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Total 193 records

    Adjoint-based design optimization of s-shaped intake geometry

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 3 November 2017 through 9 November 2017 ; Volume 1 , 2017 ; 9780791858349 (ISBN) Askari, R ; Shoureshi, P ; Soltani, M. R ; Khajeh Fard, A ; ASME ; Sharif University of Technology
    Abstract
    The S-shaped air intakes are very common shapes due to their ease in the engine-body integration or Radar Cross Section, RCS, specifications especially for fighter aircrafts. The numerical shape optimization of an S-shaped air intake using adjoint method is conducted. The flow of a specified air intake that uses S-duct M2129 is simulated using three dimensional (3D) numerical solution of Reynolds-Averaged Navier-Stokes equation along with k-ω SST turbulence model. The main purpose of this optimization scheme is to maximize the total pressure recovery (TPR). Further, the scheme is developed in such a way that would be applicable in industry thru satisfying specified constraint requirements.... 

    Investigation of the transient growth in plane jet by non-modal stability analysis

    , Article Fluid Dynamics Research ; Volume 51, Issue 5 , 2019 ; 01695983 (ISSN) Gohardehi, S ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
    Institute of Physics Publishing  2019
    Abstract
    Linear stability analysis is used to characterize the dynamics of a plane jet by incorporating non-modal stability analysis besides classical global temporal stability analysis. It is explained that similar shapes of different global modes are the result of non-normal characteristics of linearized Navier Stokes equations. Optimal initial disturbances and their eigenfunctions together with transient energy growth are obtained for different time horizons and Reynolds numbers of the jet in the linear unstable configuration. These structures are localized at the upstream of the jet nozzle at the boundary layer. The transient growth of the inlet perturbation in limited time bounds is found in the... 

    Large Eddy Simulation of multiple jets into a cross flow

    , Article Scientia Iranica ; Volume 14, Issue 3 , 2007 , Pages 240-250 ; 10263098 (ISSN) Ramezanizadeh, M ; Taeibi Rahni, M ; Saidi, M. H ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    Multiple square cross section jets into a cross flow at three different velocity ratios, namely 0.5, 1.0 and 1.5, have been computationally simulated, using the Large Eddy Simulation (LES) approach. The finite volume method is applied in the computational methodologies, using an unsteady SIMPLE algorithm and employing a non-uniform staggered grid. All spatial and temporal terms in the Navier-Stokes equations have been discretized using the Power-Law and Crank-Nicolson schemes, respectively. Mean velocity profiles at different X-locations are compared with the existing experimental and Reynolds Averaged Navier-Stokes (RANS) computational results. Although the RANS computations require much... 

    Implementation of high-order compact schemes to the iterative parabolized Navier-Stokes equations

    , Article 25th Congress of the International Council of the Aeronautical Sciences 2006, Hamburg, 3 September 2006 through 8 September 2006 ; Volume 3 , 2006 , Pages 1628-1643 Esfahanian, V ; Hejranfar, K ; Darian, H. M ; Sharif University of Technology
    Curran Associates Inc  2006
    Abstract
    The numerical solution of the parabolized Navier-Stokes (PNS) and globally iterated PNS (IPNS) equations for accurate computation of hypersonic axisymmetric flowfields is obtained by using the fourth-order compact finite-difference method. The PNS and IPNS equations in the general curvilinear coordinates are solved by using the implicit finite-difference algorithm of Beam and Warming type with a high-order compact accuracy. A shock fitting procedure is utilized in both the compact PNS and IPNS schemes to obtain accurate solutions in the vicinity of the shock. The main advantage of the present formulation is that the basic flow variables and their first and second derivatives are... 

    A hybrid model for simulation of fluid-structure interaction in water entry problems

    , Article Physics of Fluids ; Volume 33, Issue 1 , 2021 ; 10706631 (ISSN) Moradi, H ; Rahbar Ranji, A ; Haddadpour, H ; Moghadas, H ; Sharif University of Technology
    American Institute of Physics Inc  2021
    Abstract
    A hydroelastic hybrid model is developed to simulate the fluid-structure interaction in water entry problems using the partitioned approach. The interactions between a flat plate and the water are modeled by a hydroelastic model using explicit and implicit couplings. Both couplings are unstable due to numerical instability associated with the fluid added mass. To overcome the instability, an extended Wagner's model is combined with the hydroelastic model, and a hybrid model is developed. The extended Wagner's model is the extension of the classical Wagner's model that is used to estimate the fluid inertial, damping, and restoring forces of a flexible plate within the potential flow theory.... 

    Dual-code solution procedure for efficient computing equilibrium hypersonic axisymmetric laminar flows

    , Article Aerospace Science and Technology ; Volume 12, Issue 2 , 2008 , Pages 135-149 ; 12709638 (ISSN) Hejranfar, K ; Kamali Moghadam, R ; Esfahanian, V ; Sharif University of Technology
    2008
    Abstract
    An appropriate combination of the thin-layer Navier-Stokes (TLNS) and parabolized Navier-Stokes (PNS) solvers is used to accurately and efficiently compute hypersonic flowfields of equilibrium air around blunt-body configurations. The TLNS equations are solved in the nose region to provide the initial data plane needed for the solution of the PNS equations. Then the PNS equations are employed to efficiently compute the flowfield for the afterbody region by using a space marching procedure. Both the TLNS and PNS equations are numerically solved by using the efficient implicit non-iterative finite-difference algorithm of Beam and Warming. A shock fitting technique is used in both the TLNS and... 

    Finite volume simulation of gaseous microflows using modified boundary conditions

    , Article 45th AIAA Aerospace Sciences Meeting 2007, Reno, NV, 8 January 2007 through 11 January 2007 ; Volume 16 , 2007 , Pages 11313-11321 ; 1563478900 (ISBN); 9781563478901 (ISBN) Darbandi, M ; Vakilipour, S ; Rikhtegar, F ; Schneider, G. E ; Sharif University of Technology
    2007
    Abstract
    The rapid progress in fabricating and utilizing micro-electromechanical systems during the last decade has not been matched by the corresponding advances in our understanding from the unconventional physics involved in manufacturing and operation of micro devices. To avoid the complexity encountered in modeling of nonlinear Boltzmann equations, the Navier-Stokes equations can be solved considering the slip flow regime concepts. The modeling can be achieved via employing suitable slip velocity boundary conditions at the solid walls. The modified first-order slip models can, in some cases, extend the range of applicability of the Navier-Stokes solvers to around and beyond Kn=0.1, where the... 

    3D numerical analysis of velocity profiles of PD, EO and combined PD-EO flows through microchannels

    , Article 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006, Limerick, 19 June 2006 through 21 June 2006 ; Volume 2006 A , 2006 , Pages 209-214 ; 0791847608 (ISBN); 9780791847602 (ISBN) Yazdi, S ; Monazami, R ; Salehi, M. A ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    Abstract
    In this paper, a three-dimensional numerical model is developed to analyze flow characteristics of pressure driven, electroosmotic and combined pressure driven-electroosmotic flows through micro-channels. The governing system of equations consists of the electric-field and flow-field equations. The solution procedure involves three steps. The net charge distribution on the cross section of the microchannel is computed by solving two-dimensional Poisson-Boltzmann equation using the finite element method. Then, using the computed fluid's charge distribution, the magnitude of the resulting body force due to interaction of an external electric field with the charged fluid is calculated along the... 

    The step effect and particle removal from an enclosure

    , Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) Hendijanifard, M ; Saidi, M. H ; Taeibi Rahni, M ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    Abstract
    This paper reports the results of a study of the transient removal of contaminant particle from enclosures containing an obstacle. We study specially a phenomena occur sometimes called the step effect. This phenomenon may occur if the size of the obstacle is small enough in comparison with the length or height of the enclosure. These results are the basic instruments for finding a model for contaminant particle removal from an enclosure containing an obstacle. A numerical CFD code is developed and validated with different cases, and then proper two- and three-dimensional cases are modeled. The size of the obstacle affect the order of magnitude of the convection-diffusion terms in the... 

    The effects of obstacle and vent position on particle removal from an enclosure

    , Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) Hendijanifard, M ; Saidi, M. H ; Taeibi Rahni, M ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    Abstract
    This paper reports the results of a study of the transient removal of contaminant particle from enclosures. These results are the basic instruments for finding a model for contaminant particle removal from an enclosure containing an obstacle. A numerical CFD code is developed and validated with different cases, then proper two- and three-dimensional cases are modeled and improvements are done. The improvements are done by proper positioning the inlet/outlet vents. The size and position of the obstacle affect the order of magnitude of the convection-diffusion terms in the Navier-Stokes equations, hence results in different phenomena while removing the particles. One of these phenomena, the... 

    Numerical study to evaluate the important parameters affecting the hydrodynamic performance of manta ray's in flapping motion

    , Article Applied Ocean Research ; Volume 109 , 2021 ; 01411187 (ISSN) Safari, H ; Abbaspour, M ; Darbandi, M ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    Manta ray swimming or bio-inspiration propulsion system, as a special type of marine propulsion system, is used for submersible vehicles that require high-speed maneuverability and stability, such as glider and AUV. In a manta ray swimming, the thrust force is generated by a couple of undulation and oscillation of wing, so that the direction of undulation wave and oscillation is upright and perpendicular to the direction of thrust force, respectively. It is possible to combine these two movement modes (flapping motion) on the three-dimensional model without considering the effects of wing twisting and flexibility to simplify and better understand the physical behaviors or special study of... 

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

    , M.Sc. Thesis Sharif University of Technology Ezzatneshan, Eslam (Author) ; 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... 

    Developing a Hybrid Molecular-Continuum Algorithm to Simulate Gas Flow in Micro-Nano Propulsion Systems

    , Ph.D. Dissertation Sharif University of Technology Roohi Golkhatmi, Ehsan (Author) ; Darbandi, Masoud (Supervisor)
    Abstract
    With the rapid development in the application of nano-micro systems in space propulsion systems, it is necessary to obtain accurate analysis of flow field in these devices. New generation of space missions are usually performed by using a network of small-scale satellites. The mission control of such small-scale satellites requires specialized propulsion systems than produce small propulsive forces of about 1 micro-Newton. The main purpose of the current PhD thesis is analysing the flow field in different nano/micro propulsion systems by using a hybrid Navier-Stokes (NS)-direct simulation Monte Carlo (DSMC) method. Nano/micro propulsion systems experience different rarefaction regimes from... 

    Shape Optimization in Pipe

    , M.Sc. Thesis Sharif University of Technology Ghalavandi, Ebrahim (Author) ; Fotouhi Firouzabad, Morteza (Supervisor)
    Abstract
    Shape optimization can be viewed as a part of the important branch of computational mechanics called structural optimization. In structural optimization problems one tries to set up some data of the mathematical model that describe the behavior of a structure in order to find a situation in which the structure exhibits a priori given properties. Nowadays shape optimization represents a vast scientific discipline involving all problems in which the geometry (in a broad sense) is subject to optimization. The problem has to be well posed from the mechanical point of view, requiring a good understanding of the physical background. Then one has to find an appropriate mathematical model that can... 

    Analysis of Industrial Ventilation System in a Welding Shop Considering Health & Hygiene

    , M.Sc. Thesis Sharif University of Technology Behkam, Reza (Author) ; Kazem Zadeh Hannani, Siamak (Supervisor) ; Farhanieh, Bijan (Supervisor)
    Abstract
    Based on progress madein industry, considering the essence of human resource health is an inevitable subject. Ventilation is an important matter which affects the quality and efficiency of production due to its coherence with providing a healthy and suitable workplace. In this regard, there are some settings for industrial ventilation systems which are designed to satisfy related health and hygiene standards.Simulation of ventilation systems based on CFD methods is a great contribution to choose anappropriate ventilation system type. In this study, by modeling the proposed ventilation setting in a 3D environment, we are assured that the system is capable of industrial ventilation in welding... 

    Null Controllability and Stabilizability of Compressible Navier-stokes System in One Dimension

    , M.Sc. Thesis Sharif University of Technology Hosseini Khajouei, Narges Sadat (Author) ; Hesaraki, Mahmoud (Supervisor)
    Abstract
    In this thesis we study the exponential stabilization of the one dimensional compressible Navier-Stokes system, in a bounded interval locally around a constant steady state by a localized distributed control acting only in the velocity equation. In fact this is an analysis of a paper that published by Shirshendu Chowdhury, Debayan Maity, Mithily Ramaswamy and Jean-Pierre Raymond in Journal of Differential Equations. We determine a linear feedback law able to stabilize a nonlinear transformed system. Coming back to the original nonlinear system, we obtain a nonlinear feedback law able to stabilize locally this nonlinear system. The result is providing feedback control laws stabilizing... 

    Numerical Solution of Hypersonic Axisymmetric Flows Including Real Gas Effects Using Compact Finite-Difference Scheme

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

    The numerical solution of the parabolized Navier-Stokes (PNS) equations for accurate computation of hypersonic axisymmetric flowfield with real gas effects is obtained by using the fourth-order compact finite-difference method. The PNS equations in the general curvilinear coordinates are solved by using the implicit finite-difference algorithm of Beam and Warming type with a high-order compact accuracy. A shock fitting procedure is utilized in the compact PNS scheme to obtain accurate solutions in the vicinity of the shock. To stabilize the numerical solution, numerical dissipation term and filters are used. The main advantage of the present formulation is that the basic flow variables... 

    Numerical Study of Oxygen Enrichment on NO Pollution Spread in an Ignition Chamber

    , M.Sc. Thesis Sharif University of Technology Orshesh, Zohreh (Author) ; Kazemzadeh Hannani, Siamak (Supervisor)
    Abstract
    In the present study, a 3D combustion chamber was simulated using FLUENT6.32. The objectives were to obtain detailed information on the combustion characteristics and NO formation in the furnace, and also to examine the effect of Oxygen enrichment on the combustion process. The combustion chamber has internal dimensions of 60 cm wide, 90 cm high and 190 cm long. The fuel pipe diameter is 1.25 cm and the air pipe diameter is 3.5 cm. The 3-D Reynolds Averaged Navier Stokes (RANS) equations together with standard k-ε turbulence model are solved by Fluent 6.3. Air/fuel flow rate ratio is varied as 1.3, 3.2 and 5.1 and the oxygen enriched flow rates are 28, 54, 68 lit/min. NO emission was... 

    Extending a hybrid finite-volume-element method to solve laminar diffusive flame

    , Article Numerical Heat Transfer, Part B: Fundamentals ; Vol. 66, issue. 2 , August , 2014 , pp. 181-210 ; ISSN: 10407790 Darbandi, M ; Ghafourizadeh, M ; Sharif University of Technology
    Abstract
    We extend a hybrid finite-volume-element (FVE) method to treat the laminar reacting flow in cylindrical coordinates considering the collocation of all chosen primitive variables. To approximate the advection fluxes at the cell faces, we use the upwind-biased physical influence scheme PIS and derive a few new extended expressions applicable in the cylindrical frame. These expressions are derived for both the Navier-Stokes and reactive flow governing equations, of which the latter expressions are considered novel in the finite-volume formulation. To validate our derived expressions, the current results are compared with the experimental data and other available numerical solutions. The results... 

    Developing a FVBFE method on moving unstructured hybrid grid to simulate ice accretion

    , Article 43rd AIAA Thermophysics Conference 2012 ; 2012 ; 9781624101861 (ISBN) Darbandi, M ; Fard, M ; Naderi, A ; Schneider, G. E ; American Institute of Aeronautics and Astronautics (AIAA) ; Sharif University of Technology
    2012
    Abstract
    In this study, a moving mesh finite-volume-based finite-element (FVBFE) method is suitably extended to simulate the effect of supercooled liquid water droplet content on ice formation and growth on wing sections. The method benefits from the advantages of both finite-volume and finiteelement methods, which promote achieving a more accurate solution and a higher efficient procedure in ice accretion calculations. The method solves the time-dependent Navier-Stokes (NS) equations on unstructured hybrid grid distributions. In this method, the convection terms are approximated at the cell faces using a physical influence upwinding scheme. We also use linear spring approach to move the hybrid mesh....