• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.85-94
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• 2016

An experimental study is conducted for unsteady wet steam flow in a four-stage low-pressure test steam turbine. The measurements are carried out at outlets of the last two stages by using a newly developed fast response aerodynamic probe. This FRAP-HTH probe (Fast Response Aerodynamic Probe - High Temperature Heated) has a miniature high-power cartridge heater with an active control system to heat the probe tip, allowing it to be applied to wet steam measurements. The phase-locked average results obtained with a sampling frequency of 200 kHz clarify the flow characteristics, such as the blade wakes and secondary vortexes, downstream from the individual rotational blades in the wet steam environment.

• International Journal of Control, Automation, and Systems
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• v.5 no.4
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• pp.410-418
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• 2007

For the purpose of fault detection of the primary control surface, real-time estimation of the longitudinal stability and control derivatives of the DURUMI-II using the flight data is considered in this paper. The DURUM-II, a research UAV developed by KARI, is designed to have split control surfaces for the redundancy and to guarantee safety during the fault mode flight test. For fault mode analysis, the right elevator was deliberately fixed to the specified deflection condition. This study also mentions how to implement the multi-step control input efficiently, and how to switch between the normal mode and the fault mode during the flight test. As a realtime parameter estimation technique, Fourier transform regression method was used and the estimated data was compared with the results of the analytical method and the other available method. The aerodynamic derivatives estimated from the normal mode flight data and the fault mode data are compared and the possibility to detect the elevator fault by monitoring the control derivative estimated in real time by the computer onboard was discussed.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.9
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• pp.759-765
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• 2016

This paper presents the principle, dynamics modeling and control, hardware implementation, and flight test result of a hybrid-type unmanned aerial vehicle (UAV). The proposed UAV was designed to provide both hovering and fixed-wing type aerodynamic flight modes. The UAV's flight mode transition was achieved through the attitude transformation in pitch axis, which avoids a complex rotor tilt mechanism from a structural and control viewpoint. To achieve this, a different navigation coordinate was introduced that avoids the gimbal lock in pitch singularity point. Attitude and guidance control algorithms were developed for the flight control system. For flight test purposes, a quadrotor attached with a tailless fixed-wing structure was manufactured. An onboard flight control computer was designed to realize the navigation and control algorithms and the UAV's performance was verified through the outdoor flight tests.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.3
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• pp.296-314
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• 2016

This paper presents experimental and computational investigations of synthetic jets with a circular exit for improving flow control performance. First, the flow feature and vortex structure of a multiple serial circular exit were numerically analyzed from the view point of flow control effect under a cross flow condition. In order to improve separation control performance, experimental and numerical studies were conducted according to several key parameters, such as hole diameter, hole gap, the number of hole, jet array, and phase difference. Experiments were carried out in a quiescent condition and a forced separated flow condition using piezoelectrically driven synthetic jets. Jet characteristics were compared by measuring velocity profiles and pressure distributions. The interaction of synthetic jets with a freestream was examined by analyzing vortical structure characteristics. For separation control performance, separated flow over an airfoil at high angles of attack was employed and the flow control performance of the proposed synthetic jet was verified by measuring aerodynamic coefficient. The circular exit with a suitable hole parameter provides stable and persistent jet vortices that do beneficially affect separation control. This demonstrates the flow control performance of circular exit array could be remarkably improved by applying a set of suitable hole parameters.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3347-3352
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• 2007

This paper describes a research for the performance improvement of the straight-bladed vertical axis wind turbine. To improve the performance of VAWT, the individual blade pitch control method is adopted. For the wind turbine, CFD analysis is carried out by changing blade pitch angle according to the change of wind speed and wind direction. By this method, capacity and power efficiency of VAWT are obtained according to the wind speed and rotating of rotor, and could predict the overall performance of VAWT. It was manufactured to verify performance of the experimental system that consists of rotor including four blades and base. Furthermore, torque sensor and power generator were installed. Also, active controller which can change the pitch angle of the individual blade according to the wind speed and direction was used.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.19 no.2
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• pp.16-22
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• 2011

It is recognized that the control surface fault is detected by monitoring the value of the coefficients due to the control surface deviation. It is found out the control surface stuck position by comparing the trim value with the reference value. To detect and isolate the fault, two mixed methods apply to the real-time parameter estimation and similarity measure. If the scatter of aerodynamic coefficients for the fault and normal are closing nearly, fault decision is difficult. Applying similarity measure to decide for fault or not, it makes a clear and easy distinction between fault and normal. Low power processor is applied to the real-time parameter estimator and computation of similarity measure.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.2
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• pp.237-247
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• 1999

Flight parameters of a light aircraft in normal category named ChangGong-91 we identified from flight tests. Modified Maximum Likelihood Estimation (MMLE) is used to produce aerodynamic coefficients, stability and control derivatives. A Flight Training Device (FTD) has been developed based on the identified flight parameters. Flat earth, rigid body, and standard atmosphere are assumed in the FTD model. Euler angles are adapted for rotational state variables to reduce computational load. Variations in flight Mach number and Reynolds number are assumed to be negligible. Body, stability and inertial axes allow 6 second-order linear differential equations for translational and rotational motions. The equations of motion are integrated with respect to time, resulting in good agreements with flight tests.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.115-121
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• 2007

The aeroelastic analysis of rotor blades with trailing edge flaps, focused on reducing vibration while minimizing control effort, are investigated using large deflection-type beam theory in forward flight. The rotor blade aerodynamic forces are calculated using two-dimensional quasi-steady strip theory. For the analysis of forward flight, the nonlinear periodic blade steady response is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim. The objective function, which includes vibratory hub loads and active flap control inputs, is minimized by an optimal control process. Numerical simulations are performed for the steady-state forward flight of various advance ratios. Also, numerical results of the steady blade and flap deflections, and the vibratory hub loads are presented for various advance ratios and are compared with the previously published analysis results obtained from modal analysis based on a moderate deflection-type beam theory.

• Wind and Structures
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• v.16 no.3
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• pp.263-278
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• 2013

The fatigue load of a turbine blade has become more important because the size of commercial wind turbines has increased dramatically in the past 30 years. The reduction of the fatigue load can result in an increase in operational efficiency. This paper numerically investigates the load reduction of large wind turbine blades using active aerodynamic load control devices, namely trailing edge flaps. The PD and LQG controllers are used to determine the trailing edge flap angle; the difference between the root bending moment and its mean value during turbulent wind conditions is used as the error signal of the controllers. By numerically analyzing the effect of the trailing edge flaps on the wind turbines, a reduction of 30-50% in the standard deviation of the root bending moment was achieved. This result implies a reduction in the fatigue damage on the wind turbines, which allows the turbine blade lengths to be increased without exceeding the designed fatigue damage limit.

• Proceedings of the KSLP Conference
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• 2003.11a
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• pp.147-147
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• 2003

Recent aerodynamic and acoustic studies of VPI(velopharyngeal insufficiency) are non-invasive and safety, therefore, many researchers have used it to diagnose the hyper/hyponasality and articulation disorders of cleft palate patients. The purpose of this study was to estimate mainly the oropharyngeal air pressure and over all air flow in cleft lip and palate patients. The pressure-collecting catheter was positioned in the oropharyngel cavity around tongue base. Twelve adult control group and three cleft lip & palate patients were participated to this experimentation. Aerophone II was used to measure peak air flow, mean air flow, phonatory airflow, phonatory efficiency and resistance. The results were as follows: 1) Airflow of cleft lip ＆ palate patients group were higher than those of control group. Fricative sounds /s/ and /s'/ showed the statistic significance of mean airflow and volume data. 2) Intraoral air pressure of cleft lip ＆ palate patients was lower than those of control group.