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#### Preconditioned characteristic boundary conditions for solution of the preconditioned Euler equations at low Mach number flows

, Article Journal of Computational Physics ; Volume 231, Issue 12 , 2012 , Pages 4384-4402 ; 00219991 (ISSN) ; Kamali Moghadam, R ; Sharif University of Technology
2012

Abstract

Preconditioned characteristic boundary conditions (BCs) are implemented at artificial boundaries for the solution of the two- and three-dimensional preconditioned Euler equations at low Mach number flows. The preconditioned compatibility equations and the corresponding characteristic variables (or the Riemann invariants) based on the characteristic forms of preconditioned Euler equations are mathematically derived for three preconditioners proposed by Eriksson, Choi and Merkle, and Turkel. A cell-centered finite volume Roe's method is used for the discretization of the preconditioned system of equations on unstructured meshes. The accuracy and performance of the preconditioned characteristic...

#### Central Difference Finite Volume Lattice Boltzmann Method for Simulation of Incompressible Electro-Magneto-Hydrodanamic Flows

, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

In the present study, the simulation of incompressible Electro-Magneto-hydrodynamic flows is performed using a finite volume lattice Boltzmann method (FVLBM). The Boltzmann transport equation is solved using a cell-centered finite volume method on structured meshes. A central difference scheme is used to discretize the spatial derivatives and the fourth-order numerical dissipation term is added to stabilize the solution. To discretize the temporal derivative, the fourth-order Runge-Kutta time stepping scheme is applied. The standard collision-streaming lattice Boltzmann method has been used to simulate EMHD flows in the literature, however, it has several deficiencies such as the...

#### Simulation of 2D fluid–structure interaction in inviscid compressible flows using a cell-vertex central difference finite volume method

, Article Journal of Fluids and Structures ; Volume 67 , 2016 , Pages 190-218 ; 08899746 (ISSN) ; Azampour, M. H ; Sharif University of Technology
Academic Press
2016

Abstract

In the present study, the applicability and accuracy of a cell-vertex finite volume method developed are assessed in simulating 2D fluid–structure interaction in inviscid compressible flows where the nonlinear phenomena exist in both the unsteady transonic fluid flows and the large nonlinear deformation of solid structures. The unsteady Euler equations are considered as the governing equations of the fluid flow in the arbitrary Lagrangian–Eulerian form and the large nonlinear deformation of the solid structure is considered to be governed by the Cauchy equations in the total Lagrangian form. Both the domains are discretized by a second-order central-difference cell-vertex finite volume...

#### Assessment of cell-centered and cell-vertex finite volume approaches for computation of 2d structural dynamics on arbitrary quadrilateral grids

, Article CMES - Computer Modeling in Engineering and Sciences ; Volume 106, Issue 6 , 2015 , Pages 395-439 ; 15261492 (ISSN) ; Azampour, M. H ; Sharif University of Technology
Tech Science Press
2015

Abstract

In this study, cell-centered (CC) and cell-vertex (CV) finite volume (FV) approaches are applied and assessed for the simulation of two-dimensional structural dynamics on arbitrary quadrilateral grids. For the calculation of boundary nodes displacement in the CC FV approach, three methods are employed. The first method is a simple linear regression of displacement of boundary nodes from the displacement of interior cell centers. In the second method, an extrapolation technique is applied for this purpose and, in the third method; the line boundary cell technique is incorporated into the solution algorithm in an explicit manner. To study the effects of grid irregularity on the results of CC...

#### A high-order accurate implicit operator scheme for solving steady incompressible viscous flows using artificial compressibility method

, Article Computational Fluid Dynamics 2008 ; 2009 , Pages 141-145 ; Khajeh Saeed, A ; Sharif University of Technology
Springer berlin
2009

Abstract

This paper uses a fourth-order compact implicit operator scheme for solving 2D/3D steady incompressible flows using the artificial compressibility method. To stabilize the numerical solution, numerical dissipation terms and/or filters are used. Results obtained for test cases are in good agreement with the available numerical and experimental results. A sensitivity study is also conducted to evaluate the effects of grid resolution and pseudocompressibility parameter on accuracy and convergence rate of the solution. The effects of filtering and numerical dissipation on the solution are also investigated

#### Preconditioned WENO finite-difference lattice Boltzmann method for simulation of incompressible turbulent flows

, Article Computers and Mathematics with Applications ; Volume 76, Issue 6 , 2018 , Pages 1427-1446 ; 08981221 (ISSN) ; Saadat, M. H ; Sharif University of Technology
Elsevier Ltd
2018

Abstract

In this work, a preconditioned high-order weighted essentially non-oscillatory (WENO) finite-difference lattice Boltzmann method (WENO-LBM) is applied to deal with the incompressible turbulent flows. Two different turbulence models namely, the Spalart–Allmaras (SA) and k−ωSST models are used and applied in the solution method for this aim. The spatial derivatives of the two-dimensional (2D) preconditioned LB equation in the generalized curvilinear coordinates are discretized by using the fifth-order WENO finite-difference scheme and an implicit–explicit Runge–Kutta scheme is adopted for the time discretization. For the convective and diffusive terms of the turbulence transport equations, the...

#### Numerical Simulation of Incompressible Turbulent Flow with the Artificial Compressibility-Based Incompressible Smoothed Particle Hydrodynamics

, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

In the present study, an incompressible smoothed particle hydrodynamics based on the artificial compressibility method is applied for simulating the incompressible turbulent flows. The Reynolds-averaged incompressible Navier–Stokes equations using the artificial compressibility method in the Eulerian reference frame are written in the Lagrangian reference frame to provide an appropriate incompressible SPH algorithm for the turbulent flow computations. Here, the k-L_m turbulence model, which is a simplified k-ϵ turbulence model, is used and formulated in the Lagrangian reference frame. The SPH formulation implemented here is based on an implicit dual-time stepping scheme to be capable of...

#### Development of Spectral Difference Lattice Boltzmann Method for Solution of Compressible Flows

, Ph.D. Dissertation Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

In this research, the spectral difference lattice Boltzmann method (SDLBM) is developed and applied for an accurate simulation of two-dimensional (2D) inviscid and viscous compressible flows on the structured and unstructured meshes. The compressible form of the discrete Boltzmann-BGK equation is used in which multiple particle speeds have to be employed to correctly model the compressibility in a thermal fluid. Here, the 2D compressible Lattice Boltzmann (LB) model proposed by Watari is used. The spectral difference (SD) method is implemented for the solution of the LB equation in which the particle distribution functions are stored at the solution points while the fluxes are calculated...

#### Direct Numerical Simulation of External In-compressible Flow Using High-order Accurate Finite-difference Lattice Boltzmann Method

, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

In the present study, a high-order finite-difference lattice Boltzmann solver is applied for simulating steady and unsteady three-dimensional incompressible flows. To achieve an accurate and robust flow solver, the incompressible form of the lattice Boltzmann equation in the three-dimensional generalized curvilinear coordinates is discretized spatially based on the fifth-order weighted essentially non-oscillatory (WENO) finite-difference scheme. To ensure the stability and temporal accuracy of the flow solver, the fourth-order Runge-Kutta method is used for the time integration. To examine the accuracy and performance of the flow solver, different three-dimensional incompressible flow...

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

, M.Sc. Thesis Sharif University of Technology ; 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...

#### A preconditioned euler flow solver for simulation of helicopter rotor flow in hover

, Article Computational Fluid Dynamics 2010 - Proceedings of the 6th International Conference on Computational Fluid Dynamics, ICCFD 2010 ; 2011 , Pages 479-484 ; 9783642178832 (ISBN) ; Moghadam, R. K ; National Aeronautics and Space Administration; European Office for Aerospace Research and Development ; Sharif University of Technology
2011

Abstract

In the present study, a preconditioned Euler flow solver is developed to accurately and efficiently compute the inviscid flowfield around hovering helicopter rotor. The preconditioning method proposed by Eriksson is applied. The three-dimensional preconditioned Euler equations written in a rotating coordinate frame are solved by using a cell-centered finite volume Roe's method on unstructured meshes. High-order accuracy is achieved via the reconstruction of flow variables using the MUSCL interpolation technique. Calculations are carried out for an isolated rotor in hover for different conditions and the computed surface pressure distributions are compared with the experimental data. The...

####
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
;
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...

#### Solving Preconditioned Euler/Navier-Stokes Equations for Numerical Simulation of Cavitating Flows Using a Barotropic Model

, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

Cavitation can occur in many fluid systems such as pumps, nozzles, hydrofoils and submarine vehicles and therefore, numerical modeling of this phenomenon has a significant importance. In this study, the numerical simulation of the cavitating flows through the Euler/Navier-Stokes equations employing the interface capturing method associated with a barotropic state law is performed. The system of governing equations is discretized using a cell-centered finite-volume algorithm and the fluxes are evaluated using a central-difference scheme. To account for density jumps across the cavity interface, the numerical dissipation terms with suitable density and pressure sensors are used. Since...

#### Simulation of two-Dimensional Supersonic Flow in Slip Regime in Microchannel with Finite Difference Lattice Boltzmann Method

, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

In this study, the simulation of two-dimensional supersonic flows through microchannels in slip flow regime is performed using a lattice Boltzmann model (LBM). Traditional LB models have been used to simulate incompressible fluid flows and there are not suitable for modeling compressible or thermo-fluid flows. Herein, a recently developed LB model, namely, the finite difference lattice Boltzmann method (FDLBM), is employed to simulate compressible flows with embedded shocks. In this model, one can select particle velocities independently from the lattice configuration, and therefore, a correct and numerically stable multispeed thermal model by adopting more isotropic particle velocities can...

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

,
M.Sc. Thesis
Sharif University of Technology
;
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 ...

#### Development of Compact Finite-Difference Lattice Boltzmann Method for Solving Two-Phase Flows

, Ph.D. Dissertation Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

In the present thesis, a high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied for an accurate and efficient numerical simulation of liquid-vapor two-phase flows. At first, the stability of the fourth-order CFDLBM is performed by using the von Neumann stability analysis for the D2Q7 and D2Q9 lattices. The stability analysis indicates that the CFDLBM proposed is stable and thus suitable for the simulation of high Reynolds number flows. The high-order CFDLBM is then developed and applied to accurately compute 2-D and 3-D incompressible flows in the Cartesian coordinates. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized...

#### Receptivity of hypersonic flow over blunt-noses to freestream disturbances using spectral methods

, Article Computational Fluid Dynamics 2010 - Proceedings of the 6th International Conference on Computational Fluid Dynamics, ICCFD 2010, 12 July 2010 through 16 July 2010 ; July , 2011 , Pages 357-362 ; 9783642178832 (ISBN) ; Najafi, M ; Esfahanian, V ; Sharif University of Technology
2011

Abstract

The receptivity of supersonic/hypersonic flows over blunt noses to freestream disturbances is performed by means of spectral collocation methods. The unsteady flow computations are made through solving the full Navier-Stokes equations in 2D. A shock-fitting technique is used to compute unsteady shock motion and its interaction with freestream disturbances accurately in the receptivity study. The computational results for receptivity of a semi-cylinder at Mach 8 is presented and validated by comparison with available theoretical and numerical results. The study shows significant effects of the viscosity on the receptivity process

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

, M.Sc. Thesis Sharif University of Technology ; 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...

#### Development of an Incompressible Smoothed Particle Hydrodynamics Method based on Vorticity-stream Function Formulation

, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract

In the present study, an incompressible smoothed particle hydrodynamics method based on vorticity-stream function (VSF-SPH) formulation is developed and assessed for simulating steady and unsteady incompressible flows. The vorticity-stream function formulation in the Eulerian reference frame is written in a Lagrangian reference frame to provide an appropriate incompressible SPH algorithm. The advantage of the proposed smoothed particle hydrodynamics method based on the vorticity-stream function (VSF-SPH) formulation over the weakly compressible SPH (WCSPH) is that the VSF-SPH method is a truly incompressible SPH algorithm and it does not involve any approximate enforcement of the...

#### On the outflow conditions for spectral solution of the viscous blunt-body problem

, Article Journal of Computational Physics ; Volume 228, Issue 11 , 2009 , Pages 3936-3972 ; 00219991 (ISSN) ; Esfahanian, V ; Najafi, M ; Sharif University of Technology
2009

Abstract

The purpose of this paper is to study and identify suitable outflow boundary conditions for the numerical simulation of viscous supersonic/hypersonic flow over blunt bodies, governed by the compressible Navier-Stokes equations, with an emphasis motivated primarily by the use of spectral methods without any filtering. The subsonic/supersonic composition of the outflow boundary requires a dual boundary treatment for well-posedness. All compatibility relations, modified to undertake the hyperbolic/parabolic behaviour of the governing equations, are used for the supersonic part of the outflow. Regarding the unknown downstream information in the subsonic region, different subsonic outflow...