Sharif Digital Repository

Wetlands and aquatic systems are abundant on the earth. Since many biological and chemical processes take place in aquatic regions, an understanding of hydrodynamics of flow in these areas is essential. Exchange flows or gravity currents driven by horizontal density gradients constitute a significant transfer mechanism in many lentic systems. Light blockage by emergent vegetations, which are a common feature of littoral zones, leads to a horizontal density gradient and hence an exchange flow between the vegetated and the open area. Also, existence of vegetations affects the behavior of the flow by inserting the drag force to the system and damping its energy. Previous studies have modeled... 

Two phase cross flows around a body have seldom been studied until now and considering these flows can play a significant role in long-term reliability and safety of industrial systems. In this paper flow regimes, drag coefficient and void fraction around different cross-section prisms were considered. To achieve this aim, main equations of flow have been developed for investigation of drag coefficient in air-water two phase. Our numerical analyses were performed by a designed and written CFD package which is based on Eulerian-Eulerian approach. Geometries, which have been studied in this article, are: circle, rectangle and triangle, for different aspect ratio and leading edge angle,... 

In the present study, we are to investigate and calculate the drag coefficient in the secondary bag breakup regime in droplet experiment in which the liquid droplet falls into continuous air jet flow. A high speed camera is hired to record the pictures of this process. With the help of image processing techniques, parameters such as dimensionless diameter, growth of droplet, drag coefficient and etc. in secondary bag breakup regime are investigated. The liquid used in this experiments are water, gasoline and diesel fuel. Dimensionless number influencing the result of the experiment are weber and Ohnesorge numbers, with weber number ranging from 6.86 to 20.31 and Ohnesorge number ranging from... 

Determination of drag force is one of the most difficult activities in the design and development of an aircraft. Accurate estimation of drag force is very important in design studies and needs to be estimated over and over during the design trade-offs. Importance of the determination of drag force, from the performance viewpoint, is an important stage in development and evaluation of an aircraft behavior and if the thrust and drag forces are well determined, the other performance characteristics could be easily estimated. Different methods are introduced for determination of drag using flight test or system identification methods in the time domain owing some limitations, disadvantages or... 

In this thesis we study an unexpected reverse spiral turn in the final stage of the motion of rolling rings. Equations of motion for rolling rings have been derived in the framework of Newtonian and Lagrangian mechanics, and solved in the presence of air drag forces and torques. The rolling motions of ellipsoids and disks have been used to validate the governing equations of motion. Based on experimental tests, we have found that the center of mass of rings moves in an S-shape trajectory. This is in contrast to spinning disks and coins that follow a spiral path before they stop. To explain this behavior, we included the effect of air drag in the equations of motions and found that the escape... 

Drop formation from the tip of a nozzle and its motion in bulk fluid is an interesting and practical process which has widely turned researchers’ attention. Investigation into the governing physics and effective parameters on formation, deformation and motion of a drop increases the efficiency of the related industrial processes. Thus in the present study, in order to simulate this process, full Navier-Stokes equations solved by the Volume of Fluid (VOF) method in an axisymmetric domain using Fluent software as the solver. In this research, the effects of Weber number (the proportion of inertial force to surface tension force) and Ohnesorge number (which refers to the proportion of viscous... 

This project studies the effects of different blade and different velocity fields on reducing drag coefficient. A numerical simulation was set up for a circular cylinder to represent the effects of blade on reducing drag. In this study, velocity, density and the cylinder diameter were constant and different viscosities were selected for different regime flows. The computational fluid dynamic programmer FLUENT was used to simulate results for this project. Arrays of cylinders were set up to see the changes in velocity profiles and drag coefficients for a range of Re. In this study, I studied three cases of setting up blade and concentrated on friction drag coefficient and pressure drag... 

The gas-liquid interaction is one of the most important and common phenomenons in chemical, biochemical and mineral industries which is generally observed as liquid in a gas stream (droplet) or gas in a liquid stream (bubble). Although bubbles produced in the industrial applications are in the form of a group of bubbles, understanding the hydrodynamics of a single bubble in a quiescent liquid provides a starting point for studying bubble groups. It should be noted that changes in the velocity and drag coefficient of the bubbles in various fluids are essential parameters for designing gas-liquid systems. In the present research, in order to examine the effect of system parameters and... 

Drag reduction on surfaces always has been a great case of study, especially in transport industry. This project discusses the external laminar flow of a single-phase fluid over a flat plate and the effects of making rectangular tiny grooves - in micron or millimeter - on them to reduce total drag. Making grooves with appropriate geometry on surfaces causes the fluid-solid contact area on the groove's surface turn into fluid-fluid and as a result the fluid will not shed into the groove. In other words the flow instead of having a no-slip boundary condition on inner surfaces of the groove, creates vortices in them that causes a remarkable reduction in velocity gradient followed by a skin... 

The purpose of this study is design and simulation of morphing flap for a slotted airfoil to reduce drag and increase lift. Increasing lift results in a smaller flap for the same lift, resulting in less weight and less drag. Drag reduction due to morphing nature causes growth in aerodynamic efficiency. In this work, a flap designed for 0.2 and 4,700,000 Mach and Reynold numbers, respectively. Our simulation was performed using ANSYS FLUENT flow solver and POINTWISE for grid generation. Here, morphing has been applied by changing the flap mean camber line and slots, so that they have minimum interferences with the flow. For this purpose, the flap mean camber line was discretized and various... 

The aim of this investigation is the experimental study of nozzle exhaust jet flow effects on aerodynamic behavior of an air vehicle at transonic speeds. For this sake, a secondary jet injection is used by the ejector into test model. The ejector total pressure for jet injection varies between 0 (jet off) to 4 bar for simulating nozzle exhaust jet flow and supplying intake’s required mass flow rate. All tests were conducted at QRC Trisonic wind tunnel and at Mach number of 0.5 to 0.85 and angles of -4 to 6 deg. The aerodynamic force and pressure results were recorded in order to analyze the exhaust jet flow. This study revealed that the aerial vehicle drag becomes bigger than its free flight... 

In this experimental study, a series of wind tunnel tests were performed to examine the wake flow profile over three swept wings with sweep angles of 23, 33 and 40 degrees with similar aspect ratio at various conditions. The airfoil of wing was a NACA 6-series airfoil designed to provide a laminar flow on the front half of the airfoil. The tests, made at a mid aerodynamic chord Reynolds number of 8×〖10〗^5, covered an angle of attack range of -2 to 10 degree. The wing tip vortex effects are eliminated by placing an End-plate on the wing tip.The tests were carried out at two main section of wing and two various position from behind of wing. A total pressure rake and transducers was used to... 

For observing the beauties of the sea, underwater vehicles are of the most appropriate equipment. In an optimized design of a vehicle, one should consider all applied forces and moments at all positions of the vehicle. Moving near the free surface is one of the positions of underwater vehicles. So, study on flow around a body moving near free surface is the subject of extensive research in marine hydrodynamic.
The aim of the current investigation is a scrutiny of the influence of free surface effect on the flow around underwater vehicles. For this purpose, finite volume method is used to simulate flow around an axisymmetric body near free surface. In this simulation, volume of fluid... 

Motion of liquid drops into another fluid is of central importance in a variety of most commonly used industries. Vast applications of emulsions in food and drug industries as well as using of drops in liquid-liquid extraction processes and direct contact heat exchangers are examples in which dynamics of motion of drops play a significant role in operation and efficiency.
In present study, we consider the accelerated motion of Newtonian and non-Newtonian liquid drops experimentally. In order to find the effect of bulk fluid on the motion of drops, air and water are used as bulk fluid. The experiments have been done on Water, Ethanol, Ethyl acetate, n-Hexane and Toluene as Newtonian and...