Fluid Mechanics
Miralam Mahdi; Mostafa Shariatnia; Majid Rahimi
Abstract
Microbubbles are used in ultrasound imaging, targeted drug delivery, destruction of cancerous tissues, etc. On the other hand, the demographic behaviors of small bubbles under the influence of Ultrasound have not been fully detected or studied. This study investigates the effect of the radial distribution ...
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Microbubbles are used in ultrasound imaging, targeted drug delivery, destruction of cancerous tissues, etc. On the other hand, the demographic behaviors of small bubbles under the influence of Ultrasound have not been fully detected or studied. This study investigates the effect of the radial distribution of Sonazoid microbubbles on frequency response. It is shown that the optimal subharmonic response is possible by controlling the size distribution. For this reason, the numerical simulation of the dynamic behavior of a coated microbubble is performed using MATLAB coding and the modified Rayleigh-Plesset equation. The Gaussian distribution is then applied, and the frequency response is investigated. It was shown that at a constant excitation pressure of 0.4 MPa and a standard deviation of 0.2, with increasing mean radius, the fundamental response increases. The subharmonic response increases reaches a peak value and decreases. This peak value occurs for frequencies of 4,6, and 8 MHz in the mean radius of 0.8, 1 and 1.6 μm. By increasing the frequency of excitation, it is transferred to a smaller mean radius. It is also observed that the fundamental and subharmonic responses are amplified by increasing the excitation pressure. Studies show that the optimal subharmonic response can be achieved for various applications by controlling the size distribution of microbubbles.
Fluid Mechanics
Rasoul Talebian; Mansour Talebi
Abstract
In the present study, the pressure drop of the nanofluid flow of carbon-water nanotubes (CNT/water) in a helical three-tube heat exchanger with constant fluid physical properties has been experimentally evaluated. For this purpose, first, the experimental device was designed and manufactured and then ...
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In the present study, the pressure drop of the nanofluid flow of carbon-water nanotubes (CNT/water) in a helical three-tube heat exchanger with constant fluid physical properties has been experimentally evaluated. For this purpose, first, the experimental device was designed and manufactured and then the carbon-water nanotube nanofluid with volume percentages of 0.01%, 0.1%, and 0.5% was prepared and stabilized. For the experiment, two triple-tube helical heat exchangers with different geometries are considered, in which the diameter of the middle pipe varies in two geometries. The pitch of the helical coil is 100mm and the helix radius is 9.235mm. The experiment was performed on Dean numbers between 1000 and 5000. The measured and calculated data were according to the available correlation in the literature with an error of less than 4%. It is found that at low volumetric percentages of CNT, the pressure drop is almost equal to that of the base fluid, and with increasing volumetric percentage of nanoparticles, the pressure drop also increases. By changing the geometry of the tube (decreasing the middle diameter of the tube), the pressure drop decreases.
Fluid Mechanics
A Hassanvand; Mojtaba Saei Moghaddam; M. Barzegar Gerdroodbary; Y Amini
Abstract
Finding the solutions for heat and mass transfer problems is significant to reveal the main physics of engineering issues. In this work, the Adomian decomposition method is chosen as a robust analytical method for the investigation of temperature and flow features in a viscous fluid that moves between ...
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Finding the solutions for heat and mass transfer problems is significant to reveal the main physics of engineering issues. In this work, the Adomian decomposition method is chosen as a robust analytical method for the investigation of temperature and flow features in a viscous fluid that moves between two parallel surfaces. To ensure the validation of results, the outcome of the Adomian decomposition method is compared with that of the Runge-Kutta method, and reasonable agreement is observed. The comparison confirms that the Adomian decomposition method is a robust and reliable approach for solving this problem. Then, diverse parameters such as Prandtl number and squeeze number are studied. Besides, the effect of chemical reaction parameter, Eckert number, and Schmidt number are comprehensively discussed. Findings reveal that the Sherwood number rises when the chemical reaction parameter and Schmidt number increase. Also, it declines with growths of the squeeze number. Likewise, The findings confirm that the Nusselt number enhances with the rising of the Eckert number and Prandtl number, and it declines when the squeeze number increases.
Fluid Mechanics
Mohammad Reza Aligoodarz; Mohsen Dalvandi; Abdollah Mehrpanahi
Abstract
The centrifugal slurry pump is the most common slurry flow pump used in mining industries. The pump head and efficiency are affected by the size, concentration, and density of solid particle when these pumps are applied for the control of slurries. Because the suspended solids in the liquid could not ...
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The centrifugal slurry pump is the most common slurry flow pump used in mining industries. The pump head and efficiency are affected by the size, concentration, and density of solid particle when these pumps are applied for the control of slurries. Because the suspended solids in the liquid could not well absorb, store, and transmit pressure energy, they cause quite different changes in efficiency and performance curve shape. This study was conducted to investigate the variations of the mentioned factors at different flow rates using a numerical simulation of the centrifugal slurry pump. For this purpose, the 3D turbulent flow was solved by applying Reynolds-Averaged Navier-Stokes (RANS) equations using the Shear Stress Transfer (SST) turbulence model based on Eulerian-Eulerian for 45% to 120% flow rates in CFX (Ver. 17) software. The accuracy of the numerical solution was investigated by comparing the characteristic curves resulting from the numerical solution with experimental data. The obtained results show a satisfactory fitting among the calculated values from the numerical analysis and experimental data to predict pressure and velocity distribution and global performance. Moreover, by simulating the effect of different parameters of the slurry flow, their effect on the characteristic curves of the slurry pump was compared. These results reveal that the numerical solution can efficiently predict the variation trend of the slurry flow parameters.
Fluid Mechanics
K. Suneetha; S. M. Ibrahim; P. Vijaya Kumar; K. Jyothsna
Abstract
Due to the presence of rheological flow parameters and viscoelastic properties, non-Newtonian fluid structure is intricate and enticing to investigate. The flow has been made by considering variable temperature and radiation effects for the magnetohydrodynamic viscoelastic liquid past ...
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Due to the presence of rheological flow parameters and viscoelastic properties, non-Newtonian fluid structure is intricate and enticing to investigate. The flow has been made by considering variable temperature and radiation effects for the magnetohydrodynamic viscoelastic liquid past a moving vertical plate in a porous state. First order homogeneous chemical reaction, Soret number, variable temperature and concentration have been taken into account. The leading mathematical proclamation is handled analytically by perturbation strategy. The central aspiration of this work is to explore the consequences of sundry parameters on fluid flow, thermal boundary and concentration profiles. Diagram and tabular trends of the profiles are delineated with apropos parameters. Our sketches illustrate that the velocity profile exposes decelerate scenery with escalating M due to the Lorentz force in the opposite direction of flow. Temperature profile is getting accelerated owing to thermal radiation and concentration distribution is declined by boosting up the chemical reaction and Schmidt number. Diminishing nature of momentum boundary layer with Sc is also portrayed. Furthermore, at the end of this paper the effects of different parameters on skin fricition coefficient and local Nusselt number are investigated.
Fluid Mechanics
Hamidreza Ghaffarianjam; Sajad A. Moshizi; Mahdi Zamani; Mahdi Amiri Daluee
Abstract
In the present work, the study of alumina-water nanofluid heat transfer between two concentric vertical cylinders has been done by modified Buongiorno’s model (BM) to examine the impacts of temperature jump and slip velocity boundary conditions for a wide range of Knudsen number. Runge-Kutta-Fehlberg ...
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In the present work, the study of alumina-water nanofluid heat transfer between two concentric vertical cylinders has been done by modified Buongiorno’s model (BM) to examine the impacts of temperature jump and slip velocity boundary conditions for a wide range of Knudsen number. Runge-Kutta-Fehlberg method, as a standard integration scheme along with a shooting method, has been chosen for solving nonlinear ordinary differential equations (ODEs) along with boundary conditions. The main concentration of this paper is on the temperature jump since the slip velocity has been extensively examined in many studies. The presence of temperature jump boundary condition by varying Knudsen number was considered to investigate the effects of the bulk mean nanoparticle volume fraction ϕB, mixed convection parameter Nr, buoyancy parameter Ng, and heat flux ratio ε on the total dimensionless heat transfer coefficient HTC and the dimensionless pressure gradient Ndp. The obtained results indicate that temperature jump boundary condition plays a pivotal role in temperature profile, heat transfer coefficient and pressure drop; for instance, the negligence of temperature jump near walls causes to undervalue heat transfer coefficient in continuum flow regime and overestimate it in slip flow regime.
Fluid Mechanics
Vijay Kumar Dwivedi; Pooja Pathak
Abstract
There are many industrial applications of axially grooved journal bearing, especially in turbo- machinery. Stability is a very big issue for researchers, in high speed rotating machines. The axial groove journal bearing has a capacity to reduce the vibration and the ability to resolve the heating problems ...
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There are many industrial applications of axially grooved journal bearing, especially in turbo- machinery. Stability is a very big issue for researchers, in high speed rotating machines. The axial groove journal bearing has a capacity to reduce the vibration and the ability to resolve the heating problems as well as stability at a higher speed. Dynamic performance parameters and stability of axial grooved hybrid journal bearings depend on the dimensions and orientations of the groove to a great extent at higher speeds. In this work, a FORTRAN program is used to solve Reynolds governing equation. The bearing performance characteristics are simulated for the various dimensions and orientation of the groove. Non-linear journal center trajectories are drawn for different Reynolds numbers for stability analysis. It is found that the smaller groove length results in lower bearing capacity, whereas smaller groove width yields higher bearing capacity, and the turbulence decreases the stability. The groove location also strongly affects most performance parameters. The optimum location of the groove axis is obtained between 60° to 90° to the load line.
Fluid Mechanics
S. O. Salawu; A. Abolarinwa; O. J. Fenuga
Abstract
In this research, the transient analysis of radiative combustible viscous chemical reactive two-step exothermic fluid flow past a permeable medium with various kinetics, i.e., bimolecular, Arrhenius, and sensitized, are investigated. The hydromagnetic liquid is influenced by periodic vicissitudes in ...
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In this research, the transient analysis of radiative combustible viscous chemical reactive two-step exothermic fluid flow past a permeable medium with various kinetics, i.e., bimolecular, Arrhenius, and sensitized, are investigated. The hydromagnetic liquid is influenced by periodic vicissitudes in the axial pressure gradient and time along the channel axis in the occurrence of walls asymmetric convective cooling. The convectional heat transport at the wall surfaces with the neighboring space takes after the cooling law. The non-dimensional principal flow equations are computationally solved by applying convergent and absolutely stable semi-implicit finite difference techniques. The influences of the fluid terms associated with the momentum and energy equations are graphically presented and discussed quantitatively. The results show that the reaction parameter is very sensitive, and it, therefore, needs to be carefully monitored to avoid systems blow up. Also, a rise in the values of the second step term enhances the combustion rate and thereby reduces the release of unburned hydrocarbon that polluted the environment.
Fluid Mechanics
Bahador Sharifzadeh; Rasool Kalbasi; Mehdi Jahangiri
Abstract
A severe case of stenosis in coronary arteries results in turbulence in the blood flow which may lead to the formation or progression of atherosclerosis. This study investigated the turbulent blood flow in a coronary artery with rigid walls, as well as 80% single and double stenoses on blood flow. A ...
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A severe case of stenosis in coronary arteries results in turbulence in the blood flow which may lead to the formation or progression of atherosclerosis. This study investigated the turbulent blood flow in a coronary artery with rigid walls, as well as 80% single and double stenoses on blood flow. A finite element-based software package, ADINA 8.8, was employed to model the blood flow. The hemodynamic parameters of blood, such as the Oscillatory Shear Index (OSI) and the Mean Wall Shear Stress (Mean WSS) were obtained by both k-ε and k-ω turbulence models and then compared. According to the results, the negative pressure predicted by the k-ω turbulence model was several times greater than that by the k-ε turbulence model for both single and double stenoses. This, in turn, leads to the collapse of artery walls and irreparable injuries to the downstream extremity. Furthermore, the k-ω model predicted a larger reverse flow region in the post-stenotic region. In other words, the k-ω turbulence model predicts a larger part of the post-stenotic region to be prone to disease and the k-ε turbulence model predicted a higher rate of plaque growth. Moreover, the k-ω model predicted a much more intense reverse flow region than the k-ε model, which itself can lead to blood pressure disease.
Fluid Mechanics
M. Kezzar; M. R. Sari; I. Tabet; N. Nafir
Abstract
In this paper, the bioconvective nanofluid flow in a horizontal channel was considered. Using the appropriate similarity functions, the partial differential equations of the studied problem resulting from mathematical modeling are reduced to a set of non-linear differential equations. Thereafter, these ...
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In this paper, the bioconvective nanofluid flow in a horizontal channel was considered. Using the appropriate similarity functions, the partial differential equations of the studied problem resulting from mathematical modeling are reduced to a set of non-linear differential equations. Thereafter, these equations are solved numerically using the fourth order Runge-Kutta method featuring shooting technique and analytically via the Adomian decomposition method (ADM). This study mainly focuses on the effects of several physical parameters such as Reynolds number (Re), thermal parameter (𝛿𝜃), microorganisms density parameter (𝛿s) and nanoparticles concentration (𝛿f) on the velocity, temperature, nanoparticle volume fraction and density of motile microorganisms. It is also demonstrated that the analytical ADM results are in excellent agreement with the numerical solution and those reported in literature, thus justifying the robustness of the adopted Adomian Decomposition Method.
Fluid Mechanics
Ganesh Kumar; Ramesh G K; Sabir Ali Shehzad; Gireesha B.J
Abstract
In this article, we examined the behavior of chemical reaction effect on a magnetohydrodynamic Prandtl nanofluid flow due to stretchable sheet. Non-linear thermally radiative term is accounted in energy equation. Constructive transformation is adopted to formulate the ordinary coupled differential equations ...
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In this article, we examined the behavior of chemical reaction effect on a magnetohydrodynamic Prandtl nanofluid flow due to stretchable sheet. Non-linear thermally radiative term is accounted in energy equation. Constructive transformation is adopted to formulate the ordinary coupled differential equations system. This system of equations is treated numerically through Runge Kutta Fehlberg-45 method based shooing method. The role of physical constraints on liquid velocity, temperature and concentration are discussed through numerical data and plots. Also, the skin friction co-efficient, local Nusselt number and local Sherwood numbers are calculated to study the flow behavior at the wall, which is also presented in tabular form. A comparative analysis is presented with the previous published data in special case for the justification of the present results. The output reveals that for larger values of elastic and Prandtl parameter, the thickness of momentum layer enhanced and the rates of both heat and mass transport reduced. Also, increment of slip parameter decelerated both temperature and concentration filed while nonlinear form thermal radiation rapidly increases the temperature.
Fluid Mechanics
Maryam Hassani; Mohammad Bagheri Motlagh; Ramin Kouhikamali
Abstract
In this paper, numerical investigation of upward two phase flow of air-water has been studied. Different conditions of flow regimes including annular, wispy annular, slug, churn and bubbly are simulated based on Hewitt and Roberts map, and a good agreement between the experimental data of the map and ...
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In this paper, numerical investigation of upward two phase flow of air-water has been studied. Different conditions of flow regimes including annular, wispy annular, slug, churn and bubbly are simulated based on Hewitt and Roberts map, and a good agreement between the experimental data of the map and the numerical simulation has been observed. Accordingly, a proper CFD model in CFD software of Fluent with the required User Defined Function (UDF) has been obtained to simulate two phase flows of fluids with large density ratio in vertical tubes. The simulation is carried out with the volume of fluid (VOF) method and piecewise interface calculation (PLIC) algorithm for tracking the interface for the annular, wispy annular, churn and slug flow regimes and drift flux model for bubbly with proper selection of computational cell and time step sizes. Furthermore, water and air momentum fluxes have been changed and the changes to the flow patterns are studied.
Fluid Mechanics
Pedram Hanafizadeh; Amirmohammad Sattari; Seyed Erfan Hosseinidoost; Morteza Molaei; Mehdi Ashjaee
Abstract
Detecting bubble in two-phase flow has been a basic issue in two-phase flow systems. A new method for measuring the frequency of bubble formation is presented in this paper. For this purpose, an electronic device was designed and constructed which works based on a change in intensity of laser beam. For ...
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Detecting bubble in two-phase flow has been a basic issue in two-phase flow systems. A new method for measuring the frequency of bubble formation is presented in this paper. For this purpose, an electronic device was designed and constructed which works based on a change in intensity of laser beam. For this purpose, continues light beam is embedded just above the needle, which is received by a phototransistor. When bubbles go through this light beam, make a deviation on that and change the intensity of light. So, the electrical resistance between two bases of phototransistor changes and this variation sensed by an electronic board. According to the number of interruption and duration time, the frequency of bubble formation can be calculated. Liquid and gas phases of present work are water and air respectively. Tests are performed in constant liquid height (60 mm above the needle), constant needle diameter (1.6 mm), and gas flow rates between 50 to 1200 ml/hr. Also, three other methods utilized for measuring bubble frequency: image processing (IP), numerical modeling, and theoretical model. Results show that with increasing flow rate of the gas phase frequency of formation increases approximately in a linear manner. Validation of methods with IP method shows that the new device has very good accuracy for measuring bubble formation frequency. So because of the simplicity of using and low cost, it can be a superseded method of image processing.
Fluid Mechanics
Kvenu Reddy; M. Gnaneswara Reddy
Abstract
In this paper, we analyze the thermal radiation and chemical reaction impacts on MHD peristaltic motion of the Eyring-Powell fluid through a porous medium in a channel with compliant walls under slip conditions for velocity, temperature, and concentration. Assumptions of a long wave length and low Reynolds ...
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In this paper, we analyze the thermal radiation and chemical reaction impacts on MHD peristaltic motion of the Eyring-Powell fluid through a porous medium in a channel with compliant walls under slip conditions for velocity, temperature, and concentration. Assumptions of a long wave length and low Reynolds number are considered. The modeled equations are computed by using the perturbation method. The resulting non-linear system is solved for the stream function, velocity, temperature, concentration, skin-friction coefficient, heat transfer coefficient and mass transfer coefficient. The flow quantities are examined for various parameters. Temperature depresses with an enhancee in the radiation parameter, while the opposite effect is observed for the concentration. The fluid concentration enhances and depresses with generative and destructive chemical reaction respectively. The trapped bolus whose size diminishes as the Powel-Eyring parameter increases while it enhances as another Powell fluid parameter increases. The trapped bolus whose size rises when Darcy number enhances.
Fluid Mechanics
Neetu Kanaujia; Uday Singh Rajput
Abstract
Unsteady flow with magneto-hydrodynamics and heat generation through porous medium past an impulsively started vertical plate with constant wall temperature and mass diffusion is considered here. The effect studied is a combination of Hall current and chemical reaction. The motivation behind this study ...
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Unsteady flow with magneto-hydrodynamics and heat generation through porous medium past an impulsively started vertical plate with constant wall temperature and mass diffusion is considered here. The effect studied is a combination of Hall current and chemical reaction. The motivation behind this study is the applications of such kind of problems in industry. In many industrial applications electrically conducting fluid is subjected to magnetic field. The fluid is passed through porous medium. The flow may be on a plate. There may be substance on the plate which may cause chemical reaction. The solution of flow model studied here is obtained by using Laplace transform method. The respective profiles have been drawn for velocity. The numerical data have been obtained using latest software techniques available. The profiles have been analyzed and discussed. The values of Nusselt number, Sherwood number, and drag on plate have been tabulated for analysis. The findings have been summarized in conclusion section.
Fluid Mechanics
Rahim Shamsoddini
Abstract
Liquid sloshing is a common phenomenon in the transporting of liquid tanks. Liquid waves lead to fluctuating forces on the tank wall. If these fluctuations are not predicted or controlled, they can lead to large forces and momentum. Baffles can control liquid sloshing fluctuations. One numerical method, ...
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Liquid sloshing is a common phenomenon in the transporting of liquid tanks. Liquid waves lead to fluctuating forces on the tank wall. If these fluctuations are not predicted or controlled, they can lead to large forces and momentum. Baffles can control liquid sloshing fluctuations. One numerical method, widely used to model the liquid sloshing phenomena is Smoothed Particle Hydrodynamics (SPH). Because of its Lagrangian nature, SPH is suitable for simulating free surface flow. In the present study, a relatively accurate Incompressible SPH (ISPH) method improved by kernel gradient correction tensors, particle shifting algorithms, turbulence viscosity calculations, and free surface particle detectors is applied for the free surface flow modeling. In comparison to the other SPH Simulations and experimental data, these results show that the present algorithm is effective for simulating free surface problems. The present algorithm has been applied to simulate liquid sloshing phenomena, while the aim of this study is the investigation of vertical and horizontal baffle effects on the control and damping of liquid sloshing. Results show that for vertical baffles, baffle size has a major role in sloshing fluctuation damping. For horizontal baffles, also including size, the baffle base position has a significant role in liquid sloshing fluctuation damping. When horizontal baffle is near the free surface, sloshing fluctuation-damping increases.
Fluid Mechanics
Payam Rahim Masharei; Seyed Mostafa Hosseinalipour; Mohammad Javad moslemani
Abstract
Laminar mixing of glycerin in a chaotic mixer is carried by means of the blob deformation method. The mixer was a cylindrical vessel with two rotational blades which move along two different circular paths with a stepwise motion protocol. The flow visualization was performed by marking of the free surface ...
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Laminar mixing of glycerin in a chaotic mixer is carried by means of the blob deformation method. The mixer was a cylindrical vessel with two rotational blades which move along two different circular paths with a stepwise motion protocol. The flow visualization was performed by marking of the free surface of the flow with a tracer. The effects of controlling parameters such as rotational speed of blades, blades length, and rotational speed amplitude on mixing efficiency and time were analyzed by measuring of the area covered by the tracer. The results revealed that increasing rotational speed intensifies stretching and folding phenomenon, and consequently better mixing can be obtained. Also, the better condition in flow kinematic was provided to blend as stepwise motion protocol with wider amplitude adopted. A reduction in mixing time could be observed as the blades with longer length were used. In addition, it was also found that the promotion of mixing by rotational speed is more effective than that of two other parameters. The quantitative data and qualitative observations proved the potential of proposed chaotic mixer in wide range of industrial processes including chemical reaction and food processing in which laminar mixing is required.
Fluid Mechanics
Prasannakumara B.C; Shashikumar N.S; Archana M
Abstract
The steady three-dimensional boundary layer flow and heat transfer of a dusty fluid towards a stretching sheet with convective boundary conditions is investigated by using similarity solution approach. The free stream along z-direction impinges on the stretching sheet to produce a flow with different ...
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The steady three-dimensional boundary layer flow and heat transfer of a dusty fluid towards a stretching sheet with convective boundary conditions is investigated by using similarity solution approach. The free stream along z-direction impinges on the stretching sheet to produce a flow with different velocity components. The governing equations are reduced into ordinary differential equations by using appropriate similarity variables. Reduced nonlinear ordinary differential equations subjected to the associated boundary conditions are solved numerically by using Runge–Kutta fourth-fifth order method along with Shooting technique. The effects of the physical parameters like magnetic parameter, velocity ratio, fluid and thermal particle interaction parameter, Prandtl number, Eckert number and Biot number on flow and heat characteristics are examined, illustrated graphically, and discussed in detail. The results indicate that the fluid phase velocity is always greater than that of the particle phase and temperature profiles of fluid and dust phases increases with the increase of the Eckert number.
Fluid Mechanics
Javad Shahbazi Karami; GH. Payganeh
Abstract
In this study, hot metal gas forming process of AA6063aluminumtubeis studied with a focus on heat transfer of both fluid and solid phases numerically. An experimental study is simultaneously conducted to validate the numerical method. Some of the most important outputs of the present study, are velocity ...
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In this study, hot metal gas forming process of AA6063aluminumtubeis studied with a focus on heat transfer of both fluid and solid phases numerically. An experimental study is simultaneously conducted to validate the numerical method. Some of the most important outputs of the present study, are velocity distribution of fluid inside the tube as well as the fluid in the gap between tube and matrices. As a result of non-homogenous distribution of temperature on tube surface, circulating flows are generated inside the tube which may have considerable effects on heat transfer phenomenon. It is seen that in 600 s after start, number of the circulating flows doubles. Analysis of temperature distribution reveals thatmiddle part of the tube reaches 500 ̊C after 600 s from process start and other parts have higher temperature. By applying an efficient control method for heater elements, temperature distribution of the tube reaches a homogenous form.
Fluid Mechanics
M. Alemi; R. Maia
Abstract
The present study aimed to investigate two numerical solutions of the Navier-Stokes equations. For this purpose, the mentioned flow equations were written in two different formulations, namely (i) velocity-pressure and (ii) vorticity-stream function formulations. Solution algorithms and boundary conditions ...
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The present study aimed to investigate two numerical solutions of the Navier-Stokes equations. For this purpose, the mentioned flow equations were written in two different formulations, namely (i) velocity-pressure and (ii) vorticity-stream function formulations. Solution algorithms and boundary conditions were presented for both formulations and the efficiency of each formulation was investigated by considering a two-dimensional low laminar flow around a square pile in a rectangular computational domain. Simulations under the same conditions were conducted to assess the difference between results generated by both formulations. Furthermore, the accuracy of the results was analyzed through a comparison of the results with the available reference data. In addition, computational efficiency of both formulations was investigated in term of computation time. The corresponding results indicated that both formulations are adequate to the case used in the present study. Moreover, performed simulations showed that solving the vorticity-stream function form of the flow equations is faster than solving the velocity-pressure form of those equations for simulating a two-dimensional laminar flow around a square pile.
Fluid Mechanics
F. Khalighi; A. Ahmadi; A. Keramat
Abstract
Four explicit finite difference schemes, including Lax-Friedrichs, Nessyahu-Tadmor, Lax-Wendroff and Lax-Wendroff with a nonlinear filter are applied to solve water hammer equations. The schemes solve the equations in a reservoir-pipe-valve with ...
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Four explicit finite difference schemes, including Lax-Friedrichs, Nessyahu-Tadmor, Lax-Wendroff and Lax-Wendroff with a nonlinear filter are applied to solve water hammer equations. The schemes solve the equations in a reservoir-pipe-valve with an instantaneous and gradual closure of the valve boundary. The computational results are compared with those of the method of characteristics (MOC), and with the results of Godunov''s scheme to verify the proposed numerical solution. The computations reveal that the proposed Lax-Friedrichs and Nessyahu-Tadmor schemes can predict the discontinuities in fluid pressure with an acceptable order of accuracy in cases of instantaneous and gradual closure. However, Lax-Wendroff and Lax-Wendroff with nonlinear filter schemes fail to predict the pressure discontinuities in instantaneous closure. The independency of time and space steps in these schemes are allowed to set different spatial grid size with a unique time step, thus increasing the efficiency with respect to the conventional MOC. In these schemes, no Riemann problems are solved; hence field-by-field decompositions are avoided. As provided in the results, this leads to reduced run times compared to the Godunov scheme.
Fluid Mechanics
H. Chamani; H. Karimaei; M. Bahrami; S. M. Agha Mirsalim
Abstract
Nowadays, due to the increasing power of diesel engines, especially heavy duty diesel engines, and increasing gas pressure inside the combustion chamber, the forces acting on the engine bearings have dramatically raised. On the other hand, becaus eof the competition in the market, it is necessary to ...
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Nowadays, due to the increasing power of diesel engines, especially heavy duty diesel engines, and increasing gas pressure inside the combustion chamber, the forces acting on the engine bearings have dramatically raised. On the other hand, becaus eof the competition in the market, it is necessary to increase the engine bearing life and reduce its failure as much as possible. The engine bearings analysis is a vital issue in engine design process as well as other related engineering tasks such as engine power upgrading, reverse designing, and bearing failure analysis. So, many attempts have been made to simulate accurate engine bearings. In this paper, results of a thermo-elasto-hydrodynamic (TEHD) analysis of a connecting rod big end (BE) bearing of a heavy duty diesel engine are presented. Here, the oil film viscosity is considered a function of oil's local temperature and pressure. Effects of flexibility of bearing shell and connecting rod structure are also considered. Therefore, the computed oil film pressure and temperature distributions are relatively precise. In the proposed analytical procedure, at first, elasto-hydrodynamic (EHD) analysis is carried out and the averaged fluid velocity in the bearing is obtained. Then, the averaged heat transfer coefficient between oil film and crank pin is calculated, which is used as an input in TEHD analysis. Results of EHD and TEHD analyses are compared with each other and the main characteristic parameters in bearing design are reported and interpreted.
Fluid Mechanics
P. R. Mashaei Mashaei; S. M. Hosseinalipour; K. Esmailpour
Abstract
In recent years, impinging streams have received increasing interest for their high efficiency in heat and mass transfer. This numerical study was conducted to investigate flow and heat transfer characteristics of one-way opposing jets of non-Newtonian fluids. Effects of Reynolds number impinging angle, ...
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In recent years, impinging streams have received increasing interest for their high efficiency in heat and mass transfer. This numerical study was conducted to investigate flow and heat transfer characteristics of one-way opposing jets of non-Newtonian fluids. Effects of Reynolds number impinging angle, momentum ratio and flow behavior index on mixing index were evaluated. The results showed improvement of thermal mixing due to an increase in Reynolds number, flow behavior index and momentum ratio in impinging zone. This study also demonstrated that thermal mixing along the channel increased as the Reynolds number and momentum ratio decreased. Nevertheless, augmentation of the flow behavior index resulted in higher thermal mixing along the channel. The impinging angle had no significant effect on thermal mixing along the channel; but, with increasing impinging angle, thermal mixing improved in the impinging zone.
Fluid Mechanics
J. Jamaati; H. Niazmand; M. Renksizbulut
Abstract
A numerical study of 3D electrokinetic flows through micromixers was performed. The micromixers considered here consisted of heterogeneous rectangular microchannels with prescribed patterns of zeta-potential at their walls. Numerical simulation of electroosmotic flows within heterogeneous channels requires ...
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A numerical study of 3D electrokinetic flows through micromixers was performed. The micromixers considered here consisted of heterogeneous rectangular microchannels with prescribed patterns of zeta-potential at their walls. Numerical simulation of electroosmotic flows within heterogeneous channels requires solution of the Navier-Stokes, Ernest-Plank and species concentration equations. It is known that a 3D solution of these equations is computationally very intensive. Therefore, the well-known Helmholtz-Smoluchowski model is often used in numerical simulation of electroosmotic flows. According to 2D studies on electrokinetic mixing inside heterogeneous channels, existence of vortices within the flow field always increases mixing performance. Hence, it may be expected that similar observations pertain to mixing in 3D flows as well. However, investigations on 3D micromixers identified situations in which existence of vortices had little or no significant benefit to the mixing performance. Findings of the present work indicated degree of flow asymmetry as a key parameter for the mixing performance. Since 3D flows are more capable of developing asymmetrical flow patterns, they are expected to have better mixing performance than their 2D counterparts. The results presented here for different 3D cases showed that mixing performance could be improved significantly depending on the alignment of vortex plane relative to the mixing interface of the fluids. These observations confirmed that 2D simulations of mixing could not fully explain behavior of passive micromixers.
Fluid Mechanics
S. F. Ahmed
Abstract
Energy equation for turbulent flow in a rotating system was derived in terms of second order correlation tensors, where the correlation tensors were functions of space coordinates, distance between two points and time. To reveal the relationship of turbulent energy between two points, one point was taken ...
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Energy equation for turbulent flow in a rotating system was derived in terms of second order correlation tensors, where the correlation tensors were functions of space coordinates, distance between two points and time. To reveal the relationship of turbulent energy between two points, one point was taken as origin of the coordinate system. Due to rotation, the Coriolis force played an important role in the rotating system of turbulent flow. The correlation between pressure fluctuations and velocity fluctuations at the two points of flow field was applied to the turbulent energy equation, in which the Coriolis force and centrifugal force acted on the fluid.
