Active Gurney Flap Research Articles

Dynamic Stall Alleviation of a Helicopter Blade Section in Forward Flight Condition Using an Optimized Combination of Active Nose Droop and Active Gurney Flap

Dynamic Stall Alleviation of a Helicopter Blade Section in Forward Flight Condition Using an Optimized Combination of Active Nose Droop and Active Gurney Flap

Numerical Simulation of Harmonic Pitching Supercritical Airfoils Equipped with Movable Gurney Flaps

A two-dimensional numerical investigation was performed to determine the effect of an active Gurney flap on an oscillating supercritical RAE 2822 airfoil in transonic flow. The Navier-Stokes code Fluent was used to calculate the flow field around the airfoil using the Shear Stress Transport turbulence model. Dynamic simulations were based on a moving C-grid, whose harmonic pitching motion was managed using a compiled User Defined Function. Both effects of height and chordwise positioning were considered in this study. The heights of Gurney flaps ranged from 1% to 3% of airfoil chord lengths, while position ranged from the trailing edge to 10% upstream from the trailing edge. In comparison with the Baseline airfoil, the effect of the deployable Gurney flap is to enhance significantly the maximum lift and pitching-moment coefficients; however, an increment in the drag coefficient is also registered. The results indicate that the Gurney flap provides best performance close to the stall angle of attack.

Optimal Wind Turbine Operation by Artificial Neural Network-Based Active Gurney Flap Flow Control

Flow control devices have been introduced in the wind energy sector to improve the aerodynamic behavior of the wind turbine blades (WTBs). Among these flow control devices, Gurney flaps (GFs) have been the focus of innovative research, due to their good characteristics which enhance the lift force that causes the rotation of the wind turbine rotor. The lift force increment introduced by GFs depends on the physical characteristics of the device and the angle of attack (AoA) of the incoming wind. Hence, despite a careful and detailed design, the real performance of the GFs is conditioned by an external factor, the wind. In this paper, an active operation of GFs is proposed in order to optimize their performance. The objective of the active Gurney flap (AGF) flow control technique is to enhance the aerodynamic adaption capability of the wind turbine and, thus, achieve an optimal operation in response to fast variations in the incoming wind. In order to facilitate the management of the information used by the AGF strategy, the aerodynamic data calculated by computational fluid dynamics (CFD) are stored in an artificial neural network (ANN). Blade element momentum (BEM) based calculations have been performed to analyze the aerodynamic behavior of the WTBs with the proposed AGF strategy and calculate the corresponding operation of the wind turbine. Real wind speed values from a meteorological station in Salt Lake City, Utah, USA, have been used for the steady BEM calculations. The obtained results show a considerable improvement in the performance of the wind turbine, in the form of an enhanced generated energy output value and a reduced bending moment at the root of the WTB.

Flow Control on Helicopter-Rotor Blades Via Active Gurney Flap

Abstract The Active Gurney Flap (AGF) is a small, flat tab cyclically deployed and retracted at lower surface of the rotor blade near its trailing edge. It is expected that the device may improve performance of modern helicopters. The main goal of presented investigations was to develop research methodology and next to use it in studies on phenomena occurring in the flow around helicopter-rotor blades equipped with AGF. Conducted CFD simulations aimed at validation of the developed methodology as well as at significant supplementing and extension of results of experimental research. Simplified sensitivity analysis has been conducted aiming at determination of geometric and motion-control parameters of the AGF, optimal from point of view of helicopter-performance improvement. Fully three-dimensional simulations of the rotor flight aimed at determination of flight conditions, in which the use of Active Gurney Flaps could significantly improve the rotorcraft performance.

Discontinuous Galerkin Method for the Study of Active Gurney Flaps

A discontinuous Galerkin method is proposed for the solution of the Reynolds-averaged Navier–Stokes equations, for turbulent flows in two dimensions. The numerical model is applied to the solution of unsteady flows associated to an actively controlled Gurney flap located in proximity of the trailing edge of an airfoil, with oscillations up to 20 Hz. The motion of the Gurney flap is simulated through no-slip viscous wall conditions applied to the interfaces between neighboring elements that coincide with the position of the flap at a given time instant. Several configurations of deployment motions are considered under different freestream conditions to demonstrate the capability of the solver to predict accurately unsteady nonlinear problems at high Reynolds numbers. The numerical calculations are compared with experimental data in the case of the NACA 0012 airfoil.

Effect of active Gurney flaps on overall helicopter flight envelope

ABSTRACTThis paper presents a study of the W3-Sokol main rotor equipped with Gurney flaps. The effect of the active Gurney is tested at low and high forward flight speeds to draw conclusions about the potential enhancement of the rotorcraft performance for the whole flight envelope. The effect of the flap on the trimming and handling of a full helicopter is also investigated. Fluid and structure dynamics were coupled in all cases, and the rotor was trimmed at different thrust coefficients. The Gurney proved to be efficient at medium to high advance ratios, where the power requirements of the rotor were decreased by up to 3.3%. However, the 1/rev actuation of the flap might be an issue for the trimming and handling of the helicopter. The current study builds on the idea that any active mechanism operating on a rotor could alter the dynamics and the handling of the helicopter. A closed loop actuation of the Gurney flap was put forward based on a pressure divergence criterion, and it led to further enhancement of the aerodynamic performance. Next, a generic light utility helicopter was built using 2D aerodynamics of the main aerofoil section of the W3 Sokol blade along with a robust controller, and the response of the rotorcraft to control inputs was tested. This analysis proved that the 1/Rev actuation of the Gurney did not alter the handling qualities of the helicopter, and as a result, it can be implemented as a flow control mechanism for aerodynamic enhancement and retreating blade stall alleviation.

Method for Calculating Rotors with Active Gurney Flaps

This paper builds on the Helicopter Multi-Block version 2 computational-fluid-dynamics solver of the University of Liverpool and demonstrates the implementation and use of Gurney flaps on wings and rotors. The idea is to flag any cell face within the computational mesh with a solid, no-slip boundary condition. Hence, the infinitely thin Gurney can be approximated by blocking cells in the mesh. Comparison between thick Gurney flaps and infinitely thin Gurneys showed no difference on the integrated loads; the same flow structure was captured and the same vortices were identified ahead and behind the Gurney. The results presented for various test cases suggest that the method is simple and efficient, and it can therefore be used for routine analysis of rotors with Gurney flaps. Moreover, the current method adds to the flexibility of the solver because no special grids are required, and Gurney flaps can be easily implemented. Simple two-dimensional aerofoil, three-dimensional wing, and rotors in hover and forward flight were tested with fixed, linearly actuated, and swinging Gurneys, and the ability of the code to deploy a Gurney flap within the multiblock mesh is highlighted. The need for experimental data suitable for validation of computational-fluid-dynamics methods for cases of rotors with Gurney flaps is also highlighted.

Comprehensive Numerical Assessment of Rotorcraft Vibration and Noise Control Using Microflaps

Active Gurney flaps, or microflaps, are studied to determine their effectiveness in reducing noise and vibration in rotorcraft as well as improving rotor performance. The effectiveness of the microflap is examined using a comprehensive rotorcraft simulation code. The aerodynamic properties of the microflap are modeled using a nonlinear computational-fluid-dynamics-based reduced-order aerodynamic model that takes into account unsteadiness, compressibility, and time-varying freestream effects. Active control studies are conducted on a hingeless rotor configuration resembling the Messerschmitt-Bölkow-Blohm BO-105, using various spanwise microflap configurations, including single, dual, and segmented five-microflap configurations. Results indicate that the microflap is capable of substantial reductions in blade–vortex interaction noise ranging from 3 to 6 dB. Vibration reduction ranging from 70 to 90% is also demonstrated. The effect of vibration reduction on noise and vice versa is also examined, and it was found that reduction in one objective is accompanied by an increase in the other, a trend also observed when using other active control approaches. Finally, the microflap is considered for combined vibration reduction and performance enhancement at a high-speed cruise flight condition. The results clearly indicate that the microflaps are very effective for both noise and vibration reduction in helicopters, and they also have potential for rotor performance enhancement.

회전 효과를 고려한 Active Gurney Flap 의 동특성 해석

Abstract : In this study, the finite element analysis was carried out to investigate dynamic characteristics of the AGF(Active Gurney Flap) which is under development for reducing vibration and noise of the helicopter rotor system. The Gurney flap is a kind of small flat plate, mounted normal to the lower surface of the airfoil near to the trailing edge. An electric motor, L-shaped linkages and flap parts were integrated into a rotor bade, and 3~5/rev control was given to the AGF to reduce the vibration in the fixed frame. Thus, an explicit time integration method was adopted to investigate the dynamic response of the AGF with considering both centrifugal force due to the rotor rotation and active control input, and it can be seen that the vertical displacement of the AGF was satisfied to meet the design requirement. § 이 논문은 대한기계학회 2014년도 추계학술대회(2014. 11. 11-14., 김대중컨벤션센터) 발표내용을 토대로 한 논문임. † Corresponding Author, naltlguy@kari.re.kr Ⓒ 2015 The Korean Society of Mechanical Engineers

Active Gurney Flaps: Their Application in a Rotor Blade Centrifugal Field

Miniature trailing-edge effectors are segmented gurney flaps that can deploy to achieve multipurpose functions, such as performance enhancement, noise/vibration control, and/or load control on rotor blades. The unsteady aerodynamics of miniature trailing-edge effectors and a deployable plain flap (with an equivalent lift gain) are quantified experimentally at a reduced frequency of 0.21 and a Reynolds number of . These experiments are also simulated using computational fluid dynamics. The combination of the wind tunnel experiments and computational fluid dynamics are used to quantify the aerodynamic effects of miniature trailing-edge effector deployment to compare their unsteady aerodynamics to plain flaps, and to evaluate the fluid dynamics of miniature trailing-edge effectors against experimental data. The current experiments display unsteady aerodynamics that corroborate previous computational fluid dynamics findings that indicate that miniature trailing-edge effectors shed on-surface vortices during deployment, affecting the unsteady aerodynamics of the system. Computational fluid dynamics also predicted that miniature trailing-edge effectors require 1/55 power to deploy compared to a plain-flap configuration. Power reduction is a key attractor for the integration of devices on smart rotors. This work is concluded with an effort that displays that the low power requirement of miniature trailing-edge effectors enable simple deployment methods, such as the use of pressure differentials inherent to the rotor blades. The proposed pneumatic miniature trailing-edge effector configuration was tested at centrifugal forces representative of helicopter rotor blades.

Experimental investigation of a trailing edge L-shaped tab on a pitching airfoil in deep dynamic stall conditions

An L-shaped tab was tested at the trailing edge of an oscillating airfoil to evaluate its effects on blades aerodynamic performance. The tests were conducted on a NACA 23012 pitching airfoil in deep dynamic stall conditions with the L-shaped tab fixed in two different positions. When deployed the tab is attached to the airfoil upper surface so that the end prong protrudes at the airfoil trailing edge. In retracted position the tab features an angle of 9.1° with the airfoil upper surface, since its prong tip touches the airfoil trailing edge. The airloads time histories during a pitching cycle were evaluated by pressure measurements carried out on the airfoil midspan contour. The phase-averaged flow field at the trailing edge region was investigated by means of particle image velocimetry to evaluate the detailed flow physics involved in the use of the device. The experimental results indicate that the use of such a pivoting L-shaped tab can introduce similar effects to those that can be obtained by the use of an active Gurney flap. Thus, the L-shaped tab can be considered an attractive device due to its easier integration on helicopter blades.

Piezoelectric and electromagnetic solutions aimed at realizing an active Gurney flap

Gurney flaps are small devices whose dimensions are usually percentage units of the airfoil chord. A Gurney flap can change the flow field in the region of the trailing edge by introducing two contra-rotating vortices behind the flap, therein altering Kutta’s condition and circulation. This helps avoiding flow separation and moves stall occurrence to higher angles of attack. Active rotor technologies would, for instance, enable a helicopter to operate at reduced rotor tip speed while preserving flight performance capabilities. This article shows some results carried out on different, original, and feasible solutions, aimed at realizing “smart” Gurney flaps for rotorcraft blades. In particular, piezo patches, piezo stacks, and electromagnet-based solutions were exploited finding that only the last two solutions are able to satisfy specs. The last one (electromagnets) performs better from the viewpoints of implementation, cost (one order of magnitude), weight (less than 100 g with respect to 150 g of piezo stack), and power consumption (5 W with respect to 50 W).

Experimental investigation of the dynamic stall phenomenon on a NACA 23012 oscillating airfoil

An extensive experimental investigation was conducted on an oscillating NACA 23012 airfoil to study the flow structures and the consequent performances in dynamic stall conditions. The testing activity involved two different measurement techniques: fast unsteady pressure measurements and particle image velocimetry. The analysis of the experimental data set made possible to achieve a deep insight in the mechanism of the dynamic stall phenomena for the NACA 23012 airfoil in the different dynamic stall regimes. In particular, the flow velocity field measured on the airfoil upper surface described in detail the mechanism of the formation, migration and shedding of strong vortical structures characteristic of the deep dynamic stall. In addition, Gurney flap effects were investigated. The experimental results showed that it would be advantageous to deploy active Gurney flaps to improve helicopter rotor blade performances. The whole set of experimental results can be considered as a reference to validate computational fluid dynamics tools.

Performance Optimization of Wind Turbine Rotors with Active Flow Control (Part 1)

This article describes the performance optimization of wind turbine rotors with active flow control. The active Gurney flap concept was tested in the wind tunnel under dynamic AoA variations to simulate unsteady inflow conditions. A high-deflection micro flap was actuated by four digital electric servos with a maximum deflection rate of 360°/sec. A custom code was created to allow dynamic AoA variations of the test wing with simultaneous dynamic force measurements. During the dynamic investigations, various control strategies were tested, starting from standard PID controllers with semi-empirical parameter tuning models to Direct Inverse Controllers with neural network tuning strategies and pure self-learning neural network controllers. The results of the closed-loop measurements using the manually tuned PID controller showed a reduction potential for the dynamic lift loads in the range of 70% as well as a stable controller behavior. The Direct Inverse Controller not only showed a load reduction of 36.8%, but also significant improvement potential with respect to its fine-tuning.