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Simulation of detonation initiation in straight and baffled channels
, Article Scientia Iranica ; Volume 11, Issue 1-2 , 2004 , Pages 37-49 ; 10263098 (ISSN) ; Hossainpour, S ; Sharif University of Technology
Sharif University of Technology
2004
Abstract
Euler conservation equations, ideal gas state equations and simplified chemical kinetics models were used to simulate two-dimensional straight and baffled shock tubes. In a straight channel, detonation waves were initiated by a strong shock wave and allowed to travel down the channel to reach a CJ wave condition. It has been shown that a two-step reaction, kinetics model with an induction time delay, resulted in a physically plausible transient solution. The one-step kinetics model solution is only valid at the limit of a steady state CJ wave condition and should not be used for transient problems. The two-step kinetics model was then used to simulate a detonation initiation in a baffled...
Evaluation of a fourth-order finite-volume compact scheme for les with explicit filtering
, Article Numerical Heat Transfer, Part B: Fundamentals ; Volume 48, Issue 2 , 2005 , Pages 147-163 ; 10407790 (ISSN) ; Kazemzadeh Hannani, S. K ; Mashayek, F ; Sharif University of Technology
2005
Abstract
The accuracy of the large-eddy simulation (LES) of turbulent flows can be increased by using high-order numerical schemes in space and time, due to a decrease in numerical errors. This work investigates a high-order compact finite-volume scheme suitable for LES. The explicit fourth-order Runge-Kutta (RK) scheme for time marching and fourth-order compact schemes for spatial derivatives using a cell-averaged approach are implemented. Different subgrid-scale models and the effect of explicit filtering in a fully turbulent channel flow are studied. In this flow, the fourth-order compact finite-volume method in space, and fourth-order RK in time in conjunction with the dynamic Smagorinsky model...
An analytical solution for thermally fully developed combined pressure - electroosmotically driven flow in microchannels
, Article International Journal of Heat and Mass Transfer ; Volume 50, Issue 5-6 , 2007 , Pages 1087-1096 ; 00179310 (ISSN) ; Taghizadeh Manzari, M ; Hannani, S. K ; Sharif University of Technology
2007
Abstract
An analytical solution is presented to study the heat transfer characteristics of the combined pressure - electroosmotically driven flow in planar microchannels. The physical model includes the Joule heating effect to predict the convective heat transfer coefficient in two dimensional microchannels. The velocity field, which is a function of external electrical field, electroosmotic mobility, fluid viscosity and the pressure gradient, is obtained by solving the hydrodynamically fully-developed laminar Navier-Stokes equations considering the electrokinetic body force for low wall zeta potentials. Then, assuming a thermally fully-developed flow, the temperature distribution and the Nusselt...
The effect of the time dependent pressure difference on bubble dynamics in microchannels
, Article 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006, Limerick, 19 June 2006 through 21 June 2006 ; Volume 2006 A , 2006 , Pages 83-88 ; 0791847608 (ISBN); 9780791847602 (ISBN) ; Rouhani, S ; Saboohi, Y ; Sharif University of Technology
American Society of Mechanical Engineers
2006
Abstract
The physical processes responsible for bubble formation in microchannels are not well understood and lack fundamental understanding. Experimental results are not exactly in agreement with each other and there are no definite theories to explain the possible effects of different parameters. Among different parameters the microchannel hydraulic diameter can affect the bubble formation mechanism in microchannels strongly. In this paper the effect of the time dependent pressure difference between inside and outside of the bubble on bubble dynamics in microchannels have been investigated. The source of this time dependency can be the emergence of bubble embryos which produces a density...
Casson fluid flow with heat and mass transfer in a channel using the differential transform method
, Article Kuwait Journal of Science ; Volume 49, Issue 1 , 2022 , Pages 1-19 ; 23074108 (ISSN) ; Ali, K ; Ashraf, M ; Sharif University of Technology
University of Kuwait
2022
Abstract
In the present investigation, we consider the heat and mass transfer characteristics of steady, incompressible and electrically conducting Casson fluid flow in a channel. The effect of chemical reactions have also been considered. The differential transform method (DTM) is applied to a system of non-linear ODEs, and the results are obtained in the form of DTM series. The principal gain of this approach is that it applies to the non-linear ODEs without requiring any discretization, linearization or perturbation. The velocity, mass and heat transfer profiles thus obtained are in good agreement with those provided by the quasi-linearization method (QLM). Graphical results for velocity,...
Three-dimensional modeling of density current in confined and unconfined channels
, Article 2006 ASME International Mechanical Engineering Congress and Exposition, IMECE2006, Chicago, IL, 5 November 2006 through 10 November 2006 ; 2006 ; 08888116 (ISSN); 0791837904 (ISBN); 9780791837900 (ISBN) ; Firoozabadi, B ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2006
Abstract
Dense underflows are continuous currents which move down-slope due to the fact that their density is heavier than that ambient water. In this work, 2-D and 3-D density current in a channel were investigated by a set of experimental studies and the data were used to simulate the density current. The velocity components were measured using Acoustic Doppler Velocimetry (ADV). The height of density current (current's depth) was also measured. In this study, the density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. A low-Reynolds number turbulent model (Launder and Sharma, 1974) has been applied to...
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) ; 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...
3-D simulation of turbulent density
, Article 2006 ASME Joint U.S.- European Fluids Engineering Division Summer Meeting, FEDSM2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2 FORUMS , 2006 , Pages 361-367 ; 0791847500 (ISBN); 9780791847503 (ISBN) ; Firoozabadi, B ; Ghasvari Jahromi, H ; Afshin, H ; Sharif University of Technology
American Society of Mechanical Engineers
2006
Abstract
Density current is a dense fluid, which is continuously released from a source and spreads down a sloping surface inside a lighter, motionless fluid. A low-Reynolds number k-ε model (Launder and Sharma, 1974) has been used to simulate the behavior of 3-D density currents. Density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been verified with the experimental data sets. Although the k-ε Launder and Sharma model is applied here to a conservative density current, it seems the analysis is valid in general for turbidity current laden with fine particles. Copyright © 2006 by ASME
A novel mechanism for heat transfer enhancement through microchannels using electrokinetic effect
, Article 2005 ASME Summer Heat Transfer Conference, HT 2005, San Francisco, CA, 17 July 2005 through 22 July 2005 ; Volume 3 , 2005 , Pages 949-955 ; 0791847314 (ISBN); 9780791847312 (ISBN) ; Manzari, M. T ; Monazami, R ; Bazargan, V ; Sharif University of Technology
2005
Abstract
In this paper a three-dimensional numerical model is developed in order to study the heat transfer enhancement in rectangular microchannels due to electrokinetic effect. The electrokinetic body force on fluid elements gives some superior convective transport properties to the flow relative to pure pressure driven flow in microchannels. Unlike the conventional parabolic velocity profile of pressure driven laminar flow, the electrokinetic body force transforms the velocity profile to a slug-like flow. Due to sharp velocity gradient near the wall, the convective heat transfer properties of the flow are improved dramatically. Net charge distribution across the channel is obtained by solving the...
Numerical Analysis of Channel Flow over an Elastic Bump, Using Lattice Boltzmann Method- A Biological Application
, M.Sc. Thesis Sharif University of Technology ; Taeibi Rahni, Mohammad (Supervisor)
Abstract
In recent years, lattice Boltzmann method (LBM) has been developed to be used as an alternative and promising computational technique to simulate various flows. It originates from classical statistical physics. The ability to simply solve complex flows, simulating of multiphase and multi-component without need to follow the boundaries of different phases, and the inherent ability of parallel processing are notable features of this approach. On the other hand, finite element method (FEM) is widely used in many practical engineering fields, especially in solid mechanics. In this study, in addition to simulating flow over a rigid body, flow over an elastic body is also simulated with a...
Triangular labyrinth side weirs with one and two cycles
, Article Proceedings of the Institution of Civil Engineers: Water Management ; Volume 166, Issue 1 , 2013 , Pages 27-42 ; 17417589 (ISSN) ; Nekooie, M. A ; Sadeghian, H ; Ghazizadeh, M. R. J ; Sharif University of Technology
2013
Abstract
Labyrinth side weirs provide a potentially effective way to shorten the length of a channel opening with the desired water height, but the discharge coefficient needs to be found experimentally. Experiments were carried out for triangular labyrinth side weirs with one and two cycles in order to obtain the discharge coefficient. The test variables included channel opening, head angle, number of cycles, weir height, upstream water depth and discharge in a subcritical situation. The resultsshow that the discharge coefficient ratio for a triangular labyrinth to a conventional side weir could rise to more than 2 with the same flow and geometric conditions. Relationships for the De Marchi...
Hydraulic behaviour of flow over an oblique weir
, Article Journal of Hydraulic Research ; Volume 48, Issue 5 , 2010 , Pages 669-673 ; 00221686 (ISSN) ; Ansari, A ; Borghei, S. M ; Sharif University of Technology
2010
Abstract
A comprehensive set of experiments was performed on weirs placed obliquely in a rectangular open channel. The main objectives were to investigate the effect of the weir angle relative to the approach flow direction on the behaviour and the hydraulic flow characteristics and to examine methods such as using upstream guide vanes and inclined aprons to increase the effective oblique weir length. Results indicate that by increasing the oblique angle, the effective length of the oblique weir increases significantly. Relationships are provided for the threshold submergence and the effective length of the oblique weir. Design recommendations are also presented for the use of guide vanes and...
Lateral dispersion in deflected emergent aquatic canopies
, Article Environmental Fluid Mechanics ; Volume 19, Issue 4 , 2019 , Pages 833-850 ; 15677419 (ISSN) ; Davari, H ; Shoaei, F ; Sharif University of Technology
Springer Netherlands
2019
Abstract
Understanding the mechanism of dispersion within plants is essential for proper operation of natural and constructed treatment wetlands. Plant deflection induced by the current drag modifies the flow and dispersion within an aquatic canopy. In this study, we look at the effect of the deflection angle of the plants on transverse dispersion. Experiments were carried out in a current flume on an array of inclined solid rods representing a deflected emergent canopy. The stem Reynolds number varied between 90 and 360, normalized stem densities between 0.011 and 0.033, and the inclination angles between 0° and 45°. The plume development was recorded using image processing technique. A special...
3D numerical analysis of joule heating effect on electroosmotic flow in microchannels
, Article 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006, Limerick, 19 June 2006 through 21 June 2006 ; Volume 2006 A , 2006 , Pages 203-208 ; 0791847608 (ISBN); 9780791847602 (ISBN) ; Yazdi, S ; 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 the influence of the Joule heating on flow characteristics of an electroosmotic flow through square cross section micro-channels. The governing system of equations consists of three sets of equations: electric potential distribution, flow-field and energy equations. The solution procedure involves three steps. The net charge distribution on the cross section of the micro-channel 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...
Modification of standard k-epsilon turbulence model for multi-element airfoil application using optimization technique
, Article 24th AIAA Applied Aerodynamics Conference, San Francisco, CA, 5 June 2006 through 8 June 2006 ; Volume 1 , 2006 , Pages 216-227 ; 10485953 (ISSN); 1563478129 (ISBN); 9781563478123 (ISBN) ; Setayeshgar, A ; Vakili, S ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2006
Abstract
The use of multi-element airfoils has been known as a major approach to boost up the lift of wing without dramatic increase in its drag. In fact, the configuration helps to reduce the chance of flow separation over the airfoil. However, the use of a complicated geometry such as multi-element airfoil would normally cause complexity in flow behavior. The experience has shown that the flow field complexities cannot be properly modeled using standard two-equation k-epsilon turbulence model. Therefore, it is important to improve the accuracy of general turbulence models in specific applications and complex computational domains. In this work, we extend a suitable objective function based on...
Thermal transport in combined pressure - Electroosmotically driven flow in microchannels
, Article 10th Intersociety Conference on Thermal and Thermomechanical Phenomena and Emerging Technologies in Electronic Systems, ITherm 2006, San Diego, CA, 30 May 2006 through 2 June 2006 ; Volume 2006 , 2006 , Pages 63-70 ; 0780395247 (ISBN); 9780780395244 (ISBN) ; Taghizadeh Manzari, M ; Kazemzadeh Hannani, S ; Sharif University of Technology
2006
Abstract
An analytical solution is presented to study the heat transfer characteristics of the combined pressure - electroosmotically driven flow in planar microchannels. The physical model includes the Joule heating effect to predict the convective heat transfer coefficient in two dimensional microchannels. The velocity field, which is a function of external electrical field, electroosmotic mobility, fluid viscosity and the pressure gradient, is obtained by solving the hydrodynamically fully-developed laminar Navier-Stokes equations considering the electrokinetic body force for low wall zeta potentials. Then, assuming a thermally fully-developed flow, the temperature distribution and the Nusselt...
Developing an efficient multigrid strategy for solving incompressible flow
, Article 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE 2004, Anaheim, CA, 13 November 2004 through 19 November 2004 ; Volume 260 , 2004 , Pages 625-634 ; 08888116 (ISSN) ; Schneider, G. E ; Taheri, A ; Sharif University of Technology
2004
Abstract
In this work, a multigrid acceleration technique is suitably developed for solving the two-dimensional incompressible Navier-Stokes equations using an implicit finite element volume method. In this regard, the solution domain is broken into a huge number of quadrilateral finite elements. The accurate numerical solution of a flow field can be achieved if very fine grid resolutions are utilized. Unfortunately, the standard implicit solvers need more computational time to solve larger size of algebraic set of equations which normally arise if fine grid distributions are used. Past experience has shown that the convergence of classical relaxation schemes perform an initial rapid decrease of...
Interfacial instabilities in sediment suspension flows
, Article Journal of Fluid Mechanics ; Vol. 758, issue , November , 2014 , p. 312-326 ; Jalali, M. A ; Maleki, M ; Sharif University of Technology
Abstract
We report the existence of interfacial instability in the two-dimensional channel flow of a sediment suspension whose particles diffuse in the carrier fluid due to shear-induced collisions. We derive partial differential equations that govern the deformations of the interface between the sediment suspension and the clear fluid, and devise a perturbation method that preserves the positivity of the particle volume fraction. We solve perturbed momentum, particle transport and deforming interface equations to show that a Kelvin-Helmholtz-type unstable wave develops at the interface for wavelengths longer than a critical value. Short-wavelength oscillations of the interface are damped due to...
Three-dimensional modeling of density current in a straight channel
, Article Journal of Hydraulic Engineering ; Volume 135, Issue 5 , 2009 , Pages 393-402 ; 07339429 (ISSN) ; Afshin, H ; Aram, E ; Sharif University of Technology
2009
Abstract
Dense underflows are continuous currents that move downslope due to their density being heavier than that of the ambient water. In this work, a steady density current with a uniform velocity and concentration from a narrow sluice gate enters into a wide channel of lighter ambient fluid and moves forward downslope. Experiments varying inlet velocity and concentration and hence inlet Richardson numbers were conducted. Numerical simulations were also performed with a low-Reynolds number k-ε model. The results of numerical simulation agree well with the experimental data. © 2009 ASCE
Generation of Voronoi grid based on vorticity for coarse-scale modeling of flow in heterogeneous formations
, Article Transport in Porous Media ; Volume 83, Issue 3 , Oct , 2010 , Pages 541-572 ; 01693913 (ISSN) ; Mahani, H ; Sharif University of Technology
2010
Abstract
We present a novel unstructured coarse grid generation technique based on vorticity for upscaling two-phase flow in permeable media. In the technique, the fineness of the gridblocks throughout the domain is determined by vorticity distribution such that where the larger is the vorticity at a region, the finer are the gridblocks at that region. Vorticity is obtained from single-phase flow on original fine grid, and is utilized to generate a background grid which stores spacing parameter, and is used to steer generation of triangular and finally Voronoi grids. This technique is applied to two channelized and heterogeneous models and two-phase flow simulations are performed on the generated...