• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.10
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• pp.882-887
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• 2012

This paper describes on the aerodynamic characteristics of the first domestically manufactured aircraft, Buhwalho, in Korea. The computational fluid dynamics(CFD) calculations and wind tunnel test were utilized to investigate the basic aerodynamic characteristics of aircraft with control surface deflections and attitude changes. Variations of lift, drag and pitching moment due to angles of attack and control surface deflections were analyzed and also flight stability due to side force, yawing and rolling moments caused by the change of sideslip angles, rudder and aileron deflections were discussed. Through this study, the meaningful aerodynamic data by CFD calculations and wind tunnel tests were obtained and the flight characteristics based on these data were confirmed accordingly by the flight tests.

• Wind and Structures
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• v.10 no.1
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• pp.1-22
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• 2007

The suppression of aerodynamic response of long-span suspension bridges during erection and after completion by using single TMD and multi TMD is presented in this paper. An advanced finite-element-based aerodynamic model that can be used to analyze both flutter instability and buffeting response in the time domain is also proposed. The frequency-dependent flutter derivatives are transferred into a time-dependent rational function, through which the coupling effects of three-dimensional aerodynamic motions under gusty winds can be accurately considered. The modal damping of a structure-TMD system is analyzed by the state-space approach. The numerical examples are performed on the Akashi Kaikyo Bridge with a main span of 1990 m. The bridge is idealized by a three-dimensional finite-element model consisting of 681 nodes. The results show that when the wind velocity is low, about 20 m/s, the multi TMD type 1 (the vertical and horizontal TMD with 1% mass ratio in each direction together with the torsional TMD with ratio of 1% mass moment of inertia) can significantly reduce the buffeting response in vertical, horizontal and torsional directions by 8.6-13%. When the wind velocity increases to 40 m/s, the control efficiency of a multi TMD in reducing the torsional buffeting response increases greatly to 28%. However, its control efficiency in the vertical and horizontal directions reduces. The results also indicate that the critical wind velocity for flutter instability during erection is significantly lower than that of the completed bridge. By pylon-to-midspan configuration, the minimum critical wind velocity of 57.70 m/s occurs at stage of 85% deck completion.

• Advances in aircraft and spacecraft science
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• v.4 no.5
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• pp.503-514
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• 2017

The attitude control of an aircraft is usually fulfilled by means of thrusters at high altitudes. Therefore, the possibility of using also aerodynamic surfaces would produce the advantage of reducing the amount of fuel for the thrusters to be loaded on board. For this purpose, Zuppardi already considered some aerodynamic problems linked to the use of a wing flap in a previous paper. A NACA 0010 airfoil with a trailing edge flap of 35% of the chord, in the range of angle of attack 0-40 deg and flap deflections up to 30 deg was investigated. Computer tests were carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km of Earth Atmosphere. The present work continues this subject, considering the same airfoil and free stream conditions but two flap extensions of 45% and 25% of the chord and two flap deflections of 15 and 30 deg. The main purpose is to compare the influence of the flap dimension with that of the flap deflection. The present analysis is carried out in terms of: 1) percentage variation of the global aerodynamic coefficients with respect to the no-flap configuration, 2) increment of pressure and heat flux on the airfoil lower surface due to the Shock Wave-Shock Wave Interaction (SWSWI) with respect to the same quantities with no SWSWI or in no-flap configuration, 3) flap hinge moment. Issues 2) and 3) are important for the design of the mechanical and thermal protection system and of the flap actuator, respectively. Under the above mentioned test and geometrical conditions, the flap deflection is aerodynamically more effective than the flap extension, because it involves higher variation of the aerodynamic coefficients. However, tests verify that a smaller deflection angle involves the advantage of a smaller increment of pressure and heat flux on the airfoil lower surface, due to SWSWI, as well as a smaller hinge moment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.422-431
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• 2015

Wind tunnel testing to construct static aerodynamic database of KF-16 was conducted for preceding research of design of experiments in wind tunnel testing. The test model is KF-16 scaled 1/33 and it has horizontal tail, flaperon, and rudder. The experiments consist of one experiment for analyzing aerodynamic coefficients under whether or not horizontal tail is present and four experiments for analyzing aerodynamic coefficients of changes of deflection angle in control surface which are flap, flaperon, rudder, and horizontal tail. After conducting wind tunnel testing, the experimental results show that the control surface changes have a great effect on Aerodynamic characteristics.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3203-3208
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• 2007

The performance study shows the result using two different methods which are used to control missile or aircraft. One is the Thrust Vector Control(TVC) method for the aviation of next generation and the other is the present effective Shroud Jet-vane System(SJVS) method for the satellite effector development. The research was done through the performance estimation using the numerical simulation analysis, the modelling, the performance measuring using the model, the investigation of the flow visualization and aerodynamic performance with the enforced power to the vane and the result comparison.

• 한국전산유체공학회:학술대회논문집
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• 2000.10a
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• pp.176-182
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• 2000

This paper presents methods for dynamic stall control utilizing an optimization approach. Unsteady aerodynamic sensitivity code is developed using a direct diffentiation method from a discrete two-dimensional unsteady compressible Navier-Stokes code including a two-equation turbulence model. Dynamic stall control is conducted by minimizing an objective function defined at an instant instead of integrating a response for a period of time. Unsteady sensitivity derivative of the objective function is calculated by the sensitivity code, and optimization is conducted using a linear line search method at every physical time level. Examples of dynamic stall control utilizing airfoils nose radius or maximum thickness variation show very satisfactory results.

• The KSFM Journal of Fluid Machinery
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• v.15 no.2
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• pp.36-40
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• 2012

Pitch control of wind turbine is activated above rated wind speed for the purpose of rated power regulation. When we design pitch controller, its gain-scheduling is essential due to nonlinear characteristics of aerodynamic torque. In this study, 2-mass model including a vibration mode of drive-train for a 2 MW wind turbine is considered and pitch control with gain-scheduling using a linearization analysis of the nonlinear aerodynamic torque is applied. Some simulation results for the pitch gain-scheduling under step wind speed are presented and investigated. It is shown that gain-scheduling in pitch control is important especially in the region of high wind speeds when there exists a vibration mode of drive-train.

• Wind and Structures
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• v.12 no.5
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• pp.457-474
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• 2009

Techniques for stabilising slender bridges under wind loads are presented in this article. A mathematically consistent description of the acting aerodynamic forces is essential when investigating these ideas. Against this background, motion-induced aerodynamic forces are characterised using a linear time-invariant transfer element in terms of rational functions. With the help of these functions, the aeroelastic system can be described in the form of a linear, time-invariant state-space model. It is shown that the divergence wind speed constitutes an upper bound for the application of the selected mechanical actuators. Even active control with full state feedback cannot overcome this limitation. The results are derived and explained with methods of control theory.

• Wind and Structures
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• v.15 no.5
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• pp.441-462
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• 2012

This article presents theoretical investigations on techniques for the improvement of the dynamic characteristics of slender bridges under wind action. Aerodynamically effective control shields are applied as controlled actuators. The first part of the article describes the modelling of the uncontrolled aeroelastic system. Acting aerodynamic forces are consistently characterised using linear time-invariant transfer elements in terms of rational functions. On this basis, two configuration levels of the uncontrolled system are represented with linear time-invariant state-space models and investigated. The second part of the article addresses controller design and the behaviour of the controlled aeroelastic system. Both fundamental limits for stabilisation and the efficiency for attenuating the influence of gusts are described for different actuator mechanisms. The results are derived and discussed with methods of control theory.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.7
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• pp.621-630
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• 2006

The T-50 advanced trainer aircraft combines advanced aerodynamic features and a fly-by-wire flight control system in order to produce a stability and highly maneuverability. The flight control system both longitudinal and lateral-directional axes to achieve performance enhancements and improve stability. The T-50 employs the RSS concept in order to improve the aerodynamic performance in longitudinal axis and the longitudinal control laws employ the dynamic inversion with proportional-plus-integral control method. And, lateral-directional control laws employ the blended roll system both beta-betadot feedback and simple roll rate feedback with proportional control method in order to guarantee aircraft stability. This paper details the design process of developing lateral-directional control laws, utilizing the requirement of MIL-F-8785C and MIL-F-9490D. And, this paper propose the analysis of aircraft characteristics such as dutch-roll mode, roll mode, spiral mode, gain and phase margin about gains for lateral-directional inner loop feedback.