in computing fluid interface,and it is simpler to code than fronttracking techniques.The system of the Euler equations which describes the fluid flow and the level set equation which describes the interface motion is solved by high\|resolution WENO finite difference scheme.Satisfatory results are obtained for several 1D and 2D compressible two\|fluid flows subject to the stiffened equation of state.

Spatial discretization issues for the energy conservation in compressible flow problems on moving grids

Abstract: The prediction of interaction phenomena between a compressible flow in a moving domain and other models like structural ones requires that some conservation properties need to be satisfied by the numerical schemes. In this paper we investigate the important problem of the work-energy conservation within the fluid for the discrete formulation on moving grids. In the case of a compressible flow, the work performed on the fluid by the moving interface has to be properly translated in a variation of the total fluid energy. We present a numerical model that satisfies this energy conservation property without loosing some other conservation properties such as the Geometric Conservation Law.

Estimation of Equilibrium Radius of Cloud Droplet Competitively Grown in Air Parcel Containing Multi-Sized Cloud Condensation Nuclei

Abstract: ABSTRACT; Usually, for the estimation of the cloud droplet size in the equilibrium state , Kohler equation is utilized, assuming constant vapor pressure and constant temperature . However, consumption of the ambient vapor due to condensational growth decreases the ambient water vapor pressure and increases the temperature. Taking account of the variations of the water vapor content and the temperature , a new model for the estimation of the equilibrium cloud droplet size , saturation ratio and temperature has been developed with use of the mass and the heat conservation laws . These laws are applied for the control volume of the air parcel which contains multi-sized CCN. Variations of droplet size , decrement of saturation ratio and increment of temperature with CCN composition (size and number) in air parcel are simulated numerically. The results of numerical simulations with this model show that competitive growth of droplets on multi-sized CCN is controlled by large size CCN.

Investigation into the fluid dynamics of a droplet in gas flow

Abstract: Publisher Summary In this chapter, heat and mass transfer are neglected for being able to focus on the fluid dynamical intricacies problem. The chapter aims to increase the modeling complexity in the future. The present study works as an initial step of a computational fluid dynamics (CFD)-based work, directed toward a better understanding of fluid flow, heat and mass transfer in spray combustion. The attention is focused on the fluid dynamics of an isolated liquid droplet, neglecting the heat and mass transfer. Fluid dynamics of an isolated droplet in gas flow is computationally investigated. It has been shown that the flow around droplets may significantly differ from that of solid spheres, and the drag coefficient correlations originally based on the solid sphere data may not adequately be applied to describe the behavior of droplets in gas flow. It has been shown that the flow patterns around a solid sphere and a liquid droplet may considerably differ. This results in differences in the drag coefficients as the liquid droplet drag coefficient can be approximately 5-15% lower depending on the Reynolds number.

BEM for compressible fluid dynamics

Abstract: The fully developed boundary element method (BEM) numerical model of compressible fluid dynamics is presented. In particular, the singular boundary domain integral approach, which has been established for the viscous incompressible flow problem, is modified and extended to capture the compressible fluid state. As test cases a natural convection of compressible fluid in a closed cavity and an L-shape cavity are studied. This paper deals with a BEM numerical scheme developed for simulation of motion of compressible viscous fluid. The method is based on the approximate solution of the set of Navier-Stokes equations in the velocity-vorticity formulation. Particular attention is given to proper transformation of the governing differential equations into corresponding integral representations, which satisfy the continuity equation exactly, e.g. velocity and mass density field functions. The pressure field is computed by using the Poisson equation for pressure for known velocity, vorticity and mass density functions. 2 Conservation laws

On unsteady two-phase fluid flow due to eccentric rotation of a disk

Abstract: We examine the unsteady flow of a two-phase fluid generated by the nontorsional oscillations of a disk when the disk and the fluid at infinity rotate noncoaxially with the same angular velocity. The solutions are obtained for both the fluid and the particle velocities in closed form. It is found that the solutions remain valid for all values of the frequency of oscillations of the disk including the resonant frequency, which is equal to the angular velocity of rotation. But, in absence of particles, only in the case of resonance no oscillatory solution is possible, which is similar to that of solid-body rotation as pointed out by Thornley (1968). It is also shown that, unlike the case of single-disk configuration, no unique solution exists in a double-disk configuration, a result which is the reverse to that of solid-body rotation. Finally, the results are presented graphically to determine the quantitative response of the particle on the flow. 2000 Mathematics Subject Classification: 76B10. 1. Introduction. The dynamics of rotating fluids is particularly important in the analysis of flow phenomena associated with the atmospheric, oceanic, geophysical, and astrophysical problems. Thornley [3] investigated the flow generated in a semi-infinite expanse of viscous fluid bounded by the infinite rigid disk in the presence of the particles in the fluid. However, if the fluid is clean, no physically meaningful resonant solutions are possible in the existing flow configuration, which is an event similar to that of Thornley [3]. Moreover, it is found that, contrary to the case of single-disk geometry, infinite number of solutions exist for the flow confined between two noncoaxially rotating parallel disks. Finally, the results are evaluated quantitatively with a view to examine the effect of particles on the flow. 2. Formulation of the problem. We consider the flow of a two-phase fluid due to an oscillating disk in the xy-plane rotating about the z-axis normal to the disk with an angular velocity Ω in Cartesian coordinate system. The particulate fluid at z =∞ rotates, with the same angular velocity, about an axis parallel to the z-axis passing through the point (x1 ,y 1). For this type of motion the velocity fields for the fluid and the particles may be taken in the form