Owl Wing Research Articles

Low noise with wood milling "Airface" constructions

Low noise with wood milling"airface" constructions. The noise surrounds us everywhere, constituting a disruptive component of our lives. In the wood industry it is more than in other industries due to the specificity of wood processing carried out by high-speed tools. GUS data say that in 2012 as many as 53% of employees worked in noise. Hence the necessity of constant search for new methods of noise reduction. One of them is the use of a grooved surface patterned on the plumage of owls in the construction of milling heads. Their characteristic construction makes the flight of owls almost silent. this is possible due to the special construction of ailerons, which form the bearing surface of the wing. The "owl's wing" smoothes the air flow with a serrated edge and scatters the noise. This allows for almost silent flight characteristics without adversely affecting aerodynamics. Leuco has used this concept of learning from nature to make the milling tools even more aerodynamic, and to get further noise reduction effects! Leuco has submitted a patent for this aerodynamic head design called "airface".

Numerical investigation of aerodynamic and acoustic characteristics of bionic airfoils inspired by bird wing

Airfoil is the basic element of fluid machinery and aircraft, and the noise generated from that is an important research aspect. Aiming to reduce the aerodynamic noise around the airfoil, this study proposes an airfoil inspired by the long-eared owl wing and another airfoil coupled with the bionic airfoil profile, leading edge waves, and trailing edge serrations. Numerical simulations dependent on the large eddy simulation method coupled with the wall-adapting local eddy-viscosity model and the Ffowcs Williams and Hawkings equation are conducted to compare the aerodynamic and acoustic characteristics of two types of bionic airfoils at low Reynolds number condition. The simulations reveal the dipole characteristic of acoustic source and sound pressure level distribution at various frequencies. Two types of bionic airfoils show lower noise compared with the conventional NACA 0012 airfoil with a similar relative thickness of 12%. Compared with the bionic airfoil, the average value of sound pressure level at the monitoring points around the bionic coupling airfoil is decreased by 9.94 dB, meanwhile the lift-to-drag ratio also keep higher. The bionic coupling airfoil exerts a suppression of sound pressure fluctuation on the airfoil surfaces, which result from that the range and size of separation vortices are reduced and the distance between vortices and airfoil surface are increased. The tube-shaped vortices in the wake of airfoil are effectively restrained and split into small scale vortices, which are important to cause less aerodynamic noise around the bionic coupling airfoil. Consequently, a novel bionic coupling airfoil is developed with the excellent aerodynamic and acoustic performance.

Morphology Effects of Leading-edge Serrations on Aerodynamic Force Production: An Integrated Study Using PIV and Force Measurements

While the leading-edge serration in owls’ wing is known to be responsible for low noise gliding and flapping flights, the findings on its aero-acoustic role have been diverse or even controversial. Here we present an experimental study of the morphological effects of leading-edge serrations on aerodynamic force production by utilizing owl-inspired, single-feather, clean and serrated wing models with different serration lengths and spacing, and by combining Particle Image Velocimetry (PIV) and force measurements. Force measurements show that an increase in the length and density of the leading-edge serrations leads to a reduction in the lift coefficient and lift-to-drag ratio at Angles of Attack (AoAs) 15°, which owl wings often reach in flight. Furthermore PIV visualization of the flow fluctuations demonstrates that the leading-edge serration-based mechanism is consistent in all serrated wing models in terms of passive control of the laminar-turbulent transition while at AoAs > 15° similar suction flow is present at leading edge resulting in a comparable aerodynamic performance to that of the clean wing. Our results indicate the robustness and usefulness of leading-edge serration-inspired devices for aero-acoustic control in biomimetic rotor designs.

Development of efficient and silent mixed flow fan inspired by microstructure of owl wing

Development of efficient and silent mixed flow fan inspired by microstructure of owl wing

A comparative study on aerodynamic performance and noise characteristics of two kinds of long-eared owl wing models

The camber line, chord length and thickness of the airfoil are important factors affecting the aerodynamic performance and noise characteristics of the blade. In this research, the long-eared owl wing as bionic prototype and two bionic blades were constructed by using bionic reconstruction method. The one named bionic blade A is based on the long-eared owl wing, which is reconstructed according to section theory and fitting formula of the measured long-eared owl wing. The other is the three-dimensional stretched cross-sectional bionic blade B. To compare the aerodynamic performance and noise characteristics of two bionic blades, the LES method coupled with FW-H equation was adopted to simulate the flow fields and the corresponding sound fields numerically at low Reynolds number condition. The results show that the lift coefficient for the bionic blade B is larger than that for the bionic blade A when the angle of attack is in the range of 0° ~ 30°. The pressure curve of bionic blade B indicates that the pressure generated from the suction side makes a greater contribution to lift force than the pressure side, especially at the leading edge. The location of the separation bubble moves from the trailing edge to the leading edge in the suction side of the blade at α =15°. The size of vortex shedding near the surface of the bionic blade A is smaller than the bionic blade B at α = 0° and it’s caused by the deeply concaved lower surface near the wing root probably. The range of the separation bubble acts as the main influence on the noise generation. Compared with the bionic blade B, the aerodynamic noise generated by the blade A is lower and the minimum value of sound pressure level is even 12.88 dB on the y-direction. That means the special construction of the natural long-eared owl wing could suppress the unsteady pressure fluctuation on the blade surface efficiently to decrease the aerodynamic noise.

Owl-inspired leading-edge serrations play a crucial role in aerodynamic force production and sound suppression

Owls are widely known for silent flight, achieving remarkably low noise gliding and flapping flights owing to their unique wing morphologies, which are normally characterized by leading-edge serrations, trailing-edge fringes and velvet-like surfaces. How these morphological features affect aerodynamic force production and sound suppression or noise reduction, however, is still not well known. Here we address an integrated study of owl-inspired single feather wing models with and without leading-edge serrations by combining large-eddy simulations (LES) with particle-image velocimetry (PIV) and force measurements in a low-speed wind tunnel. With velocity and pressure spectra analysis, we demonstrate that leading-edge serrations can passively control the laminar-turbulent transition over the upper wing surface, i.e. the suction surface at all angles of attack (0° < AoA < 20°), and hence play a crucial role in aerodynamic force and sound production. We find that there exists a tradeoff between force production and sound suppression: serrated leading-edges reduce aerodynamic performance at lower AoAs < 15° compared to clean leading-edges but are capable of achieving both noise reduction and aerodynamic performance at higher AoAs > 15° where owl wings often reach in flight. Our results indicate that the owl-inspired leading-edge serrations may be a useful device for aero-acoustic control in biomimetic rotor designs for wind turbines, aircrafts, multi-rotor drones as well as other fluid machinery.

Distribution of the characteristics of barbs and barbules on barn owl wing feathers.

Owls are known for the development of a silent flight. One conspicuous specialization of owl wings that has been implied in noise reduction and that has been demonstrated to change the aerodynamic behavior of the wing is a soft dorsal wing surface. The soft surface is a result of changes in the shape of feather barbs and barbules in owls compared with other bird species. We hypothesized that as the aerodynamic characteristics of a wing change along its chordwise and spanwise direction, so may the shape of the barbs and barbules. Therefore, we examined in detail the shapes of the barbs and barbules in chordwise and spanwise directions. The results showed changes in the shapes of barbs and barbules at the anterior and distal parts of the wing, but not at more posterior parts. The increased density of hook radiates at the distalmost wing position could serve to stiffen that vane part that is subject to the highest forces. The change of pennulum length in the anterior part of the wing and the uniformity further back could mean that a soft surface may be especially important in regions where flow separation may occur.

Reducing Aircraft Radar Cross-Section with Owl Wing Type Serrated Trailing Edges

Reducing Aircraft Radar Cross-Section with Owl Wing Type Serrated Trailing Edges

Features of owl wings that promote silent flight.

Owls are an order of birds of prey that are known for the development of a silent flight. We review here the morphological adaptations of owls leading to silent flight and discuss also aerodynamic properties of owl wings. We start with early observations (until 2005), and then turn to recent advances. The large wings of these birds, resulting in low wing loading and a low aspect ratio, contribute to noise reduction by allowing slow flight. The serrations on the leading edge of the wing and the velvet-like surface have an effect on noise reduction and also lead to an improvement of aerodynamic performance. The fringes at the inner feather vanes reduce noise by gliding into the grooves at the lower wing surface that are formed by barb shafts. The fringed trailing edge of the wing has been shown to reduce trailing edge noise. These adaptations to silent flight have been an inspiration for biologists and engineers for the development of devices with reduced noise production. Today several biomimetic applications such as a serrated pantograph or a fringed ventilator are available. Finally, we discuss unresolved questions and possible future directions.

Noise Generation of a Bionic Airfoil Based on Owl Wings

A bionic airfoil is used to investigate a preliminary understanding of the noise mechanism generated by the flow around the owl wing. The flow indicates a transitional separation bubble on the surface and the turbulent boundary layer reattaches at the downstream end of the bubble. This causes turbulent boundary layer trailing-edge scattering noise corresponding to the broadband noise of owl wings at low Reynolds numbers. Furthermore, a large-scale vortex detaches from the bubble and then drifts downstream. Thus, a tone will be generated by the vortex shedding. However, the computations of the acoustic field for both cases, where the on-body data surface and the off-body data surface are used respectively, predominantly verify the broadband nature of the noise that well agrees with the noise scattering caused by the turbulent boundary layer passing by the sharp trailing edge. Furthermore, the significant decrease of the spectra around 2k Hz is consistent with that of silent owl wings. This fact suggests that the numerical simulations are capturing the basic physical mechanism responsible for the noise radiated by the natural owl wing. This might be able to provide a reference for engineering applications of the owl technology.

Bionic Design of Wind Turbine Blade Based on Long-Eared Owl's Airfoil.

The main purpose of this paper is to demonstrate a bionic design for the airfoil of wind turbines inspired by the morphology of Long-eared Owl's wings. Glauert Model was adopted to design the standard blade and the bionic blade, respectively. Numerical analysis method was utilized to study the aerodynamic characteristics of the airfoils as well as the blades. Results show that the bionic airfoil inspired by the airfoil at the 50% aspect ratio of the Long-eared Owl's wing gives rise to a superior lift coefficient and stalling performance and thus can be beneficial to improving the performance of the wind turbine blade. Also, the efficiency of the bionic blade in wind turbine blades tests increases by 12% or above (up to 44%) compared to that of the standard blade. The reason lies in the bigger pressure difference between the upper and lower surface which can provide stronger lift.

An analysis of silent flight of owl

The present research studies the various parameters such as its special feather materials, the serrated wings feather, long velvet down materials causing the nearly silent flight of an Owl (Barn Owl). An Owl is a bird that is quite common and is well known for its nearly silent flight. The owl contains the long velvet down feathers found on wings and legs absorb the sound frequencies. The elongated distal barbules of the Owl form a multi-layer grid porous structure which also has a positive effect on the sound absorption quality of the Owl. The leading edge serration and trailing edge fringe improves the pressure fluctuation of turbulence boundary, distribute the air rushing and accumulation of air at the end of the wing which suppress the generation of vortex sound and also solves the problem of fluttering in the wings. The owls can perform this phenomenon even at great heights because of their aerodynamically designed wings and feathers. Silent flight gives Owl ability to capture prey by stealth. The main focus and Interest of this paper is to concentrate on the silent flight of Owl and built a basic of a bionic air foil, which is extracted from the Owl wings... This research not only can give the inspiration for solving the aerodynamic noise of aircraft and engineering machine, but also can provide a new idea for the design of low-noise devices Inspired by the noise absorption structure of Owl wings. The results may be further used to build an Unmanned Air Vehicle (UAV), capable of silent flight like Owls.

Mechanical properties and size scaling of long-eared owl primary feather

Velvety down material distributed over the owl wing surface has been investigated for the silent flight characteristics. In order to promote the technical application of the owl's special soft elongated distal barbules, we presented a study on the morphological and mechanical characterisation of the barbules branched on the long-eared owl primary feather. Tensile experiments of the barbules were conducted on a developed micro-tensile tester, and viscoelastic response of their stress and strain was described by the standard linear solid model. Barbules' geometry sizes and mechanical properties were compared with those of other feather hierarchical branches (rachis, barb, barbicel). Consequently, for the whole long-eared owl primary feather, scaling relationships of both the branching diameters and mechanical properties with respect to the branching lengths were established. The purpose of this investigation was to provide a basis for the material and structure design of bionic noise reduction components used in aviation, aerospace, marine and other fields.

Mechanical properties and size scaling of long-eared owl primary feather

Velvety down material distributed over the owl wing surface has been investigated for the silent flight characteristics. In order to promote the technical application of the owl's special soft elongated distal barbules, we presented a study on the morphological and mechanical characterisation of the barbules branched on the long-eared owl primary feather. Tensile experiments of the barbules were conducted on a developed micro-tensile tester, and viscoelastic response of their stress and strain was described by the standard linear solid model. Barbules' geometry sizes and mechanical properties were compared with those of other feather hierarchical branches (rachis, barb, barbicel). Consequently, for the whole long-eared owl primary feather, scaling relationships of both the branching diameters and mechanical properties with respect to the branching lengths were established. The purpose of this investigation was to provide a basis for the material and structure design of bionic noise reduction components used in aviation, aerospace, marine and other fields.

Biomimetic optimization research on wind noise reduction of an asymmetric cross-section bar.

Background In this paper, we used the principle of biomimetics to design two-dimensional and three-dimensional bar sections, and used computational fluid dynamics software to numerically simulate and analyse the aerodynamic noise, to reduce drag and noise.Methods We used the principle of biomimetics to design the cross-section of a bar. An owl wing shape was used for the initial design of the section geometry; then the feathered form of an owl wing, the v-shaped micro-grooves of a shark’s skin, the tubercles of a humpback whale’s flipper, and the stripy surface of a scallop’s shell were used to inspire surface features, added to the initial section and three-dimensional shape.ResultsThrough computational aeroacoustic simulations, we obtained the aerodynamic characteristics and the noise levels of the models. These biomimetic models dramatically decreased noise levels.

Combined particle-image velocimetry and force analysis of the three-dimensional fluid–structure interaction of a natural owl wing

Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which therefore can serve as role models of how to overcome the well-known problems of low Reynolds number flight. The flight of the barn owl is characterized by a very low flight velocity in conjunction with a low noise emission and a high level of maneuverability at stable flight conditions. To investigate the complex three-dimensional flow field and the corresponding local structural deformation in combination with their influence on the resulting aerodynamic forces, time-resolved stereoscopic particle-image velocimetry and force and moment measurements are performed on a prepared natural barn owl wing. Several spanwise positions are measured via PIV in a range of angles of attack 6° and Reynolds numbers 40 000 120 000 based on the chord length. Additionally, the resulting forces and moments are recorded for −10° ≤ α ≤ 15° at the same Reynolds numbers. Depending on the spanwise position, the angle of attack, and the Reynolds number, the flow field on the wing’s pressure side is characterized by either a region of flow separation, causing large-scale vortical structures which lead to a time-dependent deflection of the flexible wing structure or wing regions showing no instantaneous deflection but a reduction of the time-averaged mean wing curvature. Based on the force measurements the three-dimensional fluid–structure interaction is assumed to considerably impact the aerodynamic forces acting on the wing leading to a strong mechanical loading of the interface between the wing and body. These time-depending loads which result from the flexibility of the wing should be taken into consideration for the design of future small flying air vehicles using flexible wing structures.

Particle-image velocimetry investigation of the fluid-structure interaction mechanisms of a natural owl wing

The increasing interest in the development of small flying air vehicles has given rise to a strong need to thoroughly understand low-speed aerodynamics. The barn owl is a well-known example of a biological system that possesses a high level of adaptation to its habitat and as such can inspire future small-scale air vehicle design. The combination of the owl-specific wing geometry and plumage adaptations with the flexibility of the wing structure yields a highly complex flow field, still enabling the owl to perform stable and at the same time silent low-speed gliding flight. To investigate the effects leading to such a characteristic flight, time-resolved stereoscopic particle-image velocimetry (TR-SPIV) measurements are performed on a prepared natural owl wing in a range of angles of attack and Reynolds numbers 40 000 based on the chord length at a position located at 30% of the halfspan from the owl’s body. The flow field does not show any flow separation on the suction side, whereas flow separation is found on the pressure side for all investigated cases. The flow field on the pressure side is characterized by large-scale vortices which interact with the flexible wing structure. The good agreement of the shedding frequency of the pressure side vortices with the frequency of the trailing-edge deflection indicates that the structural deformation is induced by the flow field on the pressure side. Additionally, the reduction of the time-averaged mean wing curvature at high Reynolds numbers indicates a passive lift-control mechanism that provides constant lift in the entire flight envelope of the owl.

Wind turbines with owl wings could make energy silently

Wind turbines with owl wings could make energy silently

Particle-Image Velocimetry and Force Measurements of Leading-Edge Serrations on Owl-Based Wing Models

High-resolution Particle-Image Velocimetry (PIV) and time-resolved force measurements were performed to analyze the impact of the comb-like structure on the leading edge of barn owl wings on the flow field and overall aerodynamic performance. The Reynolds number was varied in the range of 40,000 to 120,000 and the range of angle of attack was 0° to 6° for the PIV and −15° to +20° for the force measurements to cover the full flight envelope of the owl. As a reference, a wind-tunnel model which possessed a geometry based on the shape of a typical barn owl wing without any owl-specific adaptations was built, and measurements were performed in the aforementioned Reynolds number and angle of attack range. This clean wing model shows a separation bubble in the distal part of the wing at higher angles of attack. Two types of comb-like structures, i.e., artificial serrations, were manufactured to model the owl's leading edge with respect to its length, thickness, and material properties. The artificial structures were able to reduce the size of the separation region and additionally cause a more uniform size of the vortical structures shed by the separation bubble within the Reynolds number range investigated, resulting in stable gliding flight independent of the flight velocity. However, due to increased drag coefficients in conjunction with similar lift coefficients, the overall aerodynamic performance, i.e., lift-to-drag ratio is reduced for the serrated models. Nevertheless, especially at lower Reynolds numbers the stabilizing effect of the uniform vortex size outperforms the lower aerodynamic performance.

High-Speed Particle Image Velocimetry and Force Measurements of Bio-Inspired Surfaces

To evaluate the influence of the velvet-like surface mimicking the structure on the suction side of barn owl wings on the flow field and on the aerodynamic performance of the wing, high-speed particle image velocimetry and time-resolved force measurements were performed. The Reynolds number was varied in the range of , and the range of the angles of attack was for the particle image velocimetry measurements and for the force measurements. The flow over a clean-wing model whose geometry corresponds to that of the owl wing without any special adaptations was investigated as a reference case for the same Reynolds number and angle of attack range. This clean wing possesses a laminar separation bubble as the dominant flow feature. Two artificial surfaces were selected to mimic the natural surface concerning the length, density, and thickness of the filaments. The surfaces were able to reduce flow separation. Although this reduction of the separation region might have a positive influence on the pressure drag, the aerodynamic performance of the models with the artificial surfaces was significantly reduced due to the increased skin-friction drag. Furthermore, the models equipped with the velvets possessed a reduced susceptibility to changes in Reynolds number and angle of attack concerning the aerodynamic performance. It can be stated that the velvet surfaces stabilize the flow field at low Reynolds numbers, enabling the owl to fly more slowly and thus more silently.