Sharif Digital Repository

Some interface front patterns of falling droplets are studied via direct numerical solution of the full Navier-Stokes equations governing the system of droplets and the ambient surrounding media as a single-fluid model. We focus on the mutual interactions of the effects of characterizing nondimensional parameters on the formation and break-up of large cylindrical droplets. The investigation of droplet cross sections and deformation angles shows that for moderate values of the Atwood number, increasing the Eötvös number explicitly increases the deformation rate in formation and breakup phenomena. Otherwise, increasing the Ohnesorge number basically amplifies the viscous effects  

In this work, two-dimensional laminar flow and heat transfer across a heated square cylinder, covered by a porous layer in a plane channel have been numerically investigated. The flow and thermal fields inside the porous layer were simulated using BrinkmaneForchmeyer extended Darcy model. Simulations were performed in different Reynolds numbers (Re = 60, 120, 160, and 200), porosities (ω = 0.7, 0.87, and 0.96), solid to fluid thermal conductivity ratios (λR = 10, 200, and 2000) and blockage ratios (BR = 0.5, 0.25 and 0.125). The effects of the mentioned parameters on pressure drop and heat transfer rate were investigated in detail. Also, the contribution of each side of the central squared... 

A three-dimensional numerical study has been performed to investigate the influence of angle of shock waves on sonic transverse Hydrogen micro-jets subjected to a supersonic crossflow. This study focuses on mixing of the Hydrogen jet in a Mach 4.0 crossflow with a global equivalence ratio of 0.5. Flow structure and fuel/air mixing mechanism were investigated numerically. Parametric studies were conducted on the angle of shock wave by using the Reynolds-averaged Navier-Stokes equations with Menter's Shear Stress Transport turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features depending upon the angle of shock incident. These flow... 

Two and three dimensional modeling of a single cell of vanadium redox flow battery has been done thoroughly according to electrochemical and fluid mechanic equations in this study. The modeling has been done in stationary state and its results have been presented in three chemical, electrical and mechanical sub models. The parametric analysis on some of important factors in cell operation demonstrated that increase in electrode and membrane conductivity and electrode porosity contributes to electric potential increase in cells. Also operational temperature increase leads to decrease in cells' voltage. Better fluid distribution on the electrode surface area results in better cell operation,... 

To extend a procedure to ensure the safe operation of a water reactor, we develop a numerical method to compute the high frequency pressure spikes of water hammer with liquid column separation in pipes. In this regard, we first extend a finite-volume all-speed method to solve the full one-dimensional Navier-Stokes equations. This method is capable of simulating gas and liquid phases as well as the vapor-liquid one. On the other hand, the current extended method should be capable of capturing high frequency pressure spikes, which are formed due to water hammer and column separation in pipes. The existence of such high frequency spikes has been recently reported experimentally by other... 

Green iron oxide pellets are indurated with thermal treatment in pelletizing plant to achieve sufficient mechanical properties and to be used in iron-steel industry. In the first stage, the pellets are dried with hot air coming from the firing unit. High heat transfer makes the evaporation rate exceeding the outgoing steam rate from the pellets and as a result, increasing the inner pressure of the pellets and fragment. On the other hand, low heat transfer causes low production rate. Using the related equations and considering the pellets' moisture and porosity and applying the pellets' condition on parameters such as specific heat capacity and heat conductivity, an acceptable standard is... 

The present study focuses on the numerical simulation of cavitation around the NACA 0015. The unsteady behaviors of cavitation which have worthwhile applications are investigated. The cavitation patterns, velocity fields and frequency of the cavitating flow around hydrofoil is obtained. For multi phase simulation, single-fluid Navier-Stokes equations, along with a volume fraction transport equation, are employed. The bubble dynamics model is utilized to simulate phase change. SIMPLE algorithm is used for velocity and pressure computations. For discretization of equations the finite-volume approach written in body fitted curvilinear coordinates, on collocated grid, is used. In this study,... 

The present study focuses on the implementation of PISO algorithm to simulate cavitating flows. For simulation of unsteady behaviors of cavitation which have practical applications, the development of unsteady PISO algorithm based on the non-conservative approach is investigated. The effects of mixture compressibility are considered to improve accuracy of simulations. For multi-phase simulation, single-fluid Navier-Stokes equations, along with the volume fraction transport equation, are employed. The bubble dynamics model is utilized to simulate phase change. To prove capabilities of the developed PISO algorithm to simulate cavitating flows, unsteady simulation of cavitation around NACA0015... 

In this paper, the steady-state stresses in a homogeneous isotropic half-space under a moving wheel-type load with constant subsonic speed, prescribed on a finite patch on the boundary, are investigated. Navier's equations of motion in 2D case were modified via Stokes-Helmholtz resolution to a system of partial differential equations. A double Fourier-Laplace transformation procedure was employed to solve the system of partial differential equations in a new moving reference system, regarding the boundary conditions. The effects of force transmission from the contact patch to the half-space have been considered in the boundary conditions. Utilizing a property of Laplace transformation leads... 

This paper deals with the flexural instability of flexible spinning cylinders partially filled with viscous fluid. Using the linearized Navier-Stokes equations for the incompressible flow, a two-dimensional model is developed for fluid motion. The resultant force exerted on the flexible cylinder wall as the result of the fluid motion is calculated as a function of lateral acceleration of the cylinder axis in the Laplace domain. Applying the Hamilton principle, the governing equations of flexural motion of the rotary flexible cylinder mounted on general viscoelastic supports are derived. Then combining the equations describing the fluid force on the flexible cylinder with the structural... 

In the present work, numerical simulation of cross flow microfiltration of non-alcoholic beer in a tubular membrane has been studied theoretically and verified experimentally. Finite element method was used as a powerful tool for simulation. The feed stream, which flows mainly tangentially to the porous membrane surface, is modeled by the Navier-Stokes equations whereas the porous wall conditions are described by the Darcy equation that relates the pressure gradient within a flow stream to the flow rate through the permeable wall. A new model that considers transient behavior of the membrane due to fouling was used to estimate the permeate flux reduction. A pilot-scale cross flow membrane... 

In this paper, the structure of a wall jet deflected by a baffle along with the trajectory of particles has been studied. This baffle is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. An elliptic relaxation turbulence model (ν̄2-f model) has been used to simulate this submerged flow. In recent years, the ν̄2- f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proven that the ν̄2- f model is superior to other Reynolds-averaged Navier-Stokes (RANS) methods in many flows where complex flow... 

In this paper, numerical simulation is performed to investigate the effects of micro air jets on mixing of the micro hydrogen jet in a transverse supersonic flow. The fundamental flow feature of the interaction between an array of fuel and air jets is investigated in a Mach 4.0 crossflow with a fuel global equivalence ratio of 0.5. Parametric studies were conducted on the various air jet conditions by using the Reynolds-averaged Navier–Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Numerical study of eight streamwise transverse sonic fuel and air jets in a fully turbulent supersonic flow revealed an extremely complex feature of fuel and air jet interaction. The... 

Landslide-generated waves (LGWs) are among natural hazards that have stimulated attentions and concerns of engineers and researchers during the past decades. At the same period, the application of numerical modeling has been progressively increased to assess, control, and manage the risks of such hazards. This paper represents an overview of numerical studies on LGWs to explore associated recent advances and future challenges. In this review, the main landslide events followed by an LGW hazard are scrutinized. The uncertainty regarding landslide characteristics and the lack of data concerning generated tsunami properties highlights the necessity of probabilistic analysis and numerical... 

Purpose - The purpose of this paper is to present a fast, economical and practical method for mathematical modeling of aerodynamic characteristics of rectangular wing in ground (WIG) effect. Design/methodology/approach - Reynolds averaged Navier-Stokes (RANS) equations were converted to Bernoulli equation by reasonable assumptions. Also, Helmbold's equation has been developed for calculation of the slope of wing lift coefficient in ground effect by defining equivalent aspect ratio (ARe). Comparison of present work results against the experimental results has shown good agreement. Findings - A practical mathematical modeling with lower computational time and higher accuracy was presented for... 

Numerical study of pollutant emissions (NO and CO) in a Jet Stirred Reactor (JSR) combustor for methane oxidation under Elevated Pressure Lean Premixed (EPLP) conditions is presented. A Detailed Flow-field Simplified Chemistry (DFSC) method, a low computational cost method, is employed for predicting NO and CO concentrations. Reynolds Averaged Navier Stokes (RANS) equations with species transport equations are solved. Improved-coefficient five-step global mechanisms derived from a new evolutionary-based approach were taken as combustion kinetics. For modeling turbulent flow field, Reynolds Stress Model (RSM), and for turbulence chemistry interactions, finite rate-Eddy dissipation model are... 

In this study, we simulate the flow and heat transfer during hot-wire anemometry and investigate its thermal behavior and physics using the Computational Fluid Dynamics (CFD) tool. In this regard, we use the finite-volume method and solve the compressible Navier-Stokes equations numerically in slightly non-continuum flow fields. We do not use any slip flow model to include the transitional flow physics in our simulations. Using the CFD method, we simulate the flow over hot-wire and evaluate the uncertainty of CFD in thermal simulation of hot-wire in low transitional flow regimes. The domain sizes and the mesh distributions are carefully chosen to avoid boundary condition error appearances.... 

In this research, the problems of adiabatic film-cooling the flat, convex, and concave surfaces are investigated numerically. Two different radii of curvature and one row of vertical injection holes are considered. The Navier-Stokes equations are solved using a fine nonuniform multiblock staggered curvilinear grid and the SIMPLE-based finite volume method. The blowing rates are 0.5 and 1.0 and the mainstream Reynolds number is 10,000. The obtained results indicated that at a low blowing ratio, the cooling effectiveness enhances over the convex surface and reduces over the concave surface compared to the flat surface case. In comparison with the low blowing ratio, the curvature effects at a... 

Excess pressure drop induced by inertial effects limits the applicability of Darcy's law for modeling of fluid flow through porous media at high velocities. It is expected such additional pressure drop is influenced by pore/morphology of porous media. This work concerns with fundamental understanding of how throat curvature affects intrinsic properties of porous media at non-Darcy flow conditions using network modeling. Conical, parabolic, hyperbolic, and sinusoidal capillary ducts with three types of imposed anisotropy are used to construct the network in a more realistic manner. Solutions of one dimensional Navier-Stokes equation for incompressible fluid flow through converging/diverging... 

In this work, numerical investigation of a gas turbine model combustor (GTMC) was carried out using two different turbulence-chemistry interaction models: the EDC (eddy dissipation concept) and TPDF (transported probability density function). GTMC with good optical access for laser measurements provides a useful database for swirling CH4/Air diffusion flames at atmospheric pressure. Modeling was performed by solving Reynolds-averaged Navier-Stokes (RANS) and Reynolds stress model (RSM) equations for a two-dimensional (2D) axisymmetric computational domain accompanied by swirl and the combustion chamber was investigated for both reacting and nonreacting conditions. A detailed reduced...