Search for: vortex
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    Vortex transport in separating flows and role of vortical structures in reynolds stress production and distribution

    , Article 2005 ASME Fluids Engineering Division Summer Conference, Houston, TX, 19 June 2005 through 23 June 2005 ; Volume 1 PART A , 2005 , Pages 429-436 ; 0791841987 (ISBN); 9780791841983 (ISBN) Yazdani, M ; Khakpour, Y ; Sharif University of Technology
    In this paper we will present some approaches on Reynolds stress production by vortex transport phenomena and nonlinear vorticity generation in momentum equation. First of all we represent a history of recent works to describe how fluid particle motions can be associated with Reynolds stress through either displacement or acceleration terms. In the next section we will describe how vortex stretching causes the Reynolds stress production and what is the dominant effect near and far from the boundary where viscous effects have to be considered. On the other hand, some vortex considered methodologies such as those synthesize boundary layer, as a collection of vortical objects seem to be... 

    Reduced-order modeling of unsteady flows without static correction requirement

    , Article Journal of Aircraft ; Volume 42, Issue 4 , 2005 , Pages 882-886 ; 00218669 (ISSN) Behbahani Nejad, M ; Haddadpour, H ; Esfahanian, V ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2005
    A new reduced-order modeling approach is presented. This approach is based on fluid eigenmodes and without using the static correction. The vortex lattice method is used to analyze unsteady flows over two-dimensional airfoils and three-dimensional wings. Eigenanalysis and reduced-order modeling are performed using a conventional method with and without the static correction technique. In addition to the conventional method, eigenanalysis and reduced-order modeling are also performed using the new proposed method, that is, without static correction requirement. Numerical examples are presented to demonstrate the accuracy and computational efficiency of the proposed method. Based on the... 

    Experimental and numerical study of the gas-gas separation efficiency in a Ranque-Hilsch vortex tube

    , Article Separation and Purification Technology ; Vol. 138, issue , Dec , 2014 , p. 177-185 Mohammadi, S ; Farhadi, F ; Sharif University of Technology
    A brass vortextube is used to carry out a series of experiments. The main objective of the present research is to investigate the separation performances of a vortex tube (VT) for a hydrocarbon mixture. Examination is also applied to study the effects of nozzle intakes number and cold fraction on the gas species separation at specific inlet pressure 236.37 kPa in a VT with two gas mixtures (LPG as a hydrocarbon mixture and LPG-N2). A two-dimensional computational fluid dynamic (CFD) model simulation of a VT is presented. CFD code after validation is also applied to investigate the role of cold fraction and nozzle intakes number on the gas species separation. The highly rotating flow field... 

    Dispersion around a circular cylinder in surface wave motion

    , Article Scientia Iranica ; Vol. 21, issue. 3 , 2014 , p. 548-556 ; 10263098 Tofighi, M. A ; Jamali, M ; Sharif University of Technology
    In this paper, we examine fluid flow and associated dispersion around a circular cylinder under progressive surface wave motion. The flow field and vortex shedding patterns were studied using flow visualization and Particle Image Velocimetry (PIV). Several patterns of vortex shedding were identified around a single cylinder. The vortex shedding patterns under progressive wave motion are similar to those observed in planar oscillatory flow, except in the way the vortices form and in the orientation they take. The observed vortex patterns in progressive wave motion are more unstable than those in planar oscillatory flow. Using particle tracking and the Lagrangian dispersion method, the... 

    Effects of boundary layer control method on hydrodynamic characteristics and tip vortex creation of a hydrofoil

    , Article Polish Maritime Research ; Volume 24, Issue 2 , 2017 , Pages 27-39 ; 12332585 (ISSN) Ghadimi, P ; Tanha, A ; Kourabbasloo, N. N ; Tavakoli, S ; Sharif University of Technology
    De Gruyter Open Ltd  2017
    There is currently a significant focus on using boundary layer control (BLC) approach for controlling the flow around bodies, especially the foil sections. In marine engineering this is done with the hope of increasing the lift - to - drag ratio and efficiency of the hydrofoils. In this paper, effects of the method on hydrodynamic characteristics and tip vortex formation of a hydrofoil are studied. Steady water injection at the tip of the hydrofoil is simulated in different conditions by using ANSYS-CFX commercial software. Validity of the proposed simulations is verified by comparing the obtained results against available experimental data. Effects of the injection on the lift, drag, and... 

    Large eddy simulations of unconfined non-reacting and reacting turbulent low swirl jets

    , Article Flow, Turbulence and Combustion ; Volume 98, Issue 3 , 2017 , Pages 817-840 ; 13866184 (ISSN) Shahsavari, M ; Farshchi, M ; Arabnejad, M. H ; Sharif University of Technology
    Springer Netherlands  2017
    The low swirl flow is a novel method for stabilizing lean premixed combustion to achieve low emissions of nitrogen oxides. Understanding the characteristics of low swirl flows is of both practical and fundamental interest. In this paper, in order to gain better insight into low swirl stabilized combustion, large eddy simulation and dynamically thickened flame combustion modeling are used to characterize various features of non-reacting and reacting low swirl flows including vortex breakdown, shear layers’ instability, and coherent structures. Furthermore, four test cases with different equivalence ratios are studied to evaluate the effects of equivalence ratio on the flame and flow... 

    Wake interference of two identical oscillating cylinders in tandem: An experimental study

    , Article Ocean Engineering ; Volume 166 , 2018 , Pages 311-323 ; 00298018 (ISSN) Armin, M ; Khorasanchi, M ; Day, S ; Sharif University of Technology
    Elsevier Ltd  2018
    This study aims to assess the impact of the spacing between cylinders on their dynamic behaviour. Observations during this experiment have helped to identify the effect of spacing on excitation mechanism of each cylinder as well as establishing the relationship between cylinders response and the spacing between them. Arrays of cylindrical Structures in close proximity are common in variety of engineering structures, particularly in the offshore industry. If the cylinders are flexible, and are subject to excitation from fluid flow, then the dynamics is influenced by complex interactions between the cylinders, dependent on a variety of parameters. Two cylinders were flexibly mounted in tandem... 

    Numerical investigation of the effects of fin shape, antifreeze and nanoparticles on the performance of compact finned-tube heat exchangers for automobile radiator

    , Article Applied Thermal Engineering ; Volume 133 , 2018 , Pages 248-260 ; 13594311 (ISSN) Habibian, S. H ; Mostafazade Abolmaali, A ; Afshin, H ; Sharif University of Technology
    Elsevier Ltd  2018
    In this paper, heat transfer and pressure drop of air in the radiator of an internal combustion engine automobile were investigated. First, three types of fins including louvered, triangular vortex generator and rectangular vortex generator were modeled and their performance were compared with a plain fin. Effects of adding antifreeze in volume ratios of 40, 50 and 60% on the performance of louvered and rectangular vortex generator fins were investigated. Finally, the effects of adding copper oxide and aluminum oxide nanoparticles on the heat transfer improvement of louvered and rectangular vortex generator fins were simulated. The results demonstrated that louvered fin had the highest heat... 

    Particle trajectory in a bidirectional vortex flow

    , Article Particulate Science and Technology ; Volume 27, Issue 1 , 2009 , Pages 16-34 ; 02726351 (ISSN) Dehghani, S. R ; Saidi, M. H ; Mozafari, A. A ; Ghafourian, A ; Sharif University of Technology
    In this research particle trajectory in a bidirectional vortex flow has been numerically predicted and the results experimentally validated. Scale analyses of forces show their order of magnitudes and give a criterion to recognize the order of magnitude of exerting forces on the particle. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, density, and position of entering particle are assumed to be known. If the particle length scale is considered not to be comparable with the chamber length and if particle number density is low, then influence of particle on the flow field is negligible and a one-way solution is applicable. The governing equation is converted to... 

    Heat transfer enhancement of a fin-and-tube compact heat exchanger by employing magnetite ferrofluid flow and an external magnetic field

    , Article Applied Thermal Engineering ; Volume 164 , 2020 Bezaatpour, M ; Rostamzadeh, H ; Sharif University of Technology
    Elsevier Ltd  2020
    Compact heat exchangers as modern industrial devices are designed to improve heat recovery and saving energy processes in restricted spaces. In the current study, effect of a uniform external magnetic field with Fe3O4/water nanofluid for heat transfer enhancement of a fin-and-tube compact heat exchanger is numerically investigated. The obtained results are verified by the available experimental data to demonstrate accuracy of the present simulation. The results indicated that the local and average heat transfer coefficients increase around the tubes in the presence of an external magnetic field due to the vortex formation behind the tubes as well as the flow pattern alteration in the heat... 

    Analytical and Experimental Investigation of Spray Flame Front in Bidirectional Vortex Flow

    , Ph.D. Dissertation Sharif University of Technology Dehghani, Saeed Reza (Author) ; Saidi, Mohammad Hassan (Supervisor) ; Mozafari, Ali Asghar (Supervisor) ; Ghafourian, Akbar (Supervisor)
    Vortex engine has shown to be a credible substitute in thermal power and aerospace industries mainly due to their advantages such as better mixing, improved combustion, and considerable cooled walls of combustion chamber. The engine geometry and tangential inlet oxidizer create inner and outer vortices rotating in the same angular direction. The inner vortex moves from head to the end of engine in the axial direction and outer vortex moves in the opposite direction. In the vortex engine, vortices affect spray droplets and force them to have a spiral path and apply a centrifugal force on the droplets to push them towards sidewall. Also axial relative velocity of droplets and flow filed act as... 

    Experimental Study of the Pressure Distribution on the Surface of an Infinite Wing Influenced by Different Sweep Angles

    , M.Sc. Thesis Sharif University of Technology Tirandaz, Mohammad Rasoul (Author) ; Soltani, Mohammad Reza (Supervisor)
    A series of wind tunnel tests were performed to examine the effects of wing sweep and wing tip vortices on the pressure distribution of the upper surface of three wings with sweep angles of 23,33 and 40 degrees. The wing section had a laminar flow airfoil similar to that of NACA 6-series airfoils. All tests, were conducted at a chord Reynolds number of 8×〖10〗^5, and for a range of angle of attack -2 to14 degree. Generation of Wing tip vortices are eliminated by placing an End-plate on the wing tip. Static pressure distributions over the upper surface of the wing at three chordwise direction and at one spanwise direction along the quarter chord line are obtained. The results show that the... 

    Development of Optimization Algorithm for Low Speed UAVs Propellers

    , M.Sc. Thesis Sharif University of Technology Miraghaei Jafari, Zahra Sadat (Author) ; Mazaheri, Karim (Supervisor)
    Aerodynamic shape optimization has been always of great importance in aerospace design. Recent advancements in computational algorithms and hardware, has made it feasible to have advanced optimization as a standard part of desing procedure. Here we have promoted aerodynamic optimization of air propeller.
    Propeller optimization process requires a propeller performance analysis program and an efficient optimization algorithm. A vortex lattice model is used for the propeller performance analysis and a computer program is developed based on it. Experiment and litritures are used for validation of VLM code. In order to optimize the propeller peformance, propeller efficiency is applied as cost... 

    Investigation of Performance and Aeroelastic Characteristics of Wind Turbine Blades Based on Flexible Multibody Dynamics Model

    , M.Sc. Thesis Sharif University of Technology Sekandari, Mahmoud (Author) ; Ebrahimi, Abbas (Supervisor)
    Aeroelasticity analysis and prediction of wind turbines sturcture deformations are fundamental parts in their design. Increasing the size of wind turbine blades and development of Mega-watt sized wind turbines have enhanced the importance of these studies. In this study, the aeroelasticity analysis of a wind turbine blade has been done based on flexible multibody dynamics method. For this purpose, the modal approach has been used for modeling blade structure which has been considered as a flexible beam with bending and torsion degrees of freedom. The unsteady vortex lattice method has been used to calculate aerodynamic loads in order to combine with wind turbine blade structure model. Using... 

    Numerical Modeling of Terrestrial Planet Temperature Distribution Effect on Polar Vortex Forming: Venus Modeling

    , M.Sc. Thesis Sharif University of Technology Molaverdikhani, Karan (Author) ; Darbandi, Masoud (Supervisor)
    A global rotating atmosphere with polar vortex and super rotation is simulated using a simplified Venus General Circulation Model (GCM). The polar vortex is maintained strongly by meridional circulation develops in the form of a simple Hadley cell, extending from the equator to the pole in both hemispheres and rotation terrestrial planet. Venus Total Polar Vortex Parameter (PVP) was defined like globally integrated super-rotation but at polar skullcaps (60-90 deg). Venus Polar Vortex Parameter is PVP=1.5 that’s qualitatively similar to observed polar vortex. Then with study in terrestrial planet and Titan modeling, we appointed the Polar Vortex Parameter and critical limit of Polar Vortex... 

    Experimental Investigation of Flow Past a Delta Wing Model in Presence of a Canard in Supersonic Regime

    , M.Sc. Thesis Sharif University of Technology Dehghani, Parham (Author) ; Soltani, Mohammad Reza (Supervisor)
    Application of canard next to the wing have been widely used in military industry for decades. Although it’s most application is in supersonic flying objects, It has to do it’s duty in lower air speeds too. The aim of this study was to investigate the influence on the wing due to the presence of canard in supersonic flow regime. But because of the importance of the issue, significant attempts has been conducted in subsonic flow regime. High research volume, Absence of a comprehensive theory in this branch and the local defense industry demand as a developing country on the other hand, delivers the importance and applicability of the subject. Another issue of importance is that the... 

    Laboratory Study of Transverse Dispersion and Hydrodynamic of Continuous Flow Around Cylindrical Cylinders

    , M.Sc. Thesis Sharif University of Technology Soltani, Samira Sadat (Author) ; Jamali, Mirmosadegh (Supervisor)
    In this study, by performing a series of experiments, the effect of the presence of cylinders on the formation of vortices and the interaction of cylinders on each other and, finally, transverse propagation in a steady flow are investigated. The cylinder cylinders that are in the direction of the motion of the water, have a significant effect on the hydrodynamic aspects and propagation in these streams. In the pattern of flow around cylindrical cylinders, with increasing Reynolds number, the vortex behind the stem begins to oscillate and when they reach, vortices flow into the stream. The flow velocity field, the formation and vortex fluctuation, affects the process of particle propagation... 

    Aerodynamic Control of Flow Around a Rigid Wing in Flapping Motion Using Geometry Modification Methods

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Mohammad Hossein (Author) ; Ebrahimi, Abbas (Supervisor) ; Farahani, Mohammad (Supervisor)
    The physics of the flow around the wing in the oscillatory motion of the wing has various patterns, including the leading edge vortex, the tip vortex and trailing edge vortex escape. The interaction of these vortices forms a complex flow structure around the wing, which will have a direct effect on the aerodynamic performance of the wing. Therefore, controlling these structures can be considered as a way to improve the performance of the flapping wing. One of the passive flow control techniques that has recently been taken into consideration is a leading-edge protuberance method. Another type of passive flow control is geometric correction, using corrugation method. According to studies, two... 

    Numerical and Experimental Study of Induced Drag Reduction Using a Wing Grid at Low Reynolds Numbers

    , M.Sc. Thesis Sharif University of Technology Sadeghi Malek Abadi, Mahyar (Author) ; Soltani, Mohamad Reza (Supervisor) ; Banazadeh, Afshin (Supervisor) ; Farahani, Mohammad (Co-Supervisor)
    Wing grids are among devices used for increasing wing performance. Wing grids decrease wing induced drag by breaking the wing main tip vortex to smaller vortices with lower turbulence intensity value. These devices are mostly used in low Reynolds regimes, and their effectiveness decreases as the Reynolds number increases. In most researches around the world, wing grids have simple design configurations, but in this research wing grids are designed in such a way that each grid has a minimum value of induced drag respectively. So, in addition to reducing baseline wing induced drag by breaking the main vortex to smaller vortices by means of wing grid, each grid has a minimum value of induced... 

    The Spin-Orbit Interaction and Topological Vortices in Unconventional Superconductors

    , M.Sc. Thesis Sharif University of Technology Hosseinabadi, Hossein (Author) ; Kargarian, Mehdi (Supervisor)
    In this work we introduce a new proposal to realize topological superconductivity. In this model we use a ferromagnetic material with high curie temperature like Nickel in proximity to the surface of a three dimensional topological insulator or equivalently Bismuth which has surface states with strong spin-orbit coupling which makes its surface Hamiltonian similar to the surface of a three dimensional topological insulator.The surface electrons of Bismuth are Dirac fermions with strong spin-orbit interaction. The interaction of surface electrons with magnetic fluctuations in the ferromagnet induces an effective attractive electron-electron interaction among surface electrons upon integration...