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    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 Hejranfar, K ; Khajeh Saeed, A ; Sharif University of Technology
    Springer berlin  2009
    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 characteristic boundary conditions based on artificial compressibility method for solution of incompressible flows

    , Article Journal of Computational Physics ; Volume 345 , 2017 , Pages 543-564 ; 00219991 (ISSN) Hejranfar, K ; Parseh, K ; Sharif University of Technology
    The preconditioned characteristic boundary conditions based on the artificial compressibility (AC) method are implemented at artificial boundaries for the solution of two- and three-dimensional incompressible viscous flows in the generalized curvilinear coordinates. The compatibility equations and the corresponding characteristic variables (or the Riemann invariants) are mathematically derived and then applied as suitable boundary conditions in a high-order accurate incompressible flow solver. The spatial discretization of the resulting system of equations is carried out by the fourth-order compact finite-difference (FD) scheme. In the preconditioning applied here, the value of AC parameter... 

    Unsteady preconditioned characteristic boundary conditions for direct numerical simulation of incompressible flows

    , Article AIAA Journal ; Volume 58, Issue 4 , 2020 , Pages 1476-1489 Parseh, K ; Hejranfar, K ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2020
    The unsteady preconditioned characteristic boundary conditions (UPCBCs) based on the artificial compressibility (AC) method are formulated and applied at artificial boundaries for the direct numerical simulation (DNS) of incompressible flows. The compatibility equations including the unsteady terms are mathematically derived in the generalized curvilinear coordinates and then incorporated as boundary conditions (BCs) in a high-order accurate incompressible flowsolver. The spatial derivative terms of the systemof equations are discretized using the fourth-order compact finite difference (FD) scheme, consistent with the high-order accuracy required for the DNS. The time integration is carried... 

    Numerical simulation of thermobuoyant flow with large temperature variation

    , Article Journal of Thermophysics and Heat Transfer ; Volume 20, Issue 2 , 2006 , Pages 285-296 ; 08878722 (ISSN) Darbandi, M ; Hosseinizadeh, S. F ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2006
    The use of the classical Boussinesq approximation is a straightforward strategy for taking into account the buoyancy effect in incompressible solvers. This strategy is highly effective if density variation is low. However, ignoring the importance of density variation in highly thermobuoyant flow fields can cause considerable deviation from the correct prediction of fluid flow behavior and the accurate estimation of heat transfer rate. In this study, an incompressible algorithm is suitably extended to solve high-density-variation fields caused by strong natural-convection influence. The key point in this research is the way that an ordinary incompressible algorithm is extended to... 

    Rayan: A polyhedral grid co-located incompressible finite volume solver (Part I: Basic design features)

    , Article Scientia Iranica ; Volume 17, Issue 6 B , NOVEMBER-DECEMBE , 2010 , Pages 443-455 ; 10263098 (ISSN) Sani, M ; Saidi, M. S ; Sharif University of Technology
    In this work, basic design features of Rayan are documented. One of the new design features presented in this work is the way Rayan handles polyhedral grids. Grid definition is combined with the definition of the structure of the sparse coefficient matrix, thereby releasing a considerable part of the memory used by the grid to store otherwise required faces belonging to the cell part of the connectivity description. The key idea is to use a uniform way for creating the structure of the coefficient matrix from the grid connectivity description and to access that data when computing the elements of the coefficient matrix. This saving requires many modifications to the computational algorithm... 

    Evaluation of quasi-steady aerodynamic modeling for flutter prediction of aircraft wings in incompressible flow

    , Article Thin-Walled Structures ; Volume 44, Issue 9 , 2006 , Pages 931-936 ; 02638231 (ISSN) Haddadpour, H ; Dehghani Firouz Abadi, R ; Sharif University of Technology
    In this paper, the aeroelastic behavior and flutter instability of aircraft wings in subsonic incompressible flight speed regime are investigated. Quasi-steady and unsteady aerodynamic models are used for aerodynamic modeling and the obtained aeroelastic predictions are compared to those available in the specialized literature. Based on a number of test cases, it is shown that the quasi-steady aerodynamic models are inadequate for the determination of aeroelastic behavior and flutter boundary of aircraft wings in the incompressible flight speed range. © 2006 Elsevier Ltd. All rights reserved  

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

    , M.Sc. Thesis Sharif University of Technology Taheri, Sina (Author) ; Hejranfar, Kazem (Supervisor)
    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... 

    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)
    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... 

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

    , M.Sc. Thesis Sharif University of Technology Alibakhshian, Mohammad Reza (Author) ; Hejranfar, Kazem (Supervisor)
    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... 

    Hyperelastic materials behavior modeling using consistent strain energy density functions

    , Article Acta Mechanica ; Volume 213, Issue 3-4 , 2010 , Pages 235-254 ; 00015970 (ISSN) Darijani, H ; Naghdabadi, R ; Sharif University of Technology
    Springer-Verlag Wien  2010
    Hyperelastic materials have high deformability and nonlinearity in load-deformation behavior. Based on a phenomenological approach, these materials are treated as a continuum, and a strain energy density is considered to describe their hyperelastic behavior. In this paper, the mechanical behavior characterization of these materials is studied from the continuum viewpoint. For this purpose, the strain energy density is expressed as sum of independent functions of the mutual multiple of principal stretches. These functions are determined by applying the governing postulates on the form of the strain energy density. It is observed that a consistent strain energy density is expressible in terms... 

    Developing consistent inlet thermal boundary condition in micro/nano scale channels with heat transfer

    , Article 1st ASME Micro/Nanoscale Heat Transfer International Conference, MNHT08, Tainan, 6 January 2008 through 9 January 2008 ; Volume Parts A and B , 2008 , Pages 691-700 ; 0791842924 (ISBN); 9780791842928 (ISBN) Darbandi, M ; Vakilipour, S ; Sharif University of Technology
    In this work, we present a more realistic inlet boundary condition to simulate compressible and incompressible flows through micro and nano channels considering consistent momentum and heat transfer specifications there. At solid walls, a constant wall temperature with suitable jump is applied as the wall thermal boundary condition; however, two types of thermal inlet boundary conditions are investigated at the inlet. We firstly examine the classical inlet boundary condition, which specifies a uniform temperature distribution right at the real inlet. Alternatively, we apply the same boundary condition but at a fictitious place far upstream of the real channel inlet. To validate our results,... 

    Numerical study of flow and heat in long micro and nano channels

    , Article 1st ASME Micro/Nanoscale Heat Transfer International Conference, MNHT08, Tainan, 6 January 2008 through 9 January 2008 ; Volume Parts A and B , 2008 , Pages 1299-1307 ; 0791842924 (ISBN); 9780791842928 (ISBN) Darbandi, M ; Vakilipour, S ; Sharif University of Technology
    In this work, we extend a numerical tool capable of solving compressible and incompressible gas flows to study the momentum and heat transfer rates in micro/nano channels with high aspect ratio (L/H = 8000), where the compressibility effect is dominant. The constant heat flux thermal boundary condition is firstly applied at the wall. Next, the flow regime is extended to the early transition regime employing a high order slip velocity boundary condition based on the kinetic theory assumptions. The accuracy of the present results in the slip flow regimes is evaluated against other available theoretical and experimental results. The thermal and compressibility effects on the pressure and... 

    Three-dimensional compressible-incompressible turbulent flow simulation using a pressure-based algorithm

    , Article Computers and Fluids ; Volume 37, Issue 6 , 2008 , Pages 747-766 ; 00457930 (ISSN) Javadi, K ; Darbandi, M ; Taeibi Rahni, M ; Sharif University of Technology
    In this work, we extend a finite-volume pressure-based incompressible algorithm to solve three-dimensional compressible and incompressible turbulent flow regimes. To achieve a hybrid algorithm capable of solving either compressible or incompressible flows, the mass flux components instead of the primitive velocity components are chosen as the primary dependent variables in a SIMPLE-based algorithm. This choice warrants to reduce the nonlinearities arose in treating the system of conservative equations. The use of a new Favre-averaging like technique plays a key role to render this benefit. The developed formulations indicate that there is less demand to interpolate the fluxes at the cell... 

    Numerical simulation of landslide impulsive waves by incompressible smoothed particle hydrodynamics

    , Article International Journal for Numerical Methods in Fluids ; Volume 56, Issue 2 , 2008 , Pages 209-232 ; 02712091 (ISSN) Ataie Ashtiani, B ; Shobeyri, G ; Sharif University of Technology
    An incompressible-smoothed particle hydrodynamics (I-SPH) formulation is presented to simulate impulsive waves generated by landslides. The governing equations, Navier-Stokes equations, are solved in a Lagrangian form using a two-step fractional method. Landslides in this paper are simulated by a submerged mass sliding along an inclined plane. During sliding, both rigid and deformable landslides mass are considered. The present numerical method is examined for a rigid wedge sliding into water along an inclined plane. In addition solitary wave generated by a heavy box falling inside water, known as Scott Russell wave generator, which is an example for simulating falling rock avalanche into... 

    A new approach to the analytical and numerical solution of the bidirectional vortex flow

    , Article 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Cincinnati, OH, 8 July 2007 through 11 July 2007 ; Volume 5 , 2007 , Pages 4856-4869 ; 1563479036 (ISBN); 9781563479038 (ISBN) Jamaly, S. M ; Saidi, M. H ; Ghafourian, A ; Mozafari, A. A ; Dehghani, S. R ; Sharif University of Technology
    The solution for bulk fluid motion of a bidirectional coaxial vortex for application in vortex engine has been derived. The vortex engine is a novel combustion chamber in which swirl motion of reactants are used to maintain the chamber walls cool. The flow field has been considered both analytically and numerically. The model is based on incompressible, steady, axisymmetric, and non-reactive flow conditions. The governing PDEs are reduced to a system of nonlinear ODEs and then, by a coordinate transformation, their singularity has been relaxed. Solution domain has been decomposed into the inner viscous and outer inviscid regions, then, the velocity and pressure fields are obtained... 

    A boundary element method for investigation of sloshing in complex 3D containers

    , Article 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Waikiki, HI, 23 April 2007 through 26 April 2007 ; Volume 8 , 2007 , Pages 8288-8292 ; 02734508 (ISSN); 1563478927 (ISBN); 9781563478925 (ISBN) Firouz Abadi, R. D ; Haddadpour, H ; Ghasemi, M ; Sharif University of Technology
    This paper presents a matrix form model for determination of sloshing frequencies and modes in 3D liquid tanks. The governing equations of the incompressible inviscid potential flow are used to derive the governing boundary integral equation and then the boundary element method along with the collocation method is applied to obtain a matrix form standard eigenvalue problem. The sloshing mass and stiffness matrices are computed using analytical formulas which are given for quadratic boundary elements. Two typical examples are used to validate the introduced model and very good results are achieved in comparison with the exact results in the literature  

    A modified space - Time finite element method for simulation of immiscible incompressible two-phase flow in heterogeneous porous media

    , Article International Journal for Numerical Methods in Fluids ; Volume 53, Issue 8 , 2007 , Pages 1221-1242 ; 02712091 (ISSN) Ferdowsi, P. A ; Taghizadeh Manzari, M ; Sharif University of Technology
    In this paper, a modified space-time method is presented for the simulation of convection-diffusion equations. The new method differs from the original space-time method in the sense that the weight functions for space and time are different. The performance of the proposed algorithm is studied for numerical simulation of incompressible immiscible two-phase flow in porous media. The governing equations consist of one conservation of mass equation for each phase, the Darcy law and one capillary-saturation correlation for the flow. By defining a global pressure, the governing equations lead to a system of nonlinear equations in terms of this global pressure, the velocity components and the... 

    Reduced-order aerodynamic model for aeroelastic analysis of complex configurations in incompressible flow

    , Article Journal of Aircraft ; Volume 44, Issue 3 , 2007 , Pages 1015-1019 ; 00218669 (ISSN) Haddadpour, H ; Behbahani Nejad, M ; Firouz Abadi, R. D ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2007
    A general reduced-order aeroelastic model for 3-D complex geometries in subsonic incompressible flow regimes in the continuous-time domain was developed. A boundary element method (BEM) based fluid eigenanalysis solver was integrated with a finite element method (FEM) based modal technique of structural modeling. A body assumed to be a closed surface with known solid boundaries submerged in a potential flow is considered. The wake is considered to be thin and no aerodynamic loads will be supported by it. domain. The modal formulation of the aerodynamic system must be modified with a static correction method to include at least the quasi-static contribution of the higher truncated modes. The... 

    A geometric multigrid strategy on mixed finite volume element mesh to solve flow and heat

    , Article 36th AIAA Fluid Dynamics Confernce, San Francisco, CA, 5 June 2006 through 8 June 2006 ; Volume 1 , 2006 , Pages 644-657 ; 1563478102 (ISBN); 9781563478109 (ISBN) Darbandi, M ; Vakili, S ; Schneider, G. E ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2006
    In this research, a multigrid formulation is suitably developed to accelerate the convergence rate for the solution of the equations arising from the discretization of the two-dimensional incompressible Navier-Stokes equations. The governing equations are treated using an implicit finite element volume method. To achieve our purpose, the solution domain is divided into a large number of quadrilateral elements. Normally, we need utilizing very fine grid resolutions to obtain solution with sufficient accuracy. Unfortunately using the standard implicit solvers on fine grids needs huge computational time. However, it is known that the rate of convergence of classical relaxation schemes reduces... 

    Effects of turbulent models and baffle position on the hydrodynamics of settling tanks

    , Article Scientia Iranica ; Volume 13, Issue 3 , 2006 , Pages 255-260 ; 10263098 (ISSN) Tamayol, A ; Firoozabadi, B ; Sharif University of Technology
    Sharif University of Technology  2006
    In this paper, the numerical results of hydrodynamic modeling of primary settling tanks are presented. The flow field is assumed to be incompressible and non-buoyant. The effects of two different types of turbulence model, standard κ - ε and RNG, are compared with each other. The effects of an inlet baffle on the hydrodynamics of settling tanks are also studied. Results are obtained for the primary settling tank of the city of Sarnia, Ontario, Canada. The effects of the existence and position of another interior baffle in the settling tanks are also studied. Results in the different parts are compared with experimental and numerical data and showed good agreement. Comparison between two...