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Interaction of two spark-generated bubbles near a confined free surface
, Article Theoretical and Computational Fluid Dynamics ; Volume 30, Issue 3 , 2016 , Pages 185-209 ; 09354964 (ISSN) ; Shervani Tabar, M. T ; Taeibi Rahni, M ; Dadvand, A ; Sharif University of Technology
Springer New York LLC
2016
Abstract
In this paper, the oscillation of two spark-generated bubbles placed on a vertical column in close proximity to a confined free surface is considered. The confined free surface is accorded by the top opening of different configurations. These configurations include (i) a centrally perforated horizontal flat plate (θ = 90∘), (ii) vertically placed cylinder (θ = 0∘) and (iii) nozzle (θ > 0∘). The main objective of the present work is to study the effects of key parameters such as the nozzle geometry, the locations of the energy input (i.e., initial position of the bubbles with respect to each other and relative to the free surface) on the dynamics of the two bubbles and the free surface. It...
Simulation of Droplet Formation and Detachment, Using Lattice Boltzmann Method
, M.Sc. Thesis Sharif University of Technology ; Taeibi Rahni, Mohammad (Supervisor)
Abstract
The phenomena of formation and detachment of droplets are of fundamental importance in studying two-phase flows, such as spraying processes, ink jet printing, emulosin, etc. Droplets are formed under the effects of surface tension forces. After formation, forces like gravity detach the droplet from the rest of the fluid. Recent advancements in computational fluid dynamics and computers have made it feasible to have advancement in simulation of complex flows, including two-phase phenomenon. On the other hand, the lattice Boltzmann method (LBM) has been developed into an alternative and promising numerical scheme for simulating multi-component fluid flows.
In this project, formation and...
In this project, formation and...
Applicability of lattice Boltzmann method in simulation of drops and bubbles formation and transport
, Article AIP Conference Proceedings, 22 September 2014 through 28 September 2014 ; Volume 1648 , 2015 ; 0094243X (ISSN) ; 9780735412873 (ISBN) ; Alizadeh, M ; Haghshenas, M ; Salimi, H ; Najafi, M ; Miller, R ; Sharif University of Technology
2015
Abstract
Multiphase flows appear in many scientific and engineering applications. On the other hand, there has been a tremendous experimental and numerical investigation trying to understand complex fluid-fluid interfaces better. However, conventional CFD have certain limitations in complicated situations. Fortunately in the past two decades, new approaches, namely SPH and LBM (sometimes called meshless methods) have been developed. Since they are mesoscopic, they have been able to perform much better than conventional CFD. Especially, LBM is becoming more and more popular and has already been divided to many branches
Numerical study on the oscillation of a transient bubble near a confined free surface for droplet generation
, Article Theoretical and Computational Fluid Dynamics ; Vol. 28, issue. 4 , 2014 , p. 449-472 ; Shervani-Tabar, M.T ; Taeibi-Rahni, M ; Dadvand, A ; Sharif University of Technology
2014
Abstract
In the present work, the oscillation of a spark-created bubble near a confined water-air interface and the ensuing droplet generation and ejection are studied numerically using the boundary element method. The interface is accorded by the top opening of either one of the following symmetrical configurations, which are distinguished by the value of angle between their vertical symmetry axis and lateral wall (i.e., θ): (i) a centrally perforated horizontal flat plate (θ = 90°) and (ii) vertically placed cylinder (θ = 0°), nozzle (θ > 0°) and diffuser (θ < 0°). Furthermore, the influences of the effective parameters such as the strength parameter (i.e., the intensity of local energy input), the...
Effect of geometrical parameters on radiometric force in low-pressure MEMS gas actuator
, Article Microsystem Technologies ; Volume 24, Issue 5 , 2018 , Pages 2189-2198 ; 09467076 (ISSN) ; Domiri Ganji, D ; Taeibi Rahni, M ; Vakilipour, S ; Sharif University of Technology
Springer Verlag
2018
Abstract
In this paper, comprehensive numerical studies are performed to investigate the effects of the geometrical factors on the performance of the low-pressure gas actuator. The flow feature and force generation mechanism inside a rectangular enclosure with heat and cold arms as the non-isothermal walls are inclusively discussed. Also, comprehensive parametric studies are done to reveal the effects of physical parameters on the performance and characteristics of this device in different operating conditions. In this study, the Knudsen number is varied from 0.1 to 4.5 to investigate all characteristics of the thermal-driven force inside the MEMS sensor. In order to simulate a rarefied gas inside...
Effect of knudsen thermal force on the performance of low-pressure micro gas sensor
, Article European Physical Journal Plus ; Volume 132, Issue 7 , 2017 ; 21905444 (ISSN) ; Ganji, D. D ; Taeibi Rahni, M ; Vakilipour, S ; Sharif University of Technology
2017
Abstract
In this paper, Direct Simulation Monte Carlo (DSMC) simulations were applied to investigate the mechanism of the force generation inside a low-pressure gas sensor. The flow feature and force generation mechanism inside a rectangular enclosure with heat and cold arms as the non-isothermal walls are comprehensively explained. In addition, extensive parametric studies are done to study the effects of physical parameters on the performance and characteristics of this device in different operating conditions. In this research, the Knudsen number is varied from 0.1 to 4.5 (0.5 to 11torr) to reveal all the characteristics of the thermally driven force inside the MEMS sensor. In order to simulate a...
Energy transfer in a liquid filled elemental passage of a porous medium for permeability enhancement due to pulsations of a vapor bubble
, Article Mechanika ; Volume 22, Issue 1 , 2016 , Pages 25-30 ; 13921207 (ISSN) ; Shervani Tabar, M. T ; Taeibi Rahni, M ; Tabatabaei Nejad, S. A ; Sharif University of Technology
Kauno Technologijos Universitetas
2016
Abstract
In this paper, a novel method which has been proposed during the last decade for increasing of the permeability of porous media of petroleum reservoirs by transferring of energy via ultrasound waves is investigated numerically. Increasing of permeability of porous media of petroleum reservoirs results in enhancing of oil recovery. This technique is based on the idea of transferring of energy to the liquid filled porous media via the ultrasound waves and consequently producing of pulsating vapor bubbles. The generated vapor bubbles transfer the energy of ultrasound waves in the liquid filled passages of a porous medium through velocity and pressure fields in the liquid domain and in turn...
Application of molecular force for mass analysis of Krypton/Xenon mixture in low-pressure MEMS gas sensor
, Article Vacuum ; Volume 150 , April , 2018 , Pages 207-215 ; 0042207X (ISSN) ; Mosavat, M ; Domiri Ganji, D ; Taeibi Rahni, M ; Moradi, R ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Development of new techniques for detection and analysis of xenon/krypton mixtures is significant for both industrial and environmental purposes. In this research, direct simulation Monte Carlo is applied to analysis Xenon/Krypton gas mixtures through different molecular forces inside a new micro gas sensor (MIKRA). In this device, a temperature difference inside a rectangular enclosure with heat and cold arms as the non-isothermal walls induces a molecular force known as Knudsen force at low pressure condition. This force is proportional to the main characteristics of the gas mixture. In order to simulate a rarefied gas inside the micro gas detector, Boltzmann equations are applied to...
Application of direct simulation Monte Carlo for development of micro gas sensor
, Article Bulgarian Chemical Communications ; Volume 50, Issue 2 , 2018 , Pages 298-305 ; 08619808 (ISSN) ; Ganji, D. D ; Taeibi Rahni, M ; Vakilipour, Sh ; Moradi, R ; Sharif University of Technology
Bulgarian Academy of Sciences
2018
Abstract
Development of a new micro gas sensor is essential for the analysis of the outcome of gas separation devices. In this paper, direct simulation Monte Carlo (DSMC) modeling of low-pressure gas sensor was performed to investigate the effect of physical parameters on the performance and main characteristics of this type of actuator in various operating conditions. Extensive parametric studies were done and the effect of ambient pressure, temperature and gap of arms were comprehensively investigated. Our findings showed that gap size significantly influences the flow features and force generation inside the sensor. © 2018 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria
Computational Simulation of Flow over a Cylinder in Ground Effect, Using PANS
, M.Sc. Thesis Sharif University of Technology ; Taeibi-Rahni, Mohammad (Supervisor)
Abstract
Partially Averaged Navier-Stokes (PANS) turbulence approach provides a closure model for any degree of velocity field filtering, ranging from completely resolved direct numerical simulation (DNS) to completely Reynolds averaged Navier-Stokes (RANS) approach. Preliminary investigations of PANS show promising results, but there is still computational and physical issues that must be addressed. This study investigates the performance of the PANS method for turbulent flow around a cylinder in ground effect with Reynolds number of 13,200. The cylinder flow is a benchmark flow problem which has significant experimental results available for validation of PANS approach. Three different filters...
Numerical Simulation of Dynamic Stall of Consecutive Wind Turbine Blades' Airfoil
, M.Sc. Thesis Sharif University of Technology ; Taeibi-Rahni, Mohammad (Supervisor)
Abstract
Today energy sources, in any kind, have their special situation in human’s life and we must use our knowledge to manage them for effective usage by decreasing losses and finding modern renewable sources. One of the best way to achieve this purpose is increasing efficiency and improve energy generator performances under different environmental conditions. In spite of the fact that wind turbines stall dynamics behavior is under investigation for 6 years, study of dynamic stall phenomenon especially over series blades still needed. By addition to this phenomenon, improper wind turbine arrange decreases efficiency too. As a matter of fact, scrutiny of dynamics stall of wind turbines serial...
Computational Simulation of Micromixing, Using LBM
, M.Sc. Thesis Sharif University of Technology ; Taeibi-Rahni, Mohammad (Supervisor)
Abstract
Nowadays, microfluidic flow appears in many applications, such as medical, biological, and chemical industries. Where as, micromixing, which deals with mixing of microfluidic flow in micro channels, appears to be an important issue to many researchers. In such systems, molecular diffusion plays an important role. On the other hand, lattice Boltzmann method is a relatively new simulation technique for complex fluid systems and has become interesting to many researchers in computational physics. In this study, computational simulation of such mixing process, using LBM is the main objective. Different obstacle layouts inside a microchannel have been investigated. Chaotic advection and jet...
Numerical Analysis of Channel Flow over an Elastic Bump, Using Lattice Boltzmann Method- A Biological Application
, M.Sc. Thesis Sharif University of Technology ; Taeibi Rahni, Mohammad (Supervisor)
Abstract
In recent years, lattice Boltzmann method (LBM) has been developed to be used as an alternative and promising computational technique to simulate various flows. It originates from classical statistical physics. The ability to simply solve complex flows, simulating of multiphase and multi-component without need to follow the boundaries of different phases, and the inherent ability of parallel processing are notable features of this approach. On the other hand, finite element method (FEM) is widely used in many practical engineering fields, especially in solid mechanics. In this study, in addition to simulating flow over a rigid body, flow over an elastic body is also simulated with a...
Computational Simulation of Turbulent Film Cooling, Using RANS/LES Hybrid Approach and Digital Filter Based Interface Boundary Conditions
, M.Sc. Thesis Sharif University of Technology ; Taeibi-Rahni, Mohammad (Supervisor)
Abstract
Nowadays, hybrid LES/RANS approach is being widely used by many researchers. This approach uses the advantages of both LES and RANS approaches simultaneously. Hybrid approach is as accurate as LES, but its cost is much lower. The biggest problem of hybrid approach is transformation of data between RANS and LES regions. Before, precursor simulation and synthetic methods, such as Fourier series and synthetic eddy methods (SEM) have been used extensively to solve such problems. Precursor simulation is expensive, because of high cost of generation of data. On the other hand, Fourier series method is confined to simple geometries, while SEM has problem of programming. Interface condition in this...
Computational Simulation of an Incompressible/ Compressible Turbulent Jet-into-crossflow – An Innovation in Film Cooling
, Ph.D. Dissertation Sharif University of Technology ; Taeibi-Rahni, Mohammad (Supervisor) ; Darbandi, Masoud (Supervisor)
Abstract
This work deals with the computational investigation of film cooling technique, which is one the best practical way to protect gas turbine components form high thermal loads. In this regards, previous works are extensively reviewed and most important effective parameters are classified into three general categories, as geometrical parameters, flow characteristics, and physical surface factors. Each of these categories is then divided into subcategories and more details studies of each are performed. Then, a novel near-wall flow control technique of using staggered arrangement of small injection ports near a film cooling hole (combined-triple-jet; CTJ) is introduced. The fluid injected from...
A Direct Design Method Based on the 3-Dimensional Euler Equations with Application in Internal Subsonic and Supersonic Flows
,
M.Sc. Thesis
Sharif University of Technology
;
Taeibi-Rahni, Mohammad
(Supervisor)
;
Ghadak, Farhad
(Supervisor)
Abstract
In this work, a direct design approach for designing a surface shape (inverse design problem) has been developed in which both the target surface pressure and the unknown nodal coordinates appear explicitly in the formulations. The final discretized form of the governing equations (unified formulation) can be used for both analysis and shape design problems. Shape design problems in the context of the steady inviscid and compressible flow, based on the three-dimensional Euler equations, were directly solved to achieve a prescribed pressure along the solid boundaries. The AUSM+ scheme was used to discretize the flux terms in the Euler equations, in which the inviscid flux is splitted into...
A Unified Fve-Ale Approach to Solve Unsteady Laminar to Turbulent Flow on Moving Boundary Domains
, Ph.D. Dissertation Sharif University of Technology ; Darbandi, Masoud (Supervisor) ; Taeibi Rahni, Mohammad (Supervisor)
Abstract
In this study, an arbitrary Lagrangian-Eulerian (ALE) approach is incorporated with a mixed finite- volume-element (FVE) method to establish a novel moving boundary algorithm to simulate unsteady incompressible flow on non-stationary meshes. The method collects the advantages of both finite-volume and finite-element methods as well as the ALE approach in a unified algorithm capable of solving laminar, transient, and turbulent flows in fluid flow problems with moving boundaries. To enhance the robustness of the extended algorithm, we treat the convection terms at the cell faces using a physical influence upwinding scheme, while the diffusion terms are treated using bilinear finite-element...
Two-Dimensional Computational Simulation of Fluid-Solid Interaction in Tearing of a Membrane between two liquids with Different Molecular Properties and Pressures, Using SPH Method
, M.Sc. Thesis Sharif University of Technology ; Taeibi Rahni, Mohammad (Supervisor) ; Javadi, Khodayar (Supervisor)
Abstract
Smoothed particle hydrodynamics (SPH) is a meshfree method, based on Lagrangian formulation of Navier-Stokes equations, in which fluid is discretized to particles. This method is suitable and gives much better results for problems in which other methods have severe difficulties, (e.g., tracking of particles, moving boundaries, and problems with large deformations and, physical discontinuity). No need to follow a regular geometric structure in solution process and simple adaptation and coupling with methods such as finite element, are the positive characteristics of this numerical method. In this work, a systematic study of the processes, which are part of a membrane failure in a...
LBM Computational Simulation of Oscillations Caused by Formation and Detachment of Drops
, M.Sc. Thesis Sharif University of Technology ; Taeibi Rahni, Mohammad (Supervisor) ; Ebrahimi, Abbas (Supervisor)
Abstract
Formation and detachment of drops are of fundamental importance in studying two-phase flows, such as ink jet printing, emulsion, and spray. Drops are formed under the effects of surface tension forces. After formation, forces like gravity detach the drop from the rest of the fluid. The flow rate is varied from dripping to jetting regime. In this project, formation and detachment of drops were simulated, using LBM with phase field model, which can simulate flows with high-density ratios and is a robust method for applying wetting condition on the walls. Results were validated using single-phase and two-phase flows. After code validation, the oscillations caused by formation and detachment of...
Simulation and Analysis of a Reactive Flow in a Porous Media, Using LBM and GPU
, Ph.D. Dissertation Sharif University of Technology ; Taeibi Rahni, Mohammad (Supervisor) ; Esfahanian, Vahid (Co-Advisor)
Abstract
In this research, surface reaction phenomenon in porous media has been numerically simulated in pore scale. The main interesting part in this kind of physics is surface reaction exposed to a flow field. In this regard, an in-house code, based on LBM was developed. To speed-up our simulation, parallel computing was used on a GPU platform leading to a significant speed-up. Also, to model a real complex geometry, X-CT and MRI medical imaging technique were used to accurately model several complex 3D geometries. While, image processing technique was used to model our 2D geometries. The basic equilibrium equation of isopropanol dehydrogenation was considered to simulate and to analize chemical...