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    Vortex shedding modes around oscillating non-uniform double heave plates

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; 2020 Abazari, A ; Alvandi, M ; Behzad, M ; Thiagarajan, K. P ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

    Energy Extraction from Two Oscillating Airfoils in Tandem Configuration at Low-Reynolds-number Turbulent Flow

    , M.Sc. Thesis Sharif University of Technology Alapour, Sina (Author) ; Ebrahimi, Abbas (Supervisor)
    In this study, the physic of an unsteady flow surrounding two oscillating airfoils in tandem configuration at low Reynolds-numbers has been simulated in a 2D manner by utilizing the Sliding-mesh approach and K-ω-SST turbulent model in Ansys-Fluent application. The first step in this study is selecting the decent numerical grid and flow solution scheme. After choosing the proper solution for this problem, next is to verify the methodology with respect to the references. In the next step, The tandem configuration and pitching motion of the airfoils is being implemented with existing tools and the flow structure, leading-edge and trailing-edge vortex shedding and blade-vortex interactions is... 

    Experimental analysis of a Ranque-Hilsch vortex tube for optimizing nozzle numbers and diameter

    , Article Applied Thermal Engineering ; Volume 61, Issue 2 , 2013 , Pages 500-506 ; 13594311 (ISSN) Mohammadi, S ; Farhadi, F ; Sharif University of Technology
    A brass vortex tube with changeable parts is used to obtain the optimum nozzle intake numbers and diameter. The effects of inlet pressure and CF (cold fraction) are also investigated. Results illustrate that increasing the number of nozzles causes a temperature drop and the optimum nozzle diameter corresponds to quarter of vortex tube diameter. The distance between cold end orifice and nozzle intakes is investigated in this work and it is found that for a better performance, this distance should be decreased. A series of experiments conducted to investigate the CF effect on VT performance and an optimum amount for this parameter is found. A two-dimensional computational fluid dynamics... 

    Analytical study of single particle tracking in both free and forced vortices

    , Article Scientia Iranica ; Volume 20, Issue 2 , April , 2013 , Pages 351-358 ; 10263098 (ISSN) Salari, A ; Karmozdi, M ; Maddahian, R ; Firoozabadi, B ; Sharif University of Technology
    Today, the flow of gas-solid, solid-liquid and liquid-liquid mixtures is broadly used in many industries such as slurry transportation, propulsion, dredging and power generation equipment. In this paper, single solid particle motion through free and forced vortices is analytically studied. The equations are solved for cases in which the drag, pressure gradient, added mass, buoyancy and weight forces are considered individually and simultaneously. Verification has been done for the value of ReP , which confirms the solution for the first t = 0.1 s. The results show that the most important force governing particle motion is the pressure gradient force  

    Two-phase flow separation in axial free vortex flow

    , Article Journal of Computational Multiphase Flows ; Volume 9, Issue 3 , 2017 , Pages 105-113 ; 1757482X (ISSN) Aghaee, M ; Ganjiazad, R ; Roshandel, R ; Ashjari, M. A ; Sharif University of Technology
    Multi-phase flows, particularly two-phase flows, are widely used in the industries, hence in order to predict flow regime, pressure drop, heat transfer, and phase change, two-phase flows should be studied more precisely. In the petroleum industry, separation of phases such as water from petroleum is done using rotational flow and vortices; thus, the evolution of the vortex in two-phase flow should be considered. One method of separation requires the flow to enter a long tube in a free vortex. Investigating this requires sufficient knowledge of free vortex flow in a tube. The present study examined the evolution of tube-constrained two-phase free vortex using computational fluid dynamics. The... 

    Large eddy simulation of low swirl flames under external flow excitations

    , Article Flow, Turbulence and Combustion ; Volume 100, Issue 1 , 2018 , Pages 249-269 ; 13866184 (ISSN) Shahsavari, M ; Farshchi, M ; Sharif University of Technology
    Springer Netherlands  2018
    Low swirl flame characteristics under external flow excitations are numerically investigated using large eddy simulations with a dynamically thickened flame combustion model. A finite volume scheme on a Cartesian grid with a dynamic one equation eddy viscosity subgrid scale model is used for large eddy simulations. The excitations are imposed on inlet velocity profiles by a sinusoidal forcing function over a wide range of amplitudes and frequencies. Present investigation shows that although, the swirling motion of the low swirl flame is not intense enough to induce a recirculation zone in ensemble averaged results, external flow excitations increase the local swirl number upstream of the... 

    A numerical study of geometrical effects on the strouhal number of a circular cylinder

    , Article 2008 ASME International Mechanical Engineering Congress and Exposition, IMECE 2008, Boston, MA, 31 October 2008 through 6 November 2008 ; Volume 1 , 2009 , Pages 57-66 ; 9780791848623 (ISBN) Kazemifar, F ; Molai, M ; Firoozabadi, B ; Ahmadi, G ; Sharif University of Technology
    In this paper, reducing the Strouhal number of a circular cylinder is studied numerically. Two-dimensional numerical simulations of flow over a normal circular cylinder and various modified circular cylinders are carried out using FLUENT® soft ware. Two small blades are attached to a circular cylinder and the effects of variation of the blades length and the blade angle are studied numerically. The blade angle is chosen 2α=0°, 30°, 90°, 120° and 150°. The blades length is chosen l/d=0.125, 0.25, 0.375. Effects of blade angles and blade lengths were studied for both 2α=0° and 150°. Results show that increasing in blade lengths decreases the Strouhal number. Moreover, as the blade angle was... 

    Experimental study of lateral dispersion in flexible aquatic canopy with emergent blade-like stems

    , Article Physics of Fluids ; Volume 32, Issue 6 , 25 June , 2020 Jamali, M ; Sehat, H ; Sharif University of Technology
    American Institute of Physics Inc  2020
    This paper quantitatively investigates the role of flexibility of blade-like stems and, in particular, the occurrence of stem resonance on lateral dispersion in emergent aquatic canopies. Two sets of experiments are presented: single-stem and canopy tests. In the first set, the flow around single blade-like flexible model stems and the proximity to a resonant state are studied. Wake areas behind four model stems with distinct flexibilities are measured by particle image velocimetry for stem Reynolds numbers between 350 and 850. A single flexible emergent stem bends and oscillates in in-line and cross-flow directions due to periodic forcing associated with the vortex shedding. The plant... 

    A broad reconsideration of anti-vortex film cooling method using numerical optimization and an improved heat-flux model

    , Article International Journal of Heat and Fluid Flow ; Volume 89 , 2021 ; 0142727X (ISSN) Chaharlang Kiani, K ; Mazaheri, K ; Sharif University of Technology
    Elsevier B.V  2021
    This paper represents the detailed results of an evolutionary optimization framework towards the exploration of vortex mechanisms leading to effective anti-vortex film cooling. In this regards, several arrangements of triple cooling holes were studied on flat and curved geometries using differential-evolution optimization algorithm and a modified Reynolds-stress based flow solver. Depending on the flow and geometric parameters, four distinct types of vortex interaction with different cooling mechanisms were identified. The vortex-trapping mechanism, observed in the optimized upstream arrangement acts through imposing a mild downwash over the main counter-rotating vortex pair and provides the... 

    Numerical investigation of transient thermo-fluid processes in a Ranque-Hilsch vortex tube

    , Article International Journal of Refrigeration ; Volume 131 , 2021 , Pages 746-755 ; 01407007 (ISSN) Mirjalili, M ; Ghorbanian, K ; Sharif University of Technology
    Elsevier Ltd  2021
    A 2D numerical investigation is performed to better understand the transient thermo-fluid processes in a vortex tube for a cold mass fraction equal to0.44. The results along the Ranque-Hilsch vortex tube reveal a close agreement with past numerical and experimental data. The distribution of axial, radial, and tangential velocities as well as the stagnation pressure and temperature are examined at different positions for different time steps. The results indicate that the tangential velocity is the most significant velocity component and dominates the heat transfer and energy conversion processes. In addition, it is evident that the core of the cold end experiences the highest pressure... 

    An experimental investigation into a novel small-scale device for energy harvesting using vortex-induced vibration

    , Article International Journal of Low-Carbon Technologies ; Volume 16, Issue 2 , 2021 , Pages 317-325 ; 17481317 (ISSN) Moradi Gharghani, F ; Bijarchi, M. A ; Mohammadi, O ; Shafii, M. B ; Sharif University of Technology
    Oxford University Press  2021
    Renewable energies could be a good solution to the problems associated with fossil fuels. The storage of wind energy by means of small-scale devices rather than large-scale turbines is a topic that has gained lots of interest. In this study, a compact device is proposed to harvest wind energy and transform it into electrical energy, by means of oscillations of a magnet into a coil, using the concept of vortex-induced vibration (VIV) behind a barrier. For a more comprehensive investigation, this system is studied from two viewpoints of fluid mechanics (without magnet) and power generation (with the magnet). For this purpose, an oscillating plate hinging on one side and three barriers with... 

    Effect of Delta Wing Leading Edge Vortex on Pressure Distribution of Fuselagein in Subsonic Regime

    , M.Sc. Thesis Sharif University of Technology Sadri, Vahid (Author) ; Soltani, Mohammad Reza (Supervisor) ; Ghorbanian, Kaveh (Supervisor)
    The delta wing has proven to be very useful for the study and understanding of the basic features of separation-induced vortex flows since many aspects of these vortex flows can be generated with this simple shape. A phenomenon of special importance to vortical flows is vortex breakdown. Vortex breakdown remains an important and complicated phenomenon that can have negative or positive effects. The delta wing leading edge vortex is emphases in many experiments. Most of these experiments are focused on the delta wing only.In this research, emphasis is on vortex interaction of delta wing-canard-fuselage configuration. A series of low speed wind tunnel tests were carried out to investigate... 

    Investigation of Effective Parameters on Propulsion in a Vortex Engine

    , M.Sc. Thesis Sharif University of Technology Golbafian, Hamid Reza (Author) ; Mozafari, Ali Asghar (Supervisor) ; Saidi, Mohammad Hassan (Supervisor) ; Ghafourian, Akbar (Supervisor)
    Vortex flow is one of the most sophisticated fluid movements in nature which has great industrial and scientific importance. In this dissertation, in order to study the combustion process due to a vortex flow, a new experimental model of a cold wall vortex engine, was designed, fabricated and tested with oxidizer issuing tangentially toward the end of the chamber. The cold wall effect in these chambers is a result of the cool layer of oxidizer which significantly reduces the amount of heat transfer to the chamber’s wall. This experimental model was designed to withstand the massive temperature rise resulting from the usage of Polyethylene as fuel and Nitrous oxide as oxidizer. In a series of... 

    Investigation of the Leading Edge Flap Effects on the Aerodynamic Coefficients of a Cranked Arrow Delta Wing

    , M.Sc. Thesis Sharif University of Technology Karimshahian Bidgoli, Alireza (Author) ; Soltani, Mohammad Reza (Supervisor)
    In this study, investigated the simulation flow over a double-delta wing. The flow field was simulated by three dimension grid and RANS flow equation by K-ω-SST model. In order to investigate effect of AOA and leading edge flap simulated variable AOA and leading edge flap angle. The results shows created two vortex in inside and outside the wing. The vortex burst at high AOA and the Lift decrease after vortex bursting. The using leading edge flap effect on the vortex power and postpone vortex bursting and increasing wing lift coefficient in the high AOA. Also the leading edge flap effect on the pitch moment coefficient and change the pitch moment coefficient curve slope. The other effects of... 

    Wind Harvesting via Vortex Induced Vibration for Electricity Generation

    , M.Sc. Thesis Sharif University of Technology Moradi Gharghani, Farshad (Author) ; Behshad Shafii, Mohammad (Supervisor) ; Mousavi, Ali (Supervisor)
    There is a need for renewable energy sources to be more feasible. The purpose of this project is to develop a compact device that is able to harvest wind energy and transform it into electrical energy using the concept of vortex shedding. When calibrated correctly, the vortex shedding will induce resonant oscillation. Electricity would be collected from this oscillation using a magnet and coil assembly. This method was proven to work in water, but has not been applied to air currents. Our group designed and built a small-scale prototype to be tested in closed circuit wind tunnel. The wind harvester works at a moderate wind range of 3 to 5 m/s. Data was collected on the amplitude and... 

    Numerical Investigation of Vortex Shedding Control Behind a Cylinder with Swinging Thin Plates

    , M.Sc. Thesis Sharif University of Technology Bagherzadeh Chehreh, Babak (Author) ; Javadi, Khodayar (Supervisor) ; Tayyebi Rahni, Mohammad (Co-Advisor)
    Von-Karman vortex shedding is a transient aerodynamic instability which occurs in laminar flows over a bluff body in a certain condition. When this phenomenon occurs, vortices take form on upper and lower parts of the bluff body and begin to shed into an oscillatory manner affecting a significant part of the flow domain. This research focuses on Karman vortex shedding control by using two thin oscillating splitter plates. Length ratio of plates to cylinder diameter is 1 (L⁄D=1) and plates are attached at ±55 degrees (trigonometric angle). Plates are forced to oscillate at different ratios of natural vortex shedding frequencies (0.75, 1, 1.25, 1.5 and 2) for diffenet amplitudes. Simulations... 

    Vortex with fourfold defect lines in a simple model of self-propelled particles

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 93, Issue 3 , 2016 ; 15393755 (ISSN) Seyed Allaei, H ; Ejtehadi, M. R ; Sharif University of Technology
    American Physical Society  2016
    We study the formation of a vortex with fourfold symmetry in a minimal model of self-propelled particles, confined inside a squared box, using computer simulations and also theoretical analysis. In addition to the vortex pattern, we observe five other regimes in the system: a homogeneous gaseous phase, band structures, moving clumps, moving clusters, and vibrating rings. All six regimes emerge from controlling the strength of noise and from the contribution of repulsion and alignment interactions. We study the shape of the vortex and its symmetry in detail. The pattern shows exponential defect lines where incoming and outgoing flows of particles collide. We show that alignment and repulsion... 

    Best vortex tube cascade for highest thermal separation

    , Article International Journal of Refrigeration ; Volume 85 , 2018 , Pages 282-291 ; 01407007 (ISSN) Majidi, D ; Alighardashi, H ; Farhadi, F ; Sharif University of Technology
    Elsevier Ltd  2018
    The current study examines different arrangements of vortex tubes (VTs) to get higher performances for cooling and heating. The effects of thermo-physical parameters such as inlet feed temperature and inlet/outlet vortex tube pressure on generated temperature gradient are investigated. To estimate the cold outlet temperatures, the available equations in the literature are verified against our experimental data. Moreover, we propose a new equation to estimate the hot outlet temperature based on the upper limit of hot temperature (ULHT) and the lower limit of cold temperature (LLCT), verified with experimental data as well. Further, several arrangements are simulated to obtain the minimum cold... 

    Experimental Investigation of the Effects of Canard Position on the Flowfield Over the Wing of a Model

    , M.Sc. Thesis Sharif University of Technology Izadkhah, Mohammad (Author) ; Soltani, Mohammad Reza (Supervisor)
    The analysis results of air combat simulations explain fighters succeed at close air combat that are super maneuverable and at high angle of attack controllable. Closed-coupled delta wing/canard configurations play an important role in modern aircraft design. These configurations offer high trimmed lift, improved agility and maneuverability as well, as a potential for increased lift-to drag ratio, all of which make them attractive to study. Experiments were carried out in a subsonic closed circuit wind tunnel over a delta wing model under the influence of canard. Canard was set in two different vertical positions, high and mid, with respect to the wing location. Flowfield measurements were... 

    Critical Current Density Improvement in Type II Superconductors by Modifying the Type, Size and the Patterns of Pinning Centers

    , M.Sc. Thesis Sharif University of Technology Nazifi Takantapeh, Rana (Author) ; Vesaghi, Mohammad Ali (Supervisor) ; Fardmanesh, Mehdi (Supervisor)
    Motion of magnetic flux, as a result of exerting electrical current, causes dissipation and voltage difference in the type II superconducting slab. So fixing these vortices by pinning centers will increase the critical current . Enhancing the critical current by different kinds of pinning centers is interesting for a lot of theoretical and experimental research groups. At first in this project dynamics of vortices in a triangular lattice is investigated by changing the pinning force. For the case of fp=2f0 we have seen two phase transition in velocity-force plot. And also a practical pinning array of parallel lines is presented. The effect of pinning force, pinning potential width and the...