Numerical Modeling Of Fluid Flow Research Articles

Numerical Modeling of Fluid Flow and Thermal Behavior of Different Nanofluids on a Rotating Disk

The thermal and velocity profiles of various nanofluid systems on a rotating disk are simulated. Finite difference method, the orthogonal collocation method, and the differential quadrature method (DQM) of numerical approaches are used to solve the governing equations and are compared to determine the faster and more accurate solution procedure. Five nanoparticles Al, Al2O3, Cu, CuO, and TiO2 solved in three base fluids water, ethylene glycol, and engine oil are considered to be used on the disk at different volume fractions. A new general algorithm is presented for solving equations of a rotating‐disk problem quickly and accurately and it is found that the DQM method is the best approach for this numerical simulation. Heat transfer performance of a rotating disk would be much better enhanced with water based Al nanofluid. A wide range of results for different base–fluid combinations with nanoparticles is presented with untransformed 3D results and effects of the variation of different parameters provides comprehensive insight and prevents inaccurate deductions.

Anisotropy estimation of compacted municipal solid waste using pressurized vertical well liquids injection.

Waste hydraulic conductivity and anisotropy represent two important parameters controlling fluid movement in landfills, and thus are the key inputs in design methods where predictions of moisture movement are necessary. Although municipal waste hydraulic conductivity has been estimated in multiple laboratory and field studies, measurements of anisotropy, particularly at full scale, are rare, even though landfilled municipal waste is generally understood to be anisotropic. Measurements from a buried liquids injection well surrounded by pressure transducers at a full-scale landfill in Florida were collected and examined to provide an estimate of in-situ waste anisotropy. Liquids injection was performed at a constant pressure and the resulting pore pressures in the surrounding waste were monitored. Numerical fluid flow modeling was employed to simulate the pore pressures expected to occur under the conditions operated. Nine different simulations were performed at three different lateral hydraulic conductivity values and three different anisotropy values. Measured flowrate and pore pressures collected from conditions of approximate steady state were compared with the simulation results to assess the range of anisotropies. The results support that compacted municipal waste in landfills is anisotropic, provide anisotropy estimates greater than previous measurements, and suggest that anisotropy decreases with landfill depth.

Simulation of free surface flows using volume of fluid method and genetic algorithm

In this paper, details of a numerical model development for simulation of fluid flows with moving free surface are presented. The unsteady incompressible Navier–Stokes equations on a fixed grid system are used to obtain velocity and pressure values in the computational domain and volume of fluid (VOF) method is used to determine free surface location. In order to reduce numerical smearing and increase accuracy of numerical modeling of fluid flow with moving free surface, a new free surface-tracking method is proposed. The proposed method is a combination of genetic algorithm and free surface tracking method based on donor and acceptor scheme. The specification of the new combinational method can be summarized in determining orientation vector and plane constant to represent the free surface orientation in each cell. The proposed algorithm can be easily used in any unstructured grids. In this method, the fluid flow equations are explicitly discretized with the finite volume method and the projection method is used to determine the velocity and pressure magnitude in computational domain. Validity of the new solution algorithm is demonstrated through its application to the dam break and the bore motion examples.

Numerical Modelling of Fluid Flow and Thermal Phenomena in the Tundish of CSC Machine

Abstract The mathematical and numerical simulation model of the liquid steel flow in a tundish is presented in this paper. The problem was treated as a complex and solved by the finite element method. The single-strand slab tundish is used to continuous casting slabs. The internal work space of the tundish was modified by the following flow control devices. The first device was a striker pad situated in the pouring tundish zone. The second device was a baffle with three holes and the third device was a baffle without hole. The main purpose of using these devices was to cause a quiet liquid mixing as well as give directional metal flow upwards which facilitated inclusion floatation. The interaction of flow control devices on hydrodynamic conditions was received from numerical simulation. As a result of the computations carried out, the liquid steel flow and steel temperature fields were obtained. The influence of the tundish modification on velocity fields in the liquid phase of steel was estimated, because these have an essential influence on high quality of a continuous steel cast slab.

Numerical Modeling of Fluid Flow and Solidification Characteristics of Ultrasonically Processed A356 Alloys

Numerical Modeling of Fluid Flow and Solidification Characteristics of Ultrasonically Processed A356 Alloys

Pore-scale simulation of intragranular diffusion: Effects of incomplete mixing on macroscopic manifestations

[1] Diffusive mass transfer into and out of intragranular micropores (“intragranular diffusion”) plays an important role in the transport of some groundwater contaminants. We are interested in understanding the combined effect of pore-scale advection and intragranular diffusion on solute transport at the effective porous medium scale. We have developed a 3-D pore-scale numerical model of fluid flow and solute transport that incorporates diffusion into and out of intragranular pore spaces. A series of numerical experiments allow us to draw comparisons between macroscopic measures computed from the pore-scale simulations (such as breakthrough curves) and those predicted by multirate mass transfer formulations that assume complete local mixing at the pore scale. In this paper we present results for two model systems, one with randomly packed uniform spherical grains and a second with randomly packed spheres drawn from a binary grain size distribution. Non-Fickian behavior was observed at all scales considered, and most cases were better represented by a multirate mass transfer model even when there was no distinct secondary porosity (i.e., no intragranular diffusion). This suggests that pore-scale diffusive mass transfer processes between preferential flow paths and relatively immobile zones within the primary porosity may have significant impact on transport, particular in low-concentration tails. The application of independently determined mass transfer rate parameters based on an assumption of well-mixed concentrations at the pore scale tends to overestimate the amount of mass transfer that occurs in heterogeneous pore geometries in which preferential flow leads to incomplete pore-scale lateral mixing.

Numerical modelling of fluid flow through unsaturated zone using a dual-porosity approach

In this study, an attempt has been made to model fluid flow through a geological unit consisting of sandy-clay and clayey soil with significant macro pores. Considering such a geological formation using a single-continuum approach may not always be justified as the porosity and permeability contrast between the soil matrix and macro pore vary by several orders of magnitude and not by a scale factor. Under such circumstances, deducing the mean values of parameters such as porosity and permeability using conventional Representative Elementary Volume from a single continuum becomes nearly impossible. For this purpose, a numerical model has been developed to investigate the consequences of applying both equilibrium model or Single-Porosity Medium (SPM) and non-equilibrium model or Dual-Porosity Medium (DPM) approaches for the same soil types. Numerical results suggest that the depths associated with soil moisture fronts are significantly different by applying a dual continuum approach with reference to the conventional single-continuum approach.

Use of cosmogenic 129I to constrain numerical models of fluid flow in marine sediments: Application to the Blake Ridge Hydrate Province

AbstractConcentrations of cosmogenic iodine, 129I, in the pore fluid of marine sediments often indicate that the pore fluid is much older than the host sediment, even when vertical flow due to sediment compaction is taken into account. Old pore fluid has been used in previous studies to argue for pervasive upward fluid flow and a deep methane source for hydrate deposits. Alternatively, old pore fluid age may reflect more complex flow patterns. We use a two‐dimensional numerical transport model to account for the effects of topography and fractures on pore fluid pathlines when sediment permeability is anisotropic. We find that fluid focusing can cause significant lateral migration as well as regions where downward flow reverses direction and returns toward the seafloor. Longer pathlines can produce pore fluid ages much older than that expected with a one‐dimensional compaction model. For steady‐state models with geometry representative of Blake Ridge (USA), a well‐studied hydrate province, we find pore fluid ages beneath regions of topography and within fractured zones that are up to 70 Ma old. Our results suggest that the measurements of 129I/127I reflect a mixture of new and old pore fluid. However, old pore fluid need not originate at great depths. Methane within pore fluids can travel laterally several kilometers, implying an extensive source region around the deposit. This type of focusing should aid hydrate formation beneath topographic highs.

Estimation of a semi-physical GLBE model using dual EnKF learning algorithm coupled with a sensor network design strategy: Application to air field monitoring

In this paper, we present the fusion of two complementary approaches for modeling and monitoring the spatio-temporal behavior of a fluid flow system. We also propose a mobile sensor deployment strategy to produce the most accurate estimate of the true system state. For this purpose, deterministic and statistical information was used. We adopted a filtering method based on a semi-physical model which derives from a fluid flow numerical model known as lattice Boltzmann model (LBM). The a priori physical knowledge was introduced by the Navier–Stokes equations which were discretized by the lattice Boltzmann approach. Moreover, its multiple-relaxation-time (MRT) variant not only improved the stability, but also enabled the introduction of additional degrees of freedom to be estimated like the synaptic weights of a neural network. The statistical knowledge was then introduced into the model by performing a sequential learning of these parameters and an estimation of the speed field of the fluid flow starting from measurements. The low spatial density of measurements, the large amount of data inherent to environmental issues and the nonlinearity of the generalized lattice Boltzmann equations (GLBEs) enjoined us to use the ensemble Kalman filter (EnKF) for the recursive estimation procedure. A dual state-parameter estimation which results in a significantly reduced computation time was used by combining two filters consecutively activated in the same iteration. Finally, we proposed to complete the lack of spatial information of the sparse-observation network by adding a mobile sensor, which was routed to the location where the cell-by-cell output estimation error was the highest. Experimental results in the context of the standard lid-driven cavity problem revealed the presence of few zones of interest, where fixed sensors can be deployed to increase performances in terms of convergence speed and estimation quality. Finally, the study showed the feasibility of introducing some additional parameters which act as degrees of freedom, to perform large-eddy simulation of turbulent flows without numerical instabilities.

Cell culture using centrifugal microfluidic platform with demonstration on Pichia pastoris

This paper discusses the vortical flow, mixing and cell culture of Pichia pastoris using a centrifugal microfluidic (CM) chamber. The resultant "spiral toroidal vortex" in the chamber is made up of a primary vortex induced from inertial acceleration/deceleration of the chamber superposed by a secondary toroidal vortex due to Coriolis acceleration acting on the primary vortex. A validated numerical fluid-flow model with minimized numerical diffusion effect has been developed to investigate the flow and consequently mixing of two-color liquids through cyclic constant acceleration-and-deceleration in the same rotation direction until homogeneous mixing of the two liquids in the CM chamber has been established. The specific mixing time is found to improve with increase in acceleration/deceleration and angular span of the chamber. An experimental CM platform with three cell-culture chambers of different angular spans has been built and Pichia pastoris cell culture has been successfully demonstrated. Cell growth can be monitored over time on the extracted samples by measuring the optical density at 600-nm wave-length. Comparing with conventional cell culture, Pichia pastoris cultured on CM platform exhibits a very short lag (cell preparation/budding) phase prior to the log phase (cell growth). While it takes 8 to 12 h for the conventional shake flask in the lag phase, it takes only 2 h for the CM platform irrespective of initial cell concentration (8.1 × 10(4) to 8.1 × 10(5)/ml), acceleration/deceleration (10 to 32/s(2)) and angular span of the culture chamber (π/12 to π/4), representing significant time reduction. This is largely attributed to better growth conditions due to enhanced mixing and appropriate shear-stress stimulation from the efficient spiral toroidal vortex.

Effect of tumor shape and size on drug delivery to solid tumors

Tumor shape and size effect on drug delivery to solid tumors are studied, based on the application of the governing equations for fluid flow, i.e., the conservation laws for mass and momentum, to physiological systems containing solid tumors. The discretized form of the governing equations, with appropriate boundary conditions, is developed for predefined tumor geometries. The governing equations are solved using a numerical method, the element-based finite volume method. Interstitial fluid pressure and velocity are used to show the details of drug delivery in a solid tumor, under an assumption that drug particles flow with the interstitial fluid. Drug delivery problems have been most extensively researched in spherical tumors, which have been the simplest to examine with the analytical methods. With our numerical method, however, more complex shapes of the tumor can be studied. The numerical model of fluid flow in solid tumors previously introduced by our group is further developed to incorporate and investigate non-spherical tumors such as prolate and oblate ones. Also the effects of the surface area per unit volume of the tissue, vascular and interstitial hydraulic conductivity on drug delivery are investigated.

Basset force in numerical models of saltation / Bassetova síla v numerických modelech saltace částic

In numerical models of fluid flow with particles moving close to solid boundaries, the Basset force is usually calculated for the particle motion between particle-boundary collisions. The present study shows that the history force must also be taken into account regarding particle collisions with boundaries or with other particles. For saltation - the main mode of bed load transport - it is shown using calculations that two parts of the history force due to both particle motion in the fluid and to particle-bed collisions are comparable and substantially compensate one another. The calculations and comparison of the Basset force with other forces acting on a sand particle saltating in water flow are carried out for the different values of the transport stage. The conditions under which the Basset force can be neglected in numerical models of saltation are studied.

Flow in a Single Stage Centrifugal Fan With Vaneless Diffuser and Peripheral Louver Outlets

This paper presents an analysis on the air flows in a single stage centrifugal fan with a vaneless diffuser and peripheral louver outlets. The performance data of the fan are obtained experimentally. A numerical fluid flow model is developed. The agreements between the numerical and experimental results are reasonably good. The performances of the fan under various working conditions are explained by the flow structures and pressure distributions. Flow energy analysis shows that the major energy losses in the fan are the impeller loss, the diffuser loss, and the gap leakage loss. Suggestions on the design and application of fans with such architecture are given.

A numerical investigation of vapor intrusion — The dynamic response of contaminant vapors to rainfall events

The U.S. government and various agencies have published guidelines for field investigation of vapor intrusion, most of which suggest soil gas sampling as an integral part of the investigation. Contaminant soil gas data are often relatively more stable than indoor air vapor concentration measurements, but meteorological conditions might influence soil gas values. Although a few field and numerical studies have considered some temporal effects on soil gas vapor transport, a full explanation of the contaminant vapor concentration response to rainfall events is not available. This manuscript seeks to demonstrate the effects on soil vapor transport during and after different rainfall events, by applying a coupled numerical model of fluid flow and vapor transport. Both a single rainfall event and seasonal rainfall events were modeled. For the single rainfall event models, the vapor response process could be divided into three steps: namely, infiltration, water redistribution, and establishment of a water lens atop the groundwater source. In the infiltration step, rainfall intensity was found to determine the speed of the wetting front and wash-out effect on the vapor. The passage of the wetting front led to an increase of the vapor concentration in both the infiltration and water redistribution steps and this effect is noted at soil probes located 1m below the ground surface. When the mixing of groundwater with infiltrated water was not allowed, a clean water lens accumulated above the groundwater source and led to a capping effect which can reduce diffusion rates of contaminant from the source. Seasonal rainfall with short time intervals involved superposition of the individual rainfall events. This modeling results indicated that for relatively deeper soil that the infiltration wetting front could not flood, the effects were damped out in less than a month after rain; while in the long term (years), possible formation of a water lens played a larger role in determining the vapor intrusion risk. In addition, soil organic carbon retarded the transport process, and damped the contaminant concentration fluctuations.

Numerical Simulation of Temperature Field for Laser Clad Composite Coatings

A three dimensional quasi-state numerical model of fluid flow ,heat transfer process in the melted pool for composite coating was developed ,and the temperature profile were successfully calculated by finite element software. Numerical results show that when the laser power is 1.5KW, the coating melts and the matrix does not melt, forming good shape; when the laser power is 1.6KW, the thermal stress increase, the binding of substrate and coating occurs crack, the experiment is agreement with that calculated.

The Application of Horizontal and Vertical Well Patterns During Polymer Flood Processes in Anisotropic Reservoirs

Using horizontal wells in a polymer flood process, higher sweep efficiency is expected compared with the use of conventional patterns by vertical wells. However, the use of horizontal wells is very sensitive to the well pattern designed to operate the process. This article presents an analysis of how the overall performance of a polymer flood process is influenced by the well pattern using a horizontal injector and producer in different configurations. A three-dimensional numerical model for fluid flow and mass transport is used to analyze the performance of the reservoir. The potential for a horizontal well application was assessed through different scenarios in combinations of injection and production wells and reservoir anisotropy. Results from the study have demonstrated that a significant amount of additional oil can be recovered and injectivity was remarkably improved by utilizing a combination of horizontal wells. The improvement of injectivity through a horizontal injection well was higher when it was combined with a horizontal producer parallel to the injector. The overall performances in anisotropic reservoirs strongly depend on the type of wells considered and the orientation of the horizontal wells with respect to the permeability directions. A combination of horizontal wells placed parallel to the low permeability direction yields the best performance.

Multi-objective design optimization of a micro heat sink for Concentrating Photovoltaic/Thermal (CPVT) systems using a genetic algorithm

An optimization methodology for a microchannel, plate-fin heat sink suitable for the cooling of a linear parabolic trough Concentrating Photovoltaic/Thermal (CPVT) system is applied in this study. Two different microchannel configurations are considered, Fixed (FWμ) and stepwise Variable-Width (VWμ) microchannels respectively. The performance evaluation criteria comprise the thermal resistance of the heat sink and the cooling medium pressure drop through the heat sink. Initially, the effect of the geometric parameters on the heat sink thermal and hydrodynamic performance is investigated using a thermal resistance model and analytical correlations, in order to save computational time. The results of the 1-D model enable the construction of surrogate functions for the thermal resistance and the pressure drop of the heat sink, which are considered as the objective functions for the multi-objective optimization through a genetic algorithm that leads to the optimal geometric parameters. In a second step, a 3-D numerical model of fluid flow and conjugate heat transfer for the optimized FWμ heat sink is developed in order to investigate in detail the flow and thermal processes. The overall analysis demonstrates that microchannel heat sinks achieve very low values of thermal resistance and that the use of variable-width channels can significantly reduce the pressure drop of the cooling fluid. Furthermore, it is proven that the 1-D model is capable of providing a good estimate of the behavior of the heat sink.

Numerical Modeling of Fluid Flow in RH Vacuum Refining Process

In this paper, the internal flow field of RH degasser was studied by numerical simulation. The range of the reasonable gas-inlet velocity which is related to the lift gas flow rate was obtained, then the results of two different gas-inlet velocities which are the reasonable velocity and the unreasonable velocity were chosen to be analyzed. Many vortexes and some differences of the flow fields were found in the RH degasser with the two different velocities. Through these results the development of the flow field could be got and it is valuable for the production in factory.

Numerical modeling of fluid and particle behaviors in impact pulverizer

Numerical modeling of fluid flow and individual particle motion in an impact pulverizer was conducted using a Computational Fluid Dynamics (CFD)–Discrete Phase Model (DPM) coupling model. The impact pulverizer used is a dry system. Its grinding chamber consists of high-speed rotating hammers and a static concavo–convex stator. First of all, calculated results of fluid pressure in the grinding chamber were compared with the experimental ones, showing the both results were in good agreement. The fluid flow in the grinding chamber indicated that the fluid mainly swirled in the direction of the hammer rotation. The fluid flow pattern in the concaves of the stator was also swirling flow, while its velocity was much lower than that in the outside of the concaves. Analyses of the particle motion suggested that the particles were accelerated by the fluid drag force caused by the rotating hammers but not by the impact force from the hammers, resulting in impacts with the static stator at the velocity 1.4 times higher than the tip speed of hammers. The velocities and frequencies of the particle impacts with the walls of the grinding chamber were also investigated under various rotor speeds and particle sizes. As the particle size was smaller, the particle impacts with the stator were not likely to occur, and a decrease of the impact velocity was observed despite the same rotor speed. It was because the particle velocity decreased before impact with the stator due to the fluid resistance force acting on the particle in the concave. The fluid resistance force was proportional to the square of the particle size. By constant, an inertia force of the particle was proportional to the particle mass, which was equivalent to the cube of the particle size. Accordingly, the velocity of particle impact with the stator was lower when particle size was smaller. These calculated results implied that the limitations of ground particle size existed because of the decrease in the frequency and velocity when particle size was smaller.

Microscopic numerical model of fluid flow in granular material

A microscopic numerical model of fluid flow through granular materials using the discrete-element method is developed to take account of the effect of particle movement. The scheme solves for fluid pressure in void spaces surrounded by the particle elements used in the discrete-element method to consider the compressibility of fluid during particle movement and diffusion, that is flow across void spaces in a one-dimensional form of Darcy's law. The calculated fluid pressure is applied to particles involved in the void space as a body force proportional to the occupied area in the space. This microscopic two-way coupling method enables the analysis of the microscopic mechanical characteristics of granular materials associated with fluid, as many problems in geotechnics involve such interactions between particles and a pore fluid. The approach can be applied in situations with undrained dynamic loading inducing excess pore water pressure and subsequent liquefaction. The paper first describes the formulation and the numerical scheme, then two-dimensional simulations are conducted to validate the scheme.