Nafiz Alemdaroglu

Unsteady Aerodynamics of Flapping Airfoil in Hovering Flight at Low Reynolds Numbers

The major aim of flapping motion research is based on the understanding of the relation between the temporal and the spatial changes of the wake structure and the resulting instantaneous aerodynamic forces over the flapping wings. The essential physics of nonsteady airfoil problems can be observed from simplified two-dimensional experiments, and the interpretations of the behavior can be supported by theoretical or numerical models. The aim of this study is to find optimum parameters to generate maximum lift during this motion, by using numerical methods and analytical models. A great number of cases are investigated involving the changes in the parameters such as angle of attack, location of start of change of incidence, location of start of change of velocity, axis of rotation, and Re number. In addition to the instantaneous aerodynamic forces, pressure distributions and vorticity contours, the average lift and drag coefficient values are also calculated. Positive lift values along the motion are obtained for angle of attack greater than 30°. The vortices shed during the flapping motion generate the lift. A modelization program is developed by use of Duhamel integral in order to compare with DNS results.

Improvements to compressible Euler methods for low-Mach number flows

Improvements to numerical algorithms for the solution of the compressible Euler equations at low Mach numbers are investigated. To solve flow problems for a wide range of Mach numbers, from the incompressible limit to supersonic speeds, preconditioning techniques are frequently employed. On the other hand, one can achieve the same aim by using a suitably modified acoustic damping method. The solution algorithm presently under consideration is based on Roes approximate Riemann solver for non-structured meshes. The numerical flux functions are modified by using Turkels preconditioning technique proposed by Viozat for compressible Euler equations and by using a modified acoustic damping of the stabilization term proposed in the present study. These methods allow the compressible Euler equations at low-Mach number flows to be solved, and they are consistent in time. The efficiency and accuracy of the proposed modifications have been assessed by comparison with experimental data and other numerical results in the literature

Euler and Navier-Stokes Solutions for Missiles at High Angles of Attack

Anunstructured Euler e ow solverand a structured thin-layerNavier‐ Stokessolverarevalidated againstexperimentaldata andcompared withothersolversfortwo differentmissilegeometriesata Machnumberof M =2andat angles of attack ranging between 0 and 20 deg. The e rst geometry is a conventional missile geometry with an ogive nose, a cylindrical body, and four straight tail e ns. The second geometry is an unconventional missile geometry with a lenticular body and no tail e ns. Present results are found to be in good agreement with the available results, and the differences observed between them are explained in detail. The present unstructured Euler code proved to be accurate, fast, and reliable for determining the overall aerodynamic characteristics of the missiles, whereas the thin-layer Navier‐ Stokes solutions are found to be effective in predicting the detailed viscous behavior of the e owe eld over the conventional and unconventional missile geometries studied.

Trajectory Calculation of a Store Released from a Fighter Aircraft

This paper presents the results obtained for store separation from an aircraft by CFD methods. The computational results are validated against the available experimental data of a generic wing-pylon-store configuration at Mach 0.95. Two different commercially available CFD codes; CFD-FASTRAN an implicit Euler solver and an unsteady panel method solver USAERO, coupled with integral boundary layer solution procedure are used for the present calculations. CFD-FASTRAN is validated against the experimental data of generic wing-pylon-store configuration at Mach 0.95. Major trends of the separation are captured. Similar configuration is used for the comparison of unsteady panel method with Euler solution at Mach 0.3 and 0.6. Displacements, angular orientations, pressure coefficient distribution on the store in captive position and force coefficients histories during separation are used for comparison. Major trends are similar to each other while some differences in lateral and longitudinal displacements are observed. Finally, trajectories of a fuel tank separated from an F-16 fighter aircraft wing and full aircraft configurations are found at Mach 0.3 using only the unsteady panel code. The results indicate that the effect of fuselage is to decrease the drag and to increase the side forces acting on the separating fuel tank from the aircraft. It is also observed that the yawing and rolling directions of the separating fuel tank are reversed when it is separated from the full aircraft configuration when compared to the separation from the wing alone configuration.

Design of a medium range tactical UAV and improvement of its performance by using winglets

This paper presents the design, performance analysis and aerodynamic improvement of a designed medium range tactical unmanned aerial vehicle. Main requirements are set as following; cruising altitute above 3500m, endurance of approximately 10-12 hours, range of 150 km and payload of 60 kg. The conventional design phase is based on the employment of historical equations and experiences. The aerodynamic improvement process is related with rise in span efficiency by employement and comparison of different wingtip geometries, which results rise in L/D ratio, climb rate, endurance or reduction in weight, required power. In short, the study underlines a cost effective aerodynamic improvement process by reducing engineering time and complicated algorithms for an UAV. In addition, considerable difference between conceptual and CFD L/D ratio results have underlined the validation need of conceptual design outputs by nowadays computational or experimental tools.

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.

Measurements of dynamic stability derivatives using direct forced oscillation technique

The subject of the experimental investigation presented in this paper is to measure the dynamic stability derivatives of a generic combat aircraft model in the Ankara Wind Tunnel by using the direct forced oscillation technique. The model, used for the tests is the AGARD, Standard Dynamic Model (SDM). The aerodynamic loads acting on the model are measured with a five component internal strain gauge balance placed inside the oscillating model. The paper presents the experimental set-up used to create the oscillatory motion in pitch for the model and the related motion control and the data acquisition units to measure the dynamic loads, and discussed the results of the measurements.

Solar irradiation estimation on a solar powered UAV over a mission course

This paper is about solar irradiation estimation on a solar powered UAV over its mission course [1]. Solar irradiation estimation and maximizing the solar energy collection are critical for solar powered UAVs and their performance. In this paper main focus is on solar irradiation calculations and comparison of two possible flight paths for solar energy collection during a transport or inspection mission.

Optimal design of a miniature quad tilt rotor UAV

This paper describes the design procedure of a convertible miniature (mini and micro) quad tilt rotor unmanned air vehicle (UAV), which has about 2 meters of wing span, one hour of mission time and 5 kilograms of total weight. The aircraft is driven by four brushless direct current motors, and the structure of it completely made of composite materials. When the wing and tail of the aircraft are dismounted, it operates as a quad-rotor with tilting rotors. The aircraft is planned to carry a gimbal camera weighing about 700 grams. The primary operation areas of the aircraft are intelligence, surveillance and reconnaissance missions in an operational radius of 15 km. The aircraft is capable of changing its flight modes between horizontal and vertical flights as required by the mission profile.

Design and manufacturing of a high speed jet powered UAV

This paper presents the design and manufacturing of a high speed jet powered UAV which is capable of flying at M=0.5. Flight time of the UAV is 30 minutes at 1700 m above sea level. Aerodynamic and structural design of the UAV is conducted for 6g sustained and 9g instantaneous loads. Low aspect ratio blended wing-body design is decided due to low drag and high maneuverability. Structure of the UAV consists of the composite parts such as frames and skin and mechanical parts such as landing gears which are from aluminum and steel, engine holders, parachute release mechanism and etc.