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    Aerodynamic Analysis of Dual Rotors Using Potential Method and Free Wake Modeling

    , M.Sc. Thesis Sharif University of Technology Yeylaghi, Shahab (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    Potential flow solvers simplify the mathematical formulation and achieve efficient solutions. The prediction of aerodynamic of dual rotor systems using computational fluid dynamic methods is difficult task due to the interference effects between the wakes shed from the rotors. In the present work, a free wake vortex lattice method is used to predict the vertical wake and blade loading of dual rotors in hover. In this approach the blades are modeled as flat plates with zero thickness and ring vortices are distributed on the surface of each blade. When the blades rotate, vortices are shed into the wake and freely move with a local velocity induced by the effects of the vortices on the blades... 

    Numerical Simulation of Compressible Flow Using Spectral Difference Method with Quadrilateral Elements

    , M.Sc. Thesis Sharif University of Technology Kianvashrad, Nadia (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present work, the numerical simulation of 2D inviscid compressible flows by using the spectral difference (SD) method on quadrilateral meshes is performed. The SD method combines the most desirable features of structured and unstructured grid methods to attain computational efficiency and geometric flexibility. Similar to the discontinuous Galerkin (DG) and spectral volume (SV) methods, the SD scheme utilizes the concept of discontinuous and high-order local representations to achieve conservation and high accuracy. The SD method is based on the finite-difference formulation and thus its formulation is simpler than the DG and SV methods ... 

    Preconditioning Methods to Accelerate and Improve Solution of Compressible Flow around Rotor

    , Ph.D. Dissertation Sharif University of Technology Kamali Moghadam, Ramin (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, the numerical simulation of the compressible inviscid flow around helicopter rotor is performed using the solution of the preconditioned Euler equations. Three preconditioners proposed by Eriksson, Choi and Merkel, and Turkel are implemented in two- and three-dimensional upwind Euler flow solvers on unstructured meshes. The mathematical formulations of these preconditioning schemes for different sets of primitive variables are drawn and their eigenvalues and eigenvectors are compared with each others. For this aim, these preconditioning schemes are expressed in a unified formulation. A cell-centered finite volume Roe's upwind method is used for the discretization of the... 

    Solution of Compressible Flow Using Finite Volume Lattice Boltzmann Method on Unstructured Meshes

    , M.Sc. Thesis Sharif University of Technology Karbalaei baba, Ali Reza (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, the solution of compressible flows is performed using finite volume lattice Boltzmann method (FVLBM). A model associated with 13 discrete velocity vectors and 2 energy levels is used and the Boltzmann transport equation is solved using a cell-centered finite volume on structured meshes. The values of distribution functions on each cell faceare determined by averaging from their values at the two control points located on the center of two neighboring cells. The fourth-order Runge-Kutta time-stepping scheme is applied to discretize temporal derivative term. The second- and fourth-order numerical dissipation termsareadded to the algorithm to stabilize the solution when solving... 

    Numerical Simulation of Compressible Viscous Flows Using Central Difference Finite Volume Lattice Boltzmann Method

    , M.Sc. Thesis Sharif University of Technology Katal, Ali (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, 2-D compressible viscous and inviscid flows are simulated by using a finite volume Lattice Boltzmann method. Two different models, namely, the Qu model and Watari model are employed for compressible flows simulations. The first model includes 13 discrete velocity vectors and 2 energy levels in which the Maxwellian function is replaced with a simple function for describing the distribution function that is suitable for inviscid flow simulations. The second model is a thermal multi-velocity model with isotropic tensors up to seventh rank that is suitable for compressible viscous and inviscid flow simulations with arbitrary specific heats ratio. In both the models, lattice... 

    Numerical Simulation of Compressible Magnetohydrodynamic Flow Using Spectral Difference Method on Quadrilateral Grids

    , M.Sc. Thesis Sharif University of Technology Kafian, Hesam (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present work, the numerical solution of 2D inviscid compressible Magneto-hydrodynamic flow is performed by using the spectral difference (SD) method on quadrilateral grids. In this numerical method, similar to the discontinuous Galerkin (DG) and spectral volume (SV) methods, the concept of the discontinuous and high-order local representations is used to achieve conservation property and high-order accuracy. In the SD method, the test function or the surface integral is not involved and thus it has a simpler formulation than the DG and SV methods. In this numerical method, two sets of structured points, namely unknown points and flux points, are defined in each cell to support the... 

    Numerical Solution of Incompressible Turbulent Flow by Using High-Order Accurate FDLBM and Applying LES

    , M.Sc. Thesis Sharif University of Technology Poorshayegh, Zahra (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, a high-order finite-difference lattice Boltzmann method (FDLBM) is used to simulate the two-dimensional incompressible flows. Here, the incompressible form of the lattice Boltzmann (LB) equation in the two-dimensional generalized curvilinear coordinates is considered and the resulting equation is discretized based on both the third- and fifth-order upwind finite-difference schemes. The time integration of the present flow solver is performed by the fourth-order Runge-Kutta method. Several incompressible laminar flow problems are simulated to examine the accuracy and performance of the developed high-order FDLBM solver. The present results are compared with the existing... 

    Developing a Compact Finite Difference Method for Solving Fluid - Solid Interaction in Incompressible Flow

    , M.Sc. Thesis Sharif University of Technology Parseh, Kaveh (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, fluid-solid interaction (FSI) is simulated computationally by using a high-order accurate numerical method. The two-dimensional incompressible viscous flows are considered in the fluid domain. The primary problem with solutions of the incompressible Navier–Stokes equations is the difficulty of coupling changes in the velocity field with changes in the pressure field while satisfying the continuity equation. Herein, the artificial compressibility method is used to overcome this difficulty. Preconditioning is implemented to reduce the stiffness of the system of equations to increase the convergence rate of the solution. Using preconditioning, physical solutions even at low... 

    Development of Characteristic Boundary Conditions with Artificial Compressibility Method by Compact Finite-Difference Discretization

    , Ph.D. Dissertation Sharif University of Technology Parseh, Kaveh (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, the preconditioned incompressible Navier‐Stokes equations with the artificial compressibility (AC) method formulated in the generalized curvilinear coordinates are numerically solved by using a high‐order compact finite‐difference scheme for accurately and efficiently computing the incompressible flows. A fourth‐order compact finite‐difference scheme is utilized to discretize the spatial derivative terms of the resulting system of equations and the time integration is carried out based on the dual time‐stepping method. The capability of the proposed solution methodology for computing the steady and unsteady incompressible viscous flows in a wide range of Reynolds... 

    Numerical Simulation of 2D Panel Flutter in Compressible Flow using Compact Finite-Difference Method

    , M.Sc. Thesis Sharif University of Technology Vafaei Sefti, Maryam (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, the numerical simulation of the panel flutter in compressible inviscid flow is performed by the compact finite difference method. For this purpose, the 2D compressible Euler equations written in the arbitrary Lagrange-Eulerian form are considered and the resulting system of equations in the generalized curvilinear coordinates is solved by the fourth-order compact finite-difference method. An appropriate nonlinear filter is applied for the shock capturing and for the solution to be stable. The governing equation for the panel is also numerically solved by using the fourth-order compact finite difference method. The time integration in the flow domain is made by the... 

    The Predicting Power of Investors’ Sentiment for Cryptocurrency Returns

    , M.Sc. Thesis Sharif University of Technology Hejranfar, Mohammad Reza (Author) ; Arian, Hamid Reza (Supervisor) ; Hagh Panah, Farshad (Co-Supervisor)
    Abstract
    Classical financial literature believes that people's decisions in financial markets are rational and that asset prices remain at their intrinsic value. On the other hand, behavioral finance literature believes that there are limitations in investors' decision-making and the impact of decisions on emotions, and states that investors' emotions directly affect asset prices. The aim of this research is to investigate which of the famous indicators introduced in the literature as a representative of the emotional behavior of investors has a better performance in predicting the returns of cryptocurrencies. For this purpose, in the first step, the information related to the calculation of three... 

    Combustion Instability in a Silo Type Gas Turbine Combustor

    , M.Sc. Thesis Sharif University of Technology Nosrati Shoar, Somayeh (Author) ; Farshchi, Mohammad (Supervisor) ; Hejranfar, Kazem (Supervisor)
    Abstract
    Nowadays, one of the most important desires of the human being is to reduce his living environmental pollution. Using the diluted combustion systems in new gas turbines in order to produce the minimum amount of has been done to satisfy this desire. It should be noted that reducing this amount and using the lower flame temperature will result in some consequences. The most important problem occurred in industrial and aerial gas turbines are the instability of the combustion due to dilution of the fuel to air mixture which it results in heat release fluctuations. If the heat release fluctuations and acoustic pressure are in the same phases, the amplitude of the fluctuations will increase which... 

    Receptivity of High-Speed Flows over Blunt Noses using Spectral Methods

    , Ph.D. Dissertation Sharif University of Technology Najafi, Mehdi (Author) ; Hejranfar, Kazem (Supervisor) ; Esfahanian, Vahid (Co-Advisor)
    Abstract
    The receptivity, transition and stability mechanisms of supersonic and hypersonic boundary layers to freestream disturbances are one of the most complex studies in fluid mechanics. It is well known that turbulent flows generate much higher shear forces on the surface of vehicles and hence much higher viscous heating rates than a laminar flow would at the same flight conditions. Therefore, the accurate prediction of boundary layer behavior is a critical part of the aerodynamic design of high-speed vehicles and thermal protection systems. Formation of a bow shock in front of the vehicle makes the receptivity of flow-field more complex than and different from those of low-speed subsonics. Since... 

    Numerical Solution of Two-dimensional Compressible Flow Using Immersed Boundary Method with Compact Finite Difference Scheme

    , M.Sc. Thesis Sharif University of Technology Mashayekh, Erfan (Author) ; 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 Behavior of a Single Cavitating Bubble Near Solid Boundariesby solvingTwophase Navier-Stokes Equations with a Central Difference Finite Volume Method

    , M.Sc. Thesis Sharif University of Technology Mortezazadeh Dorostkar, Mohammad (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present work, the deformation and collapse of a single cavitating bubble near solid boundaries is simulated by solving the preconditioned, homogenous, multiphaseNavier-Stokes equations. Up to now, all studies in the literature performed by the volume of fluid (VOF)approach to capture the bubble surface have been based on the pressure-based category in which the flow variables are calculated through solving the Poisson equation. Here, the density-based category is applied and the solution methodology is based on the artificial compressibility approach. The compressible form of the Navier-Stokes equations is applied inside the bubble and the liquid phase is assumed to be incompressible.... 

    Numerical Analysis of Incompressible Flow around an Oscillating Airfoil Using Artificial Compressibility Approach and Vorticity Confinement Method

    , M.Sc. Thesis Sharif University of Technology Marami Zenouz, Sadaf (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, the numerical simulation of the two-dimensional incompressible flow around an oscillating airfoil is performed. For this aim, the incompressible Navier-Stokes equations based on the artificial compressibility approach written in the arbitrary Lagrangian-Eulerian form are considered. Then, the vorticity confinement method is incorporated in the formulation and the resulting system of equations is solved by a second-order central-difference finite volume method with the controllable dissipation terms. For the time integration, the implicit dual-time stepping scheme is implemented. At first, the numerical solution of the incompressible flow over the oscillating NACA0012 airfoil... 

    Numerical Simulation of Cavitating Flows with Compressibility Effects

    , M.Sc. Thesis Sharif University of Technology Mahmoudi, Zakaria (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, the numerical simulation of cavitating flows with compressibility effects is performed. The algorithm employs the multiphase Euler equations with homogeneous equilibrium model. The baseline differential equations system is similar to the one-phase system of equations and comprised of the mixture density, mixture momentums and mixture energy equations. Thephases considered for cavitating flows is liquid-vapor and liquid-gas fields. The system of governing equations is discretized using a cell-centered finite volume AUSM’s upwind scheme. The computations are presented for steady noncavitating/cavitating flows around 1D/2Dproblems for different conditions. A sensitivity study is... 

    A ¬High Order Accurate Numerical Solution of Incompressible Slip Flow in Microchannels with Heat Transfer by Using Artificial Compressibility Method

    , M.Sc. Thesis Sharif University of Technology Mohafez, Mir Hamed (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, a high-order accurate numerical solution of steady incompressible slip flow and heat transfer in 2D microchannels is presented. The numerical method used is an alternating direction implicit operator scheme which is efficiently implemented to solve the incompressible Navier-Stokes equations in the primitive variables formulation using the artificial compressibility method. To stabilize the numerical solution, numerical filters are used. The present methodology considers the solution of the Navier-Stokes equations with¬ employing different slip boundary condition¬¬ (Maxwell,¬ ¬¬Hyperbolic tangent function of Knudsen number¬ and Beskok slip models)¬ ¬¬on the wall to model... 

    Numerical Simulation of Cavitating Flows with Thermodynamic Effects

    , M.Sc. Thesis Sharif University of Technology Farajollahi, Amir Hamzeh (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, the numerical simulation of cavitating flows for cryogens fluids is performed. The algorithm employs the homogenous, multiphase Euler/Navier-Stokes equations with the interface capturing method. The thermodynamic and thermal effects substantially impact the cavitation dynamics of cryogenic fluids and therefore these effects should be considered by solving the energy equation in conjunction with the mass and momentum conservation, and updating the fluid physical properties. Here, two cavitation modeling strategies, namely, the barotropic cavitation model and the transport equation-based model are used. Both laminar and turbulent cavitating flows are studied in this work. For... 

    Numerical Simulation of Viscous Compressible Flow Around an Oscilating Airfoil Using Immersed Boundary Method

    , M.Sc. Thesis Sharif University of Technology Gholami Haghighi Fard, Morteza (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, the computation of the viscous compressible flow over two-dimensional geometries is performed by using the immersed boundary method and applying a second-order finite volume scheme. For the solution of the governing equations, a uniform Cartesian grid that is not coincident with the body surface is used and the boundary conditions on the wall are satisfied by the ghost-cell immersed boundary method. The spatial discretization of the fluid equations is carried out using the second-order central difference finite volume scheme and the time integration is performed by applying the fourth-order Runge-Kutta method. To stabilize the solution algorithm and reduce unwanted...