• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.492-497
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• 2011

Helicopter uses a rotor system to generate lift, thrust and forces, and its aerodynamic environment is generally complex. Unsteady aerodynamic environment arises such as blade vortex interaction. This unsteady aerodynamic environment induces vibratory aerodynamic loads and high aeroacoustic noise. Those are at N times the rotor blade revolutions (N/rev). But conventional rotor control system composed of pitch links and swash plate is not capable of adjusting such vibratory loads because its control is restricted to 1/rev. Many active control methodologies have been examined to alleviate the problem. The blade using active control device manipulates the blade pitch angle at arbitrary frequencies. In this paper, Active Trailing-edge Flap blade, which is one of the active control methods, is designed to modify the unsteady aerodynamic loads. Active Trailing-edge Flap blade uses a trailing edge flap manipulated by an actuator to change camber of the airfoil. Piezoelectric actuators are installed inside the blade to manipulate the trailing edge flap.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.916-921
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• 2014

In this paper, an improved small-scaled blade prototype was designed with the flap-driving mechanism classified as an active vibration reduction method, in order to reduce vibratory load in the helicopter. In detail, the previous Active Trailing-Edge Flap based on piezoelectric actuator, called SNUF(Seoul National University Flap), failed to achieve the target value (${\pm}4^{\circ}$) of the flap deflection angle. Therefore, the flap-driving mechanism design was improved, and a new piezoactuator was selected to accomplish the target value of the flap deflection angle in both static and rotating situations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.236-241
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• 2011

An active trailing-edge flap blade named as Seoul National University Flap (SNUF) blade is designed for reducing helicopter vibratory loads and the relevant aeroacoustic noise. Unlike the conventional rotor control, which is restricted to 1/rev frequency, an active control device like the present trailing-edge flap is capable of actuating each individual blade at higher harmonic frequencies i.e., higher harmonic control (HHC) of rotor. The proposed blade is a small scale blade and rotates at higher RPM. The flap actuation components are located inside the blade and additional structures are included for reinforcement. Initially, the blade cross-section design is determined. The aerodynamic loads are predicted using a comprehensive rotorcraft analysis code. The structural integrity of the active blade is verified using a stress-strain recovery analysis.

• 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 Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.326-331
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• 2007

This paper conducts a vibratory loads reduction analysis of an Advanced Active Trailing-edge Flap (AATF) blade utilizing single crystal piezoelectric actuators. For an AATF blade, a new L-L piezostack actuator using single crystal PMN-PT materials is designed. The AATF blade is designed to have similar characteristics to the Advanced Active Twist Rotor (AATR) blade. The active trailingedge flap is assumed to be 20% of the blade span and 15% of the chord, located at 75% of the blade radius. In order to conduct the vibratory loads reduction analysis of the AATF blade in forward flight, DYMORE, a multi-body dynamics analysis code, is used. The simulation result shows that the hub vibratory loads may be reduced by approximately 89% even with a much lower input-voltage when comparing with the other active rotor systems.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.7
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• pp.542-550
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• 2018

This paper presents design of a bearingless main rotor of SNUF (Seoul National University Flap) blade equipped with active trailing-edge flap to reduce the hub vibratory loads during helicopter forward flight. For that purpose, sectional design of the flexbeam is carried out using the thin-walled composite material rotating beam vibration analysis program (CORBA77_MEMB) in EDISON. Using the multi-body dynamics analysis program, DYMORE, blade dynamic characteristics and those of the loads control are examined using the active trailing-edge flap in terms of the flexbeam sectional design.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.347-352
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• 2013

Seoul National University Flap (SNUF) blade is a small-scaled rotor blade incorporating a small trailing-edge flap control surface driven by piezoelectric actuators at higher harmonics for vibration attenuation. Initially, the blade was designed using two-dimensional cross-section analysis and a geometrically exact one-dimensional beam analysis, and material configuration was finalized. Flap deflection angle of ${\pm}45^{\circ}$ was established as the criterion for better vibration reduction performance based on an earlier simulation. Flap linkage mechanism design is carried out and static bench tests are conducted to verify the flap actuation mechanism performance. Different versions of test beds are developed and tested with the flap and chosen APA 200M piezoelectric actuators. Through significant improvements, a maximum deflection of ${\pm}3.7^{\circ}$ was achieved. High frequency experiments are conducted to evaluate the performance and transfer function of the test bed is determined experimentally. As the static tests are almost completed, rotor power required for testing the blade in whirl tower (centrifugal environment) is calculated and further preparations are under way.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.499-505
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• 2012

Vibratory loads imposed by the rotating blade upon the fuselage has been one of major obstacles in rotorcrafts. A new concept of rotor blade is currently developed to adopt an Active Trailing-edge Flap (ATF) to alleviate such obstacles. The flap is mounted at 65~85% spanwise location from the rotor hub. The nominal rotational speed of the blade is as high as 1,528 RPM, to match the required tip Mach number. Structural integrity is one of the important design aspects to be maintained and monitored in this special type of rotor. This is due to that many detailed components, which drive the flap, are inserted inside the rotating blade. To conduct its structural design and analysis, CAMRAD-II and the one-dimensional beam analysis are used. At the same time, three-dimensional finite element analysis are also used, such as MSC. PATRAN/NASTRAN, in order to analyze the details of the present active blade. As a result, comparable characteristics for the present rotor are predicted by both approaches.

• Smart Structures and Systems
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• v.20 no.3
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• pp.311-328
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• 2017

The characteristics of boundary layers have significant effects on the aerodynamic forces and vibration of the wind turbine blade. The incorporation of active trailing edge flaps (ATEF) into wind turbine blades has been proven as an effective control approach for alleviation of load and vibration. This paper is aimed at investigating the effects of external trailing edge flaps on the flow pattern and velocity distribution within a boundary layer of a NREL 5MW reference wind turbine, as well as designing a new type of velocity sensors for future validation measurements. An aeroelastic-aerodynamic simulation with FAST-AeroDyn code was conducted on the entire wind turbine structure and the modifications were made on turbine blade sections with ATEF. The results of aeroelastic-aerodynamic simulations were combined with the results of two-dimensional computational fluid dynamic simulations. From these, the velocity profile of the boundary layer as well as the thickness variation with time under the influence of a simplified load case was calculated for four different blade-flap combinations (without flap, with $-5^{\circ}$, $0^{\circ}$, and $+5^{\circ}$ flap). In conjunction with the computational modeling of the characteristics of boundary layers, a bio-inspired hair flow sensor was designed for sensing the boundary flow field surrounding the turbine blades, which ultimately aims to provide real time data to design the control scheme of the flap structure. The sensor element design and performance were analyzed using both theoretical model and finite element method. A prototype sensor element with desired bio-mimicry responses was fabricated and validated, which will be further refined for integration with the turbine blade structures.

• 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.