Gust Load Research Articles

Design of a gust generator and comparison of model wind turbine and porous disc wake flows in a transverse gust

This paper outlines the similarities and differences between the wake characteristics of a porous disc and model wind turbine under transverse gust loading which is generated via a two-vane wind tunnel gust generator. Phase-locked two-dimensional two-component (2D2C) particle image velocimetry (PIV) measurements show that the capability of a porous disc in representing a wind turbine increases under gust loading. Compared to the uniform inflow case, normalized streamwise velocity plots of the porous disc and model turbine are in a better agreement under gusty inflow condition particularly in the near wake region. Comparison of the wake centerlines reveals a similar wavy wake pattern with no significant phase lag suggesting that the gust dynamics is the dominant factor in the determination of the wake dynamics.

Enhancing Flight Envelope for a Nonlinear Aeroelastic Wing-Section Using Adaptive Fuzzy Sliding Mode Control Law

This paper presents an adaptive fuzzy sliding mode controller (AFSMC) for the control of a nonlinear aeroelastic wing section. The proposed controller estimates both the model dynamics of the system and the switching control of the sliding mode. Furthermore, the designed controller’s strategy is to enhance quality and ensure flight safety by providing additional damping to the already stable system and increasing the flight speed beyond the open-loop flutter speed. The aeroelastic system describes the plunge and pitch motions of the aircraft wing-section equipped with leading and trailing edge control surfaces. Additionally, the selected two-degree-of-freedom model includes structural stiffness nonlinearities and quasi-steady aerodynamics. The simulation results show the effectiveness of the proposed controller toward suppressing flutter and LCOs and reducing the vibrational level in the subcritical flight speed range. Additionally, the designed control strategy effectively controls and derives the state trajectories to the origin despite uncertainties and gust loads.

The effect of turbulence intensity on the unsteady gust loading on a 5:1 rectangular cylinder

The present work aims to study the effects of turbulence intensity on the three-dimensional spatial distribution of unsteady gust loading on a 5:1 rectangular cylinder. Three types of grids are adopted to produce uniform turbulent flows with different turbulence intensities and constant integral scales. The experimental results show that the turbulence intensity has a noticeable influence on the gust loading. An increase in the turbulence intensity results in a stronger spanwise correlation of the fluctuating pressures on the side surfaces. To reveal the three-dimensional aerodynamic effects of turbulence, a closed-form solution of a three-dimensional aerodynamic admittance function (3D AAF) is presented based on Ribner's three-dimensional spectral tensor theory. This 3D AAF model is expressed in terms of two-dimensional aerodynamic admittance function (2D AAF) for transversely fully correlated gusts and the gust-related spanwise correlation factor. The proposed 3D AAF can explain the mechanism of the three-dimensional aerodynamic effect of turbulence, which results in a more correlated lift force. It is observed that the filtered bandwidth in the spanwise direction amplifies as the turbulence intensity decreases, suggesting that the large-scale vortices in the separated flow are contaminated by smaller eddies. Consequently, the spanwise correlation of the lift force on a 5:1 rectangular cylinder will have the opposite tendency. Notably, it is confirmed that the 2D AAF depends only on the cross-sectional shape rather than the turbulence intensity.

Gust Alleviation and Wind Tunnel Test by Using Combined Feedforward Control and Feedback Control

Gust alleviation is of great significance for improving aircraft ride quality and reducing gust load. Using aircraft response (feedback control) and gust disturbance information (feedforward control) to improve the gust alleviation effect is worthy of attention. In this paper, a combined control system (CCS) composed of feedforward control system (FFCS) and feedback control system (FBCS) is designed and analyzed. At the same time, the gust alleviation effect of the CCS, the single FFCS and the single FBCS are analyzed and compared by means of numerical simulation and wind tunnel test, respectively. Taking a flexible wing as the research object, the gust alleviation effects of three control systems under different forms of gust excitation (1-cos discrete gust, sine gust and Dryden turbulence) are analyzed by numerical simulation. In the wind tunnel test, the sine gust generated by a gust generator was used, and the gust alleviation test was carried out under different wind speeds and gust frequencies. The simulation and experimental results show that the CCS has better gust alleviation performance for various gust excitations. When comparing FFCS and FBCS, the FFCS has better robustness and control effect than the FBCS. When comparing FFCS and CCS, the better the alleviation effect of FFCS, the more difficult it is to achieve significant effect improvement by using CCS, which is obtained by adding FBCS on the FFCS.

A Polymorphing Wing Capable of Span Extension and Variable Pitch

This paper presents the development of a novel polymorphing wing capable of Active Span morphing And Passive Pitching (ASAPP) for small UAVs. The span of an ASAPP wing can be actively extended by up to 25% to enhance aerodynamic efficiency, whilst its pitch near the wingtip can be passively adjusted to alleviate gust loads. To integrate these two morphing mechanisms into one single wing design, each side of the wing is split into two segments (e.g., inboard and outboard segments). The inboard segment is used for span extension whilst the outboard segment is used for passive pitch. The inboard segment consists of a main spar that can translate in the spanwise direction. Flexible skin is used to cover the inboard segment and maintain its aerodynamic shape. The skin transfers the aerodynamic loads to the main spar through a number of ribs that can slide on the main spar through linear plain bearings. A linear actuator located within the fuselage is used for span morphing. The inboard and outboard segments are connected by an overlapping spar surrounded by a torsional spring. The overlapping spar is located ahead of the aerodynamic center of the outboard segment to facilitate passive pitch. The aero-structural design, analysis, and sizing of the ASAPP wing are detailed here. The study shows that the ASAPP wing can be superior to the baseline wing (without morphing) in terms of aerodynamic efficiency, especially when the deformation of the flexible skin is minimal. Moreover, the passive pitching near the wingtip can reduce the root loads significantly, minimizing the weight penalty usually associated with morphing.

Research on Equivalent Static Load of High-Rise/Towering Structures Based on Wind-Induced Responses

A method of assessing equivalent static wind loads that can represent all the real ultimate states of a high-rise building and towering structure has still not been fully determined in wind engineering. Based on random vibration theory, the wind-induced response and equivalent static wind loading of high-rise buildings and towering structures are investigated using the vibration decomposition method. Firstly, the structural wind-induced mean response, background response, resonant response and background and resonant coupled response are studied in the time and frequency domains. Secondly, a new gust load factor (GLF) assessment method suitable for wind-induced displacement, bending moment and shear force response at any height of the structure is proposed, and a typical high-rise building is used as an example for comparison with the previous research results, in order to verify the effectiveness of the method in this paper. The results show the following: for high-rise buildings and towering structures, the percentage of the coupled components in the total pulsation response is less than 2%, and the influence can be ignored; the GLF based on bending moment (MGLF) and the GLF based on shear force (QGLF) increase significantly with height, and the traditional GLF methods underestimate the maximum wind effects.

Dynamic responses due to the Dryden gust of an autonomous quadrotor UAV carrying a payload

AbstractUnmanned Aerial Vehicles (UAVs) have been used extensively in many applications, such as surveillance, medical transportation and delivery tasks. These applications usually involve an attachment system to connect a payload. However, when connected to such a coupled system, the UAV exhibits lower flight performance mainly due to gust loads. Mathematical modeling is used in this paper to illustrate the comparison between an UAV with a coupled system and a conventional UAV. Proportional Derivative (PD) and Sliding Mode Control (SMC) approaches are used to evaluate the vibrations of the payload, and the UAV trajectory subjected to Dryden gust. This work therefore uses these methods to investigate the dynamic response of a quadrotor-type UAV equipped with a payload and a flexible attachment system.

Coandă-Type Flow Actuation for Load Alleviation

Circulation control has the potential to improve current gust and maneuver load alleviation schemes, with the ultimate goal of reducing wing structure weight and saving fuel. A Coandă-type flow actuator is integrated on the pressure side of a two-dimensional airfoil model, and its load alleviation performance and dynamic behavior are determined experimentally. Quasi-steady force and wake measurements are conducted in a wind tunnel to quantify the effect of the actuator on lift and drag. Lift decrements of are reached for steady blowing, exceeding typical gust-induced wing loads in magnitude. For pulsed blowing, only moderate mass flow reductions of up to 25% are achieved, caused by discontinuous flow turning around the Coandă surface. Unsteady force and pressure measurements characterize the dynamic lift response to the actuation. The total onset time of the lift response, normalized by the ratio of chord length to freestream velocity, is for actuator activation and for actuator deactivation. These values are below typical onset times for gust loads (). The present results show a high-lift reduction potential and fast dynamic behavior of the Coandă-type flow actuator, making it a viable candidate for fast and effective load alleviation.

Design of Gust Load Alleviation Control Based on UD-PSO for Civil Aircraft

Abstract Civil aircraft will produce undesirable normal overload under the disturbance of vertical turbulence or gusts, which will lead to deterioration of the ride quality of passenger. To solve this problem, a design scheme of gust load alleviation (GLA) control based on UD-PSO optimization is proposed. Firstly, design a classical gust load alleviation control strategy in the control system. The GLA controller will automatically generate the control command, which is calculated by the sensor feedback signal of turbulence or gust. That is, the aileron and spoiler are deflected in the same direction to counteract the undesired normal overload; at the same time, the elevators are deflected to ensured the longitudinal stability of the aircraft. Then, selects a suitable reference model and a reasonable objective function to achieve the desired ride quality performance index. Finally, the UD-PSO algorithm is used to automatically optimize the controller parameters. The simulation results show that the load alleviation control strategy optimized based on UD-PSO can effectively reduce the gust interference, improve the ride comfort, and achieve a good control performance, which shows the effectiveness of the proposed method.

Adaptive power management algorithm for multi-source DC microgrid system

Abstract In this work, an adaptive power management algorithm is developed for a multi-source dc microgrid system. The proposed algorithm is tested with a dc microgrid system consisting of PV, wind, batteries, supercapacitors, and variable load. The PV and wind energy systems are operated in maximum power point tracking mode to extract maximum energy from the available wind power and solar irradiation. The proposed algorithm has considered wide variation in weather conditions like zero wind velocity, zero solar irradiation, wind gust, and dynamic load change at the dc bus. For these cases, the proposed algorithm maintains the dc bus voltage constant without using a communication link. The efficacy of the proposed algorithm is tested using MATLAB-Simulink. Also, the feasibility and effectiveness of the proposed algorithm are validated using OPAL-RT control platform-based experimental studies.

Unsteady Aeroelastic Analysis of the Semi Aeroelastic Hinge Including Local Geometric Nonlinearities

A recent consideration in aircraft design is the use of folding wing tips, with the aim of enabling higher aspect ratio wings with less induced drag but also meeting airport gate limitations. Of particular interest is the concept of using in flight free-floating wing tips in order to reduce aircraft gust and maneuver loads. This study investigates the effects of local geometric nonlinearities on the dynamic stability, postflutter behavior and gust response of floating wing tips. A multibody formulation is introduced to account for finite rotations of rigid folding wing tips attached through hinges on a flexible airframe structure including also aerodynamic follower forces for the folding wing tip components. It is found that the postflutter behavior is characterized by super-critical limit cycle oscillations and no subcritical instability was observed for the analyzed cases. Moreover, the wing tip gust response can vary significantly when geometric nonlinearities are accounted for whereas a small impact was observed on the main airframe structure.

Energy harvesting from the gust response of membrane wing using piezoelectrics

Micro-air vehicles face challenges in aerodynamic and endurance. This paper presents a novel gust response-based membrane wing energy harvester to solve these issues. An aero-electro-mechanical model based on CFD/CSD coupling method is established to investigate the dynamic response and the energy harvesting performance of this energy harvester under harmonic gust loads. The geometric nonlinearity of structure and aerodynamic nonlinearity are considered in this paper. The harmonic gust loads were obtained from a Navier–Stokes CFD solver based on unstructured meshes. The large deformation electro-mechanical finite element model was built based on the updated Lagrangian formulation and the principle of virtual work. The mean power density is defined to evaluate the energy harvesting performance. The effects of the external load resistance, the PVDF patch location, the gust amplitude and frequency, and Reynold number are studied, respectively. The results show that the optimal resistance of this energy harvester is 1.6kΩ, and the flexibility of the membrane wing improves the aerodynamic and energy harvesting performance greatly through increases the amplitude of odd super harmonics. The PVDF location has a relatively small impact on the energy harvesting performance except near end surfaces. The PVDF patch located at 0.1c–0.9c all can get better energy harvesting performance. When the equivalent angle of attack of gust amplitude exceeds 4 deg, the energy harvesting performance decreases slightly due to the formation and convection of leading-edge vortex. A sustained output power density of 5.31mW/cm3 is harvested at Re=25,000. The present work provides an effective theoretical basis for further studying energy harvesting of Micro air vehicles.

Investigation of load alleviation in aircraft pre-design and its influence on structural mass and fatigue

This work elaborates an aircraft pre-design process that integrates loads analysis, load alleviation, structural optimization and fatigue analysis. The consideration of maneuver and gust load alleviation in early design stages is a promising concept to reduce wing bending moments, structural mass and extend the fatigue life, as shown on two mid-range configurations: one with a backward and another one with a forward swept wing respectively. In the loads analysis, quasi-steady maneuvers and dynamic 1-cos gusts are considered. For the load alleviation, the ailerons are deflected symmetrically. While the maneuver load alleviation reacts to the commanded load factor, the gust load alleviation reacts to fluctuations in the angle of attack. With the selected loads from the simulations, the structure of the wing and horizontal tailplane (HTP) is optimized toward mass minimization. The constraints considered are material strength, buckling stability and static aeroelastic requirements. The steps comprising loads analysis and structure optimization are conducted iteratively until the wing box mass converges. The load alleviation yields a reduction of wing box mass by 2.8% on the backward and 6.1% on the forward swept wing configuration. A subsequent, qualitative fatigue analysis is carried out to compare the fatigue behaviors of the active and passive aircraft (with and without load alleviation). For the reference missions, loads due to continuous turbulence and ground-air-ground cycles are considered, and the fatigue life of the active aircraft is improved by 28% and 12% respectively, on top of the mass benefit. As a conclusion, the proposed process can serve to gain an insight into the effects of load alleviation on the design loads, mass reduction and the resulting change in the fatigue behavior of a given aircraft in the pre-design phase, before it advances to the next design stage.

Multidisciplinary Optimal Design of an Active Control System and State Estimator for an Aircraft Wing

A multidisciplinary and multi-objective optimization approach that integrates the design of the control surfaces’ sizes, active control system, and estimator for an aircraft’s wing with three control surfaces is developed in this paper. Four objectives are considered: minimizing impacts of external gust loads, maximizing stability robustness, reducing control energy consumption, and minimizing the Frobenius norm of the estimator gains. For simulation purposes, a mathematical model of a flexible wing having three ailerons is used. The control system and observer are designed simultaneously. The optimization problem is formulated and solved by NSGA-II (non-dominated sorting genetic algorithm II). The solution of the optimization problem is called the Pareto set and the corresponding set of function evaluations is called Pareto front. The properties of the Pareto set and Pareto front; sensitives of the dominant poles of the open-loop system, closed-loop system, and estimator to the airspeed; and responses of the controlled, uncontrolled, and observer models at selected objective values are obtained. The results shows that the simultaneous design of the control and estimator algorithms, and the geometry of the ailerons in the multi-objective settings is very effective, the closed-loop control system can suppress the flutter and stabilize the system, and the estimator converges very quickly and always stable regardless of the air stream velocity.

Observer-based gust load alleviation via reduced-order models*

In this paper, we investigate the design of linear active output feedback control for aircraft gust load alleviation, involving standard sensors and control surfaces. The control architecture is composed of (i) a robust observer, allowing for estimating some wing bending moments despite the wind perturbation, and (ii) a structured H∞-norm oriented control law exploiting this additional information. To cope with the complexity of the aeroelastic model and make the control and observer synthesis computationally tractable, a model reduction step, based on Petrov-Galerkin projections, is first applied. One specificity of this work is that the obtained projector is exploited in the observer design, linking the reduction and the estimation. The effectiveness of the methodology is illustrated through numerical simulation involving an open access high complexity aeroelastic model.

適応的空力弾性制御モデルの構築と風洞実験による検証 ---圧力制御と翼端変位推定---

GLA (= Gust Load Alleviation) control is an important active safety technology, especially for light-weight flexible wing aircraft with high aspect ratio wings. This paper proposes an adaptive aero-servo-elastic model for control design, including an aerodynamic load distribution estimator using in-flight partial pressure sensing. The GLA control law obtained based on the proposed model consists of pressure control and mode estimation. In general, aero-servo-elastic models require an wing structure dynamics and an aerodynamic model around the wing. However, it is difficult to construct a generic model in advance for complex unsteady aerodynamic phenomena where turbulence and vibration of flexible wings interact. In this case, the optimality and the reliability of a model-based GLA control is significantly reduced. To minimize the uncertainty of the model for unsteady aerodynamics, this method proposes the use of an autoregressive model with time-varying coefficients, which are updated in real-time based on in-flight pressure sensing. The feasibility of the proposed GLA scheme is demonstrated in terms of both pressure control and wing tip displacement estimation through wind tunnel experiments.

Aerodynamic effects of a folding wingtip to increase take-off, landing and cruise performance.

The main purpose of a folding wing tip is to allow aerodynamically efficient high aspect ratio wing. To allow a wing tip to move in flight is to alleviate the loads and achieve lower wing weight or enable wing span to maximize. Thus reduces the induced drag and improve fuel efficiency. The folding wing tip may include spring devices in order to provide an additional gust loads alleviation ability in flight. A wing without a winglet produces wingtip vortices which increases drag as the air from the bottom surface of the wing (high pressure) tries to move to the upper surface (low pressure). To avoid this and have less vortices a winglet is used, around which the flow is same on both surfaces. A folding wingtip can be set at an angle of 0° to have maximum cruise performance and aspect ratio. If the wingtip is set in the range of 15°-50° it can increase lift during take-off. This folding wingtip can access any airport in the world because if it is folded at an angle of 90°, it can meet the gate requirements and restrictions of any airport. To study the performance of this mechanism, the wing tip was designed by using CATIA V5 software. The analysis of the wingtip at different angle of attacks was done using ANSYS and XFLR 5 softwares.

A review of approaches to generate equivalent static and synthetic wind loads on tall buildings for the preliminary stage of design

The extraordinary urbanisation of cities in recent decades urges us to consider the efficient design of tall buildings. Because of the increased flexibility of slender buildings, wind loads are expected to dominate the design loads. Although there are widely accepted wind tunnel techniques for obtaining wind loads on tall buildings, they are time-consuming and may be inconvenient in the pre-concept design process, when structural engineers would like fast and low-priced methods to predict the wind loads over the height of tall buildings. This paper mainly reviews the gust loading factor including other semi-empirical approaches and mathematical approaches for generating equivalent static and synthetic wind loads on tall buildings. Although stochastic simulations and time series analysis methods have limited use in generating wind loads on tall buildings, they are also briefly examined. Based on the findings of this review the paper concludes that it is definitely viable for synthetic wind approaches to be used to speed up the preliminary design process when large numbers of structural systems need to be assessed rapidly.

Active Flow Control Devices for Wing Load Alleviation

Active flow control has not found wide application in aircraft due to a combination of technical challenges, costs, and small impact on overall aircraft performance. Future applications, like alleviating dynamic loads, could be made possible through continuous improvement of flow control methods and increasingly restrictive environmental regulations. To date, few studies deal with active flow control for load alleviation on transport aircraft wings at high Reynolds and Mach numbers. A systematic assessment of flow control methods for load alleviation is therefore carried out. Multiple flow actuation schemes for gust load alleviation through dynamic lift reduction are investigated over a range of flight conditions using two-dimensional Reynolds-averaged Navier–Stokes simulations. Unsteady gust interactions with a clean airfoil produce target loads for load alleviation. Actuator performance is consequently evaluated based on an engineering model. The results show that select fluidic actuators outperform micro-mechanical actuators at low flight speeds and feature similar steady load response as trailing edge flaps for the entire flight envelope. The Coandă jet features relatively low mass flow requirements, but necessitates minimal dual-slot blowing for baseline performance recovery. The results of this study highlight the potential of fluidic flow control schemes for implementation into a dedicated gust load alleviation system.

Gust load alleviation on an aircraft wing by trailing edge Circulation Control

This paper reports an investigation of gust load alleviation using Circulation Control for a three-dimensional wing including aerodynamic and structure interaction. The Field Velocity Method is introduced to the unsteady Reynolds averaged Navier–Stokes solutions for gust response simulations. Structural dynamic equations of motion are coupled with the unsteady Reynolds averaged Navier–Stokes solutions to consider the aeroelastic effects due to the gust response. The effects of gust load alleviation on the BAH wing using Circulation Control are tested under typical ‘one-minus-cosine’ gust profiles from certification specification defined by European Aviation Safety Agency. The results show a promising capability of Circulation Control for gust load alleviation as significant gust load alleviation effects have been achieved for both the rigid and elastic BAH wings in the test cases. For the BAH wing considering aeroelasticity, the displacement oscillations induced by gusts have been effectively suppressed by Circulation Control. The results also show that Circulation Control has the fast frequency response characteristics, where more than 50% of the total change in lift coefficient can be obtained within the non-dimensional time s =U∞tc¯=1.