Search for: advection
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    Parametric study on mixing process in an in-plane spiral micromixer utilizing chaotic advection

    , Article Analytica Chimica Acta ; Volume 1022 , 2018 , Pages 96-105 ; 00032670 (ISSN) Vatankhah, P ; Shamloo, A ; Sharif University of Technology
    Recent advances in the field of microfabrication have made the application of high-throughput microfluidics feasible. Mixing which is an essential part of any miniaturized standalone system remains the key challenge. This paper proposes a geometrically simple micromixer for efficient mixing for high-throughput microfluidic devices. The proposed micromixer utilizes a curved microchannel (spiral microchannel) to induce chaotic advection and enhance the mixing process. It is shown that the spiral microchannel is more efficient in comparison to a straight microchannel, mixing wise. The pressure drop in the spiral microchannel is only slightly higher than that in the straight microchannel. It is... 

    Computational Simulation of Micromixing, Using LBM

    , M.Sc. Thesis Sharif University of Technology Hosseini-zade, Mohammad (Author) ; Taeibi-Rahni, Mohammad (Supervisor)
    Nowadays, microfluidic flow appears in many applications, such as medical, biological, and chemical industries. Where as, micromixing, which deals with mixing of microfluidic flow in micro channels, appears to be an important issue to many researchers. In such systems, molecular diffusion plays an important role. On the other hand, lattice Boltzmann method is a relatively new simulation technique for complex fluid systems and has become interesting to many researchers in computational physics. In this study, computational simulation of such mixing process, using LBM is the main objective. Different obstacle layouts inside a microchannel have been investigated. Chaotic advection and jet... 

    Modeling of Dynamic Kill in Gas-Condensate Well

    , M.Sc. Thesis Sharif University of Technology Daneshpajouh, Abouzar (Author) ; Shad, Saeed (Supervisor)
    By exploring huge gas-condensate reservoirs, three-phase transient flow modeling demonstrates its crucial role in designing dynamic kill, relief well parameters and kill procedure of such wells. Controlling gas-condensate well needs robust transient three phase models capable of capturing discontinuities in density, geometry and velocity of phases. In this paper, two phase Advection-Upstream-Splitting-Method hybrid scheme is extended to three-phase model capable of modeling blowout and dynamic kill in gas-condensate-water wells. Density and viscosity changes are calculated using Peng-Robinson equation of state and in according, flow model parameters are corrected.The capability of this model... 

    A Direct Design Method Based on the 3-Dimensional Euler Equations with Application in Internal Subsonic and Supersonic Flows

    , M.Sc. Thesis Sharif University of Technology Nejati, Ashkan (Author) ; Taeibi-Rahni, Mohammad (Supervisor) ; Ghadak, Farhad (Supervisor)
    In this work, a direct design approach for designing a surface shape (inverse design problem) has been developed in which both the target surface pressure and the unknown nodal coordinates appear explicitly in the formulations. The final discretized form of the governing equations (unified formulation) can be used for both analysis and shape design problems. Shape design problems in the context of the steady inviscid and compressible flow, based on the three-dimensional Euler equations, were directly solved to achieve a prescribed pressure along the solid boundaries. The AUSM+ scheme was used to discretize the flux terms in the Euler equations, in which the inviscid flux is splitted into... 

    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
    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... 

    Microswimmer-induced chaotic mixing

    , Article Journal of Fluid Mechanics ; Volume 779 , 2015 , Pages 669-683 ; 00221120 (ISSN) Jalali, M.A ; Khoshnood, A ; Alam, M. R ; Sharif University of Technology
    Cambridge University Press  2015
    Efficient mixing, typically characterised by chaotic advection, is hard to achieve in low Reynolds number conditions because of the linear nature of the Stokes equation that governs the motion. Here we show that low Reynolds number swimmers moving in quasi-periodic orbits can result in considerable stretching and folding of fluid elements. We accurately follow packets of tracers within the fluid domain and show that their trajectories become chaotic as the swimmer's trajectory densely fills its invariant torus. The mixing process is demonstrated in two dimensions using the Quadroar swimmer that autonomously propels and tumbles along quasi-periodic orbits with multi-loop turning trajectories.... 

    Calibrating priestley-taylor model to estimate open water evaporation under regional advection using volume balance method-case study: chahnimeh reservoir, Iran

    , Article Journal of Applied Sciences ; Volume 8, Issue 22 , 2008 , Pages 4097-4104 ; 18125654 (ISSN) Daneshkar Arasteh, P ; Tajrishy, M ; Sharif University of Technology
    The objective of this study is to calibrate Priestley-Taylor (PT) model for estimating open water evaporation from an arid region reservoir called Chahnimeh. Chahnimeh Reservoir which is situated in the Sistan area in the southeast of Iran is being affected by regional energy advection during May to October. Therefore, common models of open water evaporation estimation such as PT require calibration. PT method was calibrated for Chahnimeh Reservoir using a volume balance method. Results showed that PT coefficient, αPT, as a constant over the year varies between 2.47±0.09 and 1.20±0.03 for two different hydrologic conditions of dry and wet. It means that there is also an intra-annular... 

    Developing implicit pressure-weighted upwinding scheme to calculate steady and unsteady flows on unstructured grids

    , Article International Journal for Numerical Methods in Fluids ; Volume 56, Issue 2 , 2008 , Pages 115-141 ; 02712091 (ISSN) Darbandi, M ; Vakilipour, S ; Sharif University of Technology
    The finite-volume methods normally utilize either simple or complicated mathematical expressions to interpolate the fluxes at the cell faces of their unstructured volumes. Alternatively, we benefit from the advantages of both finite-volume and finite-element methods and estimate the advection terms on the cell faces using an inclusive pressure-weighted upwinding scheme extended on unstructured grids. The present pressure-based method treats the steady and unsteady flows on a collocated grid arrangement. However, to avoid a non-physical spurious pressure field pattern, two mass flux per volume expressions are derived at the cell interfaces. The dual advantages of using an unstructured-based... 

    Numerical and Experimental Investigation of Supersonic Flow in an Axisymmetric Inlet

    , M.Sc. Thesis Sharif University of Technology Sepahi Younsi, Javad (Author) ; Soltani, Mohammad Reza (Supervisor)
    No considerable investigation of inlet aerodynamics has been done in our country up to now. Some numerical study in this field has been accomplished without any experimental test. To solve the inner and outer flow field of the inlet in this investigation, the numerical methods has been used and also experimental tests for code validation has been done. The inlet is an axisymmetric external compression one. In the numerical simulation the Navier-Stokes equations with explicit finite volume method have been used to model the axisymmetric, steady and turbulent flow field of the inlet in a structured grid. Viscous fluxes with a finite volume method, molecular viscosity coefficient with the... 

    A new method in two phase flow modeling of a non-uniform grid

    , Article Scientia Iranica ; Volume 16, Issue 5 B , 2009 , Pages 425-439 ; 10263098 (ISSN) Bohluly, A ; Borghei, M ; Saidi, M. H ; Sharif University of Technology
    In this paper, a two dimensional numerical model for two phase flow is presented. For interface tracking, the FGVT-VOF (Fine Grid Volume Tracking-Volume Of Fluid) method is selected. For momentum advection, an improved approach is used. In this scheme, a volume tracking step is coupled with steps of computations for the advection of momentum. A Reynolds stress algebraic equation has been implemented in the algorithm of turbulent modeling. Standard test cases are used for the verification of interface tracking and hydrodynamic modeling in laminar and turbulent conditions. The test results show that this methodology can be used in different applications of two-phase flow modeling. © Sharif... 

    Early cancer detection in blood vessels using mobile nanosensors

    , Article IEEE Transactions on Nanobioscience ; Volume 18, Issue 2 , 2019 , Pages 103-116 ; 15361241 (ISSN) Mosayebi, R ; Ahmadzadeh, A ; Wicke, W ; Jamali, V ; Schober, R ; Nasiri Kenari, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    In this paper, we propose using mobile nanosensors (MNSs) for early stage anomaly detection. For concreteness, we focus on the detection of cancer cells located in a particular region of a blood vessel. These cancer cells produce and emit special molecules, so-called biomarkers, which are symptomatic for the presence of anomaly, into the cardiovascular system. Detection of cancer biomarkers with conventional blood tests is difficult in the early stages of a cancer due to the very low concentration of the biomarkers in the samples taken. However, close to the cancer cells, the concentration of the cancer biomarkers is high. Hence, detection is possible if a sensor with the ability to detect... 

    Improved advection algorithm of computational modeling of free surface flow using structured grids

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 195, Issue 7-8 , 2006 , Pages 775-795 ; 00457825 (ISSN) Babaei, R ; Abdollahi, J ; Homayonifar, P ; Varahram, N ; Davami, P ; Sharif University of Technology
    In the present study a finite difference method has been developed to model the transient fluid flow and heat transfer. A single fluid has been selected for modeling of mold filling and The SOLA-VOF 3D technique was modified to increase the accuracy of simulation of filling phenomena for shape castings. The model was then evaluated with the experimental methods. Refereeing to the experimental and simulation results a good consistency and the accuracy of the suggested model are confirmed. © 2005 Published by Elsevier B.V  

    Numerical Simulation of Cavitating Flows with Compressibility Effects

    , M.Sc. Thesis Sharif University of Technology Mahmoudi, Zakaria (Author) ; Hejranfar, Kazem (Supervisor)
    In this study, the numerical simulation of cavitating flows with compressibility effects is performed. The algorithm employs the multiphase Euler equations with homogeneous equilibrium model. The baseline differential equations system is similar to the one-phase system of equations and comprised of the mixture density, mixture momentums and mixture energy equations. Thephases considered for cavitating flows is liquid-vapor and liquid-gas fields. The system of governing equations is discretized using a cell-centered finite volume AUSM’s upwind scheme. The computations are presented for steady noncavitating/cavitating flows around 1D/2Dproblems for different conditions. A sensitivity study is... 

    Numerical Analysis of a Supersonic Jet into a Subsonic Compressible Crossflow and the Effects on a Downstream Fin

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Masoud (Author) ; Tayyebi Rahni, Mohammad (Supervisor)
    Jet into cross-flow interaction is one of the complex and fundamental problems in fluids dynamics and heat transfer, which is observed in various applications, such as pollutant discharges, film cooing of turbine blades, combustion chamber design of jet engines, trust vectoring systems, boundary layer control, and vertical short take-off and landing (VSTOL) aircrafts. One of the applications of this kind of flow is injection of supersonic jet into subsonic compressible cross-flow, which is used in trust vectoring systems of missiles. In this research, the two-dimensional interactions of supersonic jet into subsonic compressible cross-flow were investigated as two cases: "without a fin" and... 

    Computational Simulation of Supersonic Flow in an Axisymmetric Mixed Compression Inlet

    , M.Sc. Thesis Sharif University of Technology Zarea Chavoshi, Majid (Author) ; Tayyebi Rahni, Mohammad (Supervisor) ; Ebrahimi, Abbas (Supervisor)
    Inlet performance is an important field in aerodynamic design of aerial vehicle engines. This study has been focused on nummerical investigation of inlet performance. For this purpose, a density based finite volume CFD code has been developed to solve supersonic axisymmetric flow in a mixed compression inlet. A structured multi-block grid and an explicit time discritization of Reynolds averaged Navier-Stokes (RANS) equations have been used. Furthermore, both Roe’s approximated Riemann solver and advection upwind splitting method (AUSM) have been utilized for computing inviscid flux vectors. Also, the monotone upstream centered schemes for conservation laws (MUSCL) extrapolation with Van... 

    Turbulence and additive effects on ignition delay in supersonic combustion

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 227, Issue 1 , 2013 , Pages 93-99 ; 09544100 (ISSN) Tahsini, A. M ; Sharif University of Technology
    Numerical study of two-dimensional supersonic hydrogen-air mixing layer is performed to investigate the effects of turbulence and chemical additive on ignition distance. Chemical reaction is treated using detail kinetics. Advection upstream splitting method is used to calculate the fluxes, and one-equation turbulence model is chosen here to simulate the considered problem. Hydrogen peroxide is used as an additive and the results show that inflow turbulence and chemical additive may drastically decrease the ignition delay in supersonic combustion  

    Tracer transport in naturally fractured reservoirs: Analytical solutions for a system of parallel fractures

    , Article International Journal of Heat and Mass Transfer ; Volume 103 , 2016 , Pages 627-634 ; 00179310 (ISSN) Abbasi, M ; Hossieni, M ; Izadmehr, M ; Sharifi, M ; Sharif University of Technology
    Elsevier Ltd 
    In naturally fractured reservoirs, modeling of mass transfer between matrix blocks and fractures is an important subject during gas injection or contaminant transport. This study focuses on developing an exact analytical solution to transient tracer transport problem along a discrete fracture in a porous rock matrix. Using Gauss-Legendre quadrature, an expression was obtained in the form of a double integral which is considered as the general transient solution. This solution has the ability to account the following phenomena: advective transport in fractures and molecular diffusion from the fracture to the matrix block. Certain assumptions are made which allow the problem to be formulated... 

    Simulation of compressible and incompressible flows through planar and axisymmetric abrupt expansions

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 141, Issue 11 , 2019 ; 00982202 (ISSN) Nouri Borujerdi, A ; Shafiei Ghazani, A ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2019
    In this paper, compressible and incompressible flows through planar and axisymmetric sudden expansion channels are investigated numerically. Both laminar and turbulent flows are taken into consideration. Proper preconditioning in conjunction with a second-order accurate advection upstream splitting method (AUSM+-up) is employed. General equations for the loss coefficient and pressure ratio as a function of expansion ratio, Reynolds number, and the inlet Mach number are obtained. It is found that the reattachment length increases by increasing the Reynolds number. Changing the flow regime to turbulent results in a decreased reattachment length. Reattachment length increases slightly with a... 

    A pressure-based algorithm for internal compressible turbulent flows through a geometrical singularity

    , Article Numerical Heat Transfer, Part B: Fundamentals ; Volume 75, Issue 2 , 2019 , Pages 127-143 ; 10407790 (ISSN) Nouri Borujerdi, A ; Shafiei Ghazani, A ; Sharif University of Technology
    Taylor and Francis Ltd  2019
    Compressible turbulent flow through the abrupt enlargement in pipes is studied numerically by means of Advection Upstream Splitting Method (AUSM+-up). In low Mach numbers, a pressure correction equation of elliptic type is derived. This equation is compatible with the nature of governing equations and retrieves hyperbolic characteristic at higher Mach numbers. It is shown that the proposed numerical algorithm is computationally more efficient than the preconditioned density-based methods. The flow parameters such as reattachment length, pressure loss coefficient and wall shear stress are predicted. It is found that the loss coefficient of the compressible flow rises drastically with... 

    A new method for determination of concentration profile in a transport column by gamma spectroscopy combined with genetic algorithm

    , Article Progress in Nuclear Energy ; Volume 124 , 2020 Dara, M ; Kazemi, Z ; Samadfam, M ; Sharif University of Technology
    Elsevier Ltd  2020
    A non-collimated gamma spectroscopy with fewer sampling (counting) and shorter sampling periods is developed and used to estimate the concentration profile of the radiotracers within the column. In this method, the radiotracer activity in the whole column is measured in a few different positions of the detector and then, by using an appropriate advection-dispersion model and the genetic algorithm, the concentration profile within the column is constructed. The concentration profile obtained by the new method fits very well to the experimentally obtained thin-section scanning results with RMSE less than 0.046. The uniqueness of the concentration profile obtained by the method was confirmed by...