Dilek Funda Kurtulus

Ability to forecast unsteady aerodynamic forces of flapping airfoils by artificial neural network

The ability of artificial neural networks (ANN) to model the unsteady aerodynamic force coefficients of flapping motion kinematics has been studied. A neural networks model was developed based on multi-layer perception (MLP) networks and the Levenberg–Marquardt optimization algorithm. The flapping kinematics data were divided into two groups for the training and the prediction test of the ANN model. The training phase led to a very satisfactory calibration of the ANN model. The attempt to predict aerodynamic forces both the lift coefficient and drag coefficient showed that the ANN model is able to simulate the unsteady flapping motion kinematics and its corresponding aerodynamic forces. The shape of the simulated force coefficients was found to be similar to that of the numerical results. These encouraging results make it possible to consider interesting and new prospects for the modelling of flapping motion systems, which are highly non-linear systems.

On the Unsteady Behavior of the Flow Around NACA 0012 Airfoil with Steady External Conditions at Re=1000

Even for the stationary airfoils, due to the boundary and shear layer interactions of upper and lower surface of the airfoils, alternating vortex patterns form and the flow becomes time dependent. In the current study, the unsteady behavior of the flow around a symmetric airfoil is considered as incidence angle increases. The flow patterns are presented for wide range of angles of attack values. The vortex pattern generated is analyzed numerically for different angles of attack at Re=1000 around NACA 0012 airfoil. At this Reynolds number, the flow is laminar and boundary layers are quite thick. Flow separation and unsteady vortex shedding is observed even at low angles of attack. For NACA 0012 airfoil, the unsteady vortex pattern is observed at about 8° angle of attack for Re=1000. Spectral analysis is performed for angles of attack ranging from 0° to 90°. It is presented that amplitude spectrum of lift coefficient (C1) start to shows a peak at 8° for NACA 0012 and the aerodynamic forces presents oscillatory behavior afterwards. The effect of angle of attack to wake pattern and instantaneous and mean aerodynamic coefficients are discussed. The time-averaged streamlines, pressure and skin friction coefficients are analyzed to observe the vortex formation and separation from the airfoil upper surface at this low Reynolds number.

On the wake pattern of symmetric airfoils for different incidence angles at Re = 1000

In the current study, numerical simulations are performed in order to investigate effects of incidence angle and airfoil thickness on alternating vortex pattern of symmetric airfoils at Re = 1000. This alternating vortex pattern is found to be significantly varying in shape as the incidence angle increases. The results are obtained with 1° increment from 0° to 41° and then with 10° increment from 40° until 180°. The instantaneous and mean vortex patterns are investigated around 2% thick (NACA 0002) and 12% thick (NACA 0012) airfoils. The mean lift, drag, and pitching moment coefficients in addition to Strouhal number are computed and compared with the results available in literature. It is found that the wake behind the airfoil exhibits a continuous vortex shedding pattern below 8° incidence angle for NACA 0002 and below 7° incidence angle for NACA 0012 at Re = 1000. The wake structures are classified into five different modes according to their pattern obtained from instantaneous and mean vorticity fields by also taking into account the amplitude spectrum of the lift coefficient, the instantaneous and mean aerodynamic force coefficients, velocity fields, and the longitudinal and lateral vortex spacings.

Modeling and controller design of a VTOL UAV

A tilt rotor VTOL UAV in tri-copter configuration is developed. The vehicle is modeled using the blade element formulation for the propulsion system, and the aerodynamic properties are obtained from a 3D panel code. Linear quadratic regulators and linear quadratic tracking controllers are designed for the attitude control of the aircraft in vertical takeoff and hover flight conditions. The vehicle is built and hover flight tests are carried out. The results demonstrate the success of the modeling carried out and the controller designed.

Laser Sheet Visualization for Flapping Motion in Hover

§The aim of the present study is to understand the aerodynamics phenomena and the vortex topology of the highly unsteady flapping motion. Instead of the use of real insect/bird wing geometries and motions which are highly complex and difficult to imitate by an exact modeling, a simplified model is used to understand the unsteady aerodynamics and vortex formation during the different phase of the flapping motion.

Propulsion System Selection and Modeling for a Quadrotor with Search and Rescue Mission

This study presents the development activities of a Quadrotor for search and rescue operations. There are four main specifications: The total weight of the vehicle is should be less than 4 kg, the endurance of the quadrotor should be at least 45 minutes in hovering flight, the vehicle shall carry a high resolution video camera to be transmitted live to the ground station, commertial of the shelf parts shall be used as much as possible. The initial design required the selection of the propulsion system. Five different propeller are tested with seven different brushless direct current motors. The test results indicate that the goals are achievable. Wind tunnel test results for selected propellers are also presented.

A Parametrical Study with Laser Sheet Visualization for an Unsteady Flapping Motion

§In order to better understand the vortex dynamics and evaluation of the flow structures during the unsteady flapping motion, experimental visualizations are considered. The visualizations are represented for the phenomenological analysis of the flow. The flow is assumed to be laminar with the Reynolds number of 1000. The evaluation of the complex flow topology is investigated instantaneously for the effect of the different parameters. The vortex identification is performed for the change of incidence position xa, the change of velocity position xv and the starting angle of attack α0.