NACA0012 Aerofoil Research Articles

Hybrid control of aerofoil self-noise by coupling air blowing and trailing-edge serration

Active and passive control methods have been extensively studied and employed for reducing turbulent-boundary-layer (TBL) trailing-edge (TE) noise of aerofoils, for example air blowing and TE serration. To further explore the potential of noise reduction, this paper proposes a hybrid method coupling blowing and serration at the trailing edge, and investigates the effects of air blowing, TE serration, and the hybrid blowing-serration (HBS) on the TBL TE noise of a NACA0012 aerofoil at a Reynolds number of Rec=4×105. Large eddy simulation and Ffowcs Williams–Hawkings acoustic analogy were used to analyse these effects and the respective noise reduction mechanisms. The numerical results show that the HBS method exhibits superior acoustic performance to the blowing and serration methods, with a maximum reduction of 20.5 dB in broadband noise and 5.7 dB in overall sound pressure level. It is revealed that the HBS method functions primarily through three noise reduction mechanisms. Firstly, blowing eliminates the outward flow motion at the serration root and tip, resulting in a forced flow alignment. Secondly, it weakens the turbulence energy in the near wake as for air blowing. Finally, this method mitigates spanwise coherence at the trailing edge, thereby causing destructive interference of noise sources, similar to the effect of TE serration.

Effect of structured trapezoidal riblet on flow characteristics over a NACA0015 aerofoil

Effect of structured trapezoidal riblet on flow characteristics over a NACA0015 aerofoil

Vorticity forces of coherent structures on the NACA0012 aerofoil

This study examined the impact of coherent structures on the aerodynamic forces exerted on a NACA0012 aerofoil with angles of attack $7.5^{\circ }$ and $10^{\circ }$ , and a chord-based Reynolds number $50\,000$ . The study utilized the spectral proper orthogonal decomposition (SPOD) algorithm to identify the coherent structures, and vorticity force analysis to quantify their impact on lift and drag forces. Results showed that at $10^{\circ }$ , the zeroth frequency of the first SPOD mode had a significant impact on drag and lift forces due to a large vortex structure that caused a strong flow along the suction side of the aerofoil. The first and second frequencies of the first SPOD mode represented asymmetric vortex pairs and a series of vortex pairs that determined the leading-edge separation, respectively. At $7.5^{\circ }$ , the zeroth frequency of the first mode corresponded to an oscillating near-wall stream that followed the reattachment flow pattern, while the first frequency corresponded to a counter-rotating vortex pair that originated where the flow reattaches. Finally, the second frequency of the first mode corresponded to smaller counter-rotating vortex pairs at the shear layer originated near the reattachment point. These findings suggest that coherent structures have a significant impact on aerodynamic forces exerted on aerofoils, and can be identified and quantified using the SPOD algorithm and vorticity force analysis.

A New Approach to Increase the Accuracy of a Numerical Scheme Using Modified Partial Differential Equation : Application to Meshless Methods

Meshless methods are gaining popularity for numerically solving the governing equations of Fluid Dynamics primarily because they do not require the generation of grid around the given geometry in the computational domain. They just require a point distribution with a proper connectivity, which is extremely simple to generate as compared to the grid around complex geometries. However, obtaining a higher order accurate numerical solution is difficult in case of meshless methods as it requires either a solution of a larger system of linear algebraic equations, or defect correction method coupled with inner iterations. This method becomes too much complicated if still further higher order accuracy is desired. Here an alternate method based on Modified Partial Differential Equations has been used to obtain higher order accurate solution using the meshless methods. The basic idea behind the new approach is to explicitly remove the truncation error from the Modified Partial Differential Equation (formed from the governing equations) and numerically solve the resulting equation with the meshless technique. This technique has been successfully applied for the simulation of subsonic, weak transonic, strong transonic and supersonic flow past NACA0012 aerofoil. A good match of the numerical results with the standard test results of AGARD/GAMM workshop has been.

Aerofoil Flow Sensing Using On-Board Optical Tracking of Flexible Pillar Sensors

A novel approach for sensing and characterising the flow over an aerofoil is introduced. Arrays of flexible wind-hair-like sensors distributed over an aerofoil, which are tracked remotely using high-speed imaging and processing, acting as “digital tufts”, are used to provide real-time readings of local flow information with high temporal resolution. The use case presented in this paper has the sensors embedded within the suction side of a NACA0012 aerofoil and tested in a wind tunnel for varying angles of attack in static and dynamic tests. The time-averaged signals were able to provide information pertaining to the free-stream velocity and instantaneous angle of attack. The capability of the sensor type to provide temporal flow information is also explored. The sensors were used to detect low-frequency oscillations, which are pre-cursory to stall. These are hypothesised to be linked to breathing modes of the laminar separation bubble, causing a shear-layer flapping observed on the sensors. Such low-frequency oscillations were also detected shortly before separation in the ramp-up studies.

Statistical Analysis using Taguchi Method for Designing a Robust Wind Turbine

The current paper presents the tolerance and parameter design for robust wind turbine. By utilizing the traditional Taguchi method along with its extensions, there is a way of designing a robust wind turbine by considering multiple objectives, constraints and design variables. The concept of design of experiment (DOE) i.e.; Taguchi Method is used to evaluate the constrained and unconstrained problems for the optimization. The current work produces an inexpensive and simpler approach for robust vertical axis wind turbine. DOE (Taguchi Method) of L-9 Orthogonal Array having four parameters along with their three levels i.e; type of NACA aerofoil, Reynolds number, Mach number and Angle of attack are utilized for the optimization and to derive the corresponding optimal values of CL, CD and CP. The parameters like coefficient of lift, drag and power for the wind turbine was determined by Q-Blade software, which is use for designing of wind turbine blades. From the obtained results the inferences drawn were: for CL the major impact was due to Reynolds number and least was due to angle of attack, for CD the major and minor impacting factors were angle of attack and Mach number respectively and for CP the most and least influenced parameters were Reynolds number and Mach number respectively. Also, for obtaining the optimized parameters, the Grey based Taguchi method was utilized which has the combination of orthogonal arrays and grey relational analysis. The analysis showed that the NACA0021 has the maximum lift coefficient of 1.0361 and the minimum drag coefficient of 0.02190 in the case of NACA0021 aerofoil.

Investigation on the Influence of Vortex Generators on Aerofoil

Boundary layer separation is a major cause of concern in the wind turbine and aerospace industries as it adversely affects the performance of aircraft wings and wind turbine blades. The immediate result of flow separation over an aerofoil causes decrease in lift and an increase in drag within the stall range, both of which have a negative impact on the overall performance of aerofoils in the wind turbines. To overcome this problem, vortex generators (VGs) are used for increasing lift force and thus increasing the rotational speed of the blade. They act like small protrusions on wing surfaces which helps in energizing the boundary layers thereby delaying the separation and providing a wide range of attached flow over aerofoil surface. The present research illustrates the comparative analysis on the various shapes of VGs such as rectangular, triangular and gothic by varying the angle of attacks (AoA) from 0-15. The analysis is performed on NACA0012 aerofoil, which is developed using SOLIDWORKS and analysed on ANSYS 2020 R2 software. The values of lift (Cl) and drag (Cd) coefficients with and without VGs are determined using ANSYS fluent and the contours for velocity and pressure are further mapped using CFD Post. The stall angle is evaluated for each of the VG shapes representing the maximum lift that an aerofoil can achieve. Pressure coefficient plots are studied in order to investigate the amount of pressure difference created and its influence AoA at the leading edge of the aerofoil. An overall comparison is made to determine the best VG shape that delivers maximum lift to the aerofoil. The optimum configuration found for VG is gothic shape which illustrates the maximum lift coefficient value, which is highest amongst all the three shapes.

Implementation of Taguchi method for designing a robust wind turbine

The current paper demonstrates the design parameters and tolerances for a horizontal axis wind turbine. Here we have adopted one of the DOE (design of experiment) method namely Taguchi method, a traditional approach for designing a robust wind turbine. For optimization purpose, the evaluation and estimation of various problems i.e; constrained as well as unconstrained have been done using Taguchi method. For the derivation of design parameters lift coefficient (CL), drag coefficient (CD) and power coefficient (CP) the L-9 Orthogonal array (OA) comprising of 4 parameters each with three levels (NACA aerofoil type, Mach number, Reynolds number and angle of attack) are considered. Open source Q-Blade designing software is used for determining power, lift and drag coefficients of the wind turbine. The combination of GRA and orthogonal arrays are used for attaining the optimized parameters. In this paper an investigation has been carried out on the specific NACA aerofoils 4412, 4712 and 4421. Among all the aerofoils NACA 4712 has showed the impressive results in terms of maximum lift coefficient of 0.9491and minimum drag coefficient of 0.02601. Also from signal to noise plots it can be inferred that the most influenced parameter for CL and CD is Mach number and Aerofoil for CP.

Investigation of Airfoil Design and Analysis

Abstract: In this project “Aerofoil Design and Analysis” an attempt has made to make a complete study on lift and drag coefficient of various aerofoil sections using CFD. The primary goal of this project is to learn and analyse the aerodynamic performance of wings. The objective of this study is to improve aerofoil design using the software CATIA, And Fluent Analysis using the software ANSYS. Aerofoil is a principal part of any airplane construction. How much lift force and drag force is sufficient to balance the weight of the plane is decided by the aerofoil. Aerofoils are basically divided into two categories - they are Asymmetrical and Symmetrical aerofoils. Based on their drag and lift coefficient’s variation with angle of attack, stall angle of attack and magnitude of the coefficients they are divided. Here the NACA aerofoil is modified by adding dimples on the upper half of the wing and compared with the simple one. The comparison is made on different speed and pressure on the wing and the coefficient of lift and drag.

Lattice Boltzmann Method for high Reynolds number compressible flow

We employ a Lattice Boltzmann Method (LBM) for modelling high Reynolds number (Re) compressible supersonic flow using D2Q9 lattice. In this model, a two-population thermal lattice Boltzmann (LB) is utilized in order to allow varying Prandtl number and adiabatic exponent. The equilibrium population fieq term for mass and momentum conservation is matched analytically with order of accuracy O(Ma4), while the equilibrium population gieq term for energy conservation is solved numerically through Lagrange multipliers method. By using more accurate equilibrium population gieq, the present numerical method shows the enhancement of stability, especially at high Reynolds and Mach number flows. To simulate high Reynolds and Mach number (Ma) flows efficiently, we adopt a shifted lattice scheme, stabilized by relaxation time depending on the Knudsen number. The LBM show excellent accuracy through 1D Riemann examples, capable of handling expansion shock waves and discontinuity. Our results for supersonic flow past a cylinder also find excellent agreement with experimental data in literature. Separately, we benchmark results for transonic and supersonic flows past a NACA0012 aerofoil as a demonstration of its simplicity, versatility for applications involving high Reynolds and Mach numbers (Ma∞=1.5,Re=107).

Numerical Investigation of the Aerofoil Aerodynamics with Surface Heating for Anti-Icing

The aerodynamics of an aerofoil with surface heating was numerically studied with the objective to build an effective anti-icing strategy and balance the aerodynamics performance and energy consumption. NACA0012, RAE2822 and ONERA M6 aerofoils were adopted as the test cases and the simulations were performed in the subsonic flight condition of commercial passenger aircraft. In the first session, the numerical scheme was firstly validated with the experimental data. A parametric study with different heating temperatures and heating areas was carried out. The lift and drag coefficients both drop with surface heating, especially at a larger angle of attack. It was found that the separation point on the upper surface of the aerofoil is sensitive to heating. Higher heating temperature or larger heating area pushes the shock wave and hence flow separation point moving towards the leading edge, which reduces the low-pressure region of the upper surface and decreases the lift. In the second session, the conclusions obtained are applied to inform the design of the heating scheme for NACA0012. Further guidelines for different flight conditions were proposed to shed light on the optimisation of the heating strategy.

Aerodynamics of a pitching wind turbine blade at high reduced frequencies

This paper reports the effect of high reduced frequency on the aerodynamics of wind turbine blade under a deep dynamic stall at Reynolds number 135,000, of which the cross section is NACA0012 aerofoil with a constant chord length. Large-eddy simulations (LES) at reduced frequencies 0.1 and 0.15 were validated against reference data in the literature. Our LES data suggest that the lift, drag and moment coefficients are evidently dependent on the pitching frequency. The lift coefficient at the reduced frequency 0.4 increases up to 22% during the upstroke, and 64% during the downstroke compared to at the reduced frequency 0.2. The peak drag coefficient decreases up to 26% at the reduced frequency 0.4 compared to at the reduced frequency 0.2. The phase angle of dynamic stall shifts towards the downstroke regime as the reduced frequency increases. Pitching motion at the high reduced frequency (e.g. 0.4) significantly enhances the suppression of leading edge vortex during the upstroke, and delays the reattachment of the boundary layer until a very low angle of attack in the downstroke. This study can be beneficial for improvement in the parameterisation of the operational blade element method (BEM) of wind turbine blade design.

Quadrupole noise generated from a low-speed aerofoil in near- and full-stall conditions

In this paper, direct numerical simulations are performed for low-speed flows past a NACA0012 aerofoil at high incidence angles. The aim is to investigate the significance of quadrupole noise generated due to separated shear layers, in comparison to dipole noise emanating from the aerofoil surface. The two different noise components (dipole and quadrupole) are calculated by using the Ffowcs Williams & Hawkings method in two different approaches: one with a solid surface and another with a permeable surface. The quadrupole noise is then estimated approximately by taking the relative difference between the two. The current study provides detailed comparisons between the quadrupole and dipole noise components at various observer locations in a wide range of frequencies. The comparisons are also made in terms of Mach number scaling, which differs significantly from theoretical predictions and changes rapidly with frequency. Additionally, pre-, near- and full-stall conditions are cross-examined, which reveals significant differences in the quadrupole contributions, including changes in the major source locations and frequencies. It is found that the inclusion of the quadrupole sources gives rise to the predicted noise power level at all frequencies (varying between 2 and 10 dB for an observer above the aerofoil) compared to the dipole-only case. The quadrupole contribution is far from negligible even at the low subsonic speeds (Mach 0.3 and 0.4) when aerofoil stall occurs.

Combination of propulsive thrust and rotational power for ships from a cyclic pitch Darrieus rotor sail

This study aims to analyse the ability of a Darrieus rotor to produce a combination of direct thrust for ship propulsion and rotational power for shipboard electricity generation. A multiple-streamtube model was used to simulate turbine performance using a cyclic-pitching motion of the blades. The rotor produced a useful forward component of thrust under slow-sailing conditions for wind directions coming from all but one octant, while producing useful rotational power at the same time. Directly against the wind, the Darrieus rotor sail produced negative propulsive power in terms of direct thrust, but produced useful rotational power. At other sailing angles the Darrieus rotor sail was found to be less effective in providing direct thrust to the ship than equivalent wing sails. Sailing at an angle of 45° against the wind, the Darrieus rotor sail produced 46% of the power a wing sail using the same symmetrical NACA0012 aerofoil would produce. When sailing directly with the wind, at a 180° wind angle, the Darrieus rotor sail produced 40% of the thrust of its equivalent wing sail. A ship sailing with this technology was simulated to be able to sail at about 26% of its current maximum speed on a Baltic route.

Computational analysis and design of an aerofoil with morphing tail for improved aerodynamic performance in transonic regime

AbstractThis article focuses on the aerodynamic design of a morphing aerofoil at cruise conditions using computational fluid dynamics (CFD). The morphing aerofoil has been analysed at a Mach number of 0.8 and Reynolds number of $3 \times 10^{6}$ , which represents the transonic cruise speed of a commercial aircraft. In this research, the NACA0012 aerofoil has been identified as the baseline aerofoil where the analysis has been performed under steady conditions at a range of angles of attack between $0^{^{\kern1pt\circ}}$ and $3.86^{^{\kern1pt\circ}}$ . The performance of the baseline case has been compared to the morphing aerofoil for different morphing deflections ( $w_{te}/c = [0.005 - 0.1]$ ) and start of the morphing locations ( $x_{s}/c = [0.65 - 0.80]$ ). Further, the location of the shock wave on the upper surface has also been investigated due to concerns about the structural integrity of the morphing part of the aerofoil. Based upon this investigation, a most favourable morphed geometry has been presented that offers both, a significant increase in the lift-to-drag ratio against its un-morphed counterpart and has a shock location upstream of the start of the morphing part.

The influence of the flow separation bubble and transition location on the profile drag of three 4-digit NACA aerofoil profiles

Modeling of the flow over aerofoil profiles at low Reynolds numbers is difficult due to the complex physics associated with the laminar flow separation mechanism. Two major problems arise in the estimation of profile drag: (1) the drag force at low Reynolds numbers is extremely small to be measured in a wind tunnel by force balance techniques, (2) the profile drag is usually calculated by pressure integration, hence the skin friction component of drag is excluded. In the present work, three different 4-digit NACA aerofoils are investigated. Measurements are conducted in an open-ended subsonic wind tunnel, while numerical work is performed by time Reynolds-averaged Navier Stokes (RANS) coupled with the laminar-kinetic-energy ( K-kl-w) turbulence model. The influence of the flow separation bubbles and transition locations on the profile drag is discussed and addressed. This paper gives important insights into importance of measurements at low Reynolds numbers for better aerodynamic loads predictions.

Drag Reduction Using Biomimetic Sharkskin Denticles

This paper explores the use of sharkskin in improving the aerodynamic performance of aerofoils. A biomimetic analysis of the sharkskin denticles was conducted and the denticles were incorporated on the surface of a 2-Dimensional (2D) NACA0012 aerofoil. The aerodynamic performance including the drag reduction rate, lift enhancement rate, and Lift to Drag (L/D) enhancement rate for sharkskin denticles were calculated at different locations along the chord line of the aerofoil and at different Angles of Attack (AOAs) through Computational Fluid Dynamics (CFD). Two different denticle orientations were tested. Conditional results indicate that the denticle reduces drag by 4.3% and attains an L/D enhancement ratio of 3.6%.

Sequential Data Assimilation of Turbulent Flow and Pressure Fields over Aerofoil

The present study concentrates on the global velocity and pressure fields recovery over a NACA0012 aerofoil using the adjoint-based sequential data assimilation (DA) approach. Planar particle image velocimetry (PIV) measurement is conducted in the water channel to capture the time-resolved velocity field above the aerofoil, and the velocity field data are then used for DA. The attack angle is fixed at , and the Reynolds number, based on the inflow velocity and chord length , is . Conventional pressure determination methods that use either integration or a solution of the Poisson equation are applied to compute the instantaneous pressure field from the PIV data. Dynamic detached-eddy simulation (DDES) and Reynolds-averaged Navier–Stokes (RANS) simulations using the shear strain transport model are also performed for comparison. The conventional pressure determination methods yield large errors due to the error accumulation and boundary effects, whereas the RANS simulation seriously mispredicts the flow separation, and the DDES also fails due to low mesh resolution. By solving the primary-adjoint equation system and updating the correction for the governing equations at time steps for which observations exist, DA accurately reproduces the instantaneous flowfield in the observational region, which substantially improves the prediction of pressure distribution on the aerofoil surface and the flow in the wake region. Using the observational data in half of the region, DA also improves the flow and pressure prediction in the other half region. The present DA method is therefore able to reproduce the global fields from limited measurement data.

Aerodynamic study of single corrugated variable-camber morphing aerofoil concept

AbstractCamber morphing is an effective way to control the lift generated by any aerofoil and potentially improve the range (as measured by the lift-to-drag ratio) and endurance (as measured by $C_l^{3/2}/C_d$ ). This can be especially useful for fixed-wing Unmanned Aerial Vehicles (UAVs) undergoing different flying manoeuvres and flight phases. This work investigates the aerodynamic characteristics of the NACA0012 aerofoil morphed using a Single Corrugated Variable-Camber (SCVC) morphing approach. Structural analysis and morphed shapes are obtained based on small-deformation beam theory using chain calculations and validated using finite-element software. The aerofoil is then reconstructed from the camber line using a Radial Basis Function (RBF)-based interpolation method (J.H.S. Fincham and M.I. Friswell, “Aerodynamic optimisation of a camber morphing aerofoil,” Aerosp. Sci. Technol., 2015). The aerodynamic analysis is done by employing two different finite-volume solvers (OpenFOAM and ANSYS-Fluent) and a panel method code (XFoil). Results reveal that the aerodynamic coefficients predicted by the two finite-volume solvers using a fully turbulent flow assumption are similar but differ from those predicted by XFoil. The aerodynamic efficiency and endurance factor of morphed aerofoils indicate that morphing is beneficial at moderate to high lift requirements. Further, the optimal morphing angle increases with an increase in the required lift. Finally, it is observed for a fixed angle-of-attack that an optimum morphing angle exists for which the aerodynamic efficiency becomes maximum.

An Experimental and Numerical Study on the Aerodynamic Performance of Vibrating Wind Turbine Blade with Frequency-Domain Method

A highly efficient nonlinear frequency-domain solution method is proposed and employed to investigate the aerodynamic and aeromechanical performances of an oscillating wind turbine blade aerofoil in this study. Extensive validations of a frequency-domain method against an experiment as well as a typical time-domain solution method are provided in this paper. An experiment is also designed and conducted to measure pressure distributions over an aerofoil as well as to validate the numerical model. Unsteady pressure distributions and aeroelasticity parameters of the oscillating NACA0012 aerofoil are computed at various angles of attack and Reynolds numbers. Results indicate that the difference of unsteady pressure distributions between the two surfaces of the aerofoil becomes larger as the angle of attack is increased, whereas the flow separation on the suction surface is reduced by raising the Reynolds number. The turbulent flow develops in the downstream region due to the laminar vortex shedding at lower Reynolds numbers. It is also revealed that the Reynolds number has an impact on the aeroelasticity, and the aerodynamic damping value is larger at higher Reynolds numbers. The comparison between the frequency-domain method and the time-domain method shows that the frequency-domain method is not only accurate but also computationally very efficient as the computation time is reduced by 90%.