Wei Qian

The growth of the wind energy industry has led to the production of increasingly larger wind turbine blades, some extending beyond one hundred meters. However, the substantial dimensions of these blades have significantly inflated the expenses associated with ground tests. This study introduces a novel approach based on stiffness similarity theory. We first derive scaling-similarity equations to deepen understanding the relationship between scaled blades and their full-scale counterparts. Subsequently, a scaled model is constructed based on these equations. Through the application of multi-objective optimization, the model’s accuracy is enhanced. The study’s findings demonstrate the practicality of the sub-scale method, ensuring deformation precision. This methodology presents a viable solution for conducting ground tests during the initial phases of wind turbine blade development, offering a promising alternative for the industry.

Aircraft with a twin vertical tail and leading-edge extension configuration may experience vertical tail buffeting during high-angle-of-attack maneuvering flight. This issue can lead to structural fatigue damage in the vertical tail, shortening its service life and increasing maintenance costs, ultimately compromising flight safety. Therefore, accurate prediction of buffeting loads and responses is essential during design. In the preliminary stage, wind tunnel testing is the primary means to obtain dynamic data such as fluctuating pressure and acceleration response, which can be transformed to full-scale conditions through similitude principles. However, the elastic scaling model used in buffeting tests is usually established for a specific flight condition. When the flow velocity or objective flight condition changes, the similitude relationship becomes invalid, limiting the applicability of test results and preventing full-envelope strength verification. To overcome this limitation, this study proposes a multi-objective point response prediction method for vertical tail buffeting. The method enables the prediction of full-scale responses at multiple objective flight conditions using wind tunnel data that do not strictly satisfy similitude criteria. A complete aircraft vertical tail buffet (rigid/elastic) hybrid model was developed for testing, and an Adjusted Model incorporating elastic scaling transformation was established. The proposed method was validated through experiments, demonstrating improved test data utilization and prediction accuracy across multiple-objective flight conditions.

This paper presents a preliminary investigation into the aeroelastic behavior of a tailless flying wing equipped with a rotating wingtip. Based on the configuration of Innovative Control Effectors (ICE) aircraft, an aeroelastic model of the tailless flying wing with a rotating wingtip has been developed. Both numerical simulation and wind tunnel tests (WTTs) are employed to study the aeroelastic characteristics of this unique design. The numerical simulation involves the coupling of computational fluid dynamics (CFD) and implicit dynamic approaches (IDAs). Using the CFD/IDA coupling method, aeroelastic response results are obtained under different flow dynamic pressures. The critical flutter dynamic pressure is identified by analyzing the trend of the damping coefficient, with a focus on its transition from negative to positive values. Additionally, the critical flutter velocity and flutter frequency are obtained from the WTT results. The critical flutter parameters, including dynamic pressure, velocity, and flutter frequency, are examined under different wingtip rotation frequencies and angles. These parameters are derived using both the CFD/IDA coupling method and WTT. The results indicate that the rotating wingtip plays a significant role in influencing the flutter behavior of aircraft with such a configuration. Research has shown that the rotation characteristics of the rotating wingtip are the primary factor affecting its aeroelastic behavior, and increasing both the rotation frequency and rotation angle can raise the flutter boundary and effectively suppress flutter onset.

This paper presents an innovative aeroelastic solution method called the implicit dynamic approach (IDA). The IDA is a novel technique implemented to address the complexities of structural displacement and fluid–structure interactions. At the core of this method lie the Navier–Stokes equations, which are pivotal for resolving the unsteady aerodynamic forces for studying aeroelasticity. This paper develops a time-step-coupling data-solving interface that bridges the structural dynamic and fluid dynamic domains, ensuring a seamless integration of these two critical aspects of aeroelastic analysis. To substantiate the credibility of the IDA, the aeroelastic responses of a two-dimensional wing and the benchmark supercritical wing (BSCW) are analyzed. The results obtained from these models demonstrate the IDA’s credibility and stability. The IDA proves to be reliable in predicting aeroelastic responses and offers a powerful tool for analyzing aeroelastic problems.

Large transport aircraft tend to adopt a wing layout with a high aspect ratio and swept-back angle due to the requirement of a high lift-to-drag ratio. Composite material is typically employed to ensure the light weight of the structure, causing serious static aeroelasticity problems to the aircraft. When the airplane is flying in the transonic region, its aerodynamic load is very complex, and the large load leads to large deformation of the wing, triggering geometric nonlinear effects, which further affects the static aerodynamic elasticity characteristics of the wing. In this study, in order to study the static aeroelastic characteristics of the transonic flow of a high-aspect-ratio airfoil, a new design method of the scaled similar optimization model is described, and the change in the model lift coefficient due to geometrically nonlinear static aeroelasticity effects when the angle of attack is changed was investigated by using simulation and wind tunnel test methods. In order to ensure the accuracy of the wing shape when the model was deformed greatly, this study employed the structural design scheme of the wing with the skin as the main stiffness component, and the thicknesses of different regions of the skin were used as the design variables for the stiffness optimization design. The engineering algorithm of nonlinear finite elements was used in this study to calculate the curve of lift with the angle of attack considering the geometric nonlinear static aeroelasticity effect. The results show that the similarity optimization process employed in this study can be used to complete the design of the high-speed aerostatic wing test model, and the wind tunnel test results show that geometric nonlinearity has a large impact on the lift coefficient of the wing.

Free-play-induced nonlinear dynamic behavior has been one of the most important topics of aeroelastic research in recent decades. In this paper, the describing function (DF) method is developed to investigate the complex dynamic response of a popular all-movable horizontal tail with free-play. Piecewise expressions for the time history and phase portrait of limit cycle oscillation (LCO) are derived by the developed DF method, which is conducive to understand the mechanism of free-play-induced LCO. Another advantage of the developed DF method is the ability to predict the high-order harmonics, which cannot be realized by the classic DF method. A three-dimensional (3D) all-movable horizontal tail model with torsional free-play was designed and manufactured to implement wind tunnel tests via various initial parameters. A good agreement was found between the numerical and experimental results, which can demonstrate the effectiveness of the proposed method. The influence of the initial parameters of the all-movable horizontal tail on the LCO characteristics is analyzed by both numerical calculations and wind tunnel tests. The method and results in this paper can provide a significant reference for the design of all-movable horizontal tail versus the free-play-induced LCO.

The aerodynamic configuration of large swept-back tri-wings is generally adopted for hypersonic vehicles, but the structural stiffness of the ailerons is weak, which may lead to damage due to the flutter behavior. In the initial stage of structural design, studying the flutter characteristics of tri-wing flight vehicles is necessary and can provide the stiffness index of the tri-wing structural design. To assess the flutter characteristics of tri-wing flight vehicles efficiently, a rapid modeling technique of the finite element method was used in this paper. For the structural scheme of large swept-back tri-wing flight vehicles, a structural dynamic model was modeled using the rapid modeling technique, the unsteady aerodynamic was computed using the double-lattice method, and the flutter characteristics were analyzed using the P-K method. Variable parametric studies were conducted to evaluate the effects of the stiffness of the aileron skin, the stiffness of the control mechanism, and the mass distribution of the aileron on the flutter characteristics of large swept-back tri-wing flight vehicles. The results showed that the key flutter coupling modes of such vehicles are symmetric and anti-symmetric combinations of aileron rotation and torsion. Additionally, optimizing the control mechanism stiffness and mass distribution of the aileron could improve the flutter boundary, which can be helpful in the structural design of such vehicles. The flutter optimization technique effectively improved the flutter boundary, significantly enlarged the flight envelope, and accurately provided the stiffness index for the structural design of large swept-back tri-wing flight vehicles.

In this study, an experimental investigation is performed on a scaled, all-movable horizontal tail to study the aeroelastic behaviors induced by multiple free-plays. The dynamic response in wind tunnel tests is measured by strain gauges, an accelerometer, and a binocular vision measurement system. The obtained results indicate that the present aeroelastic system exhibits highly nonlinear characteristics and undergoes two independent limit cycle oscillations (LCOs) induced by bending free-play and torsion free-play, respectively. Further, various parametric studies are conducted to evaluate the effects of the free-play angles, angle of attack, flow velocity, and gust excitation on the LCOs. It is found that the value of free-play angle has no significant effect on the critical flow velocity which leads to the occurrence of LCOs. The amplitude and frequency of LCOs increase with the increasing free-play angle and flow velocity. Moreover, the horizontal tail experiences high-order harmonic resonances when LCOs appear. Finally, the stability of limit cycles is analyzed based on the gust excitation experiment. Overall, compared to an all-movable horizontal tail with single free-play, the multiple free-plays system exhibits more complex dynamic behaviors. In this paper, the measured results of the scaled model, which has a similar mass distribution and stiffness distribution as actual aircraft, may be valuable for predicting such LCOs induced by multiple free-plays, and providing a reference for the design of all-movable horizontal tail to prevent LCOs.