Flap Actuation Research Articles

Self-Repairable Carbon Fiber-Reinforced Epoxy Vitrimer Actuator with Multistimulus Responses and Programmable Morphing.

Smart shape-changing structures in aerospace applications are vulnerable to damage in harsh environments. Balancing high mechanical performance with self-repair capabilities poses a challenge due to inherent trade-offs between strength and flexibility. To address this challenge, an asymmetric bilayer-structured actuator was fabricated using commercially available continuous carbon fiber tows (CFs) as the passive layer and a dynamic cross-linked epoxy vitrimer as the active layer. The construction of the vitrimer-CF actuator involves a simple and scalable hot-pressing process, resulting in a tensile strength of 234 MPa and an interfacial bonding strength of 405 N·m-1. This actuator exhibits remarkable deformation capability (210°/7 s) and an efficient self-repair ability under various stimuli, including thermal (60-160 °C), light (0.4-1.0 W·cm-2), electric (2-4 V), and solvent (acetone). By adjustment of the orientation angle of CFs, complex left-handed and right-handed curling structures can be achieved. Leveraging the insights from photothermal/electrothermal actuation mechanisms, a quadruped crawling robot is developed capable of crawling 4 cm with a single light illumination. The actuator can lift objects 45 times its weight when subjected to light stimuli. Additionally, a flap actuator is constructed to achieve an angle change of 63° within 10 s under an electric stimulus, enabling remote control over the aircraft flight angle. These results demonstrate the potential of the vitrimer-CF actuator for advanced applications in intelligent aerospace structures.

Self-driven intelligent curved hinge based on shape-morphing composites

The space deployable structures based on shape memory polymer composites (SMPCs) possessed excellent self-deployable performance, which effectively avoided the impact and electromagnetic pulse (EMP) caused by the explosion of pyrotechnic devices. In this work, two types of self-driven curved hinges with different angles of 80° and 115° (Type 80 and Type 115) were designed based on SMPCs. The thermomechanical properties and time–temperature-dependent viscoelastic behaviors of SMPCs were systematically investigated. The three-point bending performance and cyclic shape memory performance of the developed hinges were also characterized. In addition, the deployment performances of Type 80 driven 350 g object under different heating powers were investigated in the environment of ± 70 °C and 103 Pa atmospheric pressure. A staircase-like heating strategy was proposed to achieve precise and controllable deployment under this environment. The developed self-driven curved hinges were expected to have tremendous application potential on the flap actuators and optical payload rotating platforms of the satellites.

Active alleviation of fatigue stress on blades by adaptively maneuvered deformable trailing edge flaps (DTEF).

The concept of "smart rotor" is an evolving advancement in wind turbine which enables an intelligent active flow control in rotor. The deformable trailing edge flap (DTEF) is a part of smart rotor concept which implements a customized active load control. The trailing edge flap actuator effectively replaces the tedious blade pitch actuation and conserves the actuation energy required for pitching the entire blade. The DTEFs require a fast computing, anticipatory controller for optimally tuning the flap angle with minimal power compromise. This work analyzes the performance of advanced control strategies like model predictive control (MPC), adaptive MRAC control, and DQ controllers. The MRAC controller is found to reduce the fatigue stress by 40% and the MPC controller damps up to 70% more efficiently than the typical feedback controller. The control strategies are aided by the LiDAR-based preview wind data for the active manipulation of trailing edge flap angle control. The validation of proposed controller is done using power analysis curve and the component fatigue lifetime analysis using MLIFE software. The above analyses are done in NREL Onshore 5-MW FAST wind turbine model which could be interfaced with MATLAB with modified AeroDyn code for active flap deflection.

Optimal Sizing of Trailing Edge Flaps for Helicopter Vibration Reduction: A Response Surface Approach

On-blade active trailing edge flaps are considered for helicopter vibration reduction. A Pareto optimal multi-objective optimization approach is used to obtain the spanwise and chordwise dimensions of single and dual trailing- edge flaps. The objective of this study is to simultaneously achieve minimum hub vibration levels and minimize the flap actuation power requirement. Helicopter aeroelastic analysis is used in conjunction with an optimal controller to minimize hub vibration and flap power levels. It is found that nonlinear polynomial response surfaces based on L9 orthogonal array could adequately describe both the objectives. An intense sampling of the surrogate objective space is used to obtain optimal design points for the mutually conflicting objectives. A Pareto optimal design reduces vibration levels by about 70% and also reduces flap actuation power requirement by about 20%, in comparison to the initial design. The present study leads to an optimal design of trailing edge flaps which expend less power and can be further explored for self-powered control surfaces towards a self-powered smart blade design concept. The optimal designs are robust to uncertainty introduced by manufacturing.

Magnetic actuation of bistable flaps for kinetic building shades

Kinetic building envelopes can significantly improve energy efficiency by adapting to changing outdoor conditions. A challenge for the widespread implementation of kinetic envelopes is related to the complexity and cost of conventional mechanical actuation. Current trends in kinetic building design have proposed embedding smart materials for actuation within kinetic shades and simplifying the shape-morphing mechanisms. This paper reports on a study that aims to characterize magneto-active elastomers (MAEs) as actuators for bistable kinetic shadings. In particular, this study seeks to determine adequate bistable and MAE configurations and their potential to deform a bistable kinetic shading setup. The studies characterize the force and displacement of two types of MAEs materials fabricated by embedding magnetic fillers into different soft polymeric matrices- polydimethylsiloxane (PDMS) and polyvinyl alcohol (PVA) hydrogel. In addition, we compared the actuation capabilities of both MAE-PDMS and MAE-PVA and studied the effect of changing the boundary condition of bistable laminates. The results suggest that MAE materials can actuate bistable composites remotely. The boundary condition study found that clamping 25% of the laminates' height reduced the magnetic field required for actuation by 29% and thus might be a suitable design strategy. This study adds magnetic actuation to the growing body of work on kinetic envelopes and smart materials, contributing to a deeper understanding of the required application conditions of MAEs.

Gust alleviation by spanwise load control applied on a forward and backward swept wing

The present paper investigates the feasibility of gust load alleviation at transonic speeds on a backward swept and a forward swept transport aircraft configuration. Spanwise-distributed control surfaces at the leading and trailing edges are employed to control gust-induced wing bending as well as wing torsion moments. The deflection amplitude and temporal flap actuation are determined by a novel scheme that builds on the aerodynamic strip theory. The aerodynamic effectiveness of the actuators is taken from a data base, computed from either 2D infinite swept wing simulations, or from yawed computations that take the effects of boundary-layer cross flow and the local sweep angle of the control surface into account. The present numerical flow simulations reveal that careful application of control laws at the trailing edge alleviates wing bending moments caused by strong vertical gusts by 85–90%, for both aircraft configurations. The application of leading-edge flaps introduces significant nonlinear aerodynamic interactions, that make the control of torsional moments comparably challenging. Here, the present results indicate that about 60% of wing torsion loads due to strong gusts can be removed.

Research on Dynamic Characteristics of Flap Actuation System Considering Joint Clearance and Flexibility

The flight control effects and flight quality of the aircraft are influenced by the flap actuation system directly. The main motivation of this research is to develop a rigid-flexible model of the flap actuation system with clearance and to explore the coupling effects of clearance joints and flexible bodies on the system’s dynamic characteristics. A modified contact force model is used to a joint with small clearance, heavy load, and large contact area. Then, the effectiveness of an embedded modeling method of this modified model is verified. Based on this method, a rigid-flexible coupling model of the flap actuation system with multi clearance joints is established. Moreover, the influence of system parameters, such as clearance size and clearance joint position, and coupling effects of the flexibility and joint clearance on dynamic responses, are analyzed. The results show that: (1) flexible bodies act as a suspension to reduce negative effects of joint clearance on dynamic responses of a clearance-contained system; (2) one flexible body can reduce the oscillation phenomenon of joint clearances, yet the suspension effect will be gradually weaken with the increase of the clearance joint number; (3) coupling effects of the elastic deformation owing to multi flexible bodies and the collision interaction between multi clearance joints make the system tend to chaos, and the system stability is reduced. This study can contribute to predicting the collision characteristics of the aircraft transmission system and improving the transmission accuracy, response speed, and stability of the aircraft.

Influence of the installation of a trailing edge flap on the vortex induced vibrations of a wind turbine blade

This work explores the use of a trailing edge flap for the mitigation of the Vortex Induced Vibrations (VIV) of a wind turbine blade in standstill. Fluid structure interaction simulations are performed, coupling a computational fluid dynamics code with a multi-body structural solver. A publicly available 96 m long wind turbine blade is selected for the study, and labeled as IEA 10MW. The effects of a flap actuation in the range [−90°, 90°] are analyzed, for a given set of inflow conditions, and compared to the aeroelastic response of the original IEA 10MW geometry. While the consideration of the flap does lead to reductions on the amplitude of the edgewise vibrations, these are only noticeable when operating outside of the design limits of the aerodynamic device. A simple non-dimensional analysis seems to indicate that the potential of the flap installation with regards to VIV mitigation is very limited, as the instability is only shifted towards different inflow conditions and the expected effects on the maximum amplitude of vibrations are minor.

Unsteady Effects of Blowing over Actuated Surfaces Using Phase-Locked Particle Image Velocimetry

An experimental study is conducted to investigate the effects of upper-surface trailing-edge blowing on a low-aspect-ratio rectangular wing with an actively actuated flap. Two wing configurations, the wing with a baseline flap and a dual-radius flap, are wind-tunnel tested at three spanwise locations to investigate the three-dimensional and unsteady effects of blowing during flap actuation at a freestream Reynolds number (based on the airfoil chord) of . Two-dimensional and stereoscopic phase-locked particle image velocimetry (PIV) measurements are used to collect data during flap actuation at different actuation speeds and blowing intensities. Proper orthogonal decomposition and modified Q criterion are used to analyze the PIV data. The wake dynamics reveal that flap actuation contributes to tip-vortex strengthening when active blowing is not present. The combination of flap actuation and active continuous blowing is more effective in controlling the boundary layer compared to the flap at rest for the same blowing intensities.

A comprehensive fracture research of an aircraft swash-plate pump

Aviation pumps are widely used to feed the actuators of the components such as the aileron, flap, slat, rudder, elevator, and landing gear of an aircraft. The swash-plate pumps are the most popular ones of the aviation pumps. This study analyses the failure of a jet aircraft’s swash-plate pump mounted on the inner wing and has the function of feeding the flap actuators. After the pump’s failure had been discovered and an investigation was performed. At first, the Foreign Object Damage (FOD) originated from a foreign particle carried by hydraulic flow attracted the doubts. But after further fractographic analysis, it was shown that a micro-crack on the slipper retainer holes had initiated the asymmetric loads and led to cross-section friction on the Swash-Plate surface. It was an Inner Object Damage (IOD). Some suggestions for preventing the lack of lubrication in the slipper retainer holes are given in this paper.

Test of an active flap system on a 4.3 MW wind turbine

This article describes a field test performed on a 4.3 MW wind turbine with one blade equipped with an active flap system. The results presented focus primarily on the steady state and periodic characterization of the active flap system in different deflection states. The tests were performed between 2020 and 2021 on a test turbine in northern Denmark in close-to-shore conditions. The active flap system is primarily characterized based on the load response of the flapwise bending moment of the blades. Flap actuations are performed both as open-loop on-off swaps (shifting between two different flap positions at fixed time intervals) and as closed-loop 1P activations (cyclic activation of the flap both in phase and counterphase with the blade azimuthal position). For the steady state swap tests, the impact on flapwise bending moment ranges between 3% and 20% depending on the flap actuation level and the wind speed. For the cyclic flap tests, the load impact is based on blade-to-blade fatigue load comparison, showing a potential load reduction of approximately 13%.

Inflow and pressure measurements on a full scale turbine with a pressure belt and a five hole pitot tube

We present an autonomous add-on measurement system for detailed aerodynamic measurements on full scale turbines. From the measured data we can derive the local aerodynamic coefficients for the blade section and e.g. compare with wind tunnel data for a similar section. This forms the basis for evaluating how well the airfoil performs on a rotor in the turbulent inflow and rotating environment. We describe the measurement system which comprises a pressure belt with 15 taps, a flyboard with the data acquisition system and a five hole pitot tube measuring the local inflow to the blade section. The system was used on a SWT-4.3-120 DD turbine in a short campaign in June 2021. A trailing edge flap system is installed on that turbine and a particular objective with the measurements was to evaluate the static and dynamic performance of the flap system. The aerodynamic measurements were correlated with the SCADA and flap actuation data. Overall the measurement system performed well and provided good data like smooth pressure distributions. The derived flap performance in the form of the delta lift coefficient was close to what has been measured in wind tunnel tests. Finally, the aerodynamic and aeroelastic dynamic time response of the flap actuation could be characterized with good precision.

Gust mitigation through closed-loop control. I. Trailing-edge flap response

In this work, we quantify and model the unsteady lift response to dynamic flap actuation from wind tunnel experiments at Re = $1.8\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The quantification relies on two newly proposed metrics that characterize the dynamic lift hysteresis and allow describing its evolution under different pitching conditions. The modeling strategy yields one nonlinear model and a set of linear models relating the unsteady airfoil lift coefficient distribution to the flap deflection angle $\ensuremath{\delta}$.

Lift Disturbance Cancellation with Rapid-Flap Actuation

Mitigation of vertical aerodynamic disturbances by means of a simple mechanical flap is investigated experimentally. A wall-to-wall NACA 0006 wing is bisected about the midchord for a 50%-chord flap length. Experiments are performed in a water tunnel at a chord-based Reynolds number of . The wing is driven in a sinusoidal vertical plunge motion as a spatially uniform, temporally varying surrogate to a vertical disturbance. Concurrently, the flap is actively deflected in a survey of kinematic parameters designed to suppress the influence of a plunge-induced disturbance. Plunge rates explored amount to disturbances incurred over a temporal range from one convective time to eight convective times. Two methodologies are employed to guide selection of flap deflection phase and amplitude necessary to preserve the baseline zero-lift state () of the undisturbed wing. In the first method, Theodorsen’s model is applied to arrive at an analytical solution to flap kinematics for a given prescribed plunge history. The theoretical derivation makes the standard assumptions of attached flow, planar wake, and no leading-edge vortical formations. Direct force measurements reveal reduction in lift transients by flap actuation of up to 87%, verifying the applicability of Theodorsen’s classical model. Further improvement is sought in a second method where empirical state-space modeling is formulated for lift cancellation. In this approach two separate lift models for wing plunge and flap deflection are constructed independently, and their superposition is employed to approximate the total lift in combined plunge and deflection motions. It is shown that although the empirical state-space approach performs similar to the inviscid theory of Theodorsen’s model, the empirical model proves more effective in suppressing the formation of the leading-edge vortex induced by plunge.

Novel Bio-Inspired Algorithm for Speed Control and Torque Ripple Reduction of Switched Reluctance Motor in Aerospace Application

Switched Reluctance Motor (SRM) is an electrical motor which operates by a reluctance torque that has stator and rotor salient poles. It also has a simple configuration and reasonable power electronics necessity for both AC and DC machines within adjustable-speed drives. The problem working on it is, SRM with doubly salient poles introduce a torque ripple in its output which leads to deteriorated performance on speed control. In this proposed work, torque ripple reduction and speed control of SRM is implemented, utilizing an asymmetrical converter with PI-PWM controller with the aid of Bio-inspired algorithms. By utilizing the best value of flux, torque ripple and integral square error of speed and settling times, controller design is performed. The proposed research work compares three optimization algorithms namely Crow Search Algorithm, an Improved Ant Lion Optimization Algorithm and Modified Chaotic Starling Particle Swarm technique to control the speed and torque reduction of SRM in aerospace applications. To obtain the optimal parameter values, optimization techniques are introduced and the optimized controller results are compared with other conventional controller results. In normal operation, the engine operates with two phases simultaneously, but it is modelled to meet the load specification, which is single and double phase faulty. Detection of fault gives a great outcome in control of an electrical drive system. Reduction of faulty operation time leads to better motor lifetime that is obtained by early detection of a fault. This paper presents how the five-phase switched reluctance motor is designed to meet the needs of flap actuators in mid-sized aircraft. Electrical systems are modelled to provide the right functionality at the right time in advanced aircraft. However, requirement of power for the landing gear and secondary flight control only a short duration. The system is powered on and off as required, thus preserving power. Control performance and fault analysis were verified by the results of the MATLAB simulation. Experiments have been carried out more effectively to compare the results obtained with those of simulations.

Predicting Wind Turbine Wake Breakdown Using a Free Vortex Wake Code

When modeling wind turbine wake recovery, the location of wake breakdown plays a crucial role. The breakdown is caused by a rapid deformation of the helical near-wake vortex structure that is triggered by the pairing of successive blade tip vortices. In this paper, the capability of a cost-efficient lifting-line free vortex wake code to accurately predict the wake breakdown location and its underlying mechanisms is demonstrated and validated against simulation results of a large-eddy simulation solver and additional data from the literature. Furthermore, this work investigates a technique to accelerate the breakdown of wind turbine wakes. The onset of wake breakdown is caused by perturbations that travel along the helical structure of the wake and grow via mutual-induction interaction between neighboring vortex filaments. To accelerate wake breakdown, the blade tip vortices are perturbed at different frequencies via trailing-edge flaps located in the outboard region of the rotor blades. Through the evaluation of the perturbation growth rates and the analysis of velocity fields, it is shown that for a multi-megawatt wind turbine operating in a turbulent wind field, the wake breakdown position can be significantly affected by a moderate flap actuation amplitude if excited at an appropriate frequency.

Cooling of Electromechanical Actuator Motors by Air Recirculation

In this study, two generic electromechanical actuators were thermally investigated whilst resisting a steady load for nine minutes. The EMA's represent flap actuators that will be housed in the aircraft wing bay. The research aimed to identify temperature hotspots and overheating concerns followed by proposing cooling methods. The motors driving the EMA's have windings on the rotor separated from the stator and housing by an airgap clearance. The airgap imposed high thermal resistance and formed insulation around the stationary rotor; thus, containing high heat and temperature variations that needed to be managed. The study employed two modifications to the original structure of the motor to numerically evaluate viable cooling options.

Pressure based active load control of a blade in dynamic stall conditions

A proportionate controller is investigated experimentally for unsteady load alleviation purposes on a 2D wing model with a trailing-edge flap. The controller acts on the velocity of the flaps, and pressure sensors are used to detect the unsteady loads, which are generated by actuating the wing model in a sinusoidal motion. Two different regimes are considered: attached flow and dynamic stall. The influence of actuation frequency and controller time lag is also studied. A reduction of 87.5% in the standard deviation of the lift is obtained for a frequency of 0.2Hz and time lag in the control system of 12ms for attached flow conditions. The reduction of the standard deviation of the lift deteriorates for increased frequency and time lag. The proposed controller is also able to reduce the loads during dynamic stall, although the reduction is smaller, close to 40%, and can negatively affect the aerodynamic damping of the model. The flap actuation is also shown to delay the onset of dynamic stall, by increasing the static stall angle with respect to the case without flap deflection.

Study on the dynamic interaction of multiple clearance joints for flap actuation system with a modified contact force model

To analyze the effects of clearance joint number and dynamic interaction on responses of the flap actuation system, a dynamic analysis model is proposed based on a modified contact force model. The modified contact force model can take contact properties with small clearance, heavy load, large contact area and variable contact stiffness coefficient into consideration for the flap actuation system. Numerical results show that the actuation system presents violent fluctuation due to the dynamic interaction between multiple clearance joints, and the clearance joint closest to the input part suffers more serious contact effects. Furthermore, the combination motion modes between the multiple clearance joints are helpful to judge and analyze the motion state and dynamic behaviors of actuation systems. These simulation findings can provide a theoretical foundation for the optimization design, control strategy and engineering experiments of the actuation systems with multiple clearances.

Separated Flow Response to Rapid Flap Deflection

The transient response of a massively separated flow over an airfoil to rapid flap actuation is presented. A NACA 0006 airfoil is oriented at a fixed incidence of 20 deg for a Reynolds number of . The experiments are performed in a water tunnel with a wing spanning the width of the test section to produce a nominally two-dimensional flowfield. The airfoil is bisected about the midchord position, resulting in a 50%-chord trailing-edge flap. The flap is rapidly deflected in a smoothed-ramp profile over a range of deflection speeds and amplitudes. The flap maneuver is completed in a fraction of a single convective time. Focus is given to a deflection amplitude of 2 deg to minimize geometric deviation from the nondeflected configuration. The desired response to such a flap motion is the evocation of vortical transients conducive to lift enhancement. Through this study, two distinct transient responses are observed that are directionally dependent on flap actuation. In motions resulting in an increase in airfoil camber, the lift is increased instantaneously to modest values before relaxation to a separated steady state. In effect, this mode expedites convergence to the steady-state value of the final airfoil configuration and is devoid of the “antilift” spike associated with the discrete actuation of conventional fluidic actuators. In motions resulting in a decrease in airfoil camber, the lift profile is characterized by an initial reduction before a surge in lift, culminating in a global peak and followed by relaxation. Both deflection modes prove disruptive to the leading-edge shear-layer dynamics through trailing-edge actuation and are cause for rollup of a leading-edge vortex. Ridges of the finite-time Lyapunov exponent field are used to determine that the net decrease in camber motion induces significant entrainment near the trailing edge, leading to a smaller recirculation region and reattachment of the flow above the suction surface trailing-edge region. The net increase in camber motion does not generate this entrainment, and therefore yields a significantly larger recirculation region.