Sharif Digital Repository

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... 

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 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... 

A complete 6DOF flight dynamic model of an elastic flapping wing (EFW), integrated with unsteady aerodynamic theory is developed. In this respect, initially efficient high fidelity modules for EFW structural dynamics (SD) as well as unsteady aerodynamics loadings (UAL) to be coupled with its flight dynamics are prepared. A modal approach is followed to model structural dynamics of plain and 3D EFWs. This is in contrast with the Euler-Bernoulli beam theory that is mostly utilized for SD in the existing literature. In addition, due to the possibility of large wing deformations as well as the existence of non-linear displacement regime for realistic EFW flights, non-linear modal approaches such... 

At this project we proceed to aero elastic modelling of a flapping wing using unsteady aerodynamic approach. Solving this model according to aerodynamic and structure coupling needs to simultaneously solve of aerodynamic and wing structure. Left side and right side of wing, each on divided into 18 elements. each element is interacting with sides element in terms of structural force and moment. In this modeling aerodynamic was modeling with unsteady aerodynamic approach (using modify theodersen function), also structure is flexible in to direction, bending and twisting. In the following it is proved that with change in flapping pattern better performance can be achieved. the effect of change... 

Supercritical airfoils have been designed for transonic flow, however due to different flight conditions, the airfoil behavior during take-off and landing of the aircraft in subsonic flow regime must be known. Experimental and numerical information derived from supercritical airfoils are less than those of conventional airfoils. Because of the special geometry of supercritical airfoils and different phenomena that occurs through flow, using such airfoils even in steady states requires precise study/analysis of the flow. Therefore, one could benefit from experimental tests to better understand flow phenomena. The objective of the present research is the study effect of mean angle of attack... 

The aeroelastic behavior of wings made of functionally graded materials in supersonic flow is studied. For this purpose the flutter speed is calculated and in the next step the post flutter behavior is investigated. The structural model is based on the classical plate theory and material properties are assumed to be graded in the thickness direction according the power law distribution in terms of the volume fraction of material constituents. The linear piston theory which is modified to include thickness effects is used for supersonic aerodynamic modeling. The nonlinear structural model based on the Von-Karman strains is considered for prediction of the post-flutter behavior of the wing.... 

In the current study, stability and nonlinear vibration of bending-torsional extensible beams conveying internal pulsatile and uniform external flow are studied. The internal and external fluid flows are assumed to be incompressible and frictionless. Applying the extensibility to the pipe along its length and using the nonlinear Euler-Bernoulli beam model and including some appropriate additional assumptions, the 3D nonlinear equations of motion of a cantilevered composite pipe is obtained. In order to derive the equations governing the fluid-structure interaction, the internal flow effect is modeled as a distributed load along the pipe which contains the inertia, Coriolis and centrifugal... 

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... 

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...