Characteristics Of Airfoil Research Articles

Analytical Study of Double Wedge Airfoil for Supersonic Applications and Shape Modification for Subsonic Applications

A Double Wedge airfoil is an airfoil for supersonic blades and wings, with a wedge like tapered sharp leading and trailing edges. The shock waves and the expansion waves govern the supersonic characteristics of the double wedge airfoil. The present work is based on the design and aerodynamic analysis of double wedge airfoil at supersonic regime and shape modification of the airfoil for subsonic regime. The flow analysis is carried out using ANSYS Fluent, which is CFD based software. The supersonic analysis is performed for Mach number of 2.0. The airfoil was modified for subsonic applications and the analysis was performed for Mach number 0.7. Blowing technique was incorporated to further improve the aerodynamic performance of the modified double wedge airfoil. From the simulated results, it was found that the co-efficient of drag of double wedge airfoil at Mach number of 2.0 agreed with the manual calculations. The modified airfoil gave optimum performance with the addition of a blowing stream at subsonic speeds.

Influence of Reynolds number on the performance of small horizontal axis wind turbine with fixed speed operation

ABSTRACT The Blade Element Momentum (BEM) theory is most commonly utilized to quickly assess the performance of horizontal axis wind turbine. However, the BEM theory requires the aerodynamic characteristic of the airfoil to evaluate the performance. Generally, the aerodynamic characteristics of airfoil in BEM theory for performance prediction of wind turbine with fixed rotor speed operation is obtained at an approximated fixed Reynolds number which may not accurately correspond to the operating Reynolds number over the blade. In the present work, the performance of a small wind turbine, with fixed rotor speed operation, and considering a range of approximated fixed Reynolds number (i.e., 0.5, 0.75, 1.00, and 1.25 million) and the operational Reynolds number over the blade for the aerodynamic characteristic of the airfoil has been evaluated and compared for a range of wind speeds i.e., 6, 8, 10, and 12 m/s. To incorporate the operational Reynolds number in the study, the aerodynamic characteristics of the airfoil have been mathematically represented as function of Reynolds number and angle of attack using an artificial neural network (ANN)-based model. The results suggest that inadequate Reynolds number consideration can led to high discrepancies up to 18.6% in power coefficient prediction.

Experimental and numerical analysis of humpback whale inspired tubercles on swept wings

PurposeWith aims to increase the aerodynamic efficiency of aerodynamic surfaces, study on flow control over these surfaces has gained importance. With the addition of flow control devices such as synthetic jets and vortex generators, the flow characteristics can be modified over the surface and, at the same time, enhance the performance of the body. One such flow control device is the tubercle. Inspired by the humpback whale’s flippers, these leading-edge serrations have improved the aerodynamic efficiency and the lift characteristics of airfoils and wings. This paper aims to discusses in detail the flow physics associated with tubercles and their effect on swept wings.Design/methodology/approachThis study involves a series of experimental and numerical analyses that have been performed on four different wing configurations, with four different sweep angles corresponding to 0°, 10°, 20° and 30° at a low Reynolds number corresponding to Rec=100,000.FindingsResults indicate that the effect of tubercles diminishes with an increase in wing sweep. A significant performance enhancement was observed in the stall and post-stall regions. The addition of tubercles led to a smooth post-stall lift characteristic compared to the sudden loss in the lift with regular wings. Among the four different wings under observation, it was found that tubercles were most effective on the 0° configuration (no sweep), showing a 10.8% increment in maximum lift and a 38.5% increase in the average lift generated in the post-stall region. Tubercles were least effective on 30° configuration. Furthermore, with an increase in wing sweep, co-rotating vortices were distinctly observed rather than counter-rotating vortices.Originality/valueWhile extensive numerical and experimental studies have been performed on straight wings with tubercles, studies on the tubercle effect on swept wings at low Reynolds number are minimal and mainly experimental in nature. This study uses numerical methods to explore the complex flow physics associated with tubercles and their implementation on swept wings. This study can be used as an introductory study to implement passive flow control devices in the low Reynolds number regime.

Influence of airfoil trailing edge on blade design and machining of small wind turbine

In the design of small wind turbine, narrow structure is often produced at the trailing edge of airfoil, which brings great difficulties to production and processing. In this paper, the airfoil sd7080 is modified by removing part of the airfoil trailing edge to meet the processing technology. Through the calculation and analysis of the Q blade software, part of the airfoil trailing edge is removed, and the airfoil and wind-wheel aerodynamic characteristics are changed. Results: Under the same angle of attack, after removing part of the airfoil trailing edge, The lift coefficient CL and drag coefficient Cd of the airfoil are reduced, α<8.6°, the lift-to-drag ratio CL/Cd decreases, α>8.6°, the lift-to-drag ratio Cl/Cd slightly increases; After removing the trailing edge of some airfoils, the wind energy utilization coefficient CP, torque and thrust of the wind turbine are slightly reduced, and the aerodynamic performance meets the use requirements. Finally, this paper introduces the blade modeling method, and processes the blade through 3D printing technology. The research provides reference significance for the initial design and processing of small wind turbine blades.

Reducing helicopter 1/rev vibration using extendable trailing-edge plate

Due to manufacturing errors and wear, helicopter rotor blades are not completely similar resulting in significant 1/rev fuselage vibration. In practice, rotor track and balance (RTB) based on neural network is used to eliminate the 1/rev vibration. This greatly increases the maintenance workload and cannot adjust the 1/rev vibration in flight. In view of this, a new RTB approach, namely, extendable trailing-edge plate (TEP), is studied in the present paper. Since TEP extension changes the profile of the baseline airfoil, the computational fluid dynamics (CFD) calculation is performed to study the aerodynamic characteristics of the airfoil with the extendable TEP under different extension amounts. Combined with the aerodynamic characteristics of the extendable TEP airfoil, a comprehensive helicopter aeromechanic analysis program adapted to the extendable TEP mechanism is used to explore the effects of the extendable TEP on the 1/rev fuselage vibration and hub loads. In addition, by analyzing the hub loads and the acceleration of the fuselage caused by the extendable TEP device, the mechanism of action is studied. Results show that the adjustment method based on extendable TEP is able to reduce the 1/rev acceleration of the fuselage by up to 85%–95%, which is about 8% higher than that of neural network-based algorithm. Therefore, the extendable TEP has great potential in RTB (i.e., eliminating rotor inherent dissimilarity). In addition, the factors that affect the 1/rev vertical vibration level of the airframe under different flight conditions are different.

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.

Insight into the effects of leading edge delamination on the aerodynamic performance of an airfoil and wind turbine

Severe erosion or delamination at the leading edge of blades has an adverse influence on the power loss of wind turbines. Obtaining relevant quantitative data and its mechanisms would help in the efficient management and maintenance of these turbines. In the present work, detailed analysis on the effects of various levels of leading edge delamination on the aerodynamics and flow characteristics of an S809 airfoil and, in turn, on the performance of the NREL phase VI rotor is conducted. The results indicated that an elongated leading edge separation bubble and two enclosed vortex systems appeared in the delaminated region of the airfoil when the delamination levels aggravate to a certain degree, while the trailing edge separation vortex can be observed for all delaminated airfoils. The aerodynamic performance of the wind turbine decreases with increasing delamination depth and increases with growing delamination depth. The most influential delamination length is 1%c, and the maximum power loss is 23.09% for the blade with the severe delamination case. A small area of deep leading edge delamination or defects may cause great power loss, which should not be ignored in practice engineering.

Aerodynamic characteristic of wind turbine with the leading edge slat and Microtab

The leading edge slat can increase the flow energy of airfoil suction surface, and Microtab can hinder the flow of pressure surface. In order to combine the advantages of two passive flow control methods, this paper creatively proposed to combine the leading edge slat with Microtab to simulate the S809 airfoil, which slat had the contour characteristics of S809 airfoil. The transition SST turbulence model was applied to estimate the aerodynamic characteristics of the S809 airfoil. According to research, the flow control approach of the leading edge slat combined with Microtab could effectively restrain the flow separation and ameliorate the aerodynamic characteristics of the S809 airfoil. For Case-12, when the airfoil angle of attack was 16.22°, the boundary layer flow separation was restrained completely, Cl was increased to 3.06 from 1.79 and increased by 171% compared with clear airfoil. Research shown that the position of slat, the position and height of the Microtab were significant factors for the aerodynamic characteristics of the S809 airfoil. Microtab position at 0.95c and height at 0.03c performed the best effect to inhibit flow separation and improve lift coefficients.

An improved LB method for predicting dynamic characteristics of Vertical Axis Wind Turbine airfoils

One of the important challenges for Vertical Axis Wind Turbine (VAWT) is to fully understand its dynamic characteristics in different operating conditions. Meanwhile, it is necessary to seek a fast and accurate method to evaluate the dynamic characteristic of VAWT. In this study, we improve the LB model by considering the operating principle of VAWT to study the dynamic characteristics of the dedicated and commonly used VAWT airfoils in different operating conditions. The results show that the improved LB model is suitable for simulating the dynamic characteristic of VAWT with a thick airfoil. Although the asymmetric airfoil shows the higher lift coefficient, their dynamic characteristic appears huge fluctuation as the increases of tip speed ratio. Moreover, at a low tip speed ratio, the advantages of the asymmetric airfoil are not obvious. While the dynamic characteristic of the symmetric airfoil is relatively stable with the variation of tip speed ratio.

Experimental Study for Separated Flow Control around Rotor Blades Using Highly Integrated Dielectric Barrier Discharge Plasma Actuator

Highly integrated dielectric barrier discharge (DBD) plasma actuators can be driven with a voltage one order of magnitude lower than that of conventional plasma actuators by properly arranging multiple electrodes, and can generate induced flow velocities of equal or greater magnitude. In addition, it is possible to control the large scale separation that occurs around the wings of aircraft and other devices, and thus to improve aerodynamic characteristics. In this study, a highly integrated DBD plasma actuator with multiple 20 electrodes was fabricated and applied to the wing surface to control the airflow from the leading edge to the trailing edge, and the aerodynamic characteristics of the NACA4412 airfoil were experimentally investigated. When the highly integrated DBD plasma actuator was driven, the lift coefficient was found to be improved compared to that with a conventional plasma actuator.

Influence of Distributed Leading-Edge Roughness on Stall Characteristics of NACA0012 Airfoil

Influence of Distributed Leading-Edge Roughness on Stall Characteristics of NACA0012 Airfoil

Influence of Lengthways Spacing and Phase Difference on Traveling Wave Energy Absorption Characteristics of Flexible Airfoils in a Diamond Array

Influence of Lengthways Spacing and Phase Difference on Traveling Wave Energy Absorption Characteristics of Flexible Airfoils in a Diamond Array

Numerical investigation of aerodynamic performance of leading edge tubercle airfoil at low Reynolds number

Numerical investigation was made to study the aerodynamic characteristics of the Tubercle NACA2412 airfoil is used in the design of aircraft wing and wind turbine blades. In this paper, computational study aimed to observe the aerodynamic characteristics of 3D airfoil NACA 2412 with peak and trough chord length as 100 mm and 80 mm respectively. The co-efficient of pressure performance of NACA2412 airfoil with tubercle leading edge profile blade used to investigate numerically for enhance the aerodynamics performance of Wind turbine. Investigation were made to find pressure distribution over the Tubercle airfoils under various freestream velocity conditions such as 5 m/s, 10 m/s, 15 m/s and 20 m/s with different angle of attacks from −30° to 30° with the step of 5°. The Spalart–Allmaras turbulent model was used to carry out simulations in the ANSYS Fluent software. Therefore, the Coefficient of pressure distribution is calculated at peak and trough of the tubercle airfoil at different operating conditions and results are plotted in the graph. It is observed that pressure distribution varies drastically near the leading edge for all velocities. Analysis for different velocities with a wide range of angle of attacks are discussed and presented with relevant details.

Simulation of Aerodynamic Performances of Flexible Flapping Wing Airfoils

Compared with fixed wings, the flapping wing has a significant aerodynamic performance advantage at low speeds and low Reynolds numbers, which draws more and more attentions. But most previous studies focus on rigid flapping airfoils, the aerodynamic performances of flexible flapping airfoils are still unclear. A fluid-solid coupling model for the flexible elliptical airfoils was developed to analyze the flow field around the airfoil, the airfoil deformation and the aerodynamic characteristics of airfoils, at different wind speeds and attack angles. Compared with the rigid airfoil, the flexible airfoil can delay the shedding time of the wake vortex and reduce the oscillation frequency of the disturbance on the lift force. The flexible airfoil significantly suppresses the disturbance of the wake flow and reduces the oscillation amplitude of disturbance. Even, the airfoil disturbance oscillation can be completely eliminated at an appropriate Young’s modulus of the airfoil. These results provide a theoretical guidance for the design of soft aircraft.

Convergence enhancement of SIMPLE-like steady-state RANS solvers applied to airfoil and cylinder flows

Iterative steady Reynolds-averaged Navier–Stokes (RANS) solvers are widely used to obtain polars representing the aerodynamic characteristics of airfoils. Unsteadiness is encountered in the flow for many of the simulated angles of attack due to phenomenon such as vortex shedding and separation bubbles. In such cases, the steady RANS solver may become numerically unstable. As a consequence it is unable to find a converged solution, with the solver residuals often entering limit cycle oscillations. The BoostConv method is an alternative to the classical Newton’s method to compute unstable steady-state solutions of dynamical systems. It has been previously applied for obtaining steady laminar solutions of the Navier–Stokes equations. However, it demonstrated a lack of robustness by failing to always find the steady-state turbulent solutions of the RANS equations. To overcome this problem, we propose a modification in the application of the BoostConv method to compute steady-state turbulent solutions of the RANS equations. The modified BoostConv method is coupled with an iterative steady RANS solver for computing converged two-dimensional steady-state flows over airfoils. The proposed modification in the application procedure introduces a relaxation parameter that improves the convergence and robustness of the BoostConv method. We show this by finding lift and drag curves with angles of attack spanning 360°for airfoils representative of those used in modern wind turbines. The flow solutions are converged to machine precision at all angles of attack using the novel application procedure of the BoostConv method. Additionally, for flow cases convergent with the original BoostConv method, the modified BoostConv method showed faster convergence rates. The proposed modification provides an enhancement of the BoostConv method that can be easily integrated into existing implementations. By improving the method’s robustness and convergence rates in finding steady-state turbulent solutions of the RANS equations, it opens up the modified BoostConv method to be used in a wide variety of industrial flow cases.

Accuracy of the Gamma Re-Theta Transition Model for Simulating the DU-91-W2-250 Airfoil at High Reynolds Numbers

Accurate computation of the performance of a horizontal-axis wind turbine (HAWT) using Blade Element Momentum (BEM) based codes requires good quality aerodynamic characteristics of airfoils. This paper shows a numerical investigation of transitional flow over the DU 91-W2-250 airfoil with chord-based Reynolds number ranging from 3 × 106 to 6 × 106. The primary goal of the present paper is to validate the unsteady Reynolds averaged Navier-Stokes (URANS) approach together with the four-equation transition SST turbulence model with experimental data from a wind tunnel. The main computational fluid dynamics (CFD) code used in this work was ANSYS Fluent. For comparison, two more CFD codes with the Transition SST model were used: FLOWer and STAR-CCM +. The obtained airfoil characteristics were also compared with the results of fully turbulent models published in other works. The XFOIL approach was also used in this work for comparison. The aerodynamic force coefficients obtained with the Transition SST model implemented in different CFD codes do not differ significantly from each other despite the different mesh distributions used. The drag coefficients obtained with fully turbulent models are too high. With the lowest Reynolds numbers analyzed in this work, the error in estimating the location of the transition was significant. This error decreases as the Reynolds number increases. The applicability of the uncalibrated transition SST approach for a two-dimensional thick airfoil is up to the critical angle of attack.

Experimental investigation of NACA-0012 airfoil instability noise with sawtooth trailing edges

This study presents an experimental study of the effect of sawtooth trailing-edge serrations on airfoil instability noise. The far-field noise measurements are obtained to investigate the noise radiation characteristics of a NACA-0012 airfoil operated at various angles of attack: 0°, 5°, and 10°, and covered Reynolds numbers of 2.87 × 105, 3.71 × 105, and 5 × 105. It is found that as the Reynolds number increases, the instability noise shifts from tonal to broadband, whereas as the angle of attack increases, it shifts from broadband to tonal. Furthermore, sawtooth trailing-edges are used to minimize instability tonal noise, leading to considerable self-noise reduction. Parametric studies of the serration amplitude 2 h and streamwise wavelength λ are performed to understand the effect of sawtooth trailing-edges on noise reduction. It is observed that the sound pressure reduction level is sensitive to both the amplitude and streamwise wavelength. Overall, the sawtooth trailing-edge with larger amplitude and smaller wavelength produce the greatest amount of noise reduction.

Aerodynamic noise characteristics of airfoils with morphed trailing edges

Numerical investigation of the aerodynamic and aeroacoustic characteristics of a symmetrical NACA 0012 airfoil developed by National Advisory Committee for Aeronautics (NACA) with a conventional hinged flap and a morphed flap has been carried out. The unsteady flow characteristics over the airfoil surface and at the airfoil wake are captured using high-fidelity Large Eddy Simulations. The tests were carried out for a freestream velocity of U∞=20 m/s, corresponding to a chord-based Reynolds number of Rc=2×105, at angles of attack α=0° and 4°. The results of the airfoil static pressure distribution show that the airfoil with morphed trailing edge produces higher values of lift coefficient than the airfoil with hinged trailing edge due to its higher suction peak resulting in larger pressure difference between the suction and pressure sides. Furthermore, from the wake-flow measurements, boundary-layer analysis, wall-pressure spectra, space–time correlation, it is concluded that the Morphed airfoil produces higher values of surface pressure fluctuations near the trailing edge which extend farther into the wake of the trailing edge compared to the Hinged airfoil. Consequently, the increased pressure fluctuations at the vicinity of the trailing edge results in a higher values of radiated far-field noise for the airfoil with morphed trailing edge flap.

CFD Comparative Study on Bended and 2D Airfoils on HAWT Performance

The design of a conventional horizontal axis wind turbine (HAWT) is based on the aerodynamic characteristics of a two-dimensional (2D) airfoil. The rotational motion and the consequent aerodynamic effects, of HAWT’s rotor, do not guarantee an optimal design point that matches the 2D airfoil characteristics. The present work studies the diversion of the flow due to the spanwise velocity component in a rotating reference frame. It suggests that a slight deviation in the flow away from the chordwise direction could alternate the characteristics of the airfoil profile. A bended profile with a circular arc was extracted from a baseline rotating blade, flattened, and modelled against the 2D S826 airfoil. The results show a substantial discrepancy in the airfoil characteristics which could influence the turbine efficiency. Therefore, it suggests using a pre-bended airfoil (3D) while modeling the blade, so the circular section will match the correct airfoil coordinates. The proposed bended-profile version was modeled against the baseline blade. This novel blade shows an augmentation in the power coefficient up to 5.4% starting from the design point to high tip speed ratios (TSR) and low wind speeds.

Lift performance enhancement for flapping airfoils by considering surging motion

The flapping motion has a great impact on the aerodynamic performance of flapping wings. In this paper, a surging motion is added to an airfoil performing pitching-plunging combined motion to figure out how it influences the lift performance and flow pattern of flapping airfoils. Firstly, the numerical methods are validated by a NACA0012 airfoil pitching case and a NACA0012 airfoil plunging case. Then, the E377m airfoil which has typical geometric characteristics of the bird-like airfoil is selected as the calculation model to study how phase differences φ1 between surging motion and plunging motion affect the aerodynamic performance of flapping airfoils. The results show that the airfoil with surging motion has comprehensively better lift performance and thrust performance than the airfoil without surging motion when 15°<φ1 < 90°. It is demonstrated that surging motion has a powerful ability to improve the aerodynamic performance of flapping airfoil by adjusting φ1. Finally, to further explore how flapping airfoil improves lift performance by considering surging motion, the flapping motions of E377m airfoil with the highest lift coefficient and lift efficiency are obtained through trajectory optimization. The surging motion is removed in the highest lift case and highest lift efficiency case respectively, and the mechanism that surging motion adjusts the aerodynamic force is analyzed in detail by comparing the vortex structure and kinematic parameters. The results of this paper help reveal the aerodynamic mechanism of bird flight and guide the design of Flapping wing Micro Air Vehicles (FMAV).