جستجوی مقالات مرتبط با کلیدواژه « روش حجم محدود » در نشریات گروه « مکانیک »

In the present study, for the first time, a finite volume coupled solver is developed for the simultaneous numerical solving of two-phase incompressible fluid flow equations at low Reynolds numbers, and for solving the the interface position equation by applying interface boundary conditions using the foam-extend platform. The studied flows with interface and mesh motion are considered to be laminar and in the range of Reynolds numbers less than 100. The Foam-extend is a fork of OpenFOAM, an opensource object-oriented C++ library for computational continuum mechanics. This solver is based on the interface tracking algorithm, which is developed using an innovative technique called zero-thickness cell. This technique removes the distance effect for the cell adjacent to the interface, and the interface is modeled with zero thickness cells. The main advantage of the present coupled solver compared to the previously developed solvers is that in this solver, all the equations in both phases are coupled with each other by cells adjacent to the interface and with an the interface position equation. All the governing equations and the interface position equation are assembled in a single linear system of equations and simultaneously solved. In fact, unlike the usual segregated procedure of solving two phase flows, where the phases are solved with lagged value boundary conditions, in the present solver, the phases are solved simultaneously with the interface conditions in an implicit manner and in the same block matrix system. The movement of the interface was done separately, and in another step. For this purpose, the kinematic condition was implemented. The computational performance of the coupled solver was evaluated by solving the equations of two-phase fluid flow inside a channel and on a backward-facing step. In the beginning, a preliminary investigation was done for the case, where both phases were completely independent and decoupled. Matching the interface with the streamlines, as well as the reasonable and justifiable movement of the surface, has been observed from the physical point of view. Also, the damping of the numerical oscillations generated on the interface and changing the flow variables will be investigated. The present results are in excellent agreement with other results reported in the literature.

The vapour absorption into the liquid falling film has occurred in various natural phenomena and its application has spread in various industries, such as the dehumidification and desalination industry. The complexity of flow dynamics, mass transfer, heat, and small dimensions of a liquid film has made its modeling and numerical simulation a key role in the investigation and studying of the effectiveness and improvement of the absorption process in a liquid film absorbent. In the present work, the effects of Reynolds number, wall temperature, and wall shape on the interfacial heat and mass transfer have been investigated. Numerical modeling has been performed using an unsteady Arbitrary Lagrangian-Eulerian interface tracking method by Fortran. The simulation results show that the deformation of the wall surface and the cooling of the wall temperature has a significant effect on the rate of gas vapor absorption into the laminar liquid film in comparison with the flat wall

Electrosmotic micropumps are a group of microfluidic devices in which the movement of a fluid stream is formed by the application of an external electric field. This field is generally applied to the micropump by means of two electrodes immersed in the electrolyte. How to install the current-carrying electrode plates in the electrolyte fluid and their placement on the passage of the fluid flow is an issue that can have adverse effects on the quality of operation of the micropump. In this article, a method can be used to overcome this problem. In this method, the electrode plates, instead of being placed in the path of the fluid flow, are connected to the wall of the micropump with the help of T-shaped connections and while affecting the fluid mass, they do not obstruct the flow of the fluid flow. Such a connection, in addition to solving the previous problem, has another advantage, which is the possibility of serializing the pumps and increasing their pressure head. All simulations performed in this paper are performed in a two-dimensional geometry between two parallel plates and the flow conditions are assumed to be steady state, laminar and incompressible. The finite volume method is used to solve the equations governing the fluid flow field, internal and external electric fields, and the distribution of positive and negative ion concentrations called Nernst-Planck. According to the results, serialization of two micropumps in comparison with micropumps of the same length increases the outlet pressure head by up to 80%.

In this paper, the effect of the passed fluid flow around a fin in the bundle of annular fins with different eccentricity on thermal stresses created in it is discussed. To solve the turbulent fluid flow equations and thermal stress in solid, the volume element with k-ε model and finite element methods are used, respectively. The results are obtained for 2 fin spacing and 4 heights of fins. Then, in each fin height, the effect of 5 eccentricities on decrease of thermal stress are considered. The results show that at each fin height there is an optimal eccentricity for which the thermal stress in the fin reaches its minimum value. The results show that the maximum decrease of thermal stress in optimal eccentricity related to fin heigh 4mm for both fin spacing of 4 mm and 8mm are 30 , 35% respectively. Also, in fin spacing of the 8 mm at different heights of 8, 6, 4, and 2 mm, the optimal eccentricities are 3, 2.25, 1.5, and 0.5 mm, respectively and in fin spacing of the 4 mm at different heights of 8, 6, 4, and 2 mm, the optimal eccentricities are 3, 2.25, 1.5, and 0.25 mm, respectively.

Heat transfer enhancement from a flat plate in which a thin blade is rotating at a certain speed in the vicinity of the plate has been investigated in the present study. For this numerical study, the finite volume method was used in which the rotation of the blade was simulated by the definition of sliding mesh and interface boundary within the computational domain. The equations of mass, momentum, and energy were solved in two-dimensional and transient form for airflow with constant physical properties using Fluent commercial software and the details of the flow and thermal fields were obtained at the top of the plate. The rotational Reynolds number of the blade has been changed in the range of 1360-5460 and the dimensionless parameter of blade-end-to-plate distance to the blade length (d/D) was ranged from 0.105 to 0.420. The results indicated that heat transfer from the plate is improved by increasing the rotational speed of the blade, especially on the front side of the rotating blade, while the effect of the d/D was effective only over a limited area of the plate central section

In this paper, the problem of perforation of the human cranial bone surface in the shape of a hemisphere using a water jet is numerically simulated in three dimensions. The simulation involves both the flow and heat transfer of the impinging water jet, and surface perforation process. The volume of fluid method was used to model the jet two-phase flow, and Johnson-Cook equation in finite element method was applied for perforating the bone surface. The obtained results show that the pressure and friction coefficients on the surface depend on the nozzle distance from the surface, and the pressure at the stagnation point increases as the nozzle distance decreases. Also, by increasing the nozzle distance, local Nusselt number along the hemisphere radius as well as maximum Nusselt decreases at the stagnation point. The effect of nozzle diameter on pressure and friction coefficients was also investigated and found that the pressure at stagnation point is increased by the nozzle diameter. The change in the jet velocity also showed that a 20% change in velocity has no significant effect on the pressure and friction coefficients, while increases the Nusselt number. In modeling the perforation process, actual properties and coefficients of bone material, such as Poisson's coefficient and Young's modulus were used. Comparison of on-site stress distribution based on Tresca and von Mises criteria showed that according to the proposed parameters, the perforation is performed properly.

The ability of baffles in increasing the hydrodynamic damping of sloshing in circular cylindrical containers is investigated in this study by analytic, numerical, and experimental methods. Baffles as separate components are installed in tanks containing fluid and can change various aspects of dynamic characteristics of sloshing. The primary objectives of this study is to examine the relative effectiveness of baffle arrangements to provide experimental data for the verification of the numerical models and to recommend a practical baffle arrangement that would be effective over a range of frequencies. The results show that the proposed baffle arrangement has a very effective effect on the damping and sloshing frequencies, and satisfies the anticipated design requirements optimally. The results also display that at liquid height close to the bottom of the container, the theoretical curve predicts that the fundamental frequency of the sloshing will decrease, while the experimental frequency not only decreases but also shows an increasing average. In addition, the results of finite element method and finite volume method in calculation of sloshing frequency and damping are highly consistent with experimental results.

Nowadays, maritime transport is increasing significantly, and the probability of collisions between ships in densely populated region has increased. In this regard, improving the ship maneuvering performance has a significant impact directly on the economy and safety of navigation. Therefore, the study of maneuver parameters is considered as a mandatory issue in the process of designing a ship. In this study, first the validation of the results has been done for the KCS. The benchmark ship at froud number 0.201 was simulated in three degrees of freedom including: surge, heave and pitch and calm water conditions, then the results were compared by computational fluid dynamics. Validation was performed according to the ITTC Recommendation by three levels of gridding, and the value of numerical uncertainty was also estimated. Uncertainty less than 12% and numerical error respect to experimental less than 6% were extracted. A good match was presented between the numerical and laboratory results. A good match was presented between the numerical and laboratory results. The two-phase flow the Volume Of Fluid (VOF) method and the DES turbulence model were used to model the flow around the hull. The effect of propeller was induced by actuator disk method and based on flowchart in ship stern.

This study consider the impact of transient flow around an annular fin on the development of thermal stress and strain. The finite volume method was used to solve the flow equations and the finite element method to solve the thermal stress equations in the solid. The fin thermal stress results were solved for two general cases with and without flow around the fin. Moreover, two scenarios were considered for the case with the flow. First, the fin was analysed in free flow and then, to be more practical, the problem of flow around one fin among a group of fins was considered. The free flow results were compared to the case with no flow. The investigations are suggestive that the thermal stresses developing in the fin are initially similar in the two cases . Furthermore, the results show that the maximum tangential stress takes place at the same location in the two cases but it is exacerbated. In addition, the tangential is not symmetrical in the case with the flow and the maximum stress, although at the base of the fin, is located in the flow front. Moreover, in the case with the flow, the two-dimensional temperature distribution results in a considerable asymmetrical thermal strain and consequently, asymmetrical thermal stress none of which are observed in the case with no flow. A careful analysis of the flow around the fin shows radial temperature distribution information to be insufficient to determine the maximum effective stress.

Microelectromechanical systems as a promising and efficient technologies of present age can bring about a great revolution in the industrial and commercial products. The increasing development of technology requires the use of wireless sensors (without power supply); so the study and modeling of micro energy harvesters is an important issue. In this paper, a micro flow sensor consists of a symmetric multilayer piezoelectric with a micro energy harvester have been modeled and simulated. In order to model this sensor, coupled equations between solid mechanics, fluid mechanics and piezoelectric have been solved with finite volume and finite element method. To ensure the solution, a fully fluid-structure interaction simulation of micro flow sensor in COMSOL Multiphysics have been presented. With the flow rate of 60 micro liter per minute, the transverse displacement of the free end of the beam is 9.5 Nano meters and the generated voltage is 2.30 millivolt.

In this study, performance of Polymer Electrolyte Membrane fuel cell (PEMFC) was investigated using a 3D transient and two-phase simulation of the cathode side of PEMFC. The governing equations were discretized by finite volume method and solved numerically using an in-house FORTRAN code. A parametric study on the liquid water formation in porous medium and the performance of the PEMFC was conducted. Among effective parameters on the performance of PEMFC, porosity and permeability of porous media, contact angle between water and solid surface, were studied. The results showed that the reduction of porosity, permeability and contact angle increase the content of liquid water in porous media. Permeability and contact angle are the most effective ones in such a way that reduction of permeability and contact angle from to and from 140 to 91 degree, respectively, reduce the average of the liquid water volume fraction (s) in catalyst layer from 0.04 to 0.16 (by factor of 3) and from 0.058 to 0.15 (59%). For the operating condition studied here, a correlation is developed for prediction of the s based on a parameter which is solely function of propreties of the porous media.

In this paper, the results of the two-dimensional and axisymmetric modeling of the methane-air pre-mixed combustion with multi-step kinetics in a porous medium with continuous porosity change have been presented. In order to determine the thermophysical and thermochemical properties of species, the CHEMKIN II program and Basic information used. Continuity equations, Navier Stokes, gas and solid phase heat transfer equations, and chemical species governing equations are solved by using of finite volume method. The SIMPLE algorithm has been used for the relationship between speed and pressure. The burner under the studied includes two preheated and combustible areas. In this paper, we study the effects of divergence angle changes and length of burner preheating area on temperature profiles andemission of pollutants. The results showed that by increasing the divergence angle, the amount of NO contamination in the burner output increases dramatically, while by increasing the length of the preheating region, the amount of emission of this pollutant in the output decreases.

In the current study impacts of fluid sloshing on the dynamic performance of a partially filled tank vehicle have been investigated. A nonlinear and three-dimensional solver of fluid flow equations were coupled with dynamic equations of a three degrees of freedom moving tank vehicle through an intermediate software to simulate the fluid sloshing behavior inside the tank and the vehicle dynamic performance influenced by liquid sloshing. The fluid sloshing solver is based on corrected Navier-Stokes equations which are included some additional terms owed to taking tank vehicles motions into account. In the present work we used “body weighted method” to consider the effects of accelerating motions of the tank on fluid’s elements. The mentioned method was used to simulate the partially filled container during accelerating horizontal motion which crashed an obstacle after a while from the start point. Computed results were compared to experimental results from literatures to valid the proposed method. The water level evolution on the left wall of the container compared to the experimental one showed a good agreement. Moreover, the two-dimensional rectangular container subjected to periodic external excitation was considered. The pressure history on the tank wall was compared to the measured impact pressure to figure out the ability of the scheme to capture the flow properties to anticipate the exerted forces on the walls. One is observed that there is a good agreement between the computed and measured results. Furthermore, the coupled tank vehicle-fluid simulation has been done during vertical excitations through passing symmetric bumps.

The present work reports of the numerical simulation of natural convection in a square enclosure with local heating of bottom and cooling from side walls. This simulation has been done to evaluate the thermal analysis of two floor radiator in a squares room. Flow and temperature fields were obtained by numerical simulation of mass, momentum and energy equations in laminar, steady and two-dimensional flows. While the amount of heat energy into room is constant, effect of parameter dimensionless Rayleigh number and strength of the heat source as well as the location of they, evaluated on flow and temperature fields. In the end, it was found that by increasing the Rayleigh number, rotational flow within the room increases and convective heat transfer is dominant.

In this paper, temperature distribution, melt flow and depth of heat affected zone (HAZ) in LASER welding of Ti6A14V Titanium alloy platen of 1.7 mm thickness have been studied. Due to high costs of practical LASER welding experiments, finite volume method was employed to predict the weld behavior on the specimen. Simulation is an superior method in finding optimized settings which reduces the costs as well. Fluid finite volume method and Open Foam software were employed in simulation. In order to verify the simulation results, experimental data obtained from weld geometry and temperature distribution were used. Buoyancy and Marangoni forces and boussinesq assumptions, were considered intently in simulation process. Moreover, thermodynamic properties were assumed independent of temperature and Gaussian heat source was employed for mechanical properties. Numerical results have good agreement with experimental results. The developed model can predict temperature distribution, melt flow in different parts of plate and melt penetration depth properly. This model can also be used for design and evaluation of welded parts.

Present paper investigates the numerical solution of two-dimensional unsteady compressible Navier-Stokes equations by a new scheme based on the finite volume method. Kinetic Energy Preserving (KEP) scheme is introduced for solving the supersonic and Transonic external compressible flow field on very fine grids (with a number of cells of the order of the Reynolds number) without artificial dissipation terms even in place of shock waves. It should be noted that the solution of flow field with this scheme in this range of speed, is presented for the first time. By discretization of the governing equations based on KEP scheme and elimination of dissipative effects, the Direct Numerical Simulation (DNS) of the flow is possible. The results of this solution for supersonic flow over flat plate and Transonic flow over the airfoil at low Reynolds numbers show that the KEP method can be presented stable and non-oscillatory solution by no artificial dissipation even in areas with shock waves. Therefore, the KEP method can be used for DNS of turbulent flows (without a modeling the turbulence phenomena itself).

Development of thermal management methods for advanced electronic devices, especially for micro and nano-scales are important issues which directly affects system performance. MicroChannel Heat Sink (MCHS) is one of the efficient technologies improving the thermal performance and some research works have been conducted in this field recently. The aim of the present paper is to investigate the nanoparticles size effects on thermal performance of a trapezoidal MCHS numerically. In the present study, employment of Water - Alumina (〖"Al" 〗_"2""O" _"3" ) and Water – CuO nanofluids is modeled using Eulerian – Eulerian two-phase approach. Solving equations of continuity, momentum and energy in the computational domain is performed via Finite Volume Method (FVM) in FLUENT with the accuracy of 〖10〗^(-6). Also, since in most studies nanofluids are simulated as a homogeneous (single phase) fluid a comparison between the present two-phase models with homogeneous modeling is conducted and it is found that two phase modeling shows 13.8% better performance in comparison with other single phase modeling. The results showed that adding of both nanoparticles increases the heat transfer in microchannel and increasing the diameter of the nanoparticles results in a decrease of heat transfer rate as Alumina and Cu-O nano particles, show 6.63% and 5.022% reduction in heat transfer rate, respetively. Also in the meantime, Alumina nanoparticles have a lower heat transfer coefficient than CuO nanoparticles. Hence, Water - CuO nanofluid is more appropriate for trapezoid geometry and by optimizing the particle size the thermal efficiency of the system can be maximized.

Supercritical fluids have substituted non-super critical fluids in some areas of industry because of their unique characteristics and have been the subject of numerous experimental, numerical and analytic studies since their discovery. In this study laminar natural convection between a hot vertical tube with constant temperature and supercritical carbon dioxide with uniform temperature at inlet is simulated by utilizing a numerical model. The simulation is a two-dimensional, pseudo-transient numerical model based on finite volume method. The main objective of this study is to investigate and analyze the effect of severe property variations of supercritical carbon dioxide on the flow and temperature field of natural convection that ultimately affect heat transfer rates with respect to non-critical natural convection. Numerical simulations have been carried out for temperature and pressure ranges of 305K to 312K and 7.5MPa to 9MPa respectively. Span and Wanger’s multi-parameter equation of state have been used directly to determine carbon dioxide properties around pseudo critical temperature for the first time. Results indicate an increased rate of total heat transfer up to 160% near pseudo-critical temperature and 118% in other temperatures for supercritical natural convection with respect to ideal gas assumption.

Three-dimensional simulations are presented on the motion of a bubble between two parallel plates at a finite Reynolds number in a combined couette-poiseuille flow. The full Navier-Stokes equations are solved by a finite difference/front tracking method on a regular, fixed and staggered grid. Interface is tracked explicitly by connecting marker points on an irregular, triangle and moving grid. The interface effects are accounted for by adding appropriate source terms into the governing equations. The effects of the dimensionless numbers, such as, Capillary number, Reynolds number, and geometric ratio on the lateral migration of a bubble are studied in detail. Simulations also show that the bubble deformation depends strongly on the Capillary number. So that, the proper non-dimensional number for the interfacial tension is the Capillary number. As the radius of the bubble increases, the equilibrium position moves closer to the centerline. Then, the gravity force was added. Bubbles are more deformed with increasing the Bond number and move to an equilibrium position closer to the centerline.

A characteristic-based approach is developed for thermo-flow with finite volume methodology (FVM) in which multidimensional characteristic (MC) scheme is applied for convective fluxes. To obtain compatibility equations and pseudo characteristics, energy equation is taken into account in the MC scheme. With this inherent upwinding technique for evaluating convective fluxes at cell interfaces, no artificial viscosity is required even at high Reynolds numbers. As benchmarks, forced convection between parallel plates and forced and mixed convection in a cavity are examined for a wide range of Reynolds, Grashof and Prandtl numbers. Results confirm the robustness of MC scheme in terms of accuracy and convergence. The results obtained by new proposed scheme are in good agreement with the standard benchmark solutions in the literature. For time descritization, fifth order Rung-Kutta and for viscous terms, the secondary cells are used. Obtained results by new characteristic method were compared by other results that were in literatures.