Sharif Digital Repository

Wing rock motion can be described as an oscillatory bank angle buildup to a constant amplitude rocking motion. This phenomenon is realized for delta wings with more than 74 degrees leading edge sweep angles, where asymmetric vortex shedding occurs before vortex breakdown. For wings with sweep angles less than 74 degrees, rocking motion occurs if the wing is in a yawed situation. In this paper, a new and simple method has been presented to predict the amplitude and frequency of oscillation of delta wings undergoing rocking motion at high angles of attack. The predicted data are in excellent agreement with those obtained by experimental studies for wings with sweep angles of 76 and 80 degrees  

In this paper, the aeroelastic behavior and flutter instability of aircraft wings in subsonic incompressible flight speed regime are investigated. Quasi-steady and unsteady aerodynamic models are used for aerodynamic modeling and the obtained aeroelastic predictions are compared to those available in the specialized literature. Based on a number of test cases, it is shown that the quasi-steady aerodynamic models are inadequate for the determination of aeroelastic behavior and flutter boundary of aircraft wings in the incompressible flight speed range. © 2006 Elsevier Ltd. All rights reserved  

An analytical procedure for aeroservoplastic stability analysis of guided supersonic flight vehicles is developed by using slender body aerodynamic theory and modal analysis techniques. The roll channel is decoupled from pitch and yaw channels by using the linearized system of equations. Results show that divergence is the only aeroelastic instability that can occur for the nonrolling flight vehicle with no-control loop and is accurately computed using the first bending mode shape. The result of the divergence analysis demonstrates that the vehicle elasticity has a destabilizing effect on the pitch and yaw channels. The inclusion of aeroservoelasticity in the analysis can cause dynamic... 

This paper presents a method for nonlinear aeroelastic analysis of a Human Powered Aircraft (HPA) wings. In these types of aircrafts there is a long wing with high flexibility. Wing flexibility coupled with the long span leads to the possibility of the large deflections during normal flight operation, so, nonlinear modal analysis technique is used for structural modeling. Unsteady linear aerodynamic theory is used for determination of aerodynamic loading on the wing (linear aerodynamics and nonlinear structure). Combining these two types of formulation yields a nonlinear aeroelastic model. Mode summation techniques along with Galerkin's method are used to determine the governing equations of... 

The nonlinear aeroelastic behavior of a three-dimensional general laminated composite plate at high supersonic Mach numbers is investigated using von Karman's large deflection plate theory and quasisteady aerodynamic theory. Galerkin's method is used to reduce the governing equations to a system of nonlinear ordinary differential equations in time, which are then solved by a direct numerical integration method. Nonlinear flutter results are presented with the effects of in-plane force, static pressure differential, fiber orientation and aerodynamic damping  

A new approach, based on a Generalized Regression Neural Network (GRNN), has been proposed to predict the unsteady forces and moments of two different models; a 70° swept delta wing in subsonic incompressible flow and a standard fighter model (SDM) in a compressible flow regime, both undergoing sinusoidal pitching motion. Extensive wind tunnel results were used for training the network and verification of the values predicted by this approach. GRNN was trained by the aforementioned experimental data and, subsequently, was used as a prediction tool to determine the unsteady longitudinal forces and moment of the two models under various conditions. Further, it was applied to extend the... 

A practical mathematical model with low computational time and good accuracy is applied to investigate theaerodynamic characteristics and static height stability of the compound wing-in-ground effect (WIG). The compound WIG consists of a main wing with low aspect ratio and an endplate, and anouter wing with high aspect ratio. To validate the present mathematical model, a numerical simulation is performed so thatnumerical results had a good agreement with the experimental data. The analysis shows that the main wing is useful in the extreme ground effect zone and the outer wing enhances performance of the compound WIG in the weak ground effect zone. In order to satisfy the static height... 

Aerodynamic performance of a Bladeless fan is numerically investigated considering the effect of five geometric parameters. Airflow through this fan was analyzed by simulating a Bladeless fan within a 2 m × 2 m × 4 m room. Analysis of the flow field inside the fan and the evaluation of its performance were obtained by solving conservations of mass and momentum equations for the aerodynamic investigations. In order to design the Bladeless fan an Eppler 473 airfoil profile was used as the cross section of the fan. Five distinct parameters, namely height of cross section of the fan, outlet angle of the flow relative to the fan axis, thickness of airflow outlet slit, hydraulic diameter, and... 

Tethered airborne wind energy systems are among emerging renewable energy technologies in recent years. These systems can harness greater power densities at higher altitudes with lower costs of installation and energy production in comparison with those from conventional ground-based energy harnessing technologies. A Buoyant Airborne Turbine (BAT) as a flying aerostat has a horizontal axis wind turbine within its shell and can elevate up to 600m. There are a number of pertinent parameters such as BAT configurations/component dimensions or its aerodynamic characteristics that impact the system total power performance. Identifying the optimum values of these parameters by conducting... 

In this study, in order to indicate the best airfoil profile for the different sections of a blade, five airfoils including S8xx, FFA, and AH series were studied. Among the most popular wind power blades for this application were selected, in order to find the optimum performance. Nowadays, modern wind turbines are using blades with multi-airfoils at different sections. On the large scale profile, SST K-ω model with different wind speed at large-scale profile was applied to the simulation of horizontal axis wind turbines (HAWT). The aerodynamic simulation was accomplished using the computational fluid dynamic (CFD) method based on the finite volume method. The governing equations applied in... 

The boundary-layer control authority of a DBD plasma actuator using surface mounted hot-film sensors is evaluated. Wind tunnel experiments on a wind-turbine blade section were established at a Reynolds number of 0.27 x 106. Aerodynamic performance of the wind-turbine blade section for both plasma-ON and plasma-OFF modes are evaluated using measurements made by both surface pressure and wake survey behind the model. Two distinct boundary-layer states are recognized. A state which occurs at the onset and in proximity of the deep stall, which is affected by the low-frequency instabilities of the separated flow. In this case, the steady actuation of plasma imparts local momentum on the nearby... 

To study of vibration effect on fluidization behaviour of high moisture materials, a laboratory vibro-fluidized bed dryer was designed and fabricated. The blower was selected based on transferring velocity of particles and pressure drop caused by airflow through the bedplate and the channels. It was centrifugal type with backward blades, static pressure of 3.5 kPa, flow rate of 0.4 m 3/s and impeller diameter of 0.4 m. The dryer was constructed with 4.9 kW electrical heater capacity, bed plate with holes diameter of I mm and 140626 holes/m 2. The dryer chamber was made of Plexiglass with 0.16×0.16 m square section and 0.5 m height The bedplate was vibrated mechanically, which was adjustable... 

This study is concerned with the general motion of a guided flexible launch vehicle idealized as a non-uniform beam under continuous thrust action. The governing equations of motion are derived following the Lagrangian approach and generalized coordinates. The rigid motion consists of the conventional vehicle velocities (rotational and translative), whereas the elastic motion, introduced through modal substitution, represents the vehicle local lateral and transverse displacements relative to a mean body axis system. A complete simulation routine has been developed, which allows for investigation of the influence of variuos vibrational forcing functions, local stiffness changes and the... 

In this paper, a new approach based on a Generalized Regression Neural Network (GRNN) has been proposed to predict the unsteady forces and moments on a 70° swept wing undergoing sinusoidal pitching motion. Extensive wind tunnel results were being used for training the network and for verification of the values predicted by this approach. The Generalized Regression Neural Network (GRNN) has been trained by the aforementioned experimental data and subsequently was used as a prediction tool to determine the unsteady longitudinal forces and moments of the pitching delta wing for various reduced frequencies. The results are in a good agreement with those determined by the previous experimental... 

With the advent of various advanced materials, the idea of flying like birds has attracted considerable attention in recent years. In addition, aeroacoustics has become an important issue and is being widely studied. In this work, based on the shape of Owls’ wings, an attempt was made to improve the aeroacoustic and aerodynamic performances of conventional aircraft wings. For this purpose, wings with different elements, namely, square, triangular, and semicircular, on their top surface were examined. In addition, three different spatial distributions of the elements according to the Owl’s wings shape were considered. For incompressible airflow, aerodynamic and aeroacoustic parameters of wing... 

A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of... 

A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of... 

The subject of the present paper is the investigation of the sharp edged gust effects on the aeroelastic behavior of a flexible wing. It is important to determine the response of the wing to the atmospheric turbulences during normal flight. So, linear modal analysis technique and linear quasi-steady aerodynamic are used for structural modeling and aerodynamic loading, respectively. Also, Lagrange method is used to obtain the system of equations of motion. Using the normal modes of free vibration, structural and aerodynamic matrices can be constructed. Then the aeroelastic instability of the system is determined using p method. Kussner function is used to model the sharp gust effects on the...