Search Results (11)

An active rotor with trailing edge flaps (TEFs) is an effective method for helicopter vibration elimination. The nonlinear hysteresis of piezoelectric actuators used to drive TEFs can adversely affect helicopter vibration control performance. In this paper, a hysteresis modeling and compensation study is performed for piezoelectric actuators used in TEFs. Firstly, the hysteresis characteristics of a rhombic frame actuator with input voltages at different frequencies are investigated by bench-top tests. Subsequently, the Bouc–Wen model is adopted to establish the hysteresis model of the piezoelectric actuator, with its parameters identified through the particle swarm optimization (PSO) algorithm. Experimental results demonstrate that the proposed model is capable of accurately capturing the hysteresis phenomenon of the piezoelectric actuator within the frequency range of 10–60 Hz. Finally, a compound control regime is established by integrating inverse Bouc–Wen model control with fuzzy PID feedback control. The experimental results indicate that the developed compound control regime can significantly suppress the piezoelectric actuator hysteresis of TEFs within the frequency bandwidth of 10–60 Hz, which lays the foundation for improving the vibration control performance of the active rotor with TEFs in the future. Full article

Conventional methods for solving Navier–Stokes (NS) equations to analyze flow fields and aerodynamic forces of airfoils with trailing edge flaps (TEFs) are known for their significant time cost. This study presents a Multi-Task Swin Transformer (MT-Swin-T) deep learning framework tailored for swift prediction of velocity fields and aerodynamic coefficients of TEF-equipped airfoils. The proposed model combines a Swin Transformer (Swin-T) for flow field prediction with a multi-layer perceptron (MLP) dedicated to lift coefficient prediction. Both networks undergo gradient updates through the shared encoder component of the Swin Transformer. Such a trained network model for computational fluid dynamics simulations is both effective and robust, significantly improving the efficiency of complex aerodynamic shape design optimization and flow control. The study further investigates the impact of integrating multi-task learning loss functions, skip connections, and the network’s structural design on prediction accuracy. Additionally, the effectiveness of deep learning in improving the aerodynamic simulation efficiency of airfoils with TEF is examined. Results demonstrate that the multi-task deep learning approach provides accurate predictions for TEF airfoil flow fields and lift coefficients. The strategic combination of these tasks during network training, along with the optimal selection of loss functions, significantly enhances prediction accuracy compared with the single-task network. In a specific case study, the MT-Swin-T model demonstrated a prediction time that was 1/7214 of the time necessitated by CFD simulation. Full article

An electrically controlled rotor (ECR), also known as a swashplateless rotor, eliminates the swashplate system to implement the primary control via the trailing-edge flaps (TEFs), which can result in enhancements in rotor performance, as well as substantial reductions in weight, drag, and cost. In this paper, the unsteady aerodynamic characteristics of the airfoil with TEF of a sample ECR under unsteady freestream condition are investigated. The CFD results are obtained with sliding and overset grid techniques that simulate the airfoil pitching and flap deflection. Comparative analysis of the aerodynamic characteristics under steady and unsteady freestream conditions at different advance ratios is conducted. At various advance ratios, the lift and drag coefficients are higher at a small angle of attack under unsteady freestream condition; however, it is the opposite at a large angle of attack. The peak values of the lift and drag coefficients show an increased trend with the increase in the advance ratio. On the contrary, the pitch moment and flap hinge moment coefficients demonstrate minor variation under unsteady freestream condition. Furthermore, the aerodynamic characteristics of airfoils become more unsteady with variation in the freestream. Therefore, the lift and drag coefficients of the ECR airfoil with TEF show significant differences between steady and unsteady freestream conditions; however, the pitch moment and the flap hinge moment coefficients show little difference. Full article

An active rotor with trailing-edge flaps (TEFs) is an effective active vibration control method for helicopters. Blade flapping dynamic characteristics have a significant effect on the active vibration control performance of an active rotor. In this study, an aeroelastic model is developed using the Hamilton principle, and a quasi-steady Theodorsen model for the airfoil with a TEF is utilized to calculate the aerodynamic loads induced by the dynamic deflection of TEFs. The accuracy of this model is validated through a comparison with the CAMRAD calculation and flight test results of a SA349/2 helicopter. Based on the modal orthogonality and the equilibrium equation of the blade flapping motion, the method of changing the blade flapping dynamic characteristics is obtained. Blade sectional characteristics are adjusted to study the effect of blade flapping dynamics on the vibration control authority of an active rotor. The simulation results demonstrate that if the modal frequency of second-order flap is tuned to close to the rotor passage frequency, the flapping dynamic characteristics are capable of enhancing the vibration control performance of the active rotor. Full article

Reducing rotor aerodynamic noise is an important challenge in helicopter design. Active flap control (AFC) on rotors is an effective noise reduction method. It changes the segment airfoil shape, aerodynamic load distribution, and the wake path of the rotor flow by adding trailing edge flaps (TEFs). Although AFC noise reduction control is easily simulated, the relevant experiments have not been widely conducted due to test technical problems and limited financial support. The acoustic characteristics of the AFC-equipped rotor, such as the placement of TEFs for noise reduction and whether multiple winglets can provide a better effect than single winglets, have not been verified in previous experiments. In this work, an AFC-equipped rotor with two TEFs was designed, and its acoustic properties were tested in the FL-17 acoustic wind tunnel with microphone arrays in the far field. The results showed that the noise reduction effect of AFC was closely related to the control frequency and phase. Increasing the control phase could move the reduction region toward the azimuth-decreasing region for far-field noise. The noise reduction in a single outboard TEF was better than that in a single inboard TEF, while the dual-TEF model performed better. In this experiment, the average noise reduction in the observation point at the lower front of the rotor could be more than 3 dB, and the maximum noise reduction could be 6.2 dB. Full article

This paper presents an unsteady flow analysis of a 3D wing with a morphing trailing edge flap (TEF) and a seamless side-edge transition between the morphed and static parts of a wing by introducing an unsteady parametrization method. First, a 3D steady Reynolds-averaged Navier–Stokes (RANS) analysis of a statically morphed TEF with seamless transition is performed and the results are compared with both a baseline clean wing and a wing with a traditional hinged flap configuration at a Reynolds number of 0.7 × 10⁶ for a range of angles of attack (AoA), from 4° to 15°. This study extends some previous published work by examining the inherent unsteady 3D effects due to the presence of the seamless transition. It is found that in the pre-stall regime, the statically morphed wing produces a maximum of a 22% higher lift and a near constant drag reduction of 25% compared with the hinged flap wing, resulting in up to 40% enhancement in the aerodynamic efficiency (i.e., lift/drag ratio). Second, unsteady flow analysis of the dynamically morphing TEF with seamless flap side-edge transition is performed to provide further insights into the dynamic lift and drag forces during the flap motions at three pre-defined morphing frequencies of 4 Hz, 6 Hz, and 8 Hz, respectively. Results have shown that an initially large overshoot in the drag coefficient is observed due to unsteady flow effects induced by the dynamically morphing wing; the overshoot is proportional to the morphing frequency which indicates the need to account for dynamic morphing effects in the design phase of a morphing wing. Full article

This article describes the development and testing of a modified, semi-empirical ONERA dynamic stall model for an airfoil with a trailing edge flap—a “smart airfoil”—pitching at reduced frequencies up to 0.1. The Reynolds number is ${10}^5$. The model reconstructs the load fluctuations associated with the shedding of multiple dynamic stall vortices (DSVs) in a time-marching solution, which makes it suitable for real-time control of a trailing edge flap (TEF). No other model captures the effect of the DSVs on the aerodynamic loads on smart airfoils. The model was refined and tuned for force measurements on a smart NACA ${64}_3$-618 airfoil model that was pitching with an inactive TEF and was validated against the measurements when the TEF was activated. A substantial laminar separation bubble can develop on this airfoil, which is challenging for modelers of the unsteady response. A closed-loop controller was designed offline in SIMULINK, and the output of the controller was applied to the TEF in a wind tunnel. The results indicated that the model has a comparable accuracy for predicting loads with the active TEF compared to inactive TEF loads. In the fully separated flow regime, the controller performed worse when dealing with the development of the laminar separation bubble and DSVs. Full article

The unsteady flow characteristics and responses of an NACA 0012 airfoil fitted with a bio-inspired morphing trailing edge flap (TEF) at near-stall angles of attack (AoA) undergoing downward deflections are investigated at a Reynolds number of 0.62 × 10⁶ near stall. An unsteady geometric parametrization and a dynamic meshing scheme are used to drive the morphing motion. The objective is to determine the susceptibility of near-stall flow to a morphing actuation and the viability of rapid downward flap deflection as a control mechanism, including its effect on transient forces and flow field unsteadiness. The dynamic flow responses to downward deflections are studied for a range of morphing frequencies (at a fixed large amplitude), using a high-fidelity, hybrid RANS-LES model. The time histories of the lift and drag coefficient responses exhibit a proportional relationship between the morphing frequency and the slope of response at which these quantities evolve. Interestingly, an overshoot in the drag coefficient is captured, even in quasi-static conditions, however this is not seen in the lift coefficient. Qualitative analysis confirms that an airfoil in near stall conditions is receptive to morphing TEF deflections, and that some similarities triggering the stall exist between downward morphing TEFs and rapid ramp-up type pitching motions. Full article

Recently, the Trailing-Edge Flap with Micro-Tab (TEF with Micro-Tab) has been exploited to enhance the performance of wind turbine blades. Moreover, it can also be used to generate more lift and delay the onset of stall. This study focused mostly on the use of TEF with Micro-Tab in wind turbine blades using NREL’s S-809 as a model airfoil. In particular, the benefits generated by TEF with Micro-Tab may be of great interest in the design of wind turbine blades. In this paper, an attempt was made to evaluate the influence of TEF with Micro-Tab on the performance of NREL’s S-809 airfoils. Firstly, a computational fluid dynamics (CFD) model for the airfoil NREL’s S-809 was established, and validated by comparison with previous studies and wind tunnel experimental data. Secondly, the effects of the flap position (H) and deflection angle (α_F) on the flow behaviors were investigated. As a result, the effect of TEF on air-flow behavior was demonstrated by augmenting the pressure coefficient at the lower surface of the airfoil at flap position 80% chord length (C) and α_F = 7.5°. Thirdly, the influence of TEF with Micro-Tab on the flow behaviors of the airfoil NREL’s S-809 was studied and discussed. Different Micro-Tab positions and constant TEF were examined. Finally, the effects of TEF with Micro-Tab on the aerodynamic characteristics of the S-809 with TEF were compared. The results showed that an increase in the maximum lift coefficient by 25% and a delay in the air-flow stall were accomplished due to opposite sign vortices, which was better than the standard airfoil and S-809 with TEF. Therefore, it was deduced that the benefits of TEF with Micro-Tab were apparent, especially at the lower surface of the airfoil. This particularly suggests that the developed model could be used as a new trend to modify the designs of wind turbine blades. Full article

This work explores the aerodynamic and aeroacoustic responses of an airfoil fitted with a harmonically morphing Trailing Edge Flap (TEF). An unsteady parametrization method adapted for harmonic morphing is introduced, and then coupled with dynamic meshing to drive the morphing process. The turbulence characteristics are calculated using the hybrid Stress Blended Eddy Simulation (SBES) RANS-LES model. The far-field tonal noise is predicted using the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy method with corrections to account for spanwise effects using a correlation length of half the airfoil chord. At various morphing frequencies and amplitudes, the 2D aeroacoustic tonal noise spectra are obtained for a NACA 0012 airfoil at a low angle of attack (AoA = 4°), a Reynolds number of 0.62 × 10⁶, and a Mach number of 0.115, respectively, and the dominant tonal frequencies are predicted correctly. The aerodynamic coefficients of the un-morphed configuration show good agreement with published experimental and 3D LES data. For the harmonically morphing TEF case, results show that it is possible to achieve up to a 3% increase in aerodynamic efficiency (L/D). Furthermore, the morphing slightly shifts the predominant tonal peak to higher frequencies, possibly due to the morphing TEF causing a breakup of large-scale shed vortices into smaller, higher frequency turbulent eddies. It appears that larger morphing amplitudes induce higher sound pressure levels (SPLs), and that all the morphing cases induce the shift in the main tonal peak to a higher frequency, with a maximum 1.5 dB reduction in predicted SPL. The proposed dynamic meshing approach incorporating an SBES model provides a reasonable estimation of the NACA 0012 far-field tonal noise at an affordable computational cost. Thus, it can be used as an efficient numerical tool to predict the emitted far-field tonal noise from a morphing wing at the design stage. Full article

Trailing edge flaps (TEFs) are high-lift devices that generate changes in the lift and drag coefficients of an airfoil. A large number of 2D simulations are performed in this study, in order to measure these changes in aerodynamic coefficients and to analyze them for a given Reynolds number. Three different airfoils, namely NACA 0012, NACA 64(3)-618, and S810, are studied in relation to three combinations of the following parameters: angle of attack, flap angle (deflection), and flaplength. Results are in concordance with the aerodynamic results expected when studying a TEF on an airfoil, showing the effect exerted by the three parameters on both aerodynamic coefficients lift and drag. Depending on whether the airfoil flap is deployed on either the pressure zone or the suction zone, the lift-to-drag ratio, C_L/C_D, will increase or decrease, respectively. Besides, the use of a larger flap length will increase the higher values and decrease the lower values of the C_L/C_D ratio. In addition, an artificial neural network (ANN) based prediction model for aerodynamic forces was built through the results obtained from the research. Full article