Smooth Wing Research Articles

Experimental and performance validation of a full-scale morphing droop nose design based on composite compliant structures

Active camber morphing technology can be used to improve aircraft performance in takeoff and landing flight conditions, while preserving a smooth wing shape. This study begins with the design of a morphing droop nose to be installed on a regional aircraft, and focuses on the manufacturing and testing of a full-scale and fully representative experimental prototype. All work is driven by the morphing shape change, which was optimized to provide the required aerodynamic performance. The adoption of a composite structure that combines a flexible skin with a compliant structure makes this device capable of achieving such a shape change, and sufficiently insensitive to external load variations. These capabilities are successfully demonstrated through experimental testing. A validation phase was conducted based on strain gauge measurements, and a motion capture system was used to identify three-dimensional shape changes due to the morphing. Finally, a validated numerical model is used to assess the aerodynamic performance of the experimental prototype.

Aerodynamic Performance Enhancement of Low Aspect Ratio Military Drone Aircraft Wing through Employing Leading Edge Tubercles

Present study aim to improve the aerodynamic performance of low Aspect Ratio (AR) military drone aircraft wing, through employing leading edge tubercle. For that purpose two wing model were design one with smooth leading edge and second with tubercle leading edge. The wing models were developed by using NACA0012 airfoil profile, whereas tubercles of amplitude 5% of chord (c) and wavelength of 11% of c is employed. The numerical simulation as performed at chord based Reynolds number of 140000 in pre-stall and post stall regime. The computational fluid dynamic simulation is performed at different angle of attack ranging from 0 degree to 25 degree with the interval of 5 degree. Computational Fluid Dynamics (CFD) results reveal that tubercle at the leading edge of the low AR wing has favorable effect on the wing performance. Aerodynamic performance of both smooth leading edge and tubercle leading edge wing is similar up to 15o angle of attack, whereas at 20 degree and 25 degree significant improvement in Lift-to-Drag L/D ratio is observed. It is estimated that at maximum increment of 53% in lift coefficient ii achieved at 25 degree angle of attack for as compared to smooth LE wing model. Moreover, maximum 20.5% decrease in drag coefficient is estimated in case of tubercle leading edge as compared to baseline model at 20 degree angle of attack. The critical observation of field around the tubercle leading edge wing is found that tubercles restrict flow separation through generation of low strength vortices; these vortices enhance momentum exchange within the boundary layer.

Adaptive robust loss for landmark detection

Using a loss function with appropriate properties to supervise the training of the neural network can substantially improve its accuracy and speed. A majority of loss functions applied to landmark detection, including Smooth ℓ1 loss, Wing loss and Adaptive Wing loss, utilize a form of piece-wise function to enhance the loss value of small errors. Still, some issues arise with these functions, such as non-differentiable, sensitivity to the outliers and additional computation to guarantee the continuity of the functions. In this paper, we propose a unified loss function called Adaptive Robust loss (ARobust loss) that is tailored for two landmark detection paradigms, i.e., coordinate regression and heatmap regression. In addition, we demonstrate the robustness, smoothness and continuity of the proposed loss function towards the two paradigms analytically. Last but not least, we validate the preeminence and accuracy of the adaptive robust loss on several landmark detection datasets by experiments. The best NME(%) results under the HRNet-W18 reached 4.52 (WFLW-Test) and 3.34 (300W-Full), respectively. In the standard task of face alignment and human pose estimation, the performance of our approach is on par with the SOTA losses. And the advantage of our proposed loss is more obvious in some challenging scenarios.

High actuation capability and smooth-deformation piezo morphing wing based on multi-layer parallel pre-compressed MFC bimorph

A single macro-fiber composite (MFC) unimorph or bimorph wing can only be applied to micro aerial vehicles (MAV) at speeds lower than 20 m/s owing to its relatively small output work. In this study, a high-actuation MFC pre-compressed bimorph actuator (MFC-PBA) multilayer parallel morphing wing is proposed for application in high-speed miniature unmanned aerial vehicles (mini-UAVs). The morphing wing adopts the proposed ribs with an arc groove and three parallel layers of MFC-PBAs to improve the output work and guarantee smooth morphing wing surface. The large deformation finite element (FE) models of a single MFC-PBA and its multilayer parallel morphing wing are established to evaluate the output deformation and output force. Subsequently, a prototype of the morphing wing is fabricated, and the actuation capabilities of the single MFC-PBAs and morphing wing are tested. The experimental and FE simulation results satisfactorily agree. The results show that at the peak driving voltage, with axial compression forces of 18 and 27 N applied to the side and middle MFC-PBAs, respectively, the deflection angle of the morphing wing reaches ±12°, which is twice that of the morphing wing without compression; and its blocking force is maintained at 1.682 N; thus, its output work has doubled. The multiphysics model of the proposed morphing wing under airflow is established to evaluate the deformation capability. The results show that the present morphing wing achieves a deflection of 5.04° on the side of the incoming flow direction, and a unit lift of 249.1 N/m at an air speed of 40 m/s and angle of attack of 15°. Consequently, the proposed morphing wing exhibits a high deformation capability. We expect the proposed morphing wing will be used for the flight control of mini-UAVs at higher speeds and larger sizes.

Airfoil trailing-edge noise and drag reduction at a moderate Reynolds number using wavy geometries

This study utilizes a hybrid aeroacoustic model to investigate how airfoils with spanwise wavy geometries can be used to reduce trailing-edge noise alongside improving the aerodynamic performance. A smooth airfoil is compared to four variants, which have spanwise surface waves of different wavelengths, at a Reynolds number of Re = 64 000 and an angle-of-attack of 1°. The first three variants have a geometry modified by a single wavelength, whereas the fourth has a surface composed of two wavelengths, which creates a more irregular surface variation. The results show that modest noise reductions of around 4 dB are achieved for the first three variants, but a much larger reduction of 17.7 dB is achieved for the fourth variant. The mechanisms behind the noise reduction are explored, and it is shown that the geometry reduces the spanwise correlation of the pressure fluctuations and also modifies the boundary layer dynamics, which contributes to the large reduction. It is further shown that a wavy geometry can reduce the drag force by reducing the shear stress over parts of the airfoil surface and by limiting the flow separation on the suction side. The fourth variant is also assessed across a wider range of angles (0°≤α≤4°) and is shown to produce less noise than the smooth wing across the entire range as well as a drag reduction for α≥1°.

The Importance of Morphology in Further Unraveling the Bumblebee Flight Paradox

Abstract The size of a bumblebee relative to its wing span would suggest that flight is not possible according to the conventional aerodynamic theories, yet nature shows that not to be true, hence the bumblebee paradox. Bumblebee wings have venations that create corrugations, with their forewing and hindwing connected with a hook-like structure, known as a hamulus. Previous investigations of bumblebee flight modeled wings as smooth surfaces or neglected their accurate morphological representation of corrugation or used a simplified body. To address these shortcomings, this work explores the significance of vein corrugation and body on lift and thrust, and morphological importance of hindwing and forewing in flapping flight. Computational fluid dynamics simulations were used to analyze an anatomically accurate bee wing and body for hovering and forward speeds. Flow analysis of corrugated and smooth wing models revealed that corrugation significantly enhanced lift by 14%. With increasing speed, the hindwing increased lift from 14% to 38% due to the combined camber created by the forewing and hindwing. A notable feature was that the leading edge vortex did not change in size when the hindwing was removed, therefore forewing pressure remained the same as when coupled with hindwing during downstroke. When the bee body was included in the model, the pressure decreased locally between the wing root to 25% of the wingspan on the dorsal side, causing lift for the corrugated model to increase by 11%. The study demonstrates the importance of accurately modeling wing corrugation and bee body in flapping flight aerodynamics to unravel the true load-lifting capacity of bumblebees.

Design and Shear Analysis of an Angled Morphing Wing Skin Module

Morphing wing skin can greatly improve the performance of aircraft by adjusting the shape of the wings according to different flight conditions. However, it is a challenge to maintain a smooth aerodynamic wing skin surface during the deformation process. Here, we propose an angled morphing wing skin module based on a silicon rubber matrix reinforced by carbon-fiber-reinforced polymer rods, which takes advantage of the tensile stress generated during shear to prevent it from wrinkling under large shear deformation. Experiments conducted on a series of wing skin modules with varying initial angles indicate that by starting from an angled configuration, the skin module can withstand a pure shear deformation of 92° without wrinkling, 53% larger than existing designs. A parametric analysis was also conducted to analyze the effects of geometric and material parameters on the wrinkle-free deformation range. Finally, a theoretical model based on the energy method was developed to unveil the underlying wrinkle prevention mechanism and to estimate the critical wrinkling angle of the skin. The proposed design can potentially greatly expand the shear morphing capability of aircraft wings, leading to larger variation in sweepback angle and therefore superior aerodynamic performance.

Experimental study of low Reynolds number effects on aerodynamics of smooth and sinusoidal leading-edge wings in the vicinity of the ground

Present study experimentally investigates the effects of ground clearance and Reynolds number on aerodynamic coefficients of smooth and sinusoidal leading-edge wings. Wind tunnel tests are conducted over a wide range of angles of attack from zero to 36 degrees, low Reynolds numbers of 30,000, 45,000 and 60,000, and also ground clearances of 0.5, 1 and ∞. Results showed that reduction of ground clearance and increment of Reynolds number cause the lift coefficient and the lift to drag ratio of both wings to be enhanced. Furthermore, the effects of Reynolds number and ground clearance on the smooth leading-edge wing are more than the sinusoidal leading-edge one. In addition, the sinusoidal leading-edge wing shows an excellent performance in the poststall region due to producing a higher lift and also by delaying the stall angle compared to the smooth leading-edge wing.

Enhancement of airfoil performance by rotating cylinder

This study used a NACA 6409 smooth wing section. Its performance is compared to an enhanced design incorporating a revolving cylinder on the upper airfoil surface. The boundary conditions for the present work were Reynolds (105), and the attack angles were (0,2,4,6,8,10,12,14,16). A turbulence model was developed (SST K-), one of the aerodynamics models. This model is well-suited for sensing flow near a wall. The cylinder was evaluated at three positions (25,50,75) percent of the chord's length. The results indicated that position (25 percent C) was optimal, as it resulted in a 24.45 percent increase in lift coefficient at the angle of attack (12). And when the results were compared to those of other studies, they revealed a significant agreement.

An aerodynamic optimization design study on the bio-inspired airfoil with leading-edge tubercles

The aim of the paper is to propose a groundbreaking method for the aerodynamic optimization design of the bioinspired wing with leading-edge tubercles. An emphasis on the optimization design of the spanwise waviness in the leading edge for delaying stall and increasing lift from the aerodynamic performance perspective has been laid in this study. For the conversion of the wavy configuration, the form parameterized approach using F-spline curves has been used to produce more variants of the leading-edge tubercles. Numerical investigations of flow characteristics which are performed using CFD computations have been used to validate the numerical scheme with experimental data. The combination of Non-dominated Sorting Genetic Algorithm II and Response Surface Method based Kriging Model has been adopted as the aerodynamic optimization strategy. As consequence, the three main components of the optimization process are incorporated into the establishment of the aerodynamic optimization design system for the bio-inspired airfoil with leading-edge tubercles. The four optimal airfoils respectively which increases the stall angle as well as the lift have been obtained in contrast to the smooth wing. The optimized bio-inspired design of this kind can be applied to flow-controlled devices for improving the efficiency of a particular operating mechanism.

Effect of Wing Corrugation on the Aerodynamic Efficiency of Two-Dimensional Flapping Wings

Many previous studies have shown that wing corrugation of an insect wing is only structurally beneficial in enhancing the wing’s bending stiffness and does not much help to improve the aerodynamic performance of flapping wings. This study uses two-dimensional computational fluid dynamics (CFD) in aiming to identify a proper wing corrugation that can enhance the aerodynamic performance of the KUBeetle, an insect-like flapping-wing micro air vehicle (MAV), which operates at a Reynolds number of less than 13,000. For this purpose, various two-dimensional corrugated wings were numerically investigated. The two-dimensional flapping wing motion was extracted from the measured three-dimensional wing kinematics of the KUBeetle at spanwise locations of r = (0.375 and 0.75)R. The CFD analysis showed that at both spanwise locations, the corrugations placed over the entire wing were not beneficial for improving aerodynamic efficiency. However, for the two-dimensional flapping wing at the spanwise location of r = 0.375R, where the wing experiences relatively high angles of attack, three specially designed wings with leading-edge corrugation showed higher aerodynamic performance than that of the non-corrugated smooth wing. The improvement is closely related to the flow patterns formed around the wings. Therefore, the proposed leading-edge corrugation is suggested for the inboard wing of the KUBeetle to enhance aerodynamic performance. The corrugation in the inboard wing may also be structurally beneficial.

Direct Numerical Simulations of a Great Horn Owl in Flapping Flight

The fluid dynamics of owls in flapping flight is studied by coordinated experiments and computations. The great horned owl was selected, which is nocturnal, stealthy, and relatively large sized raptor. On the experimental side, perch-to-perch flight was considered in an open wind tunnel. The owl kinematics was captured with multiple cameras from different view angles. The kinematic extraction was central in driving the computations, which were designed to resolve all significant spatio-temporal scales in the flow with an unprecedented level of resolution. The wing geometry was extracted from the planform image of the owl wing and a three-dimensional model, the reference configuration, was reconstructed. This configuration was then deformed in time to best match the kinematics recorded during flights utilizing an image-registration technique based on the large deformation diffeomorphic metric mapping framework. All simulations were conducted using an eddy-resolving, high-fidelity, solver, where the large displacements/deformations of the flapping owl model were introduced with an immersed boundary formulation. We report detailed information on the spatio-temporal flow dynamics in the near wake including variables that are challenging to measure with sufficient accuracy, such as aerodynamic forces. At the same time, our results indicate that high-fidelity computations over smooth wings may have limitations in capturing the full range of flow phenomena in owl flight. The growth and subsequent separation of the laminar boundary layers developing over the wings in this Reynolds number regime is sensitive to the surface micro-features that are unique to each species.

Effects of smart flap on aerodynamic performance of sinusoidal leading-edge wings at low Reynolds numbers

Sinusoidal leading-edge wings have shown a high performance after the stall region. In this study, the role of smart flaps in the aerodynamics of smooth and sinusoidal leading-edge wings at low Reynolds numbers of 29,000, 40,000 and 58,000 is investigated. Four wings with NACA 634-021 profile are firstly designed and then manufactured by a 3 D printer. Beam bending equation is used to determine the smart flap chord deflection. Next, wind tunnel tests are carried out to measure the lift and drag forces of proposed wings for a wide range of angles of attack, from zero to 36 degrees. Results show that using trailing-edge smart flap in sinusoidal leading-edge wing delays the stall point compared to the same wing without flap. However, a combination of smooth leading-edge wing and smart flap advances the stall. Furthermore, it is found that wings with smart flap generally have a higher lift to drag ratio due to their excellent performance in producing lift.

Experimental investigation of the natural and controlled disturbance development in a supersonic boundary layer on the swept wing

The results of investigation of the transverse flow inhomogeneity effect on the natural and controlled disturbance development in 3D supersonic boundary layer are considered. The transition curves were measured on a model of a smooth swept wing and on a swept wing with roughness elements of two configurations. The influence of periodic surface roughness on the growth of natural pulsations (without using a discharge) in the boundary layer is determined. In experiments with artificial disturbances it is found that the periodic modulation of mean flow can lead to stabilization of controlled disturbances in supersonic boundary layer on a swept wing. It was found out that the weak flow inhomogeneity can influence the effectiveness of the active/passive technology of supersonic boundary layer transition control, including the surface microroughness on a swept wing.

Effect of acicular vortex generators on the aerodynamic features of a slender delta wing

This study investigates the flow structures and aerodynamic performance of a slender delta wing that has a sweep angle of 65 degrees and is equipped with acicular vortex generators. The results were compared with those of a smooth wing. Particle image velocimetry (PIV) was used to visualize the flow at six different sections of the delta wing in both the chord-wise and span-wise directions at an angle of attack (AOA) of 30 degrees and a Reynolds number of Re=2.4×105. The effect of the acicular vortex generators on the vortex diameters, locations of vortex breakdown, linear convolution integral patterns, circulation, and separation were studied. The Q-criterion was used for vortex boundaries for the span-wise sections. The results show the acicular vortex generators have positive effects on the aerodynamic performance of the wing. Furthermore, the acicular wing delays the vortex breakdown in comparison with a smooth wing and increases the flow momentum near the upper wing surface and behind the wing.

Identification of a degradation of aerodynamic characteristics of a paraglider due to its flexibility from flight test

PurposeAerodynamics of paragliders is very complicated aeroelastic phenomena. The purpose of this work is to quantify the amount of aerodynamic drag related to the flexible nature of a paraglider wing.Design/methodology/approachThe laboratory testing on scaled models can be very difficult because of problems in the elastic similitude of such a structure. Testing of full-scale models in a large facility with a large full-scale test section is very expensive. The degradation of aerodynamic characteristics is evaluated from flight tests of the paraglider speed polar. All aspects of the identification such as pilot and suspension lines drag and aerodynamics of spanwise chambered wings are discussed. The drag of a pilot in a harness was estimated by means of wind tunnel testing, computational fluid dynamics (CFD) solver was used to estimating smooth wing lift and drag characteristics.FindingsThe drag related to the flexible nature of the modern paraglider wing is within the range of 4-30 per cent of the total aerodynamic drag depending on the flight speed. From the results, it is evident that considering only the cell opening effect is sufficient at a low-speed flight. The stagnation point moves forwards towards the nose during the high speed flight. This causes more pronounced deformation of the leading edge and thus increased drag.Practical implicationsThis paper deals with a detailed analysis of specific paraglider wing. Although the results are limited to the specific geometry, the findings help in the better understanding of the paraglider aerodynamics generally.Originality/valueThe data obtained in this paper are not affected by any scaling problems. There are only few experimental results in the field of paragliders on scaled models. Those results were made on simplified models at very low Reynolds number. The aerodynamic drag characteristics of the pilot in the harness with variable angles of incidence and Reynolds numbers have not yet been published.

Effects of Bio-Inspired Surface Roughness on a Swept Back Tapered NACA 4412 Wing

This paper presents the overall pros and cons of the effect of surface roughness elements over a NACA 4412 tapered, swept back half wing with a sweep angle of 30º and a dihedral angle of 5º. The tests were conducted at a Reynolds number of 4 × 105 in the IIUM Low Speed wind tunnel. Different roughness sizes and roughness locations were tested for a range of angle of attack. Lift, drag and pitching moment coefficients were measured for the smooth wing and with roughness elements. Surface roughness delays the stall angle and decreases the lift. The wing with the roughness elements located at 75% to 95% of mean chord from leading edge shows minimum drag and maximum lift compared to other locations. Significant increase in the pitching moment coefficient was found for flexible roughness elements. In case of rigid surface roughness, the effect on pitching moment is small.

Application of nonlinear pulse shaping of femtosecond pulse generation in a fiber amplifier at 500 MHz repetition rate

We numerically and experimentally demonstrate that a nonlinear pulse shaping technique based on pre-chirping management in a short gain fiber can be exploited to improve the quality of a compressed pulse. With prior tuning of the pulse chirp, the amplified pulse express different nonlinear propagating processes. A spectrum with s flat top and more smooth wings, showing a similariton feature, generates with the optimal initial pulse chirp, and the shortest pulses with minimal pulse pedestals are obtained. Experimental results show the ability of nonlinear pulse shaping to enhance the quality of compressed pulses, as theoretically expected.

Aerodynamics of a translating comb-like plate inspired by a fairyfly wing

Unlike the smooth wings of common insects or birds, micro-scale insects such as the fairyfly have a distinctive wing geometry, comprising a frame with several bristles. Motivated by this peculiar wing geometry, we experimentally investigated the flow structure of a translating comb-like wing for a wide range of gap size, angle of attack, and Reynolds number, Re = O(10) − O(103), and the correlation of these parameters with aerodynamic performance. The flow structures of a smooth plate without a gap and a comb-like plate are significantly different at high Reynolds number, while little difference was observed at the low Reynolds number of O(10). At low Reynolds number, shear layers that were generated at the edges of the tooth of the comb-like plate strongly diffuse and eventually block a gap. This gap blockage increases the effective surface area of the plate and alters the formation of leading-edge and trailing-edge vortices. As a result, the comb-like plate generates larger aerodynamic force per unit area than the smooth plate. In addition to a quasi-steady phase after the comb-like plate travels several chords, we also studied a starting phase of the shear layer development when the comb-like plate begins to translate from rest. While a plate with small gap size can generate aerodynamic force at the starting phase as effectively as at the quasi-steady phase, the aerodynamic force drops noticeably for a plate with a large gap because the diffusion of the developing shear layers is not enough to block the gap.

Aerodynamic analysis of seamless horizontal stabilizer

This project presents an investigative view into the concept of seamless aeroelastic wing and hingeless flexible trailing edge. Wings are designed to provide maximum lift and minimal drag and weight. But with conventional wings where rivets are used and the control surfaces are separately hinged, parasite drag comes into play. This project is about analysing a smooth seamless wing with hinge-less flexible trailing edge. This type of wing reduces the drag considerably and the hinge-less trailing edge leads to a minimal control demand and reduces the noise produced when the aircraft comes for landing. Seamless aeroelastic wing will function as an integrated one piece lifting and control surface. It has been designed to enhance a desirable wing camber for control by deflecting a hinge-less flexible trailing edge part instead of a traditional hinged control surface. This kind of flexible wing can be achieved either by a curved beam and disc actuation mechanism or by piezo-electric materials, whose shape change can be achieved by electricity. The intent of this project is to analyze the effects of introducing the concept of Seamless Wing to the horizontal stabilizer. While the removal of rivets and serrations that hinge the elevators to the stabilizer reduces the overall drag by a reasonable value, the overall concept of a control surface-less stabilizer where the maneuvers are done by deflecting the trailing edge offers better maneuverability.