Progress in Computational Fluid Dynamics, An International Journal (25 papers in press)
Benchmark simulations of flow past rigid bodies using an open-source, sharp interface immersed boundary method
by Utku Senturk, Daniel Brunner, Hrvoje Jasak, Nicoleta Herzog, Clarence W. Rowley, Alexander J. Smits
Abstract: This study reports benchmark results for a new immersed boundary method based finite-volume solver within the framework of the open-source toolbox foam-extend 3.2. The immersed boundary formulation uses a discrete forcing approach based on a weighted least squares approximation that preserves the sharpness of the boundary. Five test cases with increasing complexity are used. Results are also presented for the flow past a low-aspect-ratio plate that pitches about its leading edge at a Reynolds number of 2000. Force coefficient results are compared with available experimental and computational data. The results show that foam-extend 3.2 appears to be a promising open-source tool for solving flows with steady and unsteady immersed boundaries.
Keywords: Computational fluid dynamics; open source; OpenFOAM; immersed boundary method; discrete.
Investigation of numerical simulation of non-Newtonian flows dam break and dam breach in open channels using modified VOF method
by Esmail Lakzian, Mostafa Niazi
Abstract: This paper concerns modeling dam break flows of non-Newtonian Herschel-Bulkley (HB) fluid by using the volume of fluid (VOF) method and high resolution advection schemes. The VOF method is based on the fact that two or more fluids (or phases) are not interpenetrating. In the present study, a modified approach is used to overcome this problem. The OpenFoam software is employed and inter-Foam solver is used in two and three-dimensional model with non-Newtonian fluid. The numerical results of the present study are compared with analytical, numerical, and experimental results found in literature. The numerical code which is used showed better agreement with the experimental data than those using shallow water equations and PLIC method.
Keywords: Volume of Fluid Method (VOF); Dam Break flows; non-Newtonian Model.
Use of nanofluids as coolants in buoyancy-driven thermal management of embedded heating components of small-scale devices
by Massimo Corcione, Alessandro Quintino, Elisa Ricci, Andrea Vallati, Paweł Ocłoń
Abstract: A two-phase model based on the double-diffusive approach is used to perform a numerical study on natural convection of water-based nanofluids in square cavities partially heated at the bottom wall and cooled at both sides, assuming that Brownian diffusion and thermophoresis are the only slip mechanisms by which the solid phase can develop a significant relative velocity with respect to the liquid phase. The system of the governing equations of continuity, momentum and energy for the nanofluid, and continuity for the nanoparticles, is solved through a computational code which incorporates three empirical correlations for the evaluation of the effective thermal conductivity, the effective dynamic viscosity, and the thermophoretic diffusion coefficient, all based on literature experimental data. The pressure-velocity coupling is handled by the way of the SIMPLE-C algorithm. Numerical simulations are executed for three different nanofluids, using the diameter and the average volume fraction of the suspended nanoparticles, the cavity width, the heated fraction of the bottom wall, the average temperature, and the temperature difference imposed across the cavity, as independent variables. It is found that the cooperation between the solutal and thermal buoyancy forces results in a significant enhancement of the heat transfer performance of the nanofluid compared with the pure base liquid. Moreover, the impact of the nanoparticle dispersion into the base liquid is found to increase notably with increasing the average temperature, whereas, by contrast, the other controlling parameters have moderate or negligible effects.
Keywords: Nanofluid; Natural convection; Square enclosure; Partially-heated bottom wall; Twophase modeling; Enhanced heat transfer.
Colocated Pressure-Velocity Coupling in Finite Difference Methods
by Mikael Ersson
Abstract: A simple method to be used for colocated pressure-velocity coupling in incompressible flows is presented with a full derivation. A number of standard test cases are shown that demonstrate the ability of the method to produce accurate results. The method avoids spurious pressure oscillations while keeping the pressure Poisson equation stencil compact. This is obtained by discretizing the continuity and pressure derivatives with first order differences with opposite directions, i.e. backward difference for continuity and forward difference for pressure (BCFP). The equations are also approximated using a forward difference for continuity and a backward difference for pressure (FCBP). In order to obtain a second order approximation the mean between BCFP and FCBP is used, i.e. a central difference. The paper gives a useful alternative to existing methods for pressure-velocity coupling in Finite Difference Methods in which a staggered arrangement is not desirable.
Keywords: Finite Difference Method; FDM; Spurious Oscillations; Colocated Variable Arrangement; Collocated Variable Arrangement.
INVESTIGATION OF PEMFC PERFORMANCE WITH VARIOUS CONFIGURATIONS OF SERPENTINE AND INTERDIGITATED FLOW CHANNEL
by LAKSHMINARAYANAN VARADHARAJAN, Karthikeyan Palaniswamy
Abstract: The Proton Exchange Membrane Fuel Cell (PEMFC) performance is influenced by design and operating parameters like rib to channel width ratio (R: C), the depth of the channel, the number of passes on the flow channel, operating pressure, temperature, relative humidity and the inlet gases stoichiometric ratio. In this paper, the PEMFC performance in an effective area of 25 cm2 with various ribs to channel width ratios (R: C - 1:1, 1:2, 2:1 and 2:2) on serpentine and interdigitated flow channels was investigated numerically and experimentally. The numerical and experimental maximum power density deviation of serpentine and interdigitated flow channel results with rib to channel width 1:2 were found to be 12.16 % and 12.2 % respectively.
Keywords: Rib to channel width ratio; CFD; Operating parameters; Stoichiometric ratio; Design parameters; Serpentine flow channel; interdigitated flow channel.
Effects of magnetohydrodynamics on temperature and shock standoff distance in a supersonic flow over a blunt body
by Sanjiv Paudel, Saleen Bhattarai, Sudip Bhattrai
Abstract: Magnetohydrodynamics has been one of the promising ways of increasing efficiency of supersonic as well as hypersonic propulsion systems, mostly by applying magnetic fields over shockwaves. This paper presents the effects of magnetic fields with different strengths both along and transverse to an electrically conducting flow at Mach 2.94 over a blunt body using a density-based solver implemented with MHD equations in OpenFOAM. The solver utilizes Riemann method with an AUSM+ flux splitting technique along with limited linear interpolation. The effects of imposed magnetic field on temperature and shock standoff distance are observed. Movement of the shockwave due to the application of magnetic field on the geometry, along with a consequent change in shock standoff distance is presented in the paper. The influence of a magnetic fields direction on the Mach number of the flow is also shown. Likewise, the stagnation temperature of the blunt body is demonstrated to be independent to the direction of applied magnetic field.
Keywords: bow shock; flow control; supersonic; re-entry; OpenFOAM.
Choice of Model Parameters in Turbulent Gas-Solid Flow Simulations of Particle Classifiers
by Arun Appadurai, Vasudevan Raghavan
Abstract: Comprehensive numerical simulations of particle laden gas flows are complex in general and its complexity increases dramatically when real world equipment are modelled. In this study, several model parameters required to economically simulate such a flow in a lab-scale classifier are tested. Initially, numerical results obtained from a single-phase (gas alone) model of a static classifier are validated against experimental results from literature. For flows characterised with dominant swirl, Reynolds Stress Model is capable of predicting the measured gas velocities with reasonable accuracy. The single-phase model is further extended to two-phase by the addition of particle phase in a static separator through Lagrangian formulation. Several parameters such as turbulence dispersion, particle rough wall model and wall restitution coefficients are investigated. On comparing the numerical results against experimental data from literature, it is found that the accuracy of particle separation is improved with the inclusion of turbulence dispersion. Particle rough wall model and wall restitution coefficients are found to affect the flow of coarse particles only. The validated single-phase model is further used to simulate single-phase flow in a dynamic classifier with a rotor. The influence of rotor rotation is captured by using a multiple frames of reference model. The predicted results in terms of pressure drop across the classifier from the model are validated against the experimental results from literature. Physics involved in the flow inside a dynamic separator are explained using the simulated results.
Keywords: Gas-solid flow; swirl flow; particle separation; turbulence models; particle rough wall model; turbulence particle dispersion; multiple reference frame.
A local and fast interpolation method for mesh deformation
by Jing Tang, Mingsheng Ma, Bin Li, Pengcheng Cui
Abstract: In this study, a local interpolation approach is developed to deal with the deformation of a mesh containing structured and stretched viscous elements. A new strategy is proposed to compute the local influence distance at each movable mesh point. This strategy not only helps to exclude unnecessary donor points from the computation of the new position of the mesh point, but also gets those viscous elements stiffened appropriately such that they are no longer inverted easily. Further improvements on the efficiency of the proposed algorithm are achieved by parallelizing the algorithm and developing a bounding box technique to speed up the procedure of searching donor points. Meanwhile, the robustness of the proposed algorithm in the case of large boundary movement is enhanced by incorporating a state-of-the-art multi-step technique. Various numerical experiments are conducted, and the results show that the proposed algorithm could treat cases involving complex boundary movements at a low level of computing consumptions.
Keywords: mesh deformation; local interpolation; acceleration method; parallel algorithm.
Comparative RANS turbulence modelling of lost salt core viability in high pressure die casting
by Sebastian Kohlstädt, Michael Vynnycky, Alexander Neubauer, Andreas Gebauer-Teichmann
Abstract: In this work, the implementation of three turbulence models inside the open-rnsource C++ computational fluid dynamics (CFD) library OpenFOAM were tested in 2Drnand 3D to determine the viability of salt cores in high pressure die casting. A finite-volume and volume of fluid approach was used to model the two-phase flow of molten metal and air, with the latter being treated as compressible. Encouragingly, it is found that, although the choice of turbulence model seems to affect the dispersion of the two-phase interface, the force acting at the surface of the salt core depends only very weakly on the turbulence model used. The results were also compared against those obtained using the commercially available and widely-used casting software MAGMA5.
Keywords: turbulence; RANS; volume-of-fluid method; OpenFOAM; high-pressure die casting; aluminum; lost cores; salt core viability.
NUMERICAL SIMULATION OF LIQUID MASS COLLISION WITH A WALL
by Alexander Aganin, Tatiana Guseva
Abstract: Numerical simulation of high-speed liquid mass collision with dry or wetted rigid walls by the CIP-CUP method on dynamically adaptive Soroban grids is studied. A number of specially selected test problems is used for validating the resolution of the main features of the collision separately: 1D uniform liquid flow impact onto a wall, 1D plane discontinuity breakdown at the gas-liquid interface, 2D cylindrical discontinuity breakdown in liquid, blunt liquid cone and plane semi-infinite liquid flow impacts onto a dry wall in the attached shock wave mode, sharp liquid cone impact onto a dry wall in the shockless mode with laterally spreading liquid flow. The results of their calculations are in good correlation with the corresponding analytical and numerical solutions. A problem of hemispherically-ended high-speed jet collision with a wall covered by a thin liquid layer is considered as a benchmark to illustrate the capabilities of the CIP-CUP/Soroban-grid approach to resolving the main features of the high-speed liquid collision together. Its numerical solution is in good agreement with the known similar results.
Keywords: liquid jet impact; shock waves; large deformations of gas-liquid interface; Euler equations; CIP-CUP method; Soroban grid; artificial viscosity; interface capturing.
Experimental and computational study of optically-driven electrothermal vortex
by Xudong Pan, Jae-Sung Kwon, Jian Wei Khor, Steven T. Wereley
Abstract: Optically-driven electrothermal vortex flow is one of the most effective ways to induce convection in microscale domains. In this work, side view microscopic imaging is used for qualitative flow visualization as well as quantitative μPIV measurements of the vortex pattern in microfluidic chips between simple parallel-plate electrodes. The uniform electric field is generated from parallel-plate, indium tin oxide (ITO) electrodes separated by 400 μm. Alternating current (AC) electric fields at a range of frequencies (9kHz-100kHz) and voltages (5V-40V) are applied to the electrodes to drive the flow. Simultaneously, a near-infrared (1064 nm) laser beam at various intensities is focused on the bottom electrode surface of the microchannel. Strong electrothermal vortices are observed in the flow visualization experiments and measured by μPIV. A realistic computational model featuring a laser heat source and an applied electrical field is constructed. Computational simulations are performed under the same conditions as the experiments. The simulations and the experiments show the same qualitative behaviors and also agree quantitatively when comparing the maximum velocities.
Keywords: electrothermal vortex flow; qualitative flow; μPIV,optically-driven; microfluidics.
A High Order MOOD Method For Compressible Navier-Stokes Equations : Application To Hypersonic Viscous Flows
by Rodolphe Turpault, Tanh-Ha Nguyen-Bui
Abstract: A very high-order finite volumes numerical method is designed for the\r\nsimulation of Navier-Stokes equations on 2D unstructured meshes. This scheme is based on the MOOD methods described for Eulers equations, its an interesting alternative in the design of a scheme adapted to accurate simulations of flows with discontinuities, in all the domain. The main originality of our method is to include the diffusion and viscosity terms of Navier-Stokes equations. These terms are discretized with the same accuracy that convection terms. It allowss to treat the hypersonic viscous interactions with high\r\naccuracy. Numerical experiments are conducted to demonstrate the performance of the proposed method.
Keywords: MOOD Methods; High-Order; Viscous Fluids; Supersonic; Discontinuities; Simulations.
Simulating High Rayleigh Number Natural Convection in High Aspect Ratio Horizontal Rectangular Enclosures Using Code Saturne Platform
by Fahad Sarfraz Butt, Abdul Waheed Badar, Abdullah Zafar, Ajaz Bashir Janjua
Abstract: In the present study, buoyancy driven flows of water and air in very high aspect ratio (12-48) horizontal rectangular enclosures are studied numerically for Rayleigh numbers ranging from 103 to 107 using open-source CFD tools to obtain natural convection heat transfer coefficients which are then compared with established empirical correlations based on experimental results. This study has been motivated by the finding that hardly any CFD based literature on very high aspect ratio rectangular enclosures exist and also by the fact that such enclosures have numerous applications in solar thermal systems such as solar collectors, solar passive heating/cooling systems, and solar stills etc. It has been reported in the literature that at high aspect ratios, the numerical solution suffers from convergence issues. In the present study, using Code_Saturne as flow solver, the convergence issues have not risen and the error between numerical and experimental results increases with an increase in Rayleigh number bounded by maximum relative error of approximately 8%.
Keywords: CFD; Heat-Transfer; Convection; Enclosures; Code saturne.
A numerical approach to solve fluid-solid two-phase flows using time splitting projection method with a pressure correction technique
by Kambiz Farahi Moghadam, Mohammad Ali Banihashemi, Peyman Badiei, Ali Shirkavand
Abstract: This study used a vertical 2D model to simulate the sediment transport pattern in open channels by applying the EulerEuler two-phase flow model or the complete two-fluid model based on the Favre averaging method. In this study, a two-phase hydrodynamic method was developed to simulate the dynamics of water flow and sediment. The projection method with a pressure correction technique, along with the time splitting algorithm was used for the first time to solve the EulerEuler complete two-phase equations of fluid-sediment. Moreover, the conservation of mass and momentum of both phases was assured generally and partially in the equation discretization stage by providing a novel method developed from integration of the momentum and continuity equations of each phase. In addition, the horizontal and vertical velocities of both phases were discretized independently, without multiplying them by additional parameters, such as the phase concentration. At the end, the models performance in simulating the sediment flow process in a direction perpendicular to the flow was assessed. This assessment for the first time used a Favre averaging-based two-phase model to investigate longitudinal changes in the sediment profile. Moreover, the sediment concentration profile was evaluated in a specific type of flow, known as the sheet flow. Assessment of the model showed its high capability in dynamic simulation of water and sediment flows either at the flow depth or along the channel.
Keywords: complete two fluid model; Favre averaging; numerical modelling; pressure correction technique; sediment transport; timesplitting; two-phase flow; vertical 2-D model.
Computational investigation and optimization study on system performance of heat sink using perforated pin fins mounted at different angles
by Ambarish Maji, Dipankar Bhanja, Promod K. Patowari
Abstract: The current work investigates the performance of heat sink using perforated pin fins of different shapes with various perforation geometries like circular, diamond shaped and elliptical type. Three dimensional CFD simulations have been performed to explore the effects of fin shape, perforation geometry and perforation size on system performance. This work also analyzes the variations in heat transfer enhancement through elliptical and square shaped staggered pin fins with elliptical perforations mounted at different angular position on the path of the flow. Multi Objective Optimization under Ratio Analysis is applied to select the best heat sink configuration. Exergy efficiencies, entropy generations and irreversibilities are also calculated for all the fin shapes having various sizes of perforations. It is observed that heat transfer rate of perforated fins up to certain perforation number and size are always greater than their solid counterparts and with the change in perforation geometry and fin shape heat dissipation rate enhances significantly.
Keywords: Heat Transfer; Perforated fin; System performance; Angular position; Optimization; Computational fluid dynamics.
A Numerical Investigation of the Compressible Flow in the Ejector of a Vapor Ejector Refrigeration System
by Arumugam Megalingam, Viswanath Babu
Abstract: Numerical simulations of the flow in a vapor ejector have been carried out. Real gas effects are accounted for in the calculations. Both ejection as well as flow-through studies have been performed. Effects of the generator and evaporator temperatures and position of the primary nozzle have been investigated. Predicted values of the suction pressure and COP havernbeen compared with experimental values reported in the literature. In addition, secondary flow area has also been evaluated and correlated with the COP. By tracking the sonic line and the edge of the primary stream and flow separation, insights on the gas dynamic and fluid dynamic aspects of the flow field and how they influence the entrainment of the secondary stream and consequently the COP are brought out. The study reveals that, in addition to the choking of thernsecondary stream, the expansion of the primary stream and the area available for the secondary stream also play a key role in affecting the performance of the vapor ejector.
Keywords: Numerical simulation;Ejector; Real gas effects; Solar Refrigeration.
FEM Solution of MHD Flow in an Array of Electromagnetically Coupled Rectangular Ducts
by Munevver TEZER-SEZGIN, Selcuk Han AYDIN
Abstract: The magnetohydrodynamic (MHD) flow of an electrically conducting fluid is studied in an array of identical parallel ducts stacked in the direction of external magnetic field and are separated by conducting walls of arbitrary thickness. Such arrangement of electromagnetically coupled ducts arises in fusion blanket applications in which a liquid metal is used both as coolant and tritium generation. The finite element method (FEM) with SUPG stabilization is used for solving the set of coupled MHD equations. Numerical results show that, there is a significant effect of coupling the ducts with conducting walls of varying thickness, on the flow and induced current behaviors especially near the walls and for increasing values of Hartmann number. The results are presented for one, two and three coupled ducts in both co- and counter- flow configurations which induce reversal and counter-current flows.
Keywords: MHD; rectangular duct flow; stabilized FEM;.
CFD-modelling of free surface flows in closed conduits
by Katharina Teuber, Tabea Broecker, Arnau Bayon, Gunnar Nützmann, Reinhard Hinkelmann
Abstract: Computational Fluid Dynamics (CFD) is gaining an increasing importance in the
field of hydraulic engineering. This publication presents different application examples of a two-phase approach as implemented in the open source software OpenFOAM. The chosen approach is based on the volume of fluid method focusing on the simulation of flow in closed conduits. Three examples are presented: single-phase flow over a ground sill and free surface flow over a hill as well as complex free surface flow in a sewer model. The first example compares the results of different RANS turbulence models to experimental results. The results of the second example are compared to an analytical solution. In the last example the behaviour of the free surface flow is compared with the results of a model test and existing simulations using a simplified, open channel geometry for the closed conduit. For the examples analysed, the two-phase approach provides stable and reliable results.
Keywords: Computational Fluid Dynamics (CFD); Three-dimensional Models; Turbulence Simulation and Modeling; Volume of Fluid.
Immersed boundary method for a permeable sedimenting circular particle between two parallel rigid walls
by Sudeshna Ghosh
Abstract: This paper demonstrates settling of an isolated permeable circular particle in 2D, which corresponds to infinite cylinder in 3D, in a viscous, incompressible fluid contained within a two-dimensional channel. The fluid-structure interaction problem considered here is simulated numerically using the immersed boundary method wherein,the added mass is formulated using Boussinesqs approximation. This has been possible since density of the particle is slightly greater than the density of the fluid. The paper has demonstrated both analytically and numerically that settling velocity of a permeable cylinder is greater than that of an impermeable cylinder and it increases with increasing permeability. The effect of channel walls, wall effect, on a permeable particle, located initially along the centreline, is investigated. It is found that wall-effect on the setting velocity decreases as the permeability of a particle increases. Furthermore, for a given permeability wall effect on terminal settling velocity was found to decrease with decreasing fluid viscosity. In addition to such, the settling dynamics of a particle initially located at an off-centre location has been studied for different viscosity and permeability values. It is shown that numerical results are able to reproduce the expected behaviour qualitatively.
Keywords: immersed boundary method; particle suspension; sedimentation; settling velocity; fluid-structure interaction; permeable; porous.
Development of Targeted Compact Nonlinear Scheme with Increasingly High Order of Accuracy
by Kaveh Fardipour, Kamyar Mansour
Abstract: In this paper we present general formulation of targeted compact nonlinear scheme (TCNS) with increasing order of accuracy. This new scheme introduces the incremental-size and ENO-like stencil selection of targeted essentially non-oscillatory (TENO) scheme to weighted compact nonlinear scheme (WCNS). Other aim of the paper is construction of new global smoothness indicators (GSI) for TCNS. We used various benchmark problems of scalar hyperbolic equations and system of Euler equations for investigation of performance of TCNS and new GSIs.
Keywords: High-order numerical method; Weighted compact nonlinear scheme; Targeted compact nonlinear scheme; Targeted interpolation; Shock-capturing.
Theoretical Analysis and Experimental Research of Non-cavitation noise on Underwater Counter-rotation Propellers
by Zeng Sai
Abstract: The non-cavitation noise of counter-rotation propeller is a key factor for detection and recognition of underwater high-speed vehicles. This paper presents a theoretical analysis and a hybrid numerical simulation method of underwater counter-rotation propeller non-cavitation noise. An experimental verification is also included. The sound pressure spectrum model is presented to describe the non-cavitation noise of a counter-rotation propeller with application of generalized acoustic analogy method. The counter-rotation propeller noise is predicted using the frequency-domain acoustic analogy. The flow field is analysed by computational fluid dynamics based on the viscous flow theory. The flow field pressure is used for the acoustic spectrum prediction. The numerical simulation results are verified by a cavitation-tunnel experiment. Throughout the study, the counter-rotation propeller non-cavitation noise is analysed. The overall results indicate that the numerical approach is reliable for predicting non-cavitation noise of counter-rotation propeller, which is beneficial for characteristics extraction and identification of underwater high-speed vehicles.
Keywords: counter-rotation propeller; non-cavitation noise; CFD simulation; generalized acoustic analogy method; cavitation-tunnel experiment.
AN IMMERSED BOUNDARY METHOD FOR SIMULATIONS OF FLOW AND MIXING IN MICRO-CHANNELS WITH ELECTRO KINETIC EFFECTS
by Ahamed Saleel C, Irfan Anjum Badruddin
Abstract: Immersed boundary method (IBM) is a methodology in which any real stationary or moving bodies in flow or heat transfer or mixing field is treated by distinct forcing functions introduced in the respective governing equations, thereby its presence is dealt with much easiness in the computational domain. In addition, the method eases the handling of complex geometry with the use of Cartesian grids that usually do not coincide with the surface of the body. The present work proposes an extension of an IBM based on discrete forcing approach to simulate pressure driven electro osmotic flow and mixing in constricted micro channels. The fractional-step based temporal discretization and finite-volume based spatial discretization on a staggered mesh are used to solve the governing equations. Velocity fields are corrected by a pseudo-pressure term to satisfy the continuity in each computational time step. Constriction is introduced with the help of triangular blocks to enhance the mixing efficiency. Concentration forcing function is a parameter, which is newly defined in this model to satisfy the no-flux boundary condition for species concentration on the blocks (immersed boundary) and is introduced in convection-diffusion equation. The present computational model is validated with the published experimental and numerical results in the literature and finally some sample results generated by the present model is also exemplified.
Keywords: CFD; Immersed Boundary method; Forcing Functions; Finite Volume Method; Navier Stokes Equation; Fractional Step Method; Staggered Mesh; Convection-Diffusion Equation etc.
Suppressing artificial equilibrium states caused by spurious currents in droplet spreading simulations with dynamic contact angle model
by Thomas Antritter, Martin Mayer, Peter Hachmann, Martin Worner
Abstract: Accurate methods for numerical simulation of dynamic wetting and spreading phenomena are a valuable tool to support the advancement of related technological processes such as inkjet-printing. Here, it is demonstrated that numerical methods employing dynamic contact angle models are prone to artificial equilibrium states caused by
spurious (parasitic) currents. The capability of different approaches in reducing spurious currents for sessile and spreading droplets with low equilibrium contact angle is evaluated. To minimize the influence of spurious currents on dynamic contact angle models, a smoothing step in the evaluation of the contact line velocity is introduced in this paper. The benefit and performance of this new approach is demonstrated by algebraic volume-of-fluid simulations of spreading and receding droplets with the Kistler dynamic contact angle model.
Keywords: droplet; wetting; spreading; inkjet printing; dynamic contact angle; spurious currents; parasitic currents; numerical simulation; volume-of-fluid method; OpenFOAM.
A numerical study on the influence of liquid properties on gas-focused micro-jets
by Rizwan Zahoor, Rok Regvar, Saša Bajt, Božidar Šarler
Abstract: In this paper we present a numerical study on the influence of liquid properties on gas-focused micro-jets, such as used for sample delivery in serial femtosecond crystallography. The study is based on solving mixture formulation of Newtonian, compressible two-phase model with the finite volume method and algebraic volume of fluid for treatment of the phase-interface. The density, viscosity and surface tension of the focused fluid span around the material properties of pure water in the range of
Keywords: gas dynamic virtual nozzle; focusing gas; liquid properties; micro-jet; compressible multiphase flow; finite volume method; volume of fluid; jetting; dripping.
CFD Modeling of Hydrate Slurry Flow in a Pipeline Based on Euler-Euler Approach
by Abdallah S. Berrouk, Jiang Peng
Abstract: The presence and agglomeration of hydrates particle in oil and gas transportation pipeline can pose a major threat for the flow assurance. Avoidance of hydrate formation by injecting thermodynamic inhibitors is a common but an expensive practice. For this reason, low dosage hydrate inhibitors (LDHIs) of anti-agglomerates are being considered which allows the transport of hydrates slurries directly with minimum risk of pipeline blockage. Understanding the hydrate-containing flow characteristics is of essence to efficiently manage and transport hydrate slurries. In this work, a three- dimensional CFD model of hydrates slurry flow in pipeline was built using Eulerian-Eulerian solid-liquid multiphase approach. RANS RSM model) was used to capture the turbulence. User defined functions (UDFs) of hydrate particle size model and hydrates shear viscosity model which are derived from a correlation of experimental data were developed and integrated into the CFD model. CFD model predictions on pressure gradients at different inlet velocities and different hydrates volume fractions were compared with the experimental data. It was found that very good matching of the experimental pressure gradients was obtained for the case where Camargo and Brinkman were used. The developed numerical model was then used to study the distributions of hydrates velocity magnitude and hydrates volume fraction for different flow conditions. In addition, hydrates deposition characteristics were investigated and the hydrates deposition bed heights were determined for low inlet velocities. This study should help provide valuable insight into hydrate- laden flow properties in pipelines that might help redesign them for better flow assurance.
Keywords: Flow assurance; Hydrate slurry flow; Computational Fluid Dynamics; Euler-Euler approach; hydrate deposition.