Wavy Leading Edge Research Articles

Numerical investigation of drag reduction effects on a track bicycle fork using wings with a wavy leading edge

AbstractReynolds‐averaged Navier–Stokes (RANS) and large‐eddy simulations (LES) of the flow around wings with a wavy leading edge (WLE) are conducted in order to assess the capabilities of a passive flow control strategy for drag reduction. The intended application is indoor track cycling with controlled flow conditions. A section of a single fork rod is investigated in order to make the numerical simulations feasible. The present study reveals that net drag reduction is possible by a nonsinusoidal modification of the leading edge of the wing. However, the drag reduction effect remains limited to a few percent. While RANS and LES yield the same drag coefficient for a reference case, RANS underestimates the drag reduction effect for a longer wing and the WLE cases, but exhibits otherwise a qualitatively similar trend as the LES. With the aid of RANS, an optimal geometry is obtained defined by the wavelength‐to‐chord length ratio of and the amplitude‐to‐chord length ratio of . Corresponding LES results give an indication of the origin of drag reduction by a hampered vortex shedding. The generation of smaller and more streamwise oriented vortical flow structures at the trailing edge and behind the WLE wing is correlated with significantly reduced lift fluctuations and drag reduction.

Stall characteristics of wavy leading-edge airfoil in subsonic and transonic airflows

Based on the bioinspired wavy leading-edge, the stall characteristics of the NACA0012 airfoil are optimized. In this paper, the semicircle plus line segment is used to obtain the wavy leading edge. The aerodynamic forces of the airfoil are measured by a high-precision balance, and the detailed flow features of the airfoil are obtained by the oil flow tests. Then, combined with numerical simulation, the optimization mechanism is obtained. The operating conditions are as follows: Mach number ranging from 0.4 to 0.8, and angle of attack ranging from −4° to 25°. The results show that in high speed airflows, compared with the basic airfoil, the lift coefficient of the wavy leading-edge airfoil does not decrease sharply with the increase of the angle of attack, and the drag coefficient of the wavy leading-edge airfoil is similar to the basic airfoil; among the three types of airfoils studied, the larger wavy leading-edge feature size has better aerodynamic characteristics; combined with the numerical simulation results, it can be seen that the stall mechanism of airfoils varies at different Mach numbers. The wavy leading-edge generate streamwise vortex. The streamwise vortices increase energy transport in the boundary layer. Therefore, the separation zone moves toward the trailing edge of the airfoil, and the stall characteristics of the airfoil are optimized.

Analysis of wavy leading-edge noise reduction and source mechanism in rod-airfoil interactions

Inspired by the wings of owls and the tubercles present on humpback whales' flippers, leading-edge serrations have demonstrated the potential to mitigate airfoil–turbulence interaction noise. To deepen our understanding of the underlying mechanisms driving this noise reduction, we conducted compressible large-eddy simulations on a rod-airfoil configuration equipped with wavy leading edges (WLEs) of varying amplitudes. All tested serrations exhibited some degree of noise reduction, with the amplitude of the WLE exerting a significant influence on the overall noise reduction effect. Notably, the wavy airfoil with the largest amplitude demonstrated the most substantial noise reduction in the mid-frequency range, achieving a remarkable decrease in up to 2.2 dB in noise levels. Applying multi-process acoustic theory, we delved into sound production on surfaces and near-field structures responsible for generating noise sources. Our findings underscore a crucial mechanism contributing to noise reduction—the source cutoff effects manifested through the significant weakening of noise sources at hill regions along the serrations' surface. Stronger source cutoff effects were observed with larger WLE amplitudes. Furthermore, our study reveals that destructive relationships among sources also play a pivotal role in reducing flow noise. The reduction in mid-frequency noise results from a synergy of the source cutoff effect and destructive source relationships induced by WLEs, while the decrease in low-frequency noise primarily emanates from the source cutoff effect.

Acoustic signature and wake structure investigation of a cavitating marine propeller operating in proximity to a rudder with an optimized leading-edge pattern

The present study implements high-fidelity numerical modeling to investigate the cavitating flow around a marine propeller operating upstream of a rudder with an optimized wavy leading-edge (WLE), based on a NACA 634-021 profile bio-inspired by a pectoral flipper of a humpback whale (Megaptera novaeangliae). The aim of the study work is to identify the acoustic signature and wake structure of the propeller-rudder system, comparing it to that with a straight leading-edge (SLE) rudder. The propeller (INSEAN E779A model) operated under diverse marine maneuvering conditions (rudder angles of attack α = 0°, 10°, and 20°) with three distinct leading-edge patterns of the rudder. Large eddy simulations (LES) in conjunction with the Sauer cavitation method and the compressive volume of fluid (VOF) model were utilized to simulate the unsteady cavitating flow using the OpenFOAM platform. Additionally, the Ffowcs Williams–Hawkings (FW-H) acoustic analogy, continuous wavelet transform (CWT), and fast Fourier transform (FFT) were employed to predict and analyze the hydroacoustic response. We propose an optimized propeller-rudder configuration for minimizing the radiated sound levels, thus mitigating the harmful effects of noise pollution on marine ecosystems, while maintaining high propulsive efficiency over a wide range of operating conditions.

Experimental Investigation of the Effect of Bio-Inspired Wavy Leading-Edges on Aerodynamic Performance and Flow Topologies of the Airfoil

The characteristic of delayed airfoil stalls caused by the bio-inspired Wavy Leading-Edges (WLEs) has attracted extensive attention. This paper investigated the effect of WLEs on the aerodynamic performance and flow topologies of the airfoil through wind tunnel experiments, while also discussing the flow control mechanism of WLEs. The result shows that, at small Angle of Attack (AOA), the flow through the WLEs exhibits periodic and symmetrical characteristics, where flow vortices upwash at the trough and downwash at the crest, resulting in flow from the crest to the trough. Upwash leads to the formation of a localized three-dimensional laminar separation bubble (LSB) structure at the leading edge of the trough section. At large AOA after baseline airfoil stall, the flow on the airfoil surface of WLEs presents a two-period pattern along the spanwise direction, and the separation zone and the attachment zone appear alternately, indicating that the control effect of delayed stall is accomplished by reducing the separation zone on the airfoil surface. The alternating occurrence of the separation and attachment zones is the result of intricate interactions among flows passing through multiple WLEs. This interaction causes the convergence of high-momentum attached airflows on both sides, thereby constraining the spread of the separation from the leading edge and enabling the re-attachment of separated air. The research results of this paper provide a reference for researchers to reveal the flow control mechanism of WLEs more comprehensively.

On the reduction of the noise in a low-pressure turbine cascade associated with the wavy leading edge

The low-pressure turbine (LPT) has become a potential noise source for future ultra-high by-pass ratio engines. In this paper, the feasibility and mechanism of wavy leading edge (WLE) noise control in the LPT cascade model are analyzed. The flow field and acoustic data are obtained with the large eddy simulation and Ffowcs Williams–Hawkings methods, which are validated using experimental data. The acoustic results are compared for different models; the maximum noise reduction can achieve 8.6 and 3.7 dBA in the frequency bands of FR#2 (315–4000 Hz) and FR#4 (6300–16 000 Hz), respectively; the noise reduction does not vary proportionally to the WLE parameter. The noise source is identified in the baseline model, and then the effect of WLE amplitude and wavelength on the noise source and its control on pressure fluctuations are evaluated. The pressure statistics demonstrate that WLE with a smaller wavelength and a larger amplitude can reduce the impingement of stator wakes on the leading edge of the rotor and stabilize the pressure fluctuation. To analyze the mechanism of WLEs on noise control, the pressure spectrum in terms of amplitude and coherence coefficient is utilized to explain the excellent noise performance of the WLE model in FR#2. The proposed similarity coefficient of coherence can quantify the destructive interference level and thus the coherence characteristics of the sound source. Generally, the noise reduction level can be predicted by the combination of the similarity coefficient and the amplitude spectrum of the pressure fluctuations for the WLE models.

Coupling Bionic Design and Numerical Simulation of the Wavy Leading-Edge and Seagull Airfoil of Axial Flow Blade for Air-conditioner

It is essential to maintain the aerodynamic performance of the air-conditioning system meanwhile reducing the noises (including aerodynamic, broadband, and discrete noises), determining the consumer's comfort level. In this work, depending on the coupling of the wavy leading-edge and the seagull airfoil, the aeroacoustics noise and aerodynamic performance of the impellers with the coupling bionic blade were investigated in detail. The results indicate the aerodynamic performance was improved by the coupling bionic optimization. Moreover, the total pressure efficiency (η) of the coupling bionic blade increases by 2.28% in comparison to the original blade. Furthermore, A smaller static differential pressure is observed between the suction and pressure sides, and vortices and backflows from the pressure side to the suction side are hampered, causing a reduction in turbulence noise. Additionally, the broadband noise of the coupling bionic blade decreases by 3.59 dB. Besides, the coupling bionic blade improves the directivity of the sound pressure level, especially in the middle-frequency and low-frequency region, resulting in a decrease of 7.9 dB for the aeroacoustics noise of the coupling bionic blade. What's more, the modal analysis demonstrates the security of the designed coupling bionic blade. In generally, this work provides some inspiration to design axial flow fans with excellent aerodynamic performance and low-noise characteristics.

Wavy Leading Edge (WLE) Influence on a Rectangular Wing Using an Unsteady Analysis Approach

A rectangular wing with Wavy Leading Edge (WLE) effect was investigated experimentally and numerically. This research was carried out with the NACA 0018 profile. The morphology of humpback whale flippers, which are blunt and rounded in a specific pattern, inspired the design of the WLE. The rectangular wing was explored in pitching motion with a reduced frequency of k = 0.25 and varied aspect ratios. Multiple aspect ratios (AR) of the rectangular wing have been evaluated to determine the best wing aspect ratio, notably 3.9, 5.1, and 7.9. Only at AR 3.9 and 5.1 does the WLE perform efficiently in both upstroke and downstroke motion. WLE has a sinusoidal function shape. The improvement of lift force was stronger during upstroke motion than during downstroke motion. The stall is minimized during the pitching motion of the WLE wing, according to the numerical simulation. This result could be applied to fin stabilizers or wind turbines.

Effect of Wavy Leading Edges on Airfoil Trailing-Edge Bluntness Noise

Among the several noise-generation mechanisms of airfoil self-noise, trailing-edge bluntness noise is an important noise source, which is caused by the vortex shedding at blunt trailing edges. A numerical study on airfoil trailing-edge bluntness noise control using the bio-inspired wavy leading edges is presented in this paper. The high-fidelity, improved, delayed, detached eddy simulation (IDDES) method was used to calculate the flow field, and the acoustic analogy method was used for noise prediction. For both the blunt-trailing-edge airfoils, a baseline airfoil with a straight leading edge and a bio-inspired airfoil with a wavy leading edge were used in this study. The chord-based Reynolds number was 400,000, and there was no angle of attack. The numerical results show that the trailing-edge bluntness noise of the baseline airfoil was significantly reduced by the wavy leading edges. The sound pressure level reduction was about 3.7 dB at the characteristic frequency, and the maximum sound pressure level reduction was as high as 35 dB. The trailing-edge bluntness noise was decreased at all directional angles. The maximum overall sound pressure level reduction was 6.3 dB at 0°. In addition, by analyzing the pressure fluctuations, wake characteristics, turbulent vortex structures and spanwise correlation and coherence of the flow field, the noise-reduction mechanisms of the bio-inspired airfoil are deeply revealed.

Unsteady Aerodynamic Design of a Flapping Wing Combined with a Bionic Wavy Leading Edge

Based on the bionic design of the humpback whale fin, a passive flow control method is proposed to obtain greater flapping lift by applying the wavy leading edge structure to the straight symmetrical flapping wing. The leading edge of the conventional flapping wing is replaced by the wavy shape represented by regular trigonometric function to form a special passive flow control configuration imitating the leading edge of the humpback whale fin. The dynamic aerodynamic performance and flow field characteristics of straight wing and wavy leading edge flapping wing with different parameters are compared and analyzed by CFD numerical simulation. The simulation results show that the wavy leading edge structure changes the flow field of the baseline flapping wing and reduces the pressure on the upper surface of the flapping wing during the process of downward flapping, thereby increasing the pressure difference between the upper and lower surfaces of the flapping wing and increasing the lift. The sensitivity analysis of the design parameters shows that in order to obtain the maximum lift coefficient while losing the least thrust, the smaller amplitude should be selected on the premise of selecting the smaller wavelength. Among the configurations of different design parameters calculated in this paper, the optimal wavy leading edge flapping wing configuration increases the time average lift coefficient by 32.86% and decreases the time average thrust coefficient by 14.28%. Compared with the straight wing, it has better low-speed flight and can withstand greater take-off weight.

Identification of frequency modes and spectral content for noise suppression: Cavitation flow over 3-D hydrofoil with sinusoidal leading edge

The impetus of this study is to provide an in-depth insight into the unsteady hydrodynamic characteristics of the cavitating flow, effects of the wavy leading edge (WLE) on the noise suppression mechanism due to a cavity cloud formation, which contains condensation, detachment, collapse, spanwise flow, streamwise velocity fluctuation, and shedding phenomenon. NACA 634-021 hydrofoil was considered with WLE having a wavelength of 25% and an amplitude of 5% of the mean chord length and was compared to a straight-leading-edge (SLE) hydrofoil at cavitation numbers of [Formula: see text] and a chord-based Reynolds number of [Formula: see text]. Counter-rotation vortices were produced between the peaks of the WLE hydrofoil by destroying the horseshoe vortex and delaying the tail vortex, changing the frequency. Here, the hydrodynamic forces have also been discussed in addition to the noise. The results showed that the leading-edge vortex formation and flow separation dynamics fundamentally differed between the SLE and the WLE hydrofoil. The main difference between the WLE and SLE hydrofoil turbulent flow is the formation of counter-rotating streamwise vortices pairs. We solved the cavitating flow using the large eddy simulation (LES) approach, as well as the Kunz mass transfer model, which is performed under the framework of the OpenFOAM package.

Numerical Investigation of Flow Past Bio-Inspired Wavy Leading-Edge Cylinders

A numerical investigation is proposed to explore the flow past a novel wavy circular cylinder as a passive flow control, whose shape is determined by a sinusoidal function applied to its leading edge line, similar to studies with wavy leading-edge airfoils. The latter are motivated by the wavy-shaped tubercles found in the flippers of humpback whales, which are believed to improve their maneuverability. Our attempt is, therefore, to assess the effects of leading-edge waviness now on a simpler and canonical geometry: circular cylinders. The present work relies on iLES simulations conducted with Nektar++ at a Reynolds number of 3900. Besides the straight cylinder, two wavy geometries are assessed, which are determined by a single wavelength of 37.5% for two amplitudes, 3% and 11%, based on the mean diameter of the wavy cylinder. Our results showed that, contrary to what is usually the case with traditional wavy cylinders at similar Reynolds numbers, waviness caused a reduction in the near-wake recirculation length and an increase in the mean near-wake turbulent kinetic energy compared to the straight cylinder. This was followed by a reduction in base pressure (up to about 36%) leading to a rise in lift oscillations and also to a significant increase in the mean drag coefficient of up to about 28%. An attempt to detail the flow phenomena is provided, evidencing the emergence of counter-rotating pairs of streamwise vortices between peaks. It is argued that the differences observed in recirculation length, turbulent kinetic energy, and force coefficients start even prior to the formation of these coherent structures and end up with interactions with the near wake.

Numerical Investigation of Plasma Actuator Effects on Flow Control Over a Three-Dimensional Airfoil With a Sinusoidal Leading Edge

Abstract The impetus of the present bio-inspired work is to investigate the impact of simultaneously using wavy leading-edge (WLE) airfoils in combination with curved multidielectric barrier discharge (DBD) plasma actuators as hybrid passive and active flow control mechanisms, respectively. A precise distinction of the produced frequency and noise signals, altogether with the acoustic effect of using WLE and DBD plasma actuators, is herein analyzed with precision. Two specific DBD plasma actuators are designed to actuate at x/C = 3% and x/C = 30% on a NACA 634-021 airfoil with sinusoidal WLE that bears a wavelength of 25% and an amplitude of 5% of the mean chord length and straight-leading-edge (SLE). A large eddy simulation (LES) turbulence model was used. This includes the dynamic control of unsteady flow separation, the three-dimensional vortical structure and induced trains of vortices, the aerodynamic forces, the velocity variation, and also the spanwise flow. The momentum transfer between the main flow and boundary layer was improved by the DBDs-induced vortices train and formed streamwise counter-rotating pair-of-vortices over the tubercle. Also, both the continuous wavelet transform (CWT) and fast Fourier transform (FFT) methods were used to investigate the induced plasma flow spectral content for the WLE and SLE geometries. We witnessed an optimized flow control, by using DBD plasma actuators with the WLE airfoil, that resulted in less massive flow separation, faster turbulent transition, and a robust earlier flow reattachment. This modification was beneficial in increasing the efficiency and decreasing the noise for low Reynolds number operational conditions.

Effect of the Wavy Leading Edge to Aerodynamic Performance Improvement in A Nuclear Steam Turbine Last Stage Blade

Effect of the Wavy Leading Edge to Aerodynamic Performance Improvement in A Nuclear Steam Turbine Last Stage Blade

Optimizing Effect of Wavy Leading Edge (WLE) in Rectangular Wing and Taper Wing

Experimental and numerical research have been performed to investigate the Wavy Leading Edge (WLE) effect on the rectangular wing. The WLE is inspired by humpback whale flipper morphology which is blunt and rounded in certain form pattern. This flipper shape plays an important role for its behaviour specially capturing their prey. This advantage could be applied to other systems such as fin stabilizers or wind turbines. Steady cases in various aspect ratios were conducted to find out the optimum effect of WLE with baseline NACA 0018 profile at Reynolds number 1.4 x 105. The chord length of the wing (c) was 125 mm. The WLE shape defined as wavelength (W) 8% of c and amplitude (d) is 5% of c. The aspect ratio (AR) variations were 1.6; 3.9; 5.1; 7.9 and 9.6. A simple rectangular form of the wing was selected to analysis the WLE effect on the various ARs. The taper wing shape is applied to find out the WLE effect at the AR 7.9. three types of taper ratio (TR) are 0.1; 0.3 and 0.5. The results show that the WLE on the taper wing has better advantage to control the stall in steady case. Another impressive result was the WLE wing with AR 7.9 and TR 0.3 has the best lift coefficient and pressure distribution.Keywords: stall, wavy leading edge, steady case, rectangle wing, taper wing, aspect ratio.

Numerical study on hydrodynamic performance and flow noise of a hydrofoil with wavy leading-edge

Flow control based on bionics provides new research ideas for noise reduction. As one of the flow control methods, the wavy leading edge (WLE) inspired by the leading edge tubercles of the humpback whale is proposed in this paper. The hydrodynamic performance and flow noise of a National Advisory Committee for Aeronautics 0020 hydrofoil subjected to three WLEs are numerically investigated. A hybrid numerical method of large eddy simulation combined with the Ffowcs Williams–Hawkings equation is adopted to obtain the unsteady flow properties and predict the far-field noise. At a Reynolds number of 3.05 × 105, the simulation results show that the addition of WLEs can reduce the lift coefficient fluctuation but will increase the drag coefficient slightly. In addition, the WLE can reduce the OverAll Sound Pressure Level of the hydrofoil by up to 7.28 dB. The analysis of the flow features shows that the WLE can reduce the pressure fluctuation on the hydrofoil surface, which is directly beneficial to the noise reduction. Moreover, the WLE enhances the spanwise flow of the hydrofoil, produces streamwise vortices, and reduces the spanwise coherence coefficient at both the leading edge and trailing edge.

Bionic leading-edge protuberances and hydrofoil cavitation

Cavitation is a challenging and complex phenomenon in hydraulic machineries such as pumps, turbines, and marine propellers. The shedding and collapse of the cavitation cloud are responsible for hydraulic instability. Recently, the modified wavy leading-edge hydrofoil has attracted considerable attention for passive cavitation control. To reduce hydrofoil cavitation, the leading-edge protuberances of humpback whale flippers were introduced in hydrofoil modification, and its effect on the cavitation flow was investigated in the present study. First, a sinusoidal modification method for the leading-edge of the hydrofoil was adopted. The lift and drag coefficients, cavitation morphology, and flow characteristics of the basic and bionic hydrofoils were numerically calculated using the large eddy simulation method, and the accuracy of the numerical model was verified via comparison with available experimental results. Then, the wavelengths (0.25C, 0.5C) and amplitudes (0.05C, 0.12C) of the leading-edge protuberances were varied to study the effects of the structural parameters on the cavitation. The results indicated that the wavy leading-edge can improve the lift–drag characteristics, restrain the hydrofoil cavitation, and reduce the cavitation volume by approximately 30%. Reducing the wavelength and increasing the amplitude help restrain the instability of cavitation shedding. Increasing the amplitude can reduce the pressure amplitude by approximately 60%, significantly reduce the cavitation volume, and enhance the cavitation suppression.

Mitigation of transonic shock buffet on a supercritical airfoil through wavy leading edges

Mitigation of the shock buffet phenomenon over a supercritical airfoil by means of wavy leading edges (WLEs) is analyzed with implicit large eddy simulations. A Dassault Aviation's V2C airfoil is simulated in a transonic flow with Re∞=5.0×105 and M∞=0.7 at α=7.0°. This airfoil profile is designed for transonic flows, delaying the onset of wave drag and decreasing the skin friction drag. The results of this upstream flow condition on a straight airfoil are a large oscillation of lift and drag coefficients. In the first part, time-averaged aerodynamic characteristics over a straight leading edge (SLE) airfoil and three modified airfoils with different wavy amplitudes are compared. The results show that overall WLE airfoils are more efficient than SLE ones, and the airfoil with the lowest amplitude (h = 0.0075) is the most efficient, increasing the lift coefficient and decreasing the drag coefficient. Flow unsteadiness plays a key role for airfoils in transonic flows at moderate and high angles of attack. Hence, the second part of the paper is a detailed unsteady analysis of flow phenomena. The starting point is an investigation of unsteady aerodynamic performance. It is observed that WLE airfoils are capable of significantly decreasing low-frequency oscillations' amplitude, identified with shock buffet. The best performance is obtained with h = 0.0125 where a high-frequency oscillation becomes the dominant unsteady phenomenon. High-frequency oscillations are identified through the application of a frequency filtering method to the flow field. It is proved that the oscillation on the SLE airfoil is related to vortex shedding, while the one on WLE airfoils is related to laminar separation bubble (LSB) breathing. Overall, the unsteady analysis shows a connection between shock buffet and LSB breathing phenomena on wavy airfoils and identifies the WLE amplitude as a key parameter to control this relation and mitigate the shock buffet.

Aerodynamic performance and wake development of airfoils with wavy leading edges

A comprehensive numerical investigation is performed to study the aerodynamic performance and wake development of a NACA0012 airfoil with wavy leading edges (WLE). The WLEs are in the form of sinusoidal profiles with two design parameters of amplitude and wavelength. Parametric studies of the amplitude and wavelength are conducted to better understand the effect of WLEs. The chord length based Reynolds number is 400 000 and the angle of attack varies from 0° to 20°. For angles of attack less than the stall angle, steady Reynolds-averaged Navier–Stokes (RANS) computations are carried out using the SST (Shear Stress Transportation) k–ω turbulence model. For the post-stall angles of attack, unsteady simulations are carried out using the SST–SAS (Scale-Adaptive Simulation) model to solve the transient separation flow. The numerical results indicate that the aerodynamic performance of the wavy airfoil is sensitive to both the amplitude and wavelength of the WLEs. The WLE with a larger amplitude and smaller wavelength results in a worse aerodynamic performance. The drag coefficient is decreased significantly by the WLEs in the post-stall region. In addition, the wavy airfoils possess a soft stall process without the abrupt loss of the lift when the amplitude is large enough. The wake profiles for the wavy airfoils differ significantly from those for a conventional airfoil, especially for high angles of attack. In the post-stall regime of the baseline airfoil, the wavy airfoils have a higher wake deficit compared to the baseline airfoil, but the turbulence kinetic energy is reduced significantly. The leading edge separation vortex generated by the baseline airfoil is broken down into small vortices by the wavy modification, leading to a reduced lift and drag fluctuations.

Effect of Wavy Leading-Edges on Wings in Different Planetary Atmospheres

Effect of Wavy Leading-Edges on Wings in Different Planetary Atmospheres