Sharif Digital Repository

The main subject of this research is to investigate the effects of two parallel wingtip vortices on each other. In fact, the goal is to determine how far apart the two runways should be when two aircraft take off from parallel runways at the same time so that the effects of the two wingtip vortices on adjacent aircraft are minimized. This research study is important to prevent the occurrence of tragic accidents caused by the failure to observe safe separation between aircraft. It is believed that the failure to observe the minimum separation and the subsequent occurrence of accidents are due to the significant increase in the volume of air traffic in the world. For this reason, the... 

Present research focuses on providing a reasonable solution for separation control through arrays of discrete wall jets. In this thesis, quasi-radial wall jet actuators have been introduced and theirs application in separation control (boundary layer control) have been investigated for the first time. This study includes two phases. The first phase is dedicated to investigation of physics and functional nature of wall jet actuators. In this phase, using numerical simulations, wall jet actuators in different situations have been studied and it was shown that arrays of quasi-radial jets have better performance than arrays of three-dimensional jets in creating a combine two-dimensional wall... 

Micropumps are one of the most important devices in the field of microfluidics which have many applications in various fields of engineering. Electrostatic excitation is one of the types of excitation mechanisms in micropumps that is widely used in microelectromechanical systems due to its low power consumption and easier control. In this research, first, the physics of droplets on the surface studied, important dimensionless numbers and other factors influencing microfluidic phenomena are investigated. The effective parameters of the droplet motion and the mechanism of this motion are described. Besides, the phenomenon of electrowetting, one of the phenomena in the field of dynamics of... 

Drawing inspiration from natural phenomena can provide simple solutions for creating new inventions. The graceful spinning and aerodynamic properties of maple leaves motivated a study on their rotation mechanics and physics, ultimately leading to the design of a propeller blade inspired by their shape and properties. Given that each maple tree produces thousands of leaves varying in dimensions, an average shape was calculated using digitizer software and Excel. Due to the small size of the leaves, one leaf was selected for 3D scanning. From various sections of the scanned leaf, airfoils were extracted and propellers were designed using SolidWorks software. Observing that these leaves... 

This research investigates the use of baffles in sector jets for film cooling of turbine blades. The goal of this study is to compare the cooling performance in three conditions: sector jet without baffles (one 90-degree arc), with one baffle (two 45-degree arcs), and with two baffles (three 30-degree arcs). The effect of using this type of cooling is also compared to the crossflow jet, which is the simplest type of cooling jet. In all conditions, the mass flow ratio is constant and equal to 1. The problem is solved for a turbine blade with the “AGTB-B1” airfoil. The problem is first solved with the Transition SST turbulence model, and the results are used as the initial conditions for the... 

Bubble collapse near a rigid wall with rapid and non-spherical compression of the internal gas can lead to destructive and unfavorable effects such as erosion, noise, and a fall-off in the performance of devices. Despite the fact that several investigations on this phenomena have been carried out under various conditions, studies indicate that the collapse of a single cavitation bubble next to the liquid jet injected from the wall's side and their interaction have not been studied so far. To achieve this goal, the present study deals with the three-dimensional simulation of the two-phase flow field from the Eulerian point of view. OpenFOAM has been used to solve the equations of conservation... 

Cloud cavitation is one of the major challenges faced by hydrodynamic systems, occurring unsteadily around submerged and moving components such as propellers and rudders. This phenomenon, observed in various industries—including marine propulsion, turbomachinery, and hydrodynamic systems—can cause shock waves, erosion, undesirable vibrations, and efficiency losses, particularly due to the collapse of vapor bubbles near solid surfaces. In this research, to control and mitigate the effects of cloud cavitation, the influence of semi-spherical surface microstructures on a three-dimensional Clark-Y hydrofoil was investigated through both numerical simulations and experimental studies. The... 

In recent decades, due to the need for higher efficiency, reduced size and weight, and improved reliability, the development of non-combustion microturbines powered by compressed air has gained significant importance. Owing to their simple design, low weight, and high efficiency, these systems have found wide applications in precision industrial and medical instruments. One of the critical issues in designing such turbines is the sensitivity analysis of the rotor output torque with respect to design parameters, since small variations in geometry and flow conditions can lead to significant changes in performance. Accordingly, in the present study, the effects of three key parameters,... 

In this research special type of jets those calls Arc-Shape Jets are studied. The meaning of this research is an effort to introduce this types of jets as a new method to film-cooling approach. In the primary section, the fitness of this scheme on a flat plate is studied. After this section, according to the results, this method is implemented on a turbine blade surface. According to the results, this method of film-cooling has suitable effectiveness in lateral direction, this has a reason of radially injection of the coolant jet. The main feature of this concept is operating by mass flow rate of much lower than other schemes. So that in a regular injection of a 45 degrees of actuator arc,... 

Cavitation is a phenomenon that liquid turns into vapor in constant temperature. Cavitation has been assorted into variant models that cloud cavitation is one of them. Cloud cavitation has an unsteady regime which shed cavity into its surrounding that contribute to oscillations, shocks and efficiency reduction of hydrodynamic machines. Triping of boundary layer for enhancing turbulent intensity is a method for preventing cloud cavitation. In this thesis firstly we have simulated boundary layer on 2D NACA0015 hydrofoil with 8 degree attack angle and no cav( ) condition. According to laminar separation location, we have placed some artificial cavity generator(ACG) with size of boundary layer... 

The aim of this study was the performance analysis of the effect of guide vanes in a quasi-radial wall jet to improve the flow separation control on the wing composed of NACA4415. In order to achieve this goal, first, by examining two geometries of "quasi-radial wall jet" and "arced-shape wall jet", the effect of jet's internal flow on separation control improvement has been studied and arced-shape wall jet has been chosen as a suitable replacement for the uniform quasi-radial wall jet, which has changed the radial velocity distribution of the jet output from uniform to non-uniform. Also, increasing the radial component of the jet output velocity and improving the separation control have... 

Increasing the efficiency of gas turbines is directly related to the increase in the inlet gas temperature. There exist, however, limitations on increasing the temperature of the inlet gas, such as materials and metallurgy restrictions. There have been numerous methods to overcome and lessen these restrictions. In fact, two conventional ways proposed so far, are film cooling and effusion cooling. In fact, film cooling is used in many applications to reduce convective heat transfer to a turbine blade surface. In addition, Effusion-cooling is the next logical step in gas turbine blade cooling in which the flow through effusion-cooling holes is, due to their small size and the lesser amount of... 

In this thesis, aerodynamic and aero thermodynamic effects associated with local heat addition into an inviscid steady state high speed flow are studied, numerically. This local heat, can be generated by a C.W laser, has a cylindrical shape and a Gaussian distribution in space. The loctation of the heat source, focal point of the laser, is considered to be upstream of the shock wave generated by a squared obstacle. The free stream Mach is 6 and the angle of attack is zero. Also, the center of this focal point is located on the symmetry line of the square. This kind of heat addition into high speed flow leads to wave drag reduction. Various parameters can affect this kind of flow control.... 

The present study is aimed at investigating experimental methods to control and stabilize the oscillatory effects of sheet/cloud cavitation. Two methods were investigated: The use of artificial cavitation generating appendages, which had a two dimensional geometry similar to that of vortex generators. Employing air injection into the cavity from different locations on the chord of the hydrofoil and a comparison of the stability achieved from each case by analyzing pictures captured from a high-speed camera. To conduct these experiments, a cavitation tunnel along with measurement devices were used. Four different appendages were tested as artificial cavitation generators, which were in two...