Sharif Digital Repository

Aeroelasticity analysis and prediction of wind turbines sturcture deformations are fundamental parts in their design. Increasing the size of wind turbine blades and development of Mega-watt sized wind turbines have enhanced the importance of these studies. In this study, the aeroelasticity analysis of a wind turbine blade has been done based on flexible multibody dynamics method. For this purpose, the modal approach has been used for modeling blade structure which has been considered as a flexible beam with bending and torsion degrees of freedom. The unsteady vortex lattice method has been used to calculate aerodynamic loads in order to combine with wind turbine blade structure model. Using... 

Today, renewable energies such as solar and wind power are replaced to fossil fuel. Wind turbines are two categories; horizontal axis and vertical axis. Vertical axis turbines are not dependent on wind direction and since equipments are installed at the bottom of these turbine towers, maintenance is easy. Among vertical axis turbines, performance of darrieus turbine is better. The aim of this thesis is, analysis and preliminary designing of 1-kilowatt darrieus wind turbine, based on climate of the country, for using in urban environments or areas where there is no economic justification for development of power grid systems. In this regard, statistical data base is made up of vertical axis... 

Rotating detonation engines are capable of reaching a higher efficiency in comparison with ordinary engines, due to utilizing pressure gained combustion wave. In this study, the feasibility of a laboratory sample RDE with an annular geometry of diameter of 76 mm has been studied and then designed and constructed. In this sample, hydrogen and standard air were separately injected into the combustion chamber of detonation. The injection of fuel flow and air flow are axial and radial, respectively. The designed geometry is flexible in terms of changing the injection geometry and detonation channel wide, which provided the possibility of testing for a variety of injection and detonation... 

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

The physics of the flow around the wing in the oscillatory motion of the wing has various patterns, including the leading edge vortex, the tip vortex and trailing edge vortex escape. The interaction of these vortices forms a complex flow structure around the wing, which will have a direct effect on the aerodynamic performance of the wing. Therefore, controlling these structures can be considered as a way to improve the performance of the flapping wing. One of the passive flow control techniques that has recently been taken into consideration is a leading-edge protuberance method. Another type of passive flow control is geometric correction, using corrugation method. According to studies, two... 

Using flapping motions, birds produce aerodynamic forces required to fly. Flapping wing aerodynamics is one of the most complicated problems in unsteady aerodynamic field. Experimental study on the structure, the way of production and growth and the feasibility of controlling the leading edge vortex are the main goals of this research in order to improve the aerodynamic performance of flapping wings. Since leading edge vortex structure appears in both upstroke and downstroke of a complete storke in flapping motion, controlling the structure in one of the half-storkes can provide the possibility of having a better aerodynamic performance. In this research, the wing is designed and... 

Heat exchanger is considered as one of the most widely used equipment in many industries such as the aerospace, oil and gas, and power generation ones. In recent years, computers have made it easier to design and test the performance of heat exchangers. However, these designs should be rechecked in other manners. Wind tunnel, as an important and well-known system, has been widely used to verify and, if necessary, to check the heat exchanger designs and to improve the performance of available heat exchangers. Obviously, the use of non-standard wind tunnels can result in poor experimental results to judge the correct performance of the designed or existing heat exchangers. It is because this... 

The issue of solid and fluid interaction in horizontal axis wind turbines with diameter of more than 120 meters is one of the most important researching subjects of this type of turbines. This issues needs quick and exact solutions because of the high computational cost of fluid and structural domains.In this research a quick method with acceptable accuracy has been suggested which is based on computational fluid dynamic to examine the aeroelastic behavior of rotor and wind turbine tower. The actuator disc method in two domains of axisymmetric and three-dimensional has been used to compute aerodynamic forces. For this purpose a code has been written in C++ to set down virtual momentum on... 

Formation and detachment of drops are of fundamental importance in studying two-phase flows, such as ink jet printing, emulsion, and spray. Drops are formed under the effects of surface tension forces. After formation, forces like gravity detach the drop from the rest of the fluid. The flow rate is varied from dripping to jetting regime. In this project, formation and detachment of drops were simulated, using LBM with phase field model, which can simulate flows with high-density ratios and is a robust method for applying wetting condition on the walls. Results were validated using single-phase and two-phase flows. After code validation, the oscillations caused by formation and detachment of... 

Nowadays one of the main challenges facing fluid dynamics simulations is the long duration of numerical calculations. The goal of this research is to use FPGAs (Field Programmable Gate Arrays) to accelerate fluid dynamics solutions. First, the ability of FPGAs in mathematical operations on floating point numbers is studied. Then, various fluid dynamics problems are implemented on the FPGA hardware, and each one is solved separately. Unsteady 1D Couette problem, 2D potential flow (Laplace equation), incompressible viscous fluid flow over a backward facing step, and compressible inviscid flow over a bump are some of the problems in question. FPGA is an integrated circuit containing a number of... 

Inlet performance is an important field in aerodynamic design of aerial vehicle engines. This study has been focused on nummerical investigation of inlet performance. For this purpose, a density based finite volume CFD code has been developed to solve supersonic axisymmetric flow in a mixed compression inlet. A structured multi-block grid and an explicit time discritization of Reynolds averaged Navier-Stokes (RANS) equations have been used. Furthermore, both Roe’s approximated Riemann solver and advection upwind splitting method (AUSM) have been utilized for computing inviscid flux vectors. Also, the monotone upstream centered schemes for conservation laws (MUSCL) extrapolation with Van... 

The purpose of this research is to design and construct a test stand for the study of the kinematic and flow pattern of bluff bodies oscillating motion due to the induction of wake vortices. An experimental investigation was conducted to explore the effect of bluff bodies cross section to optimize the amount of electrical energy withdraw by electromagnetic harvester. The tests are carried out on cylinders with square section and rectangular sections with a length to width ratio of 1/2 and 2/1 and height of 50 cm, at speeds of 5 to 35 m/s in eiffel type wind tunnel. The effect of cylinder cross-section on the amount of energy harvested showed that the amplitude of oscillation in square-shaped... 

In present research, a new system of energy extraction from water flow has been studied and optimized. This semi-active energy harvesting system consists of an airfoil that is connected to the generator by an arm. The passage of water causes the airfoil to move, so the hydrodynamic forces on the airfoil will cause the arm to move and finally the generator. In this research, complete dynamic modeling of this energy extraction system including generator, airfoil, controller and actuator modeling is presented and the governing dynamic equations are extracted using this modeling for dynamic simulation. Two dimensional fluid simulations have also been performed using fluent software. Finally, in... 

For validation of simulation, plasma actuator was modelled on a flat plate in quiescent flow, which is result in low-speed jet near the wall. The results were compared with similar model and were showed good agreement with them. After that, blade was modelled in three-dimensional manner with MRF technique and periodic method and the results were validated in clean situation (absence of plasma). In the following, turbine was analysed with a code, which was written in MATLAB software based on BEM method and the results were compared with present CFD simulation. Then, plasma actuator was used in chordwise in parts of the blade to improve wind turbine performance. Also it was used in spanwise... 

This thesis investigates the stall control over an airfoil employing dual excitation of separated shear layers with DBD plasma actuators. This research is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14° and 300000, respectively. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the trailing edge, are exploited to control the baseline flow. Surface pressure distribution, as well as the dominant natural frequency associated with flow structures in the wake, are evaluated. Based on the active actuators, three controlled cases are considered in the present study. In the first... 

Flow control means changing the optimal flow behavior of the fluid in accordance with the desired targets, such as decreasing drag force, increasing the lift force or lift to drag ration, as well as manipulating the separation of the flow from the surface. So far, little research has been done on increasing the airflow performance through the active control of the trailing edge flow. Gurney flap is a great tool, and its experimental results show a significant increase lift force in the airfoil. In this study, it is possible experimentally to use plasma actuators to create microtap and garney flap artificial for enhancing the aerodynamic performance of airfoil by controlling the flow field at... 

It is necessary to evaluate the effect of the lifting arms of VTOL UAVs in increasing the drag of UAV and reducing the flight endurance of the cruise phase. In this study, the adverse effect of the lifting subsystem and its accessories on reducing the aerodynamic efficiency of the wing and optimizing its design for the cruise phase is studied. The base UAV is an integrated wing-body drone with a 2.12 m wing span, 7 kg maximum take-off weight and with about 65 km / h horizontal flight speed. To investigate the possibility of reducing the adverse aerodynamic effect of the arms of the lifting system, different positions are selected in terms of the geometric dimensions of the arms and their... 

In this study, the physic of an unsteady flow surrounding two oscillating airfoils in tandem configuration at low Reynolds-numbers has been simulated in a 2D manner by utilizing the Sliding-mesh approach and K-ω-SST turbulent model in Ansys-Fluent application. The first step in this study is selecting the decent numerical grid and flow solution scheme. After choosing the proper solution for this problem, next is to verify the methodology with respect to the references. In the next step, The tandem configuration and pitching motion of the airfoils is being implemented with existing tools and the flow structure, leading-edge and trailing-edge vortex shedding and blade-vortex interactions is... 

The purpose of this study is to investigate a flapping hydrofoil with semi-active kinematics for energy harvesting and evaluate the effect of different dynamic parameters and structures on its performance. The turbulent flow field with Re = 5 × 105 around a NACA 0015 hydrofoil is simulated by URANS method using commercial software and the dynamics of the oscillating hydrofoil is modeled as a mass-spring-damper set in combination with the fluid solver. The sliding mesh method is used for the pitching motion of the hydrofoil with a reduced frequency of 0.14 in combination with the dynamic mesh method for Transitional motion. Initially, the oscillating hydrofoil was considered as a single... 

In this study, the effect of two inverted piezoelectric flags arrangement on energy harvesting and the kinematics of limited amplitude oscillations which occurs due to flutter instability has been studied experimentally. For this purpose, first a study on piezoelectric materials for application in energy harvesting was carried out. Then, constraints and effective parameters of the inverted flag problem were obtained in terms of structure, fluid and electricity coupling. In the next step, according to these constraints and parameters, a test platform was designed and was built for experimental tests. A circuit with low amount of loss was designed and built to measure the perceptual power....