Trailing-edge Devices Research Articles

Methodology for Evaluating a Distributed Variable-Camber Trailing-Edge System in Preliminary Aircraft Design

A controlled adjustment of the wing camber during cruise flight by an extension of each separate flap allows for wing shape optimization, depending on the current mission point including the prevailing conditions, contributing to an increase in efficiency. This is referred to as variable camber (VC). This paper aims to investigate a methodology for a retrofit application of VC technology with differential flap setting, especially for a segmented trailing-edge system at the overall aircraft level in the preliminary design phase. In addition, an assessment is conducted to clarify whether actuation on the basis of a central shaft system or a decentralized power-by-wire system is advantageous. The investigation is based on a commercial aircraft with a maximum takeoff mass of 270 t and compares the potential of a VC application with an aerostructural twist optimization of the wing. Different configurations of the trailing-edge flaps, ranging from a common two-flap configuration up to a configuration with six trailing-edge devices, are covered in order to give a holistic implementation recommendation, including actuation and flap segmentation. Depending on the reference aircraft, the study shows a considerable fuel-saving potential for VC applications, e.g., 3.5% for the pre-optimized reference on a long-range mission.

Neural-Network-Based Model for Trailing-Edge Flap Loads in Preliminary Aircraft Design

Accurately predicting the forces and moments acting on trailing-edge devices under different flight conditions is a critical aspect in the design of the kinematics and actuation for high-lift or variable-camber applications. However, accurate modeling without elaborated computational fluid dynamics (CFD) analyses in the subsonic and transonic regimes needs a sophisticated model. Thus, the objective of this paper is to create such a model that accurately predicts the forces and moments acting on flaps during different flight conditions while remaining applicable to the preliminary aircraft design. The target values in this model are the three-dimensional (3D) forces and moments on the flap, which were obtained through 3D CFD simulations. The chosen input values required for the model include two-dimensional airfoil data, and wing geometry data for three different aircraft types: short-, medium-, and long-range, including a high-aspect-ratio configuration. Among several potential approaches, a neural network was deemed to be the most promising for predicting the target values. The neural network was used as a regression tool to accelerate the model development process in the preliminary aircraft design. Consequently, multiple studies were conducted on how the setup of the neural network, including the number of neurons, activation functions, and initialization, influences the results. The results reveal that the developed neural network accurately predicts the flap forces and moments with a mean deviation of under 2% for the vertical force Fz and the lateral force Fx and under 4% for the moment My.

Numerical Study of the Effect of the Trailing-Edge Devices (Gurney Flap and Divergent Trailing-edge Flap) on the Aerodynamic Characteristics of an Airfoil in Transonic Flow for Drone Applications

Numerical Study of the Effect of the Trailing-Edge Devices (Gurney Flap and Divergent Trailing-edge Flap) on the Aerodynamic Characteristics of an Airfoil in Transonic Flow for Drone Applications

Increase in high-lift devices efficiency of swept wing

The use of Fowler flaps and slotted slats in sweptwing aircraft is the standard solution to increase wing lift at take off and landing. In the literature this solution is known as a classical option of high-lift system of commercial subsonic aircraft. The results of numerical and experimental studies of some solutions intended to increase the efficiency of classical high-lift devices are presented. The concept of the trailing-edge devices called "the adaptive flap" is considered as a way to improve flap efficiency. The adaptive concept is characterized by the integration of spoiler downward deflection to the Fowler flap function. Integration of the spoiler with a movable flap provided an increase of lift in the linear region due to flaps deflected to a higher angle. The steeper upwash angle at a leading-edge device may be the reason of an early stall of the main wing. To protect the leading edge a slotted Kruger flap with streamline form has been used. Preliminary design of classical and improved high-lift systems included the determination of aerodynamic shapes and the optimized position for the high-lift devices. Aerodynamic analysis and design were carried out using 2D RANS Navier-Stokes method. A comparison of computed results has shown visible aerodynamic advantages of an improved high-lift system for maximum lift coefficient and refining the behavior of stall characteristics at high angles of attack. The results of wind tunnel tests of aircraft model with adaptive flap showed its effectiveness.

Experimental investigation of porous materials for trailing-edge noise reduction

The introduction of quiet short take-off and landing for civil aircraft operations in close proximity to the population poses important technological challenges. One critical aspect is the realization of extreme lift augmentation at low acoustic emissions. The aircraft concept selected to achieve this goal is a high-lift system equipped with an active flow-control non-slotted flap and a droop nose. For this specific configuration, trailing edge noise becomes a dominant noise source. Porous materials as a passive means for trailing-edge noise reduction are selected and characterized. Results of extensive experimental investigations in the acoustic wind tunnel Braunschweig are presented and discussed to point out the potential and limitations of the selected porous devices. Practical issues related to material manufacturing and integration into the wind tunnel model are addressed. The noise reduction potential of passive porous trailing-edge devices is found to strongly depend on both these aspects. Issues related to the characterization of the porous materials properties are described. Although porous materials are found to be successful at reducing trailing-edge noise emissions, the results indicate that there is still a need for more generic investigations to further clarify the parametric dependencies between noise reduction and material properties.

Reynolds number effects of supercritical airfoil with mini-TED in transonic flow

In order to accurately investigate the Reynolds number influence of supercritical airfoil with miniature trailing-edge devices (mini-TED) under transonic conditions. The supercritical airfoil pressure measurement test of high Reynolds number was conducted in the European transonic wind tunnel. The reliability of the high Reynolds number numerical calculation method was validated by the wind tunnel test results. The calculation results are in good agreement with the wind tunnel test results, indicating that the high Reynolds number calculation accuracy could meets the investigation requirement. The transonic flow of supercritical airfoil with mini-TED in the range of Reynolds number 3×106∼50×106 and Mach number 0.76 was simulated using the validated calculation method. Due to the existence of mini-TED, the Reynolds number influence self-adjustment range of the supercritical airfoil disappeared, while the influence magnitude and sensitivity reduced. At the same time, the supercritical airfoil’s linear influence of Reynolds number effects has been changed, and the Reynolds number prediction method based on pressure distribution is no longer applicable. After considering the influence of Reynolds number, the detailed design of supercritical wing with mini-TED could be conducted to improve its reliability and economy in the application of advanced aircraft.

Analysis of Novel Morphing Trailing Edge Flap Actuated by Multistable Laminates

This paper presents an analysis of a novel morphing trailing edge flap design for a wind turbine rotor blade with embedded multistable composite plates. Morphing trailing edge devices are promising candidates for reducing loads in variable wind conditions and turbulent flows as well as capable of changing the shape rapidly. The application of multistable laminates allows large deformations with modest actuation demand, without the need for a continuous supply of energy. They can undergo snap-through with the help of Macro Fiber Composites actuator patches. A rectangular multistable plate is designed with the optimal location of actuators, aiming at two-way snap-through without the loss of bistability. A multi-objective derivative-free optimization scheme is used to minimize the snap-through voltages and maximize the out-of-plane displacements. The designed multistable plates with actuators are embedded at a suitable location of the morphing trailing edge flap. As the multistable plates snap, the flap deflects to a new position. The mechanism of the new morphing concept is simulated and analyzed with finite element tools.

Numerical simulation of flapping airfoil with alula

Bionic micro aerial vehicles have become popular because of their high thrust efficiency and deceptive appearances. Leading edge or trailing edge devices (such as slots or flaps) are often used to improve the flight performance. Birds in nature also have leading-edge devices, known as the alula that can improve their flight performance at large angles of attack. In the present study, the aerodynamic performance of a flapping airfoil with alula is numerically simulated to illustrate the effects of different alula geometric parameters. Different alula relative angles of attack β (the angle between the chord line of the alula and that of the main airfoil) and vertical distances h between the alula and the main airfoil are simulated at pre-stall and post-stall conditions. Results show that at pre-stall condition, the lift increases with the relative angle of attack and the vertical distance, but the aerodynamic performance is degraded in the presence of alula compared with no alula, whereas at post-stall condition, the alula greatly enhances the lift. However, there seems to be an optimal relative angle of attack for the maximum lift enhancement at a fixed vertical distance considering the unsteady effect, which may indicate birds can adjust the alula twisting at different spanwise positions to achieve the best flight performance. Different alula geometric parameters may affect the aerodynamic force by modifying the pressure distribution along the airfoil. The results are instructive for design of flapping-wing bionic unmanned air vehicles.

A CFD benchmark of active flow control for buffet prevention

This paper will present the main results of the aerodynamic design and analysis for flow control applied to trailing edge of wings and profiles. This work has been conducted in the framework of the European project AFLoNext aiming at developing technologies allowing for an improvement of the performance and loads situation in the operational domain. The technologies are expected to provide an increase in aerodynamic efficiency and a structural weight reduction for the design flight conditions with a potential for 1–2% fuel savings and corresponding emission reduction. Numerical simulations are performed on 2D and 3D test cases. Where available, a comparison with experimental data is performed. High-speed flow is considered, to investigate a transonic configuration representative of cruise conditions. Trailing edge devices (TED) such as fluidic Gurney flaps or micro-jets for circulation control are used for assessing the possibility of delaying the buffet onset or increasing the maximum achievable lift, thus extending the flight envelope of an aircraft. The purpose of the present paper is to present the result of the work performed by the different partners involved in the project.

Impact of Morphing Trailing Edges on Mission Performance for the Common Research Model

Nonmorphing, conventional aircraft wings are designed for a compromise of good performance at a variety of flight conditions. Accordingly, such wings perform suboptimally when considered at a single flight condition. Morphing trailing-edge devices offer an opportunity to change this wing design paradigm by allowing wings to adapt to varying flight conditions. This adaptability weakens the correlation between performance at various flight conditions and increases the robustness of the wing’s performance, providing closer-to-optimal performance at each flight condition. To study the isolated aerodynamic effects of this increased robustness, we perform a number of aerodynamic and aerostructural shape optimizations of a morphing trailing-edge device that can change the shape of the rear 10% of the wing at a variety of flight conditions on the Common Research Model aircraft configuration. The aerodynamically optimized morphing configuration yields a 1.0% fuel burn reduction for a long-range mission. When performing aerostructural optimization, which considers structural deformations and structural weight reductions enabled by active load alleviation, the fuel burn reduction is 2.7%.

Numerical analysis of the influence of inertial loading over morphing trailing edge devices

Larger and more flexible wind turbine blades are currently being manufactured. Those highly flexible blades suffer from loading of aeroelastic nature which increases the fatigue damage. Smart blade concepts are being developed to reduce the aerodynamic loading. The state of the art favors the discrete deformable trailing edge concept. Many authors have reported adequate performance of this type of actuators in reducing the blade vibrations. However, the question of whether the actuator can maintain its authority under strong external loading remains still answered. To solve this question, actuator models that include the loading produced by the blade vibration are required. In this article, a smart morphing trailing edge model is presented that includes the inertial forces produced by the blade dynamics. The model is applied to a commercial actuator and the influence of its parameters is analyzed. Finally, a simple estimation of the inertial loading produced by a 35-m wind turbine blade at the flutter instability condition is analyzed to understand the design requirements of this type of systems.

Trailing-edge flow control for wind turbine performance and load control

This paper reports an investigation into the performance of trailing-edge flow control devices on horizontal axis wind turbines by solving the three dimensional Reynolds averaged Navier-Stokes equations in the rotational framework. The validation case selected for this work is the NREL Phase VI blade with wind tunnel experimental data. The trailing-edge flow control devices studied include microtabs and microjets installed near the trailing-edge of the rotating blade. The divergent trailing-edge is also included in the study as a passive flow control device due to its practical interest. These trailing-edge devices are implemented on the fixed-pitch NREL Phase VI blade, using the original performance and flow characteristics as a benchmark. Both 2D and 3D simulations are carried out in order to investigate the suitability of the 2D blade sectional design analysis and control for the actual 3D rotating blades.

Poro-Serrated Trailing-Edge Devices for Airfoil Self-Noise Reduction

This paper represents the continuation of the works previously published in Chong et al. (“Self-Noise Produced by an Airfoil with Nonflat Plate Trailing-Edge Serrations,” AIAA Journal, Vol. 51, No. 11, 2013, pp. 2665–2677), who used several nonflat plate serrated trailing edges for the reduction of airfoil self-noise. The poro-serrated concept developed in the current work improves substantially the overall noise performance of the nonflat plate trailing-edge serration type. The use of porous metal, synthetic foams, or thin brush bundles to fill the gaps between adjacent members of the sawtooth can completely suppress the bluntness-induced vortex shedding tonal noise. Most important, up to 7 dB turbulent boundary layer–trailing-edge broadband noise reduction can simultaneously be achieved without compromising the aerodynamic performances in lift and drag. The poro-serrated trailing edges do not cause any noise increase throughout the frequency range investigated here. The reduction of the turbulent broadband noise is primarily caused by the serration effect, but under a condition that the sawtooth surface must be solid and nonporous. The primary role of the porous metal foams in a poro-serrated trailing edge is to suppress the vortex shedding tonal noise. However, an optimum selection of the porous material is also found to be able to further reduce the broadband noise level. The new serrated trailing-edge concept developed here has the potential to improve the industrial worthiness of the serration technology in achieving low noise radiation in fan and turbine blades.

Helicopter Vibratory Loads Alleviation through Combined Action of Trailing-Edge Flap and Variable-Stiffness Devices

The aim of this paper is the assessment of the capability of controllers based on the combined actuation of flaps and variable-stiffness devices to alleviate helicopter main rotor vibratory hub loads. Trailing-edge flaps are positioned at the rotor blade tip region, whereas variable-stiffness devices are located at the pitch link and at the blade root. Control laws are derived by an optimal control procedure based on the best trade-off between control effectiveness and control effort, under the constraint of satisfaction of the equations governing rotor blade aeroelastic response. The numerical investigation concerns the analysis of performance and robustness of the control techniques developed, through application to a four-bladed helicopter rotor in level flight. The identification of the most efficient control configuration is also attempted.

Experimental and simulated control of lift using trailing edge devices

Two active aerodynamic load control (AALC) devices coupled with a control algorithm are shown to decrease the change in lift force experienced by an airfoil during a change in freestream velocity. Microtabs are small (1% chord) surfaces deployed perpendicular to an airfoil, while microjets are pneumatic jets with flow perpendicular to the surface of the airfoil near the trailing edge. Both devices are capable of producing a rapid change in an airfoil's lift coefficient. A control algorithm for microtabs has been tested in a wind tunnel using a modified S819 airfoil, and a microjet control algorithm has been simulated for a NACA 0012 airfoil using OVERFLOW. In both cases, the AALC devices have shown the ability to mitigate the changes in lift during a gust.

A Retrospective of High-Lift Device Technology

The present paper deals with the most adopted technical solutions for the enhancement of the lift force of a wing. In fact, during several flight conditions (such as take off and landing), the lift force needs to be dramatically enhanced. Both trailing edge devices (such as flaps) and leading edge ones (such as slats) are described. Finally, the most advanced aerodynamic solutions to avoid the separation of the boundary layer from aircraft wings at high angles of attack are reviewed. Keywords—High lift devices, Trailing Edge devices, Leading Edge devices, Boundary Layer Control devices.

Performance Optimization of Wind Turbine Rotors with Active Flow Control (Part 2)

This article discusses the performance optimization of wind turbine rotors with active flow control. An extensive multi-parameter investigation with a thorough matrix-grading system was performed to identify the most suitable solution for industrial quality, short/mid-term implementation on actual utility scale wind turbines. A very wide selection of aerodynamic flow control solutions was analyzed based on extensive multi-disciplinary literature review and through aerodynamic and aeroelastic simulations. It is suggested that the trailing edge devices have the most favorable performance in the field of system integration and mechanical design performance. Compliant structures like the flexible flap keep the number of moving parts to a minimum while maintaining high performance and manufacturing simplicity. The use of flexible and elastic materials based on polymers or rubber material improves the lightning strike resistance of these solutions and allows for low-cost large-scale production. The actuator principle, sensitivity, and reliability are decisive parameters, and pneumatic actuators seem to strike a good balance between performance, cost, and reliability.

Steady Aerodynamics of Miniature Trailing-Edge Devices in Transonic Flows

The steady aerodynamic effect of miniature trailing-edge devices on a supercritical airfoil was investigated in transonic flow both experimentally and numerically. The investigations were performed for the Gurney flap, the split flap, and the divergent trailing edge, and they showed a strong influence on the supersonic flow regime, influencing the lift and drag characteristics. At constant lift, a redistribution of the lift generation from the front to the rear part of the airfoil takes place. Total-drag reductions can be achieved by the reduction of wave drag. The influences of the different types of miniature trailing-edge devices are shown. The investigation of the influence of geometry parameters showed that the variation of the height of the Gurney flap and of the deflection angle of the split flap have similar effects. Perforation of the miniature trailing-edge devices showed only a small influence. The investigation of the influence of the freestream parameters indicated that increases in Mach number and Reynolds number increase the miniature trailing-edge device effect. A drag-optimal application is possible with adaptive miniature trailing-edge devices, and the same performance is achieved by an adaptive Gurney flap and an adaptive split flap. A comparison with a flexible trailing edge could identify performance advantages of the miniature trailing-edge devices.

Trailing edge noise mitigation investigation for wind turbine blades

Wind turbines offer one of the most mature technologies for providing large scale renewable energy to society in an economically viable way. Although not on par with the price of conventional energy sources yet, the cost of energy has been steadily decreasing as the technology continues to develop. Unfortunately, like with all energy sources, there are some problems with this form of generation. Among these, sound emissions from wind turbines are one of the problems people who live close to the installed machines may be exposed to. Past studies show that these noise emissions are dominated by aeroacoustic noise and of the many mechanisms that lead to aeroacoustic noise, the interaction between the unsteady flow and the trailing edge seems to constitute the largest portion of the overall sound spectrum. Modifications to the trailing edge geometry will change how the fluid interacts with the trailing edge and can be used to change the resulting noise emission. This study will investigate the effect passive trailing edge devices have on the overall noise emission from a wind turbine, in an attempt to reduce the aeroacoustic noise being generated by the turbine.

Experimental Study of Plasma Flow Control on Highly Swept Delta Wing

A ERODYNAMIC flow control based on plasma actuators is now in expansion, because plasma actuators are fully electronic with nomoving parts; they have an extremely fast response, very low mass, low input power, and the easy ability to simulate their effect in numerical flow solvers [1]. In particular, they areflexible, so that they can be formed to various shapes and located on the air vehicles with relative ease. There are no other known actuators that have such flexibility [2]. There are many different plasma actuators, including dielectric barrier discharge (DBD), direct current glow discharge, radio frequency glow discharge, and filamentary arc discharges. Suchomel et al. [3] provided an overview of different plasma generation technologies currently under investigation for aeronautical applications. The actuator used here is based on surface DBD. This new discharge was invented by Roth et al. and protected by a U.S. patent since 1995 [4]. The surface plasma has considerably influenced research on airflow control by plasmas, because the simplicity of its use allowed many researchers in aerodynamics to work on this subject (without necessarily being specialists in plasma generation [5]). Velocity measurements indicate that theprimary result of the averagedplasmainduced body forces is the formation of a wall jet that imparts momentum to the fluid [1]. The plasma actuators for aerodynamic flow control can be applied for different purposes. Examples include boundary layer control [6], lift augmentation and separation control for airfoils [7,8], and control of the dynamic stall vortex on oscillating airfoils [9]. More recently, the plasma actuator has been demonstrated on application in three-dimensional vortical flow controls on delta wings and unmanned aerial vehicle (UAVs) [2,10–12]. Patel et al. [10] used the DBD plasma actuators for hingeless flow control over the 1303 unmanned combat air vehicle wing. Control was implemented at the wing leading edge to provide longitudinal control without the hinged control surfaces. Force balance results showed considerable changes in the lift characteristics of thewing for the plasma-controlled cases, when comparedwith the baseline cases. Compared with the conventional traditional trailing-edge devices, the plasma actuators were demonstrated to have a significant improvement in the control authority in the 15 to 35 deg angle-ofattack range, thereby extending the operational flight envelope of the wing. In addition to the lift modification, Nelson et al. [11] studied the plasma actuator to provide roll control at high angles of attack on a scaled 1303 UAV configuration. It was found to have excellent roll control capability, which was very responsive. Greenblatt et al. [2] investigated the DBD plasma actuator active control of a leadingedge vortex on a semispan delta wing at typical micro aerial vehicle Reynolds numbers. The plasma actuator produced a plasma-induced jet inward from the leading edge. The maximum CL ( 36 deg) increased by 0.2 in the poststall region at the optimum reduced frequency F 1 1. Visbal and Gaitonde [12] deployed asymmetric DBD plasma actuators on the apex of a 75 deg swept delta wing to control the vortical flows by numerical simulation. The actuator was placed at x=c 0:08 and extended in a spanwise direction. The strength of the plasma actuator was chosen to be Dc 2400. The changes near the apex of the wing, induced by the plasma, resulted in significant downstream displacements of the vortex breakdown location. This effect could be potentially beneficial for roll control authority at high angles of attack. Following actuation, the unsteady shear layer evolved into a steady pattern, characterized by stationary helical subvortices. The origin of these steady substructures appeared to be linked to the increase in axial velocity within the secondary vortex, induced by the momentum injection of the actuator. In this technical note, the configurations of the plasma actuator on the delta wing, similar to that used in Visbal and Gaitonde’s simulation [12], are used. The plasma actuators are mounted in different chordwise locations on the leeward side of the delta wing. The effect of the location of the plasma actuator on the aerodynamic performance of the delta wing is studied by the balanced force measurement in the wind tunnel. At last, the smokewire visualization is used to present the flow structure variation induced by the plasma actuator.