Sharif Digital Repository

Analysis of flow in fluidized beds, a common chemical reactor, is of much current interest due to its fundamental as well as industrial importance. Experimental data for the successive increments of the pressure fluctuations time series in a fluidized bed are analyzed by computing a multiscale probability density function (PDF) of the increments. The results demonstrate the evolution of the shape of the PDF from the short to long time scales. The deformation of the PDF across time scales may be modeled by the log-normal cascade model. The results are also in contrast to the previously proposed PDFs for the pressure fluctuations that include a Gaussian distribution and a PDF with a power-law... 

Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using RANS method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly, and requires meticulous laboratory equipment; therefore, utilizing numerical methods and developing a virtual laboratory seems highly efficient. In the present study, the... 

In this study, in order to indicate the best airfoil profile for the different sections of a blade, five airfoils including S8xx, FFA, and AH series were studied. Among the most popular wind power blades for this application were selected, in order to find the optimum performance. Nowadays, modern wind turbines are using blades with multi-airfoils at different sections. On the large scale profile, SST K-ω model with different wind speed at large-scale profile was applied to the simulation of horizontal axis wind turbines (HAWT). The aerodynamic simulation was accomplished using the computational fluid dynamic (CFD) method based on the finite volume method. The governing equations applied in... 

The application of incinerators for the municipal solid waste (MSW) is growing due to the ability of such instruments to produce energy and, more specifically, reduce waste volume. In this paper, a numerical simulation of the combustion process with the help of the computational fluid dynamics (CFD) inside a portable (mobile) incinerator has been proposed. Such work is done to investigate the most critical parameters for a reliable design of a domestic portable incinerator, which is suitable for the Iranian food and waste culture. An old design of a simple incinerator has been used to apply the natural gas (NG), one of the available cheap fossil fuels in Iran. After that, the waste height,... 

Numerical simulations of the turbulent flow around single and side-by-side piles at different spacing ratios (centre-to-centre distance to the pile diameter) with flow Reynolds number of 105 on the fixed flat-bed are presented. The calculations are performed using the computational fluid dynamics model, FLOW-3D, which solves the Navier–Stokes equations in three dimensions with a finite-volume method. The numerical results of time-averaged flow patterns around single and side-by-side piles are validated using the available experimental measurements. At the downstream of the single pile, dimensionless vortex shedding frequency (Strouhal number) is estimated as 0.22. The maximum values of bed... 

The overall design of cold gas propulsion systems is pretty complicated when considering the mission requirements, operating constraints and functional limitations imposed by the mechanical components. To address this complication, a precise design process is proposed, which attempts to optimize the cost of operation as well as to minimize the waste volume and weight by using multi-objective trade-off analysis. This analysis is based on a set of ordinary differential equations that are solved iteratively to describe the optimal behavior of the system. Therefore, a numerical code is being developed to give insight on the design sensitivity with respect to uncertainties on the design... 

Development of orbital shaking technology for enhanced mixing with lower mechanical demand has been receiving significant attention since the advent of advanced mixing schemes. Amongst shaken bioreactors, microtiter plates play significant role both for research and industrial purposes due to their capability of handling tiny amount of liquid in parallel experimentations. Detailed understanding of complicated Flow hydrodynamics thus seems to be considered a continual effort, as it is responsible for efficient gas-liquid mass transfer. Computational fluid dynamics (CFD) technique is shown to be a suitable numerical method in particular for discovering concealed flow facts, which can reliably... 

Purpose: To determine the outward permeability of retina-choroid-sclera (RCS) layer for different ophthalmic drugs and to develop correlations between drug physicochemical properties and RCS permeability. Methods: A finite volume model was developed to simulate pharmacokinetics in the eye following drug administration by intravitreal injection. The RCS permeability was determined for 32 compounds by best fitting the drug concentration-time profile obtained by simulation with previously reported experimental data. Multiple linear regression was then used to develop correlations between best fit RCS permeability and drugs physicochemical properties. Results: The RCS drug permeabilities had... 

Bladeless fan is a novel fan type that has no observable impeller, usually used for domestic applications. Numerical investigation of a Bladeless fan via Finite Volume Method was carried out in this study. The fan was placed in center of a 4×2×2m room and 473 Eppler airfoil profile was used as cross section of the fan. Performance and noise level of the fan by solving continuity and momentum equations as well as noise equations of Broadband Noise Source (BNS) and Ffowcs Williams and Hawkings (FW-H) in both steady state and unsteady conditions were studied. Flow increase ratio of the fan was captured. Furthermore, BNS method could find outlet slit of the air as the main source of the noise... 

Bladeless fan is a novel type of fan with an unusual geometry and unique characteristics. This type of fan has been recently developed for domestic applications in sizes typically up to 30cm diameter. In the present study, a Bladeless fan with a diameter of 60cm was designed and constructed, in order to investigate feasibility of its usage in various industries with large dimensions. Firstly, flow field passed through this fan was studied by 3D modeling. Aerodynamic and aeroacoustic performance of the fan were considered via solving the conservation of mass and momentum equations in their unsteady form. To validate the acoustic code, NACA 0012 airfoil was simulated in a two dimension domain... 

Abstract: Underwater vehicles when yawed to free stream flow, like submarines in a turning maneuver, produce large vortical separated regions. This vortical flow affects acoustic, body drag, control effectiveness and maneuverability. A suitable way to reduce the effects of this separated flow is to use vortex generators. The main goal of this study is to investigate the effect of the vortex generator on the flow field around a standard underwater model employing the vortex generators by using the oil flow visualization method in wind tunnel only in yaw direction (0° ≤ β ≤ 30° angles of attack, due to the experimental cost) and the CFD method in the pitch direction (0° ≤ α ≤ 30° angles of... 

Trimaran vessels are developed for different applications and hydrodynamic behavior of such vessels is different than usual mono-hulls. In this paper hydrodynamic resistance and maneuvering of a trimaran with Wigley body form are investigated. The effects of outriggers position in four different longitudinal and two transverse locations are studied. For hydrodynamic simulations a CFD code has been developed and used. This code is capable for simulating three dimensional, time dependent, two phases, viscous flow coupled with rigid body motion. Formulation and solution algorithm are described in detail. Different case studies have been performance and numerical results have shown good... 

The use of collocated grid schemes in control-volume-based methods has resulted in developing different strategies for coupling mass and momentum governing equations. Defining two different velocity components at cell faces is one remedy to suppress the possible checkerboard problem in the solution domain. These velocity components are widely known as convected and convecting velocities which are normally used in the momentum and mass governing equations, respectively. However, the linearization of the nonlinear governing equations generates a number of lagged velocity components which must be carefully treated in a manner to preserve the conceptual definition of the convected and convecting... 

Blade film cooling is one of the best methods to improve efficiency of gas turbines. In this work, two different methods of film cooling, namely, slot injection and discrete hole injection have been numerically studied on a flat plate. Incompressible, stationary, viscous, turbulent flow has been simulated using the FLUENT CFD code with the standard k-s model. The study of injection angle and velocity ratio show that the optimum film cooling in both methods, occurs at the jet angle of 30° but with the velocity ratio of 1.5 for slot case and 0.5 for discrete hole case. The study of jet aspect ratio in discrete hole method, shows that stretching the hole in spanwise direction increases the film... 

During the past two decades, the lattice Boltzmann (LB) method has been introduced as a class of computational fluid dynamic methods for fluid flow simulations. In this method, instead of solving the Navier Stocks equation, the Boltzmann equation is solved to simulate the flow of a fluid. This method was originally developed based on uniform grids. However, in order to model complex geometries such as porous media, it can be very slow in comparison with other techniques such as finite differences and finite elements. To eliminate this limitation, a number of studies have aimed to formulate the lattice Boltzmann on the unstructured grids. This paper deals with simulating fluid flow through a... 

This study considers blood flow in total cavopulmonary connection (TCPC) morphology created in Fontan surgical procedure in patients with a single ventricle heart disease. Ordinary process of TCPC operation reduces pulmonary blood flow pulsatility since the right ventricle being bypassed. This reduction may limit the long term outcome of Fontan circulation. There is an idea of increasing pulmonary flow pulsations by keeping Main Pulmonary Artery (MPA) partially open while it was closed in ordinary TCPC operation. The purpose of the present study is to verify the effects of Antegrade Flow (AF) coming through stenosed MPA on pulmonary flow pulsations. The 3D geometry is reconstructed from CT... 

In this paper, the ball valve performance is numerically simulated using an unstructured CFD (Computational Fluid Dynamics) code based on the finite volume method. Navier-Stokes equations in addition to a transport equation for the vapor volume fraction were coupled in the RANS solver. Separation is modeled very well with a modification of turbulent viscosity. The results of CFD calculations of flow through a ball valve, based on the concept of experimental data, are described and analyzed. Comparison of the flow pattern at several opening angles is investigated. Pressure drop behind the ball valve and formation of the vortex flow downstream the valve section are also discussed. As the... 

This paper describes optimization of the combustion chamber geometry and injection timing of a new generation of EF7 engine, where CNG is directly injected to the combustion chamber, with the aim of providing the best mixture at low and high speeds. The Multi-Objective Genetic Algorithm (MOGA) is coupled with the KIVA Computational Fluid Dynamics (CFD) code, with grid generation, in order to maximize the flammable mass of the mixture. This would result in better combustion and improved fuel economy. The optimization variables related to the combustion chamber are seven geometry variables and injection timing. Through the present optimization, a great improvement in mixture distribution is... 

A brass vortex tube with changeable parts is used to obtain the optimum nozzle intake numbers and diameter. The effects of inlet pressure and CF (cold fraction) are also investigated. Results illustrate that increasing the number of nozzles causes a temperature drop and the optimum nozzle diameter corresponds to quarter of vortex tube diameter. The distance between cold end orifice and nozzle intakes is investigated in this work and it is found that for a better performance, this distance should be decreased. A series of experiments conducted to investigate the CF effect on VT performance and an optimum amount for this parameter is found. A two-dimensional computational fluid dynamics...