Sharif Digital Repository

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... 

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... 

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... 

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... 

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,... 

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... 

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... 

The interaction of the vortices and helicopter’s blades is the most significant source of generating the main rotor’s noise, especially in landing and rising. The kind of this noise is broadband and it is produced because of establishing the vortices behind the forward blade, their interaction with backward blade, changing their structures and creating turbulency loading. The known method for modeling of the interaction of the vortices structures and solid surfaces is the simple compounding the rod and airfoil. In this project, by using this method, the noise of the interaction of vortex and blade is modeled in the Reynolds number of 48000 with LES and FW-H Analogy as a hibrid method in... 

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... 

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.... 

Ice accretion may cause malfunction or serious performance degradation in outdoor facilities and structures, such as aircraft, ship, locks and dams, offshore platforms, solar panels, wind turbines, power transmission towers and lines, and sports facilities, leading to huge economic loss or even loss of human lives. Icephobic materials, typically applied in the form of coatings, have received growing attention in the last decade. This work focuses on surfaces with a surface tension gradient which has icephobic properties. various surface tension gradients such as linear, exponential, cycloid and parabola have been imposed on a surface in order to achieve the shortest time for a droplet to... 

The present thesis investigates the micro-droplet dynamics in an inclined channel covered with flexible structures. For this purpose, the DPD (dissipative particle dynamics) method is used to study the behavior of particles present in the flow, including the droplet, the fluid around the droplet, and polymeric structures. This model leads to a more accurate representation of flow hydrodynamics and indicates the way for exploring and understanding complex fluid properties in real flows. The first part of the thesis deals with the dynamics of rising bubbles attached to a vertical wall under different wettability conditions. Even though bubbles rising freely in a liquid have extensively been... 

The main purpose of the current study is to control the boundary layer of the flow passing over the wing and the lift force enhancement. In this research has been tried to introduce a new generation of passive flow control and use bumpy surface structures to control the separated flow and increase the aerodynamic efficiency. Therefore, the wing with the hawk bird’s airfoil section has been designated. Then, assuming a viscous, incompressible flow and a low Reynolds number range (about 2 × 105), the flow formation and boundary layer development on this wing has been investigated. Subsequently, bump structures have been settled on the upper surface of this wing. The numerical simulations have... 

Smoothed particle hydrodynamics (SPH) is a meshfree method, based on Lagrangian formulation of Navier-Stokes equations, in which fluid is discretized to particles. This method is suitable and gives much better results for problems in which other methods have severe difficulties, (e.g., tracking of particles, moving boundaries, and problems with large deformations and, physical discontinuity). No need to follow a regular geometric structure in solution process and simple adaptation and coupling with methods such as finite element, are the positive characteristics of this numerical method. In this work, a systematic study of the processes, which are part of a membrane failure in a... 

Boundary layer control has long been and still is considered to reduce drag. In this research, the effect of quasi-spherical structures on the control of boundary layer is investigated. First, flow over a NACA0015 airfoil was investigated. Then, flow over the same airfoil with quasi-spherical bumps on its upper surface was numerically simulated and the result of these two situations were compared. The dimensions and numbers of the bumps in longitudinal and lateral directions (different case studies) were chosen using trial and error. The three-dimensional, incompressible, and turbulent flow governing equations were numerically solved, using FVM and the OpenFOAM software. To get preliminary... 

The limitations of metals in tolerating thermal stresses is one of the main obstacles in increasing temperature of combustion products. In addition, strong desires to use higher temperatures than are allowed for metals, have led to use of different cooling methods for protecting surfaces adjacent to hot gases. Previous valid studies show that more than 25% of research in the field of gas turbine is related to their blades cooling. On the other hand, one of the very important methods of cooling such surfaces is film cooling. The results of this and previous researches conducted by the team of this thesis’ supervisors can for instance help designers to predict more suitable positions for... 

Aircraft Range extension is a very common modification for today’s aircraft. Using the conformal fuel tanks is an appropriate method for today’s military and civil aircraft. In this thesis, a Design method has been developed for designing these tanks using DSM, CFD and DOE. The main goal in developing the method was to be able to consider these tanks as an add-on feature for the aircraft, which can be designed after the aircraft production. The main aspects of designing the tanks was to identify the consequences of adding the tanks to the aircraft. Due to limited resources, only the Longitudinal static and dynamic stability of the aircraft has been considered.The method introduced here shows... 

Von-Karman vortex shedding is a transient aerodynamic instability which occurs in laminar flows over a bluff body in a certain condition. When this phenomenon occurs, vortices take form on upper and lower parts of the bluff body and begin to shed into an oscillatory manner affecting a significant part of the flow domain. This research focuses on Karman vortex shedding control by using two thin oscillating splitter plates. Length ratio of plates to cylinder diameter is 1 (L⁄D=1) and plates are attached at ±55 degrees (trigonometric angle). Plates are forced to oscillate at different ratios of natural vortex shedding frequencies (0.75, 1, 1.25, 1.5 and 2) for diffenet amplitudes. Simulations...