Bionic Airfoil Research Articles

Numerical study on bionic airfoil fins used in printed circuit plate heat exchanger

Abstract Airfoil printed circuit heat exchangers (PCHEs) possess exceptional comprehensive performance. In recent years, extensive research has been conducted on the layout and structure optimization of airfoil fins. As biomimetic technologies gradually mature, bionics has achieved numerous outcomes in optimizing airfoil aerodynamic characteristic. Inspired by the sailfish geometry, four types of bionic airfoils are proposed based on the NACA 0015 airfoil, to enhance the thermal-hydraulic performance of the airfoil PCHEs. The results show that while the four types of sailfish airfoils are effective in terms of drag reduction, their overall performance at the same pumping power is suboptimal, with only one type providing an advantage at the low Re region. Moreover, airfoils with concave head curves further increase the weakening of heat transfer by the velocity boundary layer.

Numerical study on aerodynamic and noise performance of bionic asymmetric airfoil with surface grooves

Based on the asymmetric NACA4412 baseline airfoil, a bionic airfoil with surface grooves is presented. For the bio-inspired airfoil, non-smooth grooves are placed on the trailing edge of NACA4412 airfoil. To reveal the effects of non-smooth structures of the trailing edge on the aerodynamic and noise performance of airfoil, large eddy simulation and Ffowcs Williams–Hawkings acoustic analogy are adopted to investigate the aerodynamic performance and acoustic characteristics of the baseline NACA4412 airfoil and bionic airfoil at the chord-based Reynolds number, Re = 1.2 ×105. The numerical results show that the aerodynamic performance of the bionic airfoil is better than that of the baseline airfoil when the angle of attack is 14°. For all the sound frequencies studied in this study, the overall sound pressure level of the bionic airfoil is reduced by 2.0 dB at angle of attack is 14°. At the same time, the mechanisms of flow control and noise reduction of non-smooth surface grooves at the trailing edge are also revealed. As a result, the presence of surface grooves near the trailing edge of the airfoil can effectively improve the aerodynamic performance and reduce the aerodynamic noise of the traditional asymmetric airfoil, especially at high angles of attack.

USTButterfly: A Servo-Driven Biomimetic Robotic Butterfly

Different from birds, bats, flies, and other flying creatures that generate propulsions by flapping a pair of wings, butterflies with two pairs of wings have their peculiar flight aerodynamics. In this paper, a servo-driven biomimetic robotic butterfly, named USTButterfly, is designed to study the flight mechanism of biological butterflies. First, instead of using a single actuator to drive two pairs of wings, two servos are introduced to independently drive the left and right wings, thereby realizing tailless control of the robotic butterfly. Next, a bionic airfoil is designed inspired by the wing structure of the Glasswing butterfly. Wing geometry analysis indicates that USTButterfly well matches the morphological characteristics of biological butterflies. Finally, a multi-camera motion capture system is used to measure the flight characteristics of the robotic butterfly, and the results demonstrate that despite a larger Reynolds number, USTButterfly shares a similar coupled wing-bsody interaction with biological butterflies in the climbing flight. USTButterfly opens up a new way to study the flight specializations of biological butterflies, and offers a potential alternative paradigm for existing unmanned aerial vehicles.

Study on Flow Control and Noise Reduction of Bionic Airfoil Based on Intelligent Optimization Algorithm

Study on Flow Control and Noise Reduction of Bionic Airfoil Based on Intelligent Optimization Algorithm

Study on Nonlinear Correlation in Modal Coefficients of the Bionic Airfoil

Applying bionic airfoils is essential in enlightening the design of rotating machinery and flow control. Dynamic mode decomposition was used to reveal the low dimensional flow structure of Riblets, Seagull, and Teal bionic airfoils at low Reynolds numbers 1 × 105 and is compared with NACA4412 airfoils. The attack angle of the two-dimensional airfoil is 19°, and the SST k-ω turbulence model and ANSYS fluent were used to obtain the transient flow field data. The sparse identification of nonlinear dynamics reveals the nonlinear correlation between modal coefficients and establishes manifold dynamics. The results show that the bionic airfoil and NACA4412 airfoil have the same type of nonlinear correlation, and the dimension and form of the minimum reduced-order model are consistent. The modal coefficients always appear in the manifold equation in pairs with a phase difference of 90°. The dimension of the manifold equation is two-dimensional, and the absolute value of the coefficient corresponds to the fundamental frequency of airfoil vortex shedding. The reconstructed flow field based on the manifold equation is highly consistent with the numerical simulation flow field, which reveals the accuracy of the manifold equation. The relevant conclusions of this study emphasize the unity of the nonlinear correlation of bionic airfoils.

Simulation research on hydrodynamic performance of wave glider airfoil

To improve the wave energy utilization rate of the wave glider as the research goal, research on the improvement of the hydrodynamic performance of the airfoil of the wave glider was carried out. First, we extract the bionic airfoil A and the standard airfoil C and draw the design airfoil B and the regular airfoil D. Secondly, using ANSYS Fluent, the hydrodynamic performance of the four airfoils under different inflow velocities and angles of attack is studied. Finally, data analysis shows that under the same attack angle, the lift coefficient, drag coefficient, and lift-drag ratio of the airfoil are not affected by the incoming flow velocity. Under the same incoming flow velocity, when the attack angle is 5°-13°, the bionic wing Type A is slightly better than the design airfoil B, obviously better than the standard airfoil C and regular airfoil D. Considering the hydrodynamic performance and material cost, it can be seen that the B airfoil is the optimal airfoil in this study. The comparative analysis of four airfoils provides a research basis for improving the wave energy utilization rate of the wave glider.

Numerical and experimental investigation of bionic airfoils with leading-edge tubercles at a low-Re in considering stall delay

The hydrodynamic characteristics and suction side flow behaviour of bionic airfoils are investigated numerically and experimentally at a low Reynolds number (Re). Hydrodynamic coefficient curves indicate that the hydrodynamic performance of the bionic airfoils is sensitive to the amplitude but not to the wavelength. When the amplitude is large enough, the bionic airfoils do not stall. As determined from numerical results and dye visualization, the bionic airfoils exhibit a double periodic flow pattern in the wingspan direction, and the trough-1 cross-section exhibits prominent separation at the leading edge, while the inflow flow attaches to the airfoil surface until the trailing-edge at the trough-2 cross-section. Because the vortex pairs formed by each group of adjacent tubercles interact with each other, the effective angle of attack (AOA) at the trough-2 cross-section is decreased, delaying the stall. In the post-stall region, the lift coefficient (CL) of each bionic airfoil is larger than that of the reference airfoil. The vortex pairs generated by the tubercles are completely mixed downstream, bringing more energy from the far wall to the near wall. The flow separation is delayed on both sides, and the effective AOA is decreased.

Aerodynamic performance of horizontal axis wind turbine with application of dolphin head-shape and lever movement of skeleton bionic airfoils

In order to continuously develop the special airfoil for wind turbine and further improve the energy efficiency of wind turbine, based on the bionic airfoil Dol-Rot 24° that was proposed by the streamline contour of the Phocoenoides Dalli, another novel bionic airfoil is constructed combined with the lever movement shape of the dolphin skeleton, and the airfoil is named Dol-Rot 24°-2. For the cross section of NREL phase VI horizontal axis wind turbine blade (S809 airfoil), Dol-Rot 24°, and Dol-Rot 24°-2 are adopted and numerically simulated to quantitatively analyze from both aspects of aerodynamic performance and noise characteristics. Using the above two novel airfoils profiles, two 3D bionic blades named Dol-Blade-1 and Dol-Blade-2 suitable for NREL phase VI HAWT are established. The results show that: compared with S809 airfoil, Dol-Rot 24°-2 airfoil can greatly improve the lift coefficient, while Dol-Rot 24° airfoil can more effectively inhibit the flow separation on the suction surface. In terms of noise characteristics, compared with S809 airfoil, the noise of the two types of dolphin airfoils does not increase significantly. In addition, Dol-Blade-1 can comprehensively improve the low-speed shaft torque of the blade, while the load of the wind turbine hardly changes. The low-speed shaft torque of Dol-Blade-2 is even better than that of Dol-Blade-1. However, the blade root bending moment of Dol-Blade-2 increases obviously, which inevitably increases the load of the wind turbine. In this paper, the new bionic method is proposed to improve the wind energy utilization of wind turbine on the premise of strictly controlling the aerodynamic noise and load level of blade. The research results of this paper can provide a reference for the optimization of energy efficiency and noise research of NREL phase VI HAWT.

Aero-acoustics Investigation of a Bionic Airfoil Horizontal Axis Wind Turbine Using LES-DCS Approach

The wind turbine noise has become an important issue in the current green energy field, therefore, it is necessary to use new and advantageous methods to study the problem. This research employed the LBM-DCS method to investigate the wake sound radiation characteristics for a bionic airfoil horizontal axis wind turbine, combining the large eddy simulation (LES) model and the wall-adapting local eddy-viscity (WALE) model. The obtained results show that the aeroacoustic model used here is reasonable and effective, which are consistent with the relevant experimental measurement result. The appearance and changing characteristics of the acoustic radiation ring have been discussed and analyzed to a certain extent. Based on the accumulation of this research, we will combine more experimental data to carry out a further systematic investigation on the acoustic radiation characteristics to the wind turbine.

Using the combined flow control accessory to the aerodynamic performance enhancement of bio-inspired seagull airfoils

An airfoil with good stability and a high lift-drag ratio can effectively improve the stability and aerodynamic performance of the wind turbine blade. Inspired by the excellent gliding performance of the seagull wings, the unique profile and structure of the seagull wings are first extracted to restructure the bionic airfoil. Then, the flow control accessory combined the bionic flap and Gurney flap is introduced to further improve the static and dynamic aerodynamic performance of bionic seagull airfoil. Under different Reynolds numbers, the effects of the combined flow control accessory on the bionic seagull airfoil are investigated using the numerical simulation method. Based on the analysis of flow fields, the flow control mechanism of the combined flow control accessory on the stall characteristics of bionic seagull airfoil is revealed. The results show that for the static stall characteristics, when the flow control accessory is applied to the bionic airfoil, the static lift coefficient of the airfoil is increased by 15% at Reynolds numbers of Re 2.0 × 105. For the dynamic stall characteristics, the lift coefficient of the airfoil is improved during the whole dynamic stall process, the maximum is increased by 13.12%, and the area of the dynamic hysteresis loop is reduced.

Noise reduction of bionic coupling blades of horizontal axis wind turbine

Many bio-inspired researches for aerodynamic noise control of wind turbine have been carried out and obtained effective results. Inspired by the silent flight of owl, in this paper, the airfoil of owl's wing and the asymmetric sawtooth structure of the feather have been extracted and reconstructed on the prototype wind turbine blades. The bionic airfoil blade and bionic coupling blade have been designed separately and compared with prototype blade. To obtain the asymmetric sawtooth structure with better acoustic performance, the sawtooth parameters are selected by orthogonal test. The influence of airfoil and asymmetric sawtooth for acoustic performance of blade has been investigated with large eddy simulation method and Ffowcs Williams-Hawkings analogy method. The results show that the bionic coupling blade has a larger surface pressure difference compared with the prototype blade and thus has better aerodynamic performance. The airfoil-structure coupling method can effectively reduce the aerodynamic noise of the blade without affecting the directivity of the acoustic, and optimized blade can reduce the noise by up to 8.42 dB. The blade coupling airfoil has an inhibitory effect on intermediate and high frequency noise. After adding asymmetric sawtooth trailing edge, the noise in the low frequency and intermediate frequency range is further reduced.

Effect of the asymmetric bio-inspired trailing-edge serrations on sound suppression in a coupled owl-based airfoil

Trailing-edge noise plays a dominant part in blades coping with low inflow turbulence at the low Mach number. An important reason for the dramatic noise reduction of owls is on account of the distinct wing morphology of the trailing edge. In particular, its excellent hunting advantages are closely related to the angle of attack. Based on that, the bio-inspired trailing-edge design with oblique-arc profile were retrofitted to the coupled airfoil with 40% cross section of the owl wing in this study, which is contributed to break the limitation of the sound suppression of the conventional serration. High-resolution large eddy simulations combined with the acoustic analogy method are employed to perform the simulation under the specific attack angles with 0° and 15° . The results show that the potential of high-efficiency and low-noise bionic airfoil is exceedingly realized at the attack angle with 0° . The overall sound power level of the coupled airfoil is reduced by 5.47 dB compared with the smooth airfoil. An additional 3.68 dB noise reduction advantage over conventional serrations. Affected by the trailing-edge serrations, the coherent vortex structures with tube-shaped vortices in spanwise direction are dissipated into the horseshoe-type vortices, which implies that more acoustic energy of the coupled bionic airfoil is dissipated. In contrast, the wake gap flow with attack angle of 15° is conducive to intensify the turbulent wake flow that is prone to generate the V-shaped pressure fluctuations. Extra stronger broadband noise is emitted by the coupled airfoil in the longitudinal direction when the regular large-scale wake vortices of the smooth airfoil are broken into the more widespread out-of-order vortices. Consequently, the design of the innovative trailing-edge serrations is contributed to utilize the fluid physics behind it to implement a broader sound suppression strategy.

Aeroacoustic investigation of asymmetric oblique trailing-edge serrations enlighted by owl wings

Trailing-edge noise is the dominant contributor to the noise generated by aircraft and wind turbines. Serrations on the trailing edge play a crucial role in suppressing the aerodynamic noise of an airfoil, and bionic airfoil sections are confirmed to be rewarding to sound suppression. However, how these characteristics affect the noise emission is still unknown. In this study, the bio-inspired oblique trailing-edge serrations are embedded within the trailing edge of the airfoil with unique cross section of the owl wing, which differs from the previous design. The noise reduction mechanism of coupled airfoils with innovative asymmetric and conventional trailing-edge serrations are explored at a low Mach number. Numerical results show that the largest lift-to-drag ratio with 17.69 and the smallest sound pressure level with 15.72 dB for the airfoil with bio-inspired oblique serrations are obtained among the investigated airfoils. An additional noise reduction of 3.68 dB can be achieved by using innovative asymmetric serrations. Moreover, the widespread large-scale disordered vorticities triggered by smooth airfoil on the pressure side are detached into the smaller-scale vortices triggered by coupled airfoil. The spanwise correlation reflecting the noise emission is significantly decreased. Distinguishingly, more turbulent kinetic energy and pressure fluctuations are emitted in the longitudinal direction on account of the intense collision of the airflow and the gap flow generated by conventional serrations. It is expected that this in-depth study of sound suppression will serve as an essential guide for airfoil design and noise control for micro-aircraft and fluid machinery coping with disturbing areas.

Investigation of aerodynamic forces and flow field of an H-type vertical axis wind turbine based on bionic airfoil

This paper investigates the effect of bionic airfoil on the aerodynamic characteristic and flow field of an H-type vertical axis wind turbine (VAWT). The pressure acting on the blade surface and flow field around the blade were predicted at different tip speed ratios (TSRs) and the angles of attack were predicted by numerical simulation. As a result, it was showed that the maximum value of lift force coefficient was 0.723 for baseline airfoil at the angle of attack 12° and was 0.743 for bionic airfoil at the angle of attack 14°. When the angle of attack was equal or greater than 14°, the static bionic airfoil showed better lift characteristic. Moreover, the maximum value of power coefficient occurred at TSR = 2.58 for the simulation, but the maximum value of torque coefficient was identified at TSR = 2.19. Meanwhile, the growth rates of the power coefficient were 7.02% at TSR = 1.38, 7.35% at TSR = 2.19, and 3.42% at TSR = 2.58 for simulation between baseline blades and bionic blades. The power performance of VAWT improved in dynamic stall for bionic airfoil by delaying stall on the blade's surface and promoting the laminar-to-turbulent transition to improve the power performance of wind turbine at the low TSRs for the mainstream wind velocity of 8.0 m/s. The research results were helpful to predict the performance of VAWTs under various wind environments and to improve the aerodynamic performance of VAWTs.

Dynamic Stall Characteristics of the Bionic Airfoil with Different Waviness Ratios

A dynamic stall will cause dramatic changes in the aerodynamic performance of the blade, resulting in a sharp increase in the blade vibration load. The bionic leading-edge airfoil with different waviness ratios, inspired by the humpback whales flipper, is adopted to solve this problem. In this study, based on the NACA0015 airfoil, the three-dimensional unsteady numerical simulation and sliding mesh technique are used to reveal the flow control mechanism on the dynamic stall of the bionic wavy leading edge. The effects of the waviness ratio on the dynamic stall characteristics of the airfoil are also investigated. The results show that the peak drag coefficient is dramatically reduced when a sinusoidal leading edge is applied to the airfoil. Although the peak lift coefficient is also reduced, the reduction is much smaller. When the waviness ratio R is 0.8, the peak drag coefficient of the airfoil is reduced by 17.14% and the peak lift coefficient of the airfoil is reduced by 9.20%. The dynamic hysteresis effect is improved gradually with an increasing waviness ratio. For the bionic airfoil with R = 1.0, the area of the hysteresis loop is the smallest.

Numerical Simulation of Flow over Bionic Airfoil

In this study, the aerodynamic performance of bionic airfoil was numerically studied by CFD method. The bionic airfoil was represented by the combination of airfoil and a small trailing edge flap. A variety of configurations were calculated to study the effect of flap parameters, such as the flap angle, position, and shape, on the bionic airfoil aerodynamic characteristics based on two layouts which were that (1) there was a tiny gap between the airfoil and the flap and (2) there was no gap between the two. The results showed that the flap angle and position had significant effects on the aerodynamic performance of the airfoil with the two layouts. Compared with the clean airfoil, the maximum lift coefficients of the first layout and the second layout could be increased by 10.9% and 7.9%, respectively. And the effective angle of attack (AoA) range for improving the lift-to-drag ratio could reach 7°. The flap shape also affected the airfoil aerodynamic characteristics, and the flap with the sinusoid curve shape showed ideal performance.

Investigation on aerodynamic performance of wind turbine blades coupled with airfoil and herringbone groove structure

The advantage of wind energy is significant to the improvement of energy structure. This paper is mainly to demonstrate a bionic design for wind turbine blades inspired by the airfoil of owl wing and the herringbone groove structure of owl feathers. The blade of A 200 W horizontal axis wind turbine is taken as prototype blade. The design of bionic airfoil blade is based on 50% and 70% cross section airfoils of owl wing, which is combined with the parameters of the prototype blade. The design of bionic coupling blade is based on bionic airfoil blade, which is coupled with the herringbone groove structure. Numerical simulation is utilized to study the aerodynamic performance of all blades. These simulations utilize an incompressible Reynolds-averaged Navier–Stokes solver and shear stress transport k–ω turbulent model at different tip speed ratios (TSRs). Results show that the power coefficient (Cp) of bionic airfoil blades is higher than that of prototype blade in the TSR of 6–9; the Cp of bionic coupling blades is higher than that of bionic airfoil blades in the TSR of 6–10. The larger curvature of leading edge of blades leads to larger flow velocity, which leads to the smaller pressure on the leeward surface. The herringbone groove structure enhances the flow attachment by generating vortices, which reduces the pressure on the leeward surface of bionic coupling blades. Compared with the prototype blade and bionic airfoil blade, the pressure difference between the windward surface and the leeward surface of the bionic coupling blade is larger.

Numerical study on the airfoil self-noise of three owl-based wings with the trailing-edge serrations

Previous publications have summarized that three special morphological structures of owl wing could reduce aerodynamic noise under low Reynolds number flows effectively. However, the coupling noise-reduction mechanism of bionic airfoil with trailing-edge serrations is poorly understood. Furthermore, while the bionic airfoil extracted from natural owl wing shows remarkable noise-reduction characteristics, the shape of the owl-based airfoils reconstructed by different researchers has some differences, which leads to diversity in the potential noise-reduction mechanisms. In this article, three kinds of owl-based airfoils with trailing-edge serrations are investigated to reveal the potential noise-reduction mechanisms, and a clean airfoil based on barn owl is utilized as a reference to make a comparison. The instantaneous flow field and sound field around the three-dimensional serrated airfoils are simulated by using incompressible large eddy simulation coupled with the FW-H equation. The results of unsteady flow field show that the flow field of Owl B exhibits stronger and wider-scale turbulent velocity fluctuation than that of other airfoils, which may be the potential reason for the greater noise generation of Owl B. The scale and magnitude of alternating mean convective velocity distribution dominates the noise-reduction effect of trailing-edge serrations. The noise-reduction characteristic of Owl C outperforms that of Barn owl, which suggests that the trailing-edge serrations can suppress vortex shedding noise of flow field effectively. The trailing-edge serrations mainly suppress the low-frequency noise of the airfoil. The trailing-edge serration can suppress turbulent noise by weakening pressure fluctuation.

Design approach and hydrodynamic characteristics of a novel bionic airfoil

Airfoil is the basic structure in the field of fluid machinery and is widely used in aerospace, petrochemical, and hydraulic machinery. In this study, three nonbionic airfoils (Sdown, Slevel, and Sup) in the side direction of sturgeon and three bionic airfoils (Stop1, Stop2, and Stop3) in the top direction of sturgeon were established via the B-spline curve-fitting technique. Different schemes were simulated by applying large eddy simulation. The simulation results are consistent with the experimental results. The lift coefficient of an asymmetric bionic airfoil is significantly greater than that of a symmetric airfoil, with Sdown scheme having the largest lift coefficient. The vortex region is related to velocity fluctuation and Reynolds stress distribution. When the vortex region is close to the tail edge, it has a minimal effect on the mainstream. The leading edge of the asymmetric bionic airfoil is prone to vortices, and the vortex area is associated with the upwarping angle of the leading edge. The leading edge of the symmetric bionic airfoil tends to form a stable vortex structure; as the stable vortex area expands, the lift coefficient increases correspondingly. These findings can provide theoretical support for the design of hydraulic blades.

Research on aerodynamic performance of a novel dolphin head-shaped bionic airfoil

Based on the special streamline profile of the Phocoenoides dalli head, this paper innovatively proposes to transform the NACA 0018 airfoil into a novel airfoil whose leading edge is similar to the streamline profile of the Phocoenoides dalli head, and makes corresponding minor adjustments to this new airfoil according to the dolphin’s motion behavior, and eventually obtains three kinds of dolphin head-shaped new airfoils including the Original Dolphin Airfoil, the Smooth Transition Dolphin Airfoil and the Deflected Dolphin Airfoil. Due to different deflection angles, the Deflected Dolphin Airfoil is then subdivided into five different types. The aerodynamic performances of these three dolphin head-shaped new airfoils as well as the NACA 0018 airfoil are simulated by using the SST k-ω model at Re = 1.6 × 105. The results show that: Compared with the NACA 0018 airfoil, firstly, the aerodynamic performances of three kinds of dolphin head-shaped airfoils are quite different from each other because of the change of the curvature and the radius of the leading edge. Secondly, by comparing the lift and drag coefficients of the Deflected Dolphin Airfoils with five deflection angles, it is speculated that there is an optimal deflection angle for the Deflected Dolphin Airfoil under the conditions of this paper. Eventually, the deflection angle of 24° is found to be the optimal value among these five different deflection angles. The results of this study can provide reference for improving the performance of blade design, such as the rotating mechanical blades, the aeronautical blades, etc.