Search for: vortex
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    Turbulent decaying swirling flow in a pipe

    , Article Heat Transfer Research ; Volume 49, Issue 16 , 2018 , Pages 1559-1585 ; 10642285 (ISSN) Aghakashi, V ; Saidi, M. H ; Sharif University of Technology
    Begell House Inc  2018
    In this work, a solution is applied to investigate the heat transfer characteristics in a pipe with turbulent decaying swirling flow by using the boundary layer integral scheme. The governing equation is solved using the forth-order Runge-Kutta scheme resulting in thermal boundary-layer thickness and dimensionless heat transfer coefficient, namely, the Nusselt number. Both forced- and free-vortex profiles are considered for the tangential velocity component. A comparison of the results obtained for the Nusselt number with available experimental data shows that this scheme has good capability in predicting the heat transfer parameters of swirling flow especially in the entrance region of a... 

    Numerical investigation of supercritical combustion of H2-O2

    , Article Energy and Fuels ; Volume 32, Issue 3 , 2018 , Pages 3851-3868 ; 08870624 (ISSN) Mardani, A ; Barani, E ; Sharif University of Technology
    American Chemical Society  2018
    This study investigates GH2/LOX coaxial jet flame at trans- and supercritical conditions using the Reynolds averaged Navier-Stokes approach. Four two-equation-turbulence models, three real equation of states, two chemical mechanisms, and three different chamber pressures are examined. Predictions show good agreement with measurements qualitatively and quantitatively. Based on the results, the predictions of the Soave-Redlich-Kwong equation of state (EOS) are closer to the experiment, while the Aungier-Redlich-Kwong EOS has more deviation than the others. Moreover, the k-ω shear stress transport model has better performance than the other turbulence models. It is also found that the flow... 

    A superconductor THz modulator based on vortex flux flow

    , Article IEEE Transactions on Applied Superconductivity ; Volume 19, Issue 4 , 2009 , Pages 3653-3657 ; 10518223 (ISSN) Sarreshtedari, F ; Hosseini, M ; Chalabi, H. R ; Moftakharzadeh, A ; Zandi, H ; Khorasani, S ; Fardmanesh, M ; Sharif University of Technology
    A terahertz modulator based on the Type-II superconductor flux flow oscillator has been proposed. Analytical calculations are presented and the effects of intrinsic and extrinsic parameters such as disorder strength of crystal, penetration depth, frequency, and amplitude of the modulated current on the radiation power spectrum have been studied. The proposed structure also exhibits a mixer-like behavior, in the sense that its output harmonics range from the washboard frequency up to the superconductor gap frequency, so the input signal is practically mixed with the washboard frequency and its harmonics. The modulation index for each harmonic of this modulator has also been investigated. This... 

    Numerical simulation of drag reduction in microgrooved substrates using lattice-boltzmann method

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 141, Issue 7 , 2019 ; 00982202 (ISSN) Asadzadeh, H ; Moosavi, A ; Etemadi, A ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2019
    We study drag reduction of a uniform flow over a flat surface due to a series of rectangular microgrooves created on the surface. The results reveal that making grooves on the surface usually leads to the generation of secondary vortices inside the grooves that, in turn, decreases the friction drag force and increases the pressure drag force. By increasing the thickness of the grooves to the thickness of the obstacle, the pressure drag increases due to the enhancement of the generated vortices and the occurrence of separation phenomenon and the friction drag reduces due to a decrease of the velocity gradient on the surface. In addition, by increasing the grooves depth ratio, the pressure... 

    Bending-torsional stability analysis of aerodynamically covered pipes with inclined terminal nozzle and concurrent internal and external flows

    , Article Journal of Fluids and Structures ; Volume 94 , 2020 Askarian, A. R ; Rahmanian, M ; Haddadpour, H ; Dehghani Firouz Abadi, R ; Sharif University of Technology
    Academic Press  2020
    Stability analysis of a cantilevered pipe with an inclined terminal nozzle as well as simultaneous internal and external fluid flows is investigated in this study. The pipe is embedded in an aerodynamic cover with negligible mass and stiffness simply to streamline the external flow and avoid vortex induced vibrations. The structure of pipe is modeled as an Euler–Bernoulli beam and effects of internal fluid flow including flow-induced inertia, Coriolis and centrifugal forces and the follower force induced by the exhausting jet are taken into account. In addition, neglecting the compressibility effect and using the unsteady Wagner model, aerodynamic loading is determined as a distributed... 

    A rigorous algebraic-analytical method for pore network extraction from micro-tomography images

    , Article Journal of Hydrology ; Volume 590 , 2020 Barzegar, F ; Masihi, M ; Azadi Tabar, M ; Sharif University of Technology
    Elsevier B.V  2020
    Static and dynamic properties of porous media are highly dependent on its internal geometry. CT scan images are generally used to characterize porous media geometry. Direct simulation of fluid flow on CT scan images is possible but considerably time-consuming. In this study, a new method was developed for extracting a simplified representation known as “pore network model” by utilizing a rigorous algebraic-analytical method. By using a moving frame in the 3D matrix of the CT scan image and stepwise identifying-removing of image components, running time for a 4003 voxels sample in a typical computer system decreased to less than 350 s. The identification of throats was based on a new... 

    Microflow in lid-driven microcavity with various aspect ratios

    , Article 46th AIAA Aerospace Sciences Meeting and Exhibit ; 2008 ; 9781563479373 (ISBN) Darbandi, M ; Daghighi, Y ; Vakilipour, S ; Schneider, G. E ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2008
    In this work, a finite-volume-element method1-4 is suitably extended to simulate the rarefied gas flow in lid-driven cavities with different height to width ratios. The flow conditions are chosen in a manner to cover the free molecular transition regime to the continuum one. As the hydrodynamic diameter of a driven cavity becomes comparable with the mean free path of the gas molecules in the cavity, the flow can no longer be considered as being in thermodynamic equilibrium; hence, a variety of non-equilibrium or rarefaction effects emerge. In this study, we show that the non-equilibrium effects in lid-driven cavity can be encountered and they become more serious in lower Knudsen numbers. We... 

    Impact of dielectric barrier discharge plasma on the wake of a wind turbine blade section oscillating in plunge

    , Article Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy ; 2021 ; 09576509 (ISSN) Maleki, G. H ; Davari, A. R ; Soltani, M. R ; Sharif University of Technology
    SAGE Publications Ltd  2021
    Effects of dielectric barrier discharge plasma have been studied on the wake velocity profiles of a section of a 660 kW wind turbine blade in plunging motion in a wind tunnel. The corresponding unsteady velocity profiles show remarkable improvement when the plasma actuators were operating and the angles of attack of the model were beyond the static stall angles of the airfoil. As a result the drag force was considerably reduced. It is further observed that the plasma-induced flow attenuates the leading edge vortices that are periodically shed into wake and diminishes the large eddies downstream. The favorable effects of the plasma augmentation are shown to occur near the uppermost and... 

    Jet into cross flow boundary layer control an innovation in gas turbine blade cooling

    , Article 35th AIAA Fluid Dynamics Conference and Exhibit, Toronto, ON, 6 June 2005 through 9 June 2005 ; 2005 ; 9781624100598 (ISBN) Javadi, K ; Taeibi Rahni, M ; Darbandi, M ; Sharif University of Technology
    New standpoint of turbulent coolant jets into crossflow, which have numerous applications in traditional and modern technology, especially in gas turbine blades, is presented in this work. It is more than half a century that, many researchers have been studying jet into cross flow to understand its behavior and to predict and control it better. Previous studies indicate that, the main attentions had been on: a- geometrical parameters such as: inclined and compound jet angles, hole's shape, jet's array arrangements, jet's spacing, and jet's channel depth, b- flow characteristics like: blowing ratio, density ratio, jet and cross flow Reynolds numbers, and turbulence intensity. Here, we have... 

    Mold filling simulation in the injection molding process with openFOAM software for non-isothermal newtonian fluid

    , Article Proceedings of the 2nd IASTED Asian Conference on Modelling, Identification, and Control, AsiaMIC 2012 ; 2012 , Pages 291-296 ; 9780889869110 (ISBN) Fazelpour, F ; Vafaeipour, M ; Etemadi, H ; Dabbaghian, A ; Bardestani, R ; Dehghan, M ; Sharif University of Technology
    Injection molding is one of the most important manufacturing processes for mass production of complex plastic parts. In this study, mold filling is simulated by using the OpenFOAM software for Non- isothermal Newtonian fluid. The OpenFOAM is an open source software that is used in Computational Fluid Dynamics (CFD) tools. The studied mold shape has a rectangular structure with a gate for Newtonian fluid injection. The simulation carried out at non-isothermal conditions and two-dimensional flow is considered. The velocity, shear stress and temperature changes in different parts of the mold are critically studied. We show that vortex formation plays an important role on changes of shear stress... 

    Multi-response optimization followed by multivariate calibration for simultaneous determination of carcinogenic polycyclic aromatic hydrocarbons in environmental samples using gold nanoparticles

    , Article RSC Advances ; Volume 6, Issue 106 , 2016 , Pages 104254-104264 ; 20462069 (ISSN) Rezaiyan, M ; Parastar, H ; Hormozi Nezhad, M. R ; Sharif University of Technology
    Royal Society of Chemistry 
    In this study, a multivariate-based strategy was developed for simultaneous determination of thirteen carcinogenic polycyclic aromatic hydrocarbons (PAHs) in water samples using gold nanoparticles (AuNPs) as solid-phase extraction (SPE) sorbent combined with gas chromatography (GC). The extraction technique is based on the strong affinity between citrate-capped AuNPs and PAHs. Furthermore, characterization of AuNPs was performed by UV-vis spectroscopy and transmission electron microscopy (TEM) techniques. A rotatable central composite design (CCD) combined with multiple linear regression (MLR) was used for designing the extraction procedure and developing models using the GC peak areas of 13... 

    Flow physics exploration of surface tension driven flows

    , Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Volume 518 , 2017 , Pages 30-45 ; 09277757 (ISSN) Javadi, K ; Moezzi Rafie, H ; Goodarzi Ardakani, V ; Javadi, A ; Miller, R ; Sharif University of Technology
    Surface tension driven passive micro-pumping relies mainly on the surface tension properties. To have control over surface tension driven passive micro-pumps (STD-PMPs), it is essential to understand the physical background of the fluid flow in these pumps. Hence, the purpose of this work is to give an exploration of the flow physics of a STD-PMP. In this regard, computer simulation is used to give detailed information about the flow pattern and physical phenomena at different conditions. To this end, a droplet of water, with a specified diameter, is placed onto an entry port connected to another droplet at the exit port via a microchannel. The results indicate that the pumping process, in... 

    Experimental study of three-dimensional flow field around a complex bridge pier

    , Article Journal of Engineering Mechanics ; Volume 136, Issue 2 , 2010 , Pages 143-154 ; 07339399 (ISSN) Beheshti, A. A ; Ataie Ashtiani, B ; Sharif University of Technology
    In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching... 

    Numerical simulation of vortex engine flow field: One phase and two phases

    , Article Journal of Thermal Science ; Volume 18, Issue 3 , 2009 , Pages 226-234 ; 10032169 (ISSN) Najafi, A. F ; Saemi, S. D ; Saidi, M. H ; Sharif University of Technology
    Aiming at improving efficiency in combustion systems, the study on droplet behavior and its trajectory is of crucial importance. Vortex engine is a kind of internal combustion engine which uses swirl flow to achieve higher combustion efficiency. One of the important advantages of designing vortex engine is to reduce the temperature of walls by confining the combustion products in the inner vortex. The scopes of this investigation are to study vortex engine flow field as well as effective parameters on fuel droplet behavior such as droplet diameter, droplet initial velocity and inlet velocity of the flow field. The flow field is simulated using Reynolds Stress Transport Model (RSM). The...