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flow-simulation
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Computational Simulation of Turbulent Endwall Effects in Gas Turbines, Using LES Approach
,
M.Sc. Thesis
Sharif University of Technology
;
Tayyebi Rahni, Mohammad
(Supervisor)
;
Ramezanizadeh, Mahdi
(Supervisor)
Abstract
The most common three-dimensional flows accuring in axial turbomachineries are endwall flows. These flows, which depend on inner hub and on external surface of airfoils are called secondary flows. In modern turbines, these flows reduce turbine efficiency up to about 3 percent.Many sientists are interested in investigation such flows. In this study, turbulent endwall flows are modeled using large eddy simulation approach. Also, SIMPLE algoritm and Smagorinsky subgrid scale model are used. Non-orthogonal curvilinear coordinate system and structural grid are implemented.To verify the results, they were compared with some existing experimental data which, showed that current numerical results...
Numerical Solution of Two-dimensional Compressible Flow Using Immersed Boundary Method with Compact Finite Difference Scheme
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In this study, the viscous compressible flow is simulated over two-dimensional geometries by using the immersed boundary method and applying a high-order accurate numerical scheme. A fourth-order compact finite-difference scheme is used to accurately discretize the spatial derivative terms of the governing equations and the time integration is performed by the fourth-order Runge–Kutta scheme. To regularize the numerical solution and eliminate spurious modes due to unresolved scales, nonlinearities and inaccuracies in implementing boundary conditions, high-order low-pass compact filters are applied. A uniform Cartesian grid that is not coincident with the body surface is used and the boundary...
Simulation of Fluid Flow in Nanotubes by Non-Equilibrium Molecular Dynamics
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
Abstract
One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the...
Dynamic Modeling and Experimental Study of Asphaltene Deposition in Wellbore Considering Mechanism of Precipitation, Aggregation and Deposition
,
Ph.D. Dissertation
Sharif University of Technology
;
Ghotbi, Cyrus
(Supervisor)
;
Dabir, Bahram
(Co-Supervisor)
;
Taghikhani, Vahid
(Co-Supervisor)
Abstract
Efforts to identify, predict, and resolve problems linked to asphaltenes and flow assurance have resulted in the development of numerous laboratory and modelling techniques. However, there has been little research on the molecular structure of asphaltenes and how it relates to solubility, stability, aggregation, and deposition behavior. Not only was a thorough structural analysis of asphaltene extracted from three samples of light, medium, and heavy oil performed in this study, but medium oil asphaltene was also fractionated into three sub-fractions based on solubility, with minimum, medium, and maximum solubility, and each subfraction was subjected to a structural analysis. All asphaltene...
Studying and Reviewing the Modification, Completion or Change of the Classical Theories Used in the Simulation of Resin Injection Network for Manufacturing of a Large Composite Structure by Means of Vacuum Infusion Process
, M.Sc. Thesis Sharif University of Technology ; Abedian, Ali (Supervisor)
Abstract
In recent years, liquid resin injection processes for aviation applications have been considered an alternative to conventional autoclave-based processes. At present, these processes have challenges that have been denied industry trust due to their inability to be objectively reproducible. In the last decade, some software has been developed to simulate the vacuum injection process, but this software does not have enough capability to predict the injection network, and an operator with sufficient empirical knowledge must use this software. In recent years, researchers have used this softwares to simulate the process, but so far no software has been developed that can offer injection...
Evaluation of the Effect of Connected Vehicles Speed and Acceleration Parameters on Freeways Safety and Efficiency
, M.Sc. Thesis Sharif University of Technology ; Nassiri, Habibollah (Supervisor)
Abstract
Autonomous Vehicles have received much consideration in different trends in recent two decades. Autonomous Vehicles refer to vehicles that can drive without a driver and perform all driving tasks automatically, so eliminating the driver's role can affect various aspects. In this research, the effects of Autonomous Vehicles on the improvement of the traffic condition is studied. To this end, freeway’s performance parameters including travel time and traffic speed at the time of a traffic accident in mixed traffic conditions have been simulated. Considering that the braking behavior, acceleration, and speed changes of the Autonomous Vehicle are effective on the evaluation parameters, five...
Dissipative particle dynamics simulation of electroosmotic flow in nanoscale channels
, Article 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Orlando, FL, 4 January 2010 through 7 January 2010 ; 2010 ; 9781600867392 (ISBN) ; Zakeri, R ; Schneider, G. E ; Sharif University of Technology
2010
Abstract
This Paper presents the simulation of electroosmotic flow in nanochannels using the dissipative particle dynamics (DPD) method. Most of the past electroosmotic phenomenon studies have been carried out using the continuum flow assumptions. However, there are many electroosmotic applications in nanoscales NEMS and microscales MEMS, which need to be treated using non-continuum flow assumptions. We simulate the electroosmotic flow within the mesoscopic scale using the DPD method. Contrary to the ordinary molecular dynamics method, the DPD method provides less computational costs. We will show that the current DPD results are in very good agreement with other available non-DPD results. To expand...
Flow of a PTT fluid through planar contractions - Vortex inhibition using rounded corners
, Article ASME 2010 International Mechanical Engineering Congress and Exposition, IMECE 2010, Vancouver, BC, 12 November 2010 through 18 November 2010 ; Volume 7, Issue PARTS A AND B , November , 2010 , Pages 601-607 ; 9780791844441 (ISBN) ; Ramazani S. A, A ; Hosseini Amoli, H ; Behrang, A ; Kamyabi, A ; Sharif University of Technology
2010
Abstract
Contraction flow is one of important geometries in fluid flow both in Newtonian and non-Newtonian fluids. In this study, flow of a viscoelastic fluid through a planar 4:1 contraction with rounded corners was investigated. Six different rounding ratios (RR =0, 0.125, 0.25, 0.375, 0.438, 0.475, 0.488) was examined using the linear PTT constitutive equation at creeping flow and isothermal condition. Then the resulting PDE set including continuity, momentum, and PTT constitutive equations were implemented to the OpenFOAM software. The results clearly show vortex deterioration with increasing rounding diameter, so that when rounding corner exceeds a critical value, the vortex disappears...
Numerical simulation of heat transfer in mixed electroosmotic pressure-driven flow in straight microchannels
, Article Journal of Thermal Science and Engineering Applications ; Volume 8, Issue 2 , 2016 ; 19485085 (ISSN) ; Merdasi, A ; Vatankhah, P ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2016
Abstract
This paper investigates two-dimensional, time-independent elecroosmotic pressuredriven flow generated by a direct current electric potential with asymmetrical and symmetrical zeta potential distributions along the microchannel walls. Fluid flow through the horizontal microchannel is simulated using a numerical method. Two different cases are proposed to study the effect of electric potential on the flow field. First, negative electric potential is applied on the microchannel walls. In this case, large segments with negative electric potential are initially placed on the first half of the microchannel walls with two different arrangements. Afterward, smaller segments with negative electric...
New correlative models to improve prediction of fracture permeability and inertial resistance coefficient
, Article Transport in Porous Media ; Volume 121, Issue 3 , February , 2018 , Pages 557-584 ; 01693913 (ISSN) ; Jamshidi, S ; Pishvaie, M. R ; Sharif University of Technology
Springer Netherlands
2018
Abstract
Presence of fracture roughness and occurrence of nonlinear flow complicate fluid flow through rock fractures. This paper presents a qualitative and quantitative study on the effects of fracture wall surface roughness on flow behavior using direct flow simulation on artificial fractures. Previous studies have highlighted the importance of roughness on linear and nonlinear flow through rock fractures. Therefore, considering fracture roughness to propose models for the linear and nonlinear flow parameters seems to be necessary. In the current report, lattice Boltzmann method is used to numerically simulate fluid flow through different fracture realizations. Flow simulations are conducted over a...
Performance of combined vorticity-based gridding and dual mesh method for gravity dominated reservoir flows
, Article Journal of Petroleum Science and Engineering ; Volume 67, Issue 3-4 , 2009 , Pages 127-139 ; 09204105 (ISSN) ; Ashjari, M. A ; Sharif University of Technology
2009
Abstract
This paper presents a new combined method for accurate upscaling of two-phase displacements in highly heterogeneous reservoirs. The method has the capability to retain its high performance for various flow regimes, from viscous to gravity dominant displacements, without the need for further modifications and computational steps. Two different grids are incorporated for simulation. The grid on fine scale is used to recognize the complicated physics of flow which depends on dominated driving forces and their interaction with heterogeneity. However, to achieve a fast simulation, the global flow calculation is performed on the coarse scale grid using upscaled equivalent properties. The...
Utilizing a simulation approach for analysis of patient flow in the emergency department: a case study
, Article 15th Iran International Industrial Engineering Conference, IIIEC 2019, 23 January 2019 through 24 January 2019 ; 2019 , Pages 151-157 ; 9781728117751 (ISBN) ; Haji, B ; Shakhsi Niaei M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
Simulation has been shown to be one of the most powerful tools in many areas of the health-care system, a system which attracted the attention of researchers due to its intricacy. The main goal of this study is to evaluate the patients' flow in an emergency department (ED). Discrete event simulation (DES)has been used as the core of this research so that it offers various ways to reduce the length of stay (LOS)of patients in different segments of ED by assessing various scenarios. In particular, a new approach for verification of the simulated model will be discussed. This study reports on the results that extracted from a case study on patient record data in one of the EDs located in Tehran...
Investigation of the continuum-rarefied flow and isotope separation using a hybrid CFD-DSMC simulation for UF6 in a gas centrifuge
, Article Annals of Nuclear Energy ; 2020 ; Akbar Salehi, A ; Reza Keshtkar, A ; Mahdi Shadman, M ; Hossein Askari, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow...
Using vorticity as an indicator for the generation of optimal coarse grid distribution
, Article Transport in Porous Media ; Volume 75, Issue 2 , 2008 , Pages 167-201 ; 01693913 (ISSN) ; Firoozabadi, B ; Mahani, H ; Sharif University of Technology
2008
Abstract
An improved vorticity-based gridding technique is presented and applied to create optimal non-uniform Cartesian coarse grid for numerical simulation of two-phase flow. The optimal coarse grid distribution (OCGD) is obtained in a manner to capture variations in both permeability and fluid velocity of the fine grid using a single physical quantity called "vorticity". Only single-phase flow simulation on the fine grid is required to extract the vorticity. Based on the fine-scale vorticity information, several coarse grid models are generated for a given fine grid model. Then the vorticity map preservation error is used to predict how well each coarse grid model reproduces the fine-scale...
Computer simulation of the effect of particle stiffness coefficient on the particle-fluid flows
, Article Particulate Science and Technology ; 2021 ; 02726351 (ISSN) ; Rajabi, M ; Sharif University of Technology
Bellwether Publishing, Ltd
2021
Abstract
The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective...
Computer simulation of the effect of particle stiffness coefficient on the particle-fluid flows
, Article Particulate Science and Technology ; 2021 ; 02726351 (ISSN) ; Rajabi, M ; Sharif University of Technology
Bellwether Publishing, Ltd
2021
Abstract
The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective...
A high-order compact finite-difference lattice Boltzmann method for simulation of steady and unsteady incompressible flows
, Article International Journal for Numerical Methods in Fluids ; Vol. 75, Issue. 10 , 2014 , Pages 713-746 ; ISSN: 02712091 ; Ezzatneshan, E ; Sharif University of Technology
Abstract
A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied to accurately compute steady and unsteady incompressible flows. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized by using the fourth-order compact FD scheme, and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient incompressible flow solver. A high-order spectral-type low-pass compact filter is used to stabilize the numerical solution. An iterative initialization procedure is presented and applied to generate consistent initial conditions for the simulation of unsteady flows. A sensitivity study is also...
A new approach to counter-current spontaneous imbibition simulation using Green element method
, Article Journal of Petroleum Science and Engineering ; Vol. 119, issue , 2014 , p. 163-168 ; Pishvaie, M. R ; Sharif University of Technology
Abstract
This paper develops a two dimensional Green element simulator based on a "compatibility-equation" algorithm for simulation of counter-current spontaneous imbibition (COUCSI) process. The Green element method is a novel computational approach based on the boundary integral theory, which is regarded as a hybrid combination of both boundary and finite element methods. The superiority of the Green element method in modeling of two phase water/oil flow is at the core of this paper. The developed simulator within the context of this proposition is explored to predict the oil recovery from a one dimensional single matrix block. The results are then compared with the experimental data, and they...
Chebyshev collocation spectral lattice Boltzmann method for simulation of low-speed flows
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 91, Issue 1 , January , 2015 ; 15393755 (ISSN) ; Hajihassanpour, M ; Sharif University of Technology
American Physical Society
2015
Abstract
In this study, the Chebyshev collocation spectral lattice Boltzmann method (CCSLBM) is developed and assessed for the computation of low-speed flows. Both steady and unsteady flows are considered here. The discrete Boltzmann equation with the Bhatnagar-Gross-Krook approximation based on the pressure distribution function is considered and the space discretization is performed by the Chebyshev collocation spectral method to achieve a highly accurate flow solver. To provide accurate unsteady solutions, the time integration of the temporal term in the lattice Boltzmann equation is made by the fourth-order Runge-Kutta scheme. To achieve numerical stability and accuracy, physical boundary...
Cooperation within von Willebrand factors enhances adsorption mechanism
, Article Journal of the Royal Society Interface ; Volume 12, Issue 109 , 2015 ; 17425689 (ISSN) ; Mehrbod, M ; Ejtehadi, M. R ; Mofrad, M. R ; Sharif University of Technology
Royal Society of London
2015
Abstract
von Willebrand factor (VWF) is a naturally collapsed protein that participates in primary haemostasis and coagulation events. The clotting process is triggered by the adsorption and conformational changes of the plasma VWFs localized to the collagen fibres found near the site of injury. We develop coarse-grained models to simulate the adsorption dynamics of VWF flowing near the adhesive collagen fibres at different shear rates and investigate the effect of factors such as interaction and cooperativity of VWFs on the success of adsorption events. The adsorption probability of a flowing VWF confined to the receptor field is enhanced when it encounters an adhered VWF in proximity to the...