XFOIL Code Research Articles

Numerical investigation and aerodynamic simulation of Darrieus H-rotor wind turbine at low Reynolds numbers

ABSTRACT In order to select an airfoil suitable for the wind tunnel testing on a three-bladed Darrieus H-rotor wind turbine, several symmetrical National Advisory Committee for Aeronautics (NACA) 4-digit, NACA 4-digit, NACA 5-digit, and Selig airfoils with chord Reynolds numbers ( R e c ) of 17,890, 35,780, and 53,670 were studied. To achieve higher aerodynamic performance at Re of 17,890 to 53,670, the NACA0015 airfoil was selected. The lift coefficient ( R e c ) of the NACA0015 airfoil after shape modification has reached values of 0.788 to 0.936 at Re of 35,780 and 0.925 to 1.027 at Re of 53,670 with the same stall angle ( A o A s t a l l ) in both investigated Re, according to the results of modifying the airfoil’s thickness and chord. Additionally, the NACA0015 modified airfoil’s maximum lift-to-drag ratio coefficient ( C L / C D ) increased by 34.01% and 17.94% at Re of 35780 and 53,670, respectively. Likewise, the analysis showed that the NACA0015 modified airfoil’s maximum performance coefficient ( C P ) increased from 0.129, 0.242, 0.285, 0.308, and 0.33 to 0.152, 0.272, 0.307, 0.331, and 0.354 at Re of 100,000, 150000, 200000, 250000, and 300,000, respectively. As well as the findings demonstrated that the XFOIL code provides the most accurate overall prediction results at low Re.

A Coupled Inviscid–Viscous Airfoil Analysis Solver, Revisited

This paper presents a self-contained, comprehensive exposition and new elements of a classic airfoil analysis technique: an integral boundary-layer solver coupled to a vortex-panel potential-flow method. The resulting solver MFOIL, implemented in MATLAB and made freely available, builds on the XFOIL code and documentation, which serve as the inspiration, reference, and standard of comparison. Modifications made in the present implementation include an augmented-state coupled solver for more control in limiting the state update, a new stagnation-point formulation to reduce leading-edge oscillations in the boundary-layer variables, and a more robust treatment of the amplification rate near transition. Several results highlight these modifications and demonstrate capabilities of the code.

Development of a new aerofoil profile with a high lift-to-drag ratio for wind turbines using a low fidelity accurate optimization flow solver

Abstract A significant amount of work is performed on various aerofoil profiles to improve their characteristics for wind turbine applications. The main purpose is to increase the power output of wind turbines by increasing the lift-to-drag ratio of the aerofoil blade sections. However, most of the developed aerofoil profiles work well only at their design angles of attack and for low Reynolds numbers with a very dramatic stall that could significantly influence the characteristics of the aerofoil profiles and the performance of wind turbines. The present paper is conducted to develop a new aerofoil profile with more gradual stall characteristics that works efficiently for different operational conditions (clean and rough working conditions) similar to those encountered by wind turbines in the free environment. The new aerofoil profile was developed based on a combination between experimental Box–Behnken design and XFOIL code, measurements, and 2D simulation conducted by computational fluid dynamics (CFD) method. The established aerofoil can be used for wind turbine blades because it gives high lift-to-drag-ratios with very smooth and gradual stall characteristics even under very rough operating conditions.

Low Reynolds airfoil family for small horizontal axis wind turbines based on RG15 airfoil

The present study introduces a low Reynolds number (Re) airfoil family for the entire blade span of small wind turbines, aiming to reduce the effects related to laminar separation, improve startup response and meet acceptable levels of structural integrity. Six airfoils of varying relative thickness were designed by increasing the thickness distribution of RG15 airfoil up to 50% and adopting a rounded trailing edge with a diameter equal to 1% of the chord length. The aerodynamic performance of RG15 family was initially evaluated by means of XFOIL code at several low Reynolds numbers ranging from 60,000 to 300,000 and angles of attack between − 6° and 14°. XFOIL analysis revealed that increasing relative thickness leads to the reduction of maximum lift-to-drag ratio $$(C_{L} /C_{D} )$$ . However, this percentage reduction decreases with increasing Re. The maximum reduction in maximum $$C_{L} /C_{D}$$ was found at 60,000 Re for the thickest airfoil of RG15 family. Conversely, a growth of maximum lift coefficient $$(C_{L} )$$ was observed by increasing relative thickness. Besides, a Reynolds-Averaged Navier–Stokes (RANS) analysis was also conducted at 300,000 Re to get additional information on the flow characteristics. Comparisons between the XFOIL and RANS data were performed. The results of RANS simulations were generally in accordance with those of XFOIL. However, notable over-estimations of drag coefficient $$(C_{D} )$$ were detected. The behavior of the recirculation area behind the rounded trailing edge and that of the separation bubble near the leading edge for different values of relative thickness and angle of attack was examined. Thickening of the airfoils was found to have a beneficial impact on the appearance of separation bubbles, while no significant effect of the rounded trailing edge on $$C_{L}$$ and $$C_{D}$$ was observed.

Comparison of Experimental and Numerical Performances of a Wind Turbine Airfoil Using XFOIL and Computational Fluid Dynamics Simulation

In the present work an investigation of the lift and drag forces has been made in order to analyze the NACA63-618 wind turbine airfoil. This analysis has been performed for different angles of attack varying from -8° to 8° while holding the Reynolds number constant (Re=3×106). The calculation has been carried out using two numerical simulations methods: The Computational Fluid Dynamics (CFD) and the XFOIL code. Firstly, ANSYS® DesignModelerTM has been used to perform the geometry model, then the generation of the appropriate mesh has been done by ANSYS® ICEM CFDTM; after that, the simulation was established by ANSYS® Fluent® and finally, the XFOIL code has been used to reinforce the numerical results. After the validation of the present work by comparing both ANSYS® CFDTM and XFOIL results with the experimental data, it has been shown that between the four forms of turbulence models used in ANSYS® CFDTM simulation and XFOIL analysis, only Spalart Allmaras model and XFOIL have given the best prediction results for the studied airfoil. For the three other turbulence models, Shear Stress Transport (SST) k-ω, Standard k-( and Re-Normalization Group (RNG) k-( the drag coefficient has presented some deviations in comparison with results issued from the wind tunnel measurements.

Investigation of the technological deviations influence on the aerodynamic characteristics of unmanned aerial vehicles

At the stage of serial production, all the potential of the aircraft must find a practical realization. Such features of the contour such as projecting rivets, surface waviness, steps, cracks, and flashing lights cause the additional drag.Methods for additional drag calculating can be found in various sources, but there is no confirmation how these methods are regular for low Reynolds numbers.The influence of technological deviations on the aerodynamic characteristics of the unmanned aerial vehicle was investigated by the computational fluid dynamics method.The study was performed in Profili 2.27 software, which uses the XFOIL code. It shows a high convergence of calculation results with experimental data for low Mach numbers and a wide range of Reynolds numbers. Each of the airfoils was considered with different positions of the deviation and with its different depth. The calculation was also performed for different Reynolds numbers.Eighteen polars of SD8040 (10%) and HN-417 (10%) airfoils were received. Twelve dependencies of drag coefficient and maximum lift coefficient from the cavity depth, its coordinate and Reynolds number were also presented in the form of tables and graphs. A comparison of the determined impact of surface deviations on aerodynamic characteristics with generalized regularities was made. As a result of the calculation, it was shown that, in general, the cavity shifting backward decreases its effect on the aerodynamic characteristics, since the thickness of the boundary layer increases and the relative cavity depth to this thickness becomes less. Mainly, the Reynolds number decreasing reduces the influence of the cavity on the airfoil aerodynamic characteristics for the same reason. The obtained results meet the known patterns and confirm the correctness of the chosen research method. The impact of the cavity with a 0.5% depth of the chord can significantly reduce the maximal lift coefficient (from 1.28 to 1.21). At the same time, it was found that the effect of deviations from the theoretical contour depends essentially on the particular airfoil shape, even if these airfoils have the same thickness and are geometrically similar. Comparisons with analytical generalizations indicated that the calculated results have one order of value, but unlike theory, they are more complex nonlinear dependences on the cavity depth.Further studies of other airfoils of different thickness and curvature with similar deviations from the theoretical contour are promising as well as using more powerful numerical methods (solving Navier-Stokes equations).

Design methodology using characteristic parameters control for low Reynolds number airfoils

In the past century, low Reynolds number airfoil design for both military and civil applications has continued to capture the interest of practitioners of applied aerodynamics. A new design methodology for airfoils has been developed, which controls the airfoil profile through 8 parameters. The airfoil aerodynamic characteristics were predicted through the XFOIL code, to optimize airfoil under mode-FRONTIER environment. The reliability verification result predicted that the XFOIL code can be used to determine the airfoil performance in the linear segment of the lift coefficient curve. Application of this methodology was demonstrated through two cases. For Case-I, airfoils design were based on E387 airfoil profile and synthetic aerodynamic performance at different angles of attack for Re=2.0×105 were considered. While for Case-II, designed airfoils were based on PSU 94-097 airfoil with synthetic aerodynamic performance at different angles of attack for Re=4.0×105. Results of both cases showed enhanced aerodynamic properties for the designed airfoils.

Airfoil optimization for wind turbine application

AbstractAn airfoil optimization method for wind turbine applications that controls the loss in performance due to leading edge contamination is developed and tested. The method uses the class‐shape‐transformation technique to parametrize the airfoil geometry and uses an adjusted version of the panel code XFOIL to calculate the aerodynamic performance. To find optimal airfoil shapes, the derivative‐free Covariance Matrix Adaptation Evolution Strategy is used in combination with an adaptive penalty function. The method is tested for the design of airfoils for the outer part of a megawatt‐class wind turbine rotor blade, and the results are compared with airfoils from Delft University. It is found that the method is able to automatically create airfoils with equal or improved performance compared with the Delft designs. For the tested application, the adjustments performed to the XFOIL code improve the maximum lift, post stall, and the overall drag predictions.

Design of advanced airfoil for stall-regulated wind turbines

Nowadays, all the modern MW-class wind turbines make use of pitch control to optimize the rotor performance and control the turbine. However, for kW-range machines, stall-regulated solutions are still attractive and largely used for their simplicity and robustness. On the design phase, the aerodynamics plays a crucial role, especially concerning the selection/design of the necessary airfoils. This is because the airfoil performance should guarantee high wind turbine performance, but also the needed machine control capabilities. In the present work, the design of a new airfoil dedicated for stall machines is discussed. The design strategy makes use of numerical optimization scheme where a gradient-based algorithm is coupled with XFOIL code and an original Bezier-curves-based parameterization to describe the airfoil shape. The performances of the new airfoil are compared in free and fixed transition conditions. In addition, the performance of the rotor is analysed comparing the impact of the new geometry with alternative candidates. The results show that the new airfoil offers better performance and control than existing candidates do.

Numerical and experimental validation of a morphed wing geometry using Price-Païdoussis wind-tunnel testing

ABSTRACTAn experimental validation of an optimised wing geometry in the Price-Païdoussis subsonic wind tunnel is presented. Two wing models were manufactured using optimised glass fibre composite and tested at three speeds and various angle-of-attack. These wing models were constructed based on the original aerofoil shape of the ATR 42 aircraft and an optimised version of the same aerofoil for a flight condition of Mach number equal to 0.1 and angle-of-attack of 0°. The aerofoil's optimisation was realised using an ‘in-house’ genetic algorithm coupled with a cubic spline reconstruction routine, and was analysed using XFoil aerodynamic solver. The optimisation was concentrated on improving the laminar flow on the upper surface of the wing, between 10% and 70% of the chord. XFoil-predicted pressure distributions were compared with experimental data obtained in the wind tunnel. The transition position was estimated from the experimental pressure data using a second derivative methodology and was compared with the transition predicted by XFoil code. The results have shown the agreement between numerical and experimental data. The wind-tunnel tests have shown that the improvement of the laminar flow of the optimised wing is higher than the value predicted numerically.

XFOIL vs CFD performance predictions for high lift low Reynolds number airfoils

Blade Element Momentum (BEM) theory is an extensively used technique for calculation of propeller aerodynamic performance. With this method, the airfoil data needs to be as accurate as possible. At the same time, Computational Fluid Dynamics (CFD) is becoming increasingly popular in the design and optimization of devices that depend on aerodynamics. For fixed and rotary wing applications, the airfoil lift over drag coefficient is the dominant airfoil performance parameter. Selecting a suitable computational tool is crucial for the successful design and optimization of this ratio. The XFOIL code, the Shear Stress Transport k−ω turbulence model and a refurbished version of k−kl−ω transition model were used to predict the airfoil aerodynamic performance at low Reynolds numbers (around 2.0×105). It has been shown that the XFOIL code gives the overall best prediction results. Also, it is not clear that CFD turbulence models, even with boundary layer transition detection capability, can compute better airfoil performance predictions data.

Optimization of hydrofoil for tidal current turbine based on particle swarm optimization and computational fluid dynamic method

Both efficiency and cavitation performance of the hydrofoil are the key technologies to design the tidal current turbine. In this paper, the hydrofoil efficiency and lift coefficient were improved based on particle swarm optimization method and XFoil codes. The cavitation performance of the optimized hydrofoil was also discussed by the computational fluid dynamic. Numerical results show the efficiency of the optimized hydrofoil was improved 11% ranging from the attack angle of 0-7? compared to the original NACA63-818 hydrofoil. The minimum pressure on leading edge of the optimized hydrofoil dropped above 15% at the high attack angle conditions of 10?, 15?, and 20?, respectively, which is benefit for the hydrofoil to avoiding the cavitation.

Displacement thickness evaluation for semi-empirical airfoil trailing-edge noise prediction model

This study proposes a criterion for evaluating the turbulent boundary layer displacement thickness when predicting airfoil trailing-edge noise with semi-empirical methods. The boundary layer integral parameter is usually employed as the typical turbulence length-scale in the classic NASA-BPM semi-empirical airfoil self-noise prediction model and its variations. Although the semi-empirical noise prediction methods have been, in theory, superseded by more complex and demanding simplified-theoretical methods, they arguably remain the most suitable methods for noise investigation during the preliminary design phase of airfoils and wind turbine blades. The purpose of the criterion discussed is to limit the adverse impact of the uncertainty associated with the scaling parameter into the overall intrinsic quality of the semi-empirical noise prediction method. The criterion may be then employed, along with computational efficiency, to sort out methods for the task of feeding the popular BPM noise prediction model and its variations. As an illustration of the application of the proposed criterion, the performance of CFD-RANS and XFoil codes are examined and compared with experimental data from turbulent, incompressible flow available from the literature in the range $$5.0 \times 10^{5} < \text{Re}_{\text{C}} < 1.5\, \times 10^{6}$$ .

An Integrated Method for Designing Airfoils Shapes

A new method for designing wind turbine airfoils is presented in this paper. As a main component in the design method, airfoil profiles are expressed in a trigonometric series form using conformal transformations and series of polynomial equations. The characteristics of the coefficient parameters in the trigonometric expression for airfoils profiles are first studied. As a direct consequence, three generic airfoil profiles are obtained from the expression. To validate and show the generality of the trigonometric expression, the profiles of the NACA 64418 and S809 airfoils are expressed by the present expression. Using the trigonometric expression for airfoil profiles, a so-called integrated design method is developed for designing wind turbine airfoils. As airfoil shapes are expressed with analytical functions, the airfoil surface can be kept smooth in a high degree. In the optimization step, drag and lift force coefficients are calculated using the XFOIL code. Three new airfoils CQ-A15, CQ-A18, and CQ-A21 with a thickness of 15%, 18%, and 21%, respectively, are designed with the new integrated design method.

Airfoil Topology Optimization using Teaching-Learning based Optimization

This paper primarily deals with the optimization of airfoil topology using teaching-learning based optimization, a recently proposed heuristic technique, investigating performance in comparison to Genetic Algorithm and Particle Swarm Optimization. Airfoil parametrization and co-ordinate manipulations are accomplished using piecewise b-spline curves using thickness and camber for constraining the design space. The aimed objective of the exercise was easy computation, and incorporation of the scheme into the conceptual design phase of a low-reynolds number UAV for the SAE Aerodesign Competition. The 2D aerodynamic analyses and optimization routine are accomplished using the Xfoil code and MATLAB respectively. The effects of changing the number of design variables is presented. Also, the investigation shows better performance in the case of Teaching-Learning based optimization and Particle swarm optimization in comparison to Genetic Algorithm.

Prediction and analysis of infra and low-frequency noise of upwind horizontal axis wind turbine using statistical wind speed model

Despite increasing concern about low-frequency noise of modern large horizontal-axis wind turbines (HAWTs), few studies have focused on its origin or its prediction methods. In this paper, infra- and low-frequency (the ILF) wind turbine noise are closely examined and an efficient method is developed for its prediction. Although most previous studies have assumed that the ILF noise consists primarily of blade passing frequency (BPF) noise components, these tonal noise components are seldom identified in the measured noise spectrum, except for the case of downwind wind turbines. In reality, since modern HAWTs are very large, during rotation, a single blade of the turbine experiences inflow with variation in wind speed in time as well as in space, breaking periodic perturbations of the BPF. Consequently, this transforms acoustic contributions at the BPF harmonics into broadband noise components. In this study, the ILF noise of wind turbines is predicted by combining Lowson’s acoustic analogy with the stochastic wind model, which is employed to reproduce realistic wind speed conditions. In order to predict the effects of these wind conditions on pressure variation on the blade surface, unsteadiness in the incident wind speed is incorporated into the XFOIL code by varying incident flow velocities on each blade section, which depend on the azimuthal locations of the rotating blade. The calculated surface pressure distribution is subsequently used to predict acoustic pressure at an observing location by using Lowson’s analogy. These predictions are compared with measured data, which ensures that the present method can reproduce the broadband characteristics of the measured low-frequency noise spectrum. Further investigations are carried out to characterize the IFL noise in terms of pressure loading on blade surface, narrow-band noise spectrum and noise maps around the turbine.

A method to evaluate the overall performance of the CAS-W1 airfoils for wind turbines

This paper presents an evaluation method with a performance parameter system of wind turbine airfoils, and then estimates the overall performance of the CAS-W1 airfoils compared with some DU airfoils with available experimental data. The CAS-W1 airfoil family is developed by Institute of Engineering Thermophysics with the XFOIL code. The family includes 11 airfoils, whose relative thickness ranges from 15% to 60%. Four thin airfoils and three thick airfoils have been measured in NF-3 wind tunnel in Northwestern Polytechnical University. Different from previous airfoil performance analysis, the evaluation herein focuses on design point, off-design performance, stalling characteristic, and performance stability. Results show that, compared with DU airfoils, thin CAS-W1 airfoils have favorable design point, good off-design performance, and could keep stable with the variation of surface roughness and Reynolds number; Three inboard airfoils have soft stall performance but ordinary design point and off-design characteristics.

New aeroelastic studies for a morphing wing

For this study, the upper surface of a rectangular finite aspect ratio wing, with a laminar airfoil cross-section, was made of a carbon-Kevlar composite material flexible skin. This flexible skin was morphed by use of Shape Memory Alloy actuators for 35 test cases characterized by combinations of Mach numbers, Reynolds numbers and angles of attack. The Mach numbers varied from 0.2 to 0.3 and the angles of attack ranged between -1° and 2°. The optimized airfoils were determined by use of the CFD XFoil code. The purpose of this aeroelastic study was to determine the flutter conditions to be avoided during wind tunnel tests. These studies show that aeroelastic instabilities for the morphing configurations considered appeared at Mach number 0.55, which was higher than the wind tunnel Mach number limit speed of 0.3. The wind tunnel tests could thus be performed safely in the 6'×9' wind tunnel at the Institute for Aerospace Research at the National Research Council Canada (IAR/NRC), where the new aeroelastic studies, applied on morphing wings, were validated.

Design and Testing of a Multi-Element Airfoil for Short-Takeoff-and-Landing Ultralight Aircraft

The design and analysis of a new airfoil to be employed on a ultralight aircraft with short takeoff and landing is presented. An inverse design philosophy has been applied and is described; the numerical analysis performed used XFOIL, MSES, and TBVOR computational codes and the effects of airfoil shape on complete aircraft performances were taken into account. A high-lift configuration, including slat and single-slotted flap geometries, has been developed and is illustrated in this paper. Exhaustive wind-tunnel tests were performed at the Department of Aerospace Engineering and the experimental results are described here. To validate numerical results and to analyze the effect of laminar bubbles on airfoil performance, the pressures on airfoil surface and in the wake were measured and flow visualizations were done using fluorescent oil. The landing configuration was also tested and an experimental optimization of flap and slat positions was carried out to obtain a high maximum lift coefficient.

ANALYSIS OF THREE WING SECTIONS

Three wing sections FX66-S-196VI, E603 and AH82–150A were analyzed. Measured data of these wing sections are published. First wing section was measured in Stuttgart University and in Delft University of Technology, when other two wing sections were measured in Stuttgart University. These wing sections have different behavior in the region of maximum lift. FX66‐S‐196VI wing section has sharp drop in lift. The stall of the second and third wing sections is smooth, though different. All wing sections are affected by laminar separation bubbles. The calculations were performed using three codes: Eppler Program System, XFOIL and RFOIL. Eppler's code uses non‐interacted inviscid plus boundary layer method. Influence of separation is estimated using empirical correction in this method. XFOIL code of Mark Drela, MIT uses interacted zonal viscous/inviscid method. The wall transpiration model in this code approximates the displacement effect on the outer inviscid flow. RFOIL is a modification of XFOIL code for application in wind turbines performed at Delft University of Technology. The code's prediction of the airfoil performance around the two dimensional maximum lift was enhanced. The comparison of calculated and measured data is presented and analyzed. Santrauka Tyrimuose analizuotos profiliu FX 66-S-196 V1, E603 ir AH82–150A charakteristiku teorines reikšmes, apskaičiuotos XFOIL, RFOIL ir PROFIL05 programomis. Gautos teorines reikšmes palygintos su jau atliktu eksperimentiniu tyrinejimu rezultatais. Pirmas profilis buvo tyrinejamas Delft technologijos universitete (Olandija) ir Štutgarto universitete (Vokietija), like du ‐ Štutgarto universitete. Visi profiliai turi skirtingas maksimalios keliamosios jegos dalis. Profilio FX 66‐S‐196 V1 keliamoji jega mažeja staiga. Kitu profiliu keliamoji jega kinta tolygiai, tačiau skirtingai. Visu profiliu ucharakteristikas itakoja laminarinis atsiskyrimo burbulas.