Sharif Digital Repository

In this research, an anistropic thin-walled beam composite is used to consider the effects of fiber orientation and lay-up configuration on the aeroelastic stability and response of an aircraft wing. The circum ferentially asymmetric stiffness (CAS) model consists of a group of non-classical effects; such as transverse shear, material anisotropic, warping inhibition, etc. The aerodynamic load has been modeled based on the strip theory and compressible unsteady flow in the finite- state form. In addition, to form the mass, stiffness and damping matrices of non-conservative aeroelastic systems the extended Galerkin’s method (EGM) and the method of separation of variables has been used. After... 

The unsteady phenomena occur in rotors of helicopters, wind turbines and compressors. Investigation of the unsteady flow is a very important test, since it can affect and restrict the performance of rotors of helicopters and wind turbine's blades when operating at high angles of attack. Dynamic tests, such as pitching and plunging oscillations are one of the best methods for studying these phenomena due to the complexity of the unsteady flows. In analyzing the results of dynamic tests one must consider the interference effects of wind tunnel walls. Different investigations show that in dynamic tests, the interference effects of flow field around the model, wind tunnel walls and support of... 

A power plant cooling tower is like a tower, which needs to be studied very carefully from the aerodynamics point of view. Both the aerodynamics forces on the plume and intake stram are affected by the local winds and the performance of cooling tower decreases. There is a symmetric turbulent flow through the cooling tower if there is no. Wind blowing creates different vorticies, which appear in the lower section of the tower. Their periodic and wuick movments causes deficiency in towers performance and efficiency. Additionally there is wind effect on the plane of cooling tower and this causes a chocked plume which is named Wind Cover. The objective of this study is to decrease the adverse... 

In this study different models of an aerodynamic particle sizer and aerodynamic focusing lens were introduced and governing equations for an aerodynamic focusing lens for flow fields and particle motions were discussed. An aerodynamic focusing lens was simulated for analyzing particle motions and flow fields. Two kinds of models are considered; One was Ahmadi`s model and the other one was Wang`s model and both models are axisymmetric. The results show that for small particles (sub 30 nanometers), Brownian motions were highly effective on transmission efficiency and producing particle beams. The two models are compared and the results show that Ahmadi`s model produce narrower particle beams... 

Flapping wing vehicles produce aerodynamic forces through the flapping motion of their wings. A sample flapping wing mechanism is studied in this project, which propulsion system consists of a battery, a DC motor, a gearbox, a flapping mechanism and a flexible membrane wing. The purpose of this study is simulation of the whole propulsion system through identification and simulation of each sub-system. In the current research, after an introduction to the flapping wing vehicles, literature of the flapping vehicles is reviewed. By studying relevant articles, lack of a comprehensive simulation of all sub-systems is observed. So the goal of this research is obtaining an appropriate tool for... 

This thesis is focused on flight dynamics modeling and analysis of an articulated Flapping Micro Air Vehicle (FMAV), where the articulating joint is placed near the wing mid chord span. The articulation modeling, its results and verification due to added degrees of freedom are considered the key motivation and novelties of this project. Initial analyses indicated that a simple articulation device such as joint is not appropriate and will not be efficient for flying FMAV. As a corrective action, a spring-damper mechanism was utilized beside the articulation. Subsequently, the kinematics’ equations are developed and verified using the MSC Automated Dynamic Analysis of Mechanical Systems... 

In recent years, in Iran, like other countries tall buildings have been constructed as a solution to space limitation problem and modern architectural matters. By increase in building height,the flexibility against wind force increase, therefore necessitating the study of buildings behavior against wind force. Traditionally most of the research done, have dealt with performance of the buildings, probability of the failure, and the serviceability level all of which relates to the amount of force in elements, the stress existing in the structure, and the amount of displacement. A substantial factor in structures, especially in tall buildings, is the comfortability of their occupants which... 

Axial compressors are utilized to increase compressible flow pressure in an efficient manner where mass flow rate is high, such as aviation engines and power generation gas turbines. The flow is compressed within this machine through several stages. Each stage consists of a rotor blade row followed by a stator blade row. Energy transfer to the air is performed on the rotor by changing its velocity vector. Then, pressure is recovered from velocity by diffusion, meanwhile turning the flow direction through stator blades. These blades have been designed and optimized with various methods evolved with developing computational and manufacturing facilities. In this thesis the aerodynamic design of... 

Classical methods in aircraft conceptual aircraft design have some deficiencies in such as low accuracy in aerodynamic derivatives estimation and incapability of verifying flight handling quality. Moreover, application of experimental equations and dependence on statistical data are other drawbacks of classical methods which are accounted as big challenges in development of unusual aircrafts. In this research, a comprehensive, rapid and practical software is developed in order to promote the conceptual aircraft design. This software provides a platform to perform various tasks such as aerodynamic measurement, nonlinear simulation, system identification and optimization simultaneously. In... 

The ultimate aim of this research is optimizing high- performance Horizontal Axis Wind Turbine (HAWT) associated with using Computational fluid dynamics (CFD) to predict the flow behavior over wind turbine blades. Computational prediction of the flow over wind turbines is a challenging numerical problem because of the complicated aerodynamics and large variation in length scales. Phenomena such as; the unsteady flow, vortex shedding of the blade tips, flow separation, complicated blade geometry due to variable twist and chord and changes in angle of attack, and highly turbulent flow over blade sections makes CFD prediction challenging, as well as interesting. The goal is to gain an in depth... 

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... 

A ten percent thick supercritical airfoil, having special previllage rather than conventional airfoils tested in a low speed wind tunnel to measure pressure distribution over the airfoil in steady and unsteady flow. Present thesis is set out to discuss effects of reduced frequency and mean angle of attack on pressure distribution during plunging motion in low-subsonic flow. Investigation of experimental data from frequency domain aspect is very challenging area in experimental aerodynamics. Therefore, the concepts of frequency domain analysis is pointed out. The analysis of experiment data is devidind in two different part, that is, steady and unsteady flow. Flow separation over the airfoil... 

The purposes of this research are one and three dimensional aerodynamic designs of a twin entry radial-inflow gas turbine's impeller. The GT4082 model Garrett turbocharger was chosen for this purpose. In order to predict existing turbine performance curves one dimensional model was prepared for whole turbine. For validating the 1d-modeling's results, widespread tests were performed on the turbine at Sharif University of Technology turbocharger lab. Comparing the results of 1d-modeling with experimental results, show 4.7% and 4% max difference for efficiency and mass parameter respectively. The wheel designing procedure started from primary design based on the mean line assumption, in 1-d... 

The present study focus is on finding a new solution to control laminar separation bubble phenomenon by combustion actuators in micro scale, which is investigated in flows with low Reynolds number surface effect and free flows. The main parameters in this problem are classified in three groups of formation location of laminar separation bubble, its length, and transition from laminar to turbulent around airfoil SD8020 in attack angle of 5 and 8 degree. Following that, the new combustion actuators in micro scale method the comparison it with cold (and hot) air jet injection is introduced to control boundary layer flow with separation bubble point of view. Some mechanisms are identified in... 

This study aims to evaluate aerodynamic coefficients of an airplane with air breathing engine experimentally. In these experiments, an ejector is used to better simulate flying conditions and aerodynamic interferences generated in inlet and exhaust engine. Therefore, at first, an ejector was designed for simultaneous simulation of exit cold flow and inlet flow of engine. All tests were conducted at QRC Trisonic wind tunnel and at Mach number of 0.5 to 0.85, angles of -4 to 6 deg. and for various amounts of pressure ejector and control surfaces angles. Finally, for the Mach number of 0.5, effect of roughness on the aerodynamic coefficients was examined. The results showed that, drag... 

Re-entry prediction and control is essential for space research, therefore study of Aerodynamics re-entry is important. Due to the particular configuration of the capsule for thermal protection in the ultrasonic phase capsule becomes unstable at supersonic speeds. The purpose of this study is to establish insight into the behavior of the re-entry in the instability region, for this purpose Fluent software is used to simulate the capsule with Orion configuration in static and dynamic flight. Dynamic simulation was performed using forced oscillation technique to amplitude and frequency of oscillation be examined separately. In zero angle of attack with low frequency, increasing the amplitude... 

Nowadays Aeroelasticity is one of most important branch of aerospace science. The Aeroelastic analysis and get on aeroelastic safety margin, is one of the major steps that must be taken in flying crafts design. Diverse software have been developed for this purpose. Due to the increasing the demands of use of composite materials in aircraft structures, need to examine the effect of various parameters such as angles and stacking sequence on the aeroelastic instability (flutter and divergence) composite aircraft structures is determined. The analysis of wind turbines as a means of extracting energy from the wind and having a large diameter blades, causing the interference effects of aerodynamic... 

Efforts to model and control surge, as the underlying instability of centrifugal compressors, were conducted. Of the three major instabilities in compressors, namely chokage, stall and surge, the latter has a significant role in limiting the available range of operation in centrifugal compressors, which are the most common devices for the transportation of Natural gas. The customary method to circumvent surge, which if occurred, could impose severe, catastrophic and irreversible damages to the machine, is to avoid the zones in which it is likely to develop by means of a recycling system. These often called "surge avoidance" or "surge prevention" schemes have the benefit of high reliability,... 

In this research, it is aimed to convert a turbojet engine to a turboshaft by replacing the exhaust nozzle with a new designed power turbine stage. The design procedure is backed up with parametric studies to increase efficiency. At first a program is written for one dimensional modelling of the stage of axial turbine. By the way, the three dimensional modelling of the stage of axial turbine with Ansys-cfx business software is done. These methods are validated by modelling the gas generator turbine and comparison of their results with experimental results. Then the power turbine including the blades and the geometry of flow walls on shaft and casing are designed. The performance of power... 

In this research, an attempt is made to obtain the geometrical and performance matching between a centrifugal compressor and a pre-designed radial inflow turbine. In this regard, constraints such as the same outer diameters, stagnation pressure, rotational speed, and power are considered. The impeller of the centrifugal compressor is designed by employing one-dimensional design method. The aerodynamic performance of the centrifugal compressor is 3-dimensionally evaluated by the commercial CFX software. A comparison of the 1D and 3D results reveals a maximum deviation of 7% indicating relatively good agreement. A sensitivity analysis on the flow coefficient and tip clearance shows a change of...