Sharif Digital Repository

Particle transport and deposition in a channel flow with elliptic obstruction is studied. Numerical simulation of fluid flow is performed using two-dimensional lattice Boltzmann method, while one-way coupling Lagrangian method for particle tracking is used. Standard particles are injected in the inlet of the channel. Gravity, Drag force, Brownian forces, and the Saffman lift are considered in equation of particle motion. The influence of geometrical parameter, ellipse aspect ratio, is studied on dispersion and deposition of particles as well as the flow parameters, such as Reynolds number. In addition, the effect of particles size -particles of 0.01-10μm in diameter- on dispersion and... 

We use the detrended fluctuation analysis (DFA), the detrended cross correlation analysis (DCCA) and the magnitude and sign decomposition analysis to study the fluctuations in the turbulent time series and to probe long-term nonlinear levels of complexity in weakly and high turbulent flow. The DFA analysis indicate that there is a time scaling region in the fluctuation function, segregating regimes with different scaling exponents. We discuss that this time scaling region is related to inertial range in turbulent flows. The DCCA exponent implies the presence of power-law cross correlations. In addition, we conclude its multifractality for high Reynold's number in inertial range. Further, we... 

A local radial basis function (RBF) meshless method is applied for solution of the Burgers' equation with different initial and boundary conditions of various complexities. Local-RBF collocation is employed for discretization in space, whilst the unsteady term is handled via a simple explicit time discretization. Moreover, in case of non-smooth initial conditions with high Reynolds numbers, a treatment is proposed for inability of local-RBF methods to solve such problems. The scheme is validated over a variety of benchmark problems and very good agreement is found with existing analytical and numerical solutions  

This paper discusses an experimental study of vertical mixing in an aquatic canopy. Vertical variation of physical characteristics of stems is fairly observed in the field and leads to variation in frontal area. This can affect both the flow and the mixing process.We experimentally investigated the effects of vertical density variation on both flow and vertical diffusion at high Reynolds numbers (turbulent flow range). Using rigid cylinders, we simulated step-like density variation in a flume. Vertical mixing coefficient was measured by recording vertical mixing of dye in the flume. The results indicate that vertical mixing coefficient decreases as density increases in depth. Velocity... 

In this research the fluid dynamics characteristics of a stellar turbulent jet flow is studied numerically and the results of three dimensional jet issued from a stellar nozzle are presented. A numerical method based on control volume approach with collocated grid arrangement is employed. The turbulent stresses are approximated using k-ε and k-ω models with four different inlet conditions. The velocity field is presented and the rate of decay at jet centerline is noted. Special attention is drawn on the influence of corner angle and number of wings on mixing in stellar cross section jets. Stellar jets with three; four and five wings and 15-65° corner angles are studied. Also the effect of... 

The aim of this work is to investigate flow hydrodynamics in porous media. Random non-overlapping spherical particles in a cylindrical geometry were produced as a porous media. Navier-Stokes equations in three-dimensional porous packed bed have been solved and dimensionless pressure drop has been studied for a fluid flow through the porous media at different Reynolds numbers (based on pore permeability and interstitial fluid velocity). The numerical results are in good agreement with those reported by Macdonald (1979) in the range of Reynolds numbers studied. At higher Reynolds numbers turbulent models such as large eddy simulation (LES) and Reynolds stress model (RSM) also have been... 

A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied to accurately compute steady and unsteady incompressible flows. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized by using the fourth-order compact FD scheme, and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient incompressible flow solver. A high-order spectral-type low-pass compact filter is used to stabilize the numerical solution. An iterative initialization procedure is presented and applied to generate consistent initial conditions for the simulation of unsteady flows. A sensitivity study is also... 

Generally, the flow in settling tanks is stratified, but the effect of buoyancy force on the flow field depends on the inlet concentration of particles and flow bulk velocity. A common approach for increasing settling tanks performance is to use baffles which can reduce effects of the unfavorable phenomena such as short circuiting between inlet and outlet and density currents in primary and secondary settling tanks, respectively. The suitable position of the baffles is related to the importance of buoyancy force. As a result, effects of inlet Reynolds and Froude numbers on the strength of buoyancy force are studied for a secondary settling tank and the results show that neither Reynolds nor... 

In this article, a three-dimensional numerical simulation is performed to investigate the effect of magnetic field on the heat transfer of ferrofluid inside a tube which is equipped with twisted tape. This work comprehensively focused on the flow feature and temperature distribution of ferrofluid in presence of non-uniform magnetic field while ferrofluid swirled inside a tube with twisted tape. In this study, it is assumed that the ferrofluid is single phase and laminar and constant heat flux is applied on the outside of the tube. The magnetic field is established by wire in parallel direction with the axis of the tube. The base fluid is water with 0.86 Vol% Nano particles (Fe3O4). The... 

In this work, a high-order weighted essentially nonoscillatory (WENO) finite-difference lattice Boltzmann method (WENOLBM) is developed and assessed for an accurate simulation of incompressible flows. To handle curved geometries with nonuniform grids, the incompressible form of the discrete Boltzmann equation with the Bhatnagar-Gross-Krook (BGK) approximation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting lattice Boltzmann equation in the computational plane are solved using the fifth-order WENO scheme. The first-order implicit-explicit Runge-Kutta scheme and also the fourth-order Runge-Kutta explicit time integrating scheme are...