Typical Airfoil Research Articles

Cross-section analysis of wind turbine blades: comparison of failure between glass and carbon fiber

Wind energy stands as one of the most important renewable energy sources. Large scale wind turbine blades are mainly based on fiber reinforced polymer composites, as an efficient way to further improve their performance reducing the weight of their blades. The problem of the microstructure material failure of the interior support mechanism for a – high power – horizontal axis wind turbine blade is investigated in this study. A finite element model is developed, simulating the load-bearing box girder of the blade with a given airfoil shape, size, type, and position of the interior longitudinal beams and shear-webs. Previous work showed the challenging topics of material properties, design, computational analysis techniques, and load response of a blade cross-section. In order to shed some light at a local level, a comparison of the most common composite blade materials concerning stress distributions and also displacements, which are critical for optimal blade design, is presented. A failure criterion is applied based on the shell finite element analysis of the model, in order to demonstrate the stress levels throughout every ply of the composite materials of the box girder and locate the initiation of fracture. Failure results concerning both glass and carbon materials are presented.

Active Flutter Suppression of Stochastic Airfoil with Uncertain Pitch Stiffness

Flutter suppression of a typical airfoil with uncertain pitch stiffness by feedback control of its trailing-edge surface is analyzed. The pitch stiffness coefficient is modeled by a quadratic function of a bounded random variable with the bounded probability density function, thus the airfoil system becomes a stochastic structure depending on its random parameter. It is found that just like its deterministic counterpart the flutter suppression of stochastic airfoil system can also be realized by feedback control.

Experimental study on the aeroelastic behavior of a typical airfoil section with superelastic shape memory alloy springs

An experimental study on the aeroelastic behavior of a 2-degree-of-freedom typical airfoil section with superelastic shape memory alloy springs is reported. Shape memory alloy helical springs are included in the pitch degree-of-freedom of the typical section so that the effects of pseudoelastic hysteresis on the aeroelastic behavior of the system can be investigated. The experimental identification of the aeroelastic parameters is described. Wind tunnel tests are conducted for different shape memory alloy springs’ preload levels, airflow speeds, and initial conditions. It is shown that the linear unstable post-flutter behavior is transformed into stable limit cycle oscillations of acceptable amplitudes over a range of airflow speeds due to pseudoelastic hysteresis. Therefore, shape memory alloy springs can be effectively exploited to passively enhance the aeroelastic behavior of a typical section.

A Contribution to the Thermal Modeling of Bump Type Air Foil Bearings: Analysis of the Thermal Resistance of Bump Foils

A detailed analysis of the effective thermal resistance for the bump foil of air foil bearings (AFBs) is performed. The presented model puts emphasis on the thermal contact resistances between the bump foil and the top foil as well as between the bump foil and the base plate. It is demonstrated that most of the dissipated heat in the lubricating air film of an air foil bearing is not conducted by microcontacts in the contact regions. Instead, the air gaps close to the contact area are found to be thin enough in order to effectively conduct the heat from the top foil into the bump foil. On the basis of these findings, an analytical formula is developed for the effective thermal resistance of a half bump arc. The formula accounts for the geometry of the bump foil as well as for the surface roughness of the top foil, the bump foil, and the base plate. The predictions of the presented model are shown to be in good agreement with measurements from the literature. In particular, the model predicts the effective thermal resistance to be almost independent of the applied pressure. This is a major characteristic property that has been found by measurements but could not be reproduced by previously published models. The presented formula contributes to an accurate thermohydrodynamic (THD) modeling of AFBs.

Optimum section selection procedure for horizontal axis tidal stream turbines

Stochastic behavior of renewable energy sources forces designers to optimize the energy converters for the purpose of capturing the maximum amount of available energy. The performance of horizontal axis wind and tidal turbines mainly depends on the geometrical properties such as chord and twist distributions and also the types of sections which are utilized along the blade. The purpose of presented paper is introducing a procedure which can be utilized in order to select the optimum sections for horizontal axis tidal turbines for the purpose of increasing the turbine performance. The presented procedure also can be applied for horizontal axis wind turbines. For the purpose of evaluating the performance of the proposed method, two design types (chord and twist distributions) of tidal turbines are selected as case studies. Power coefficient is considered as objective function, and three types of hydrofoils namely NACA63-8xx, NACA44xx, and RISO-A1-xx are selected as candidate solutions. A blade element momentum theory model is used for calculating the power coefficient. The discrete ant colony optimization algorithm is selected as optimization tool. The results indicate that the utilization of the proposed method will considerably decrease the required process time for obtaining the optimum sections across the blade span, and also it is shown that using different types of sections across the blade span can increase the power coefficient of the turbine. The importance of the proposed method will be significant when various types of hydrofoils and airfoils can be considered as candidate sections across the blade span.

Design and integration sensitivity of a morphing trailing edge on a reference airfoil: The effect on high-altitude long-endurance aircraft performance

Trailing edge modification is one of the most effective ways to achieve camber variations. Usual flaps and aileron implement this concept and allow facing the different needs related to take-off, landing, and maneuver operations. The extension of this idea to meet other necessities, less dramatic in terms of geometry change yet useful a lot to increase the aircraft performance, moves toward the so-called morphing architectures, a compact version of the formers and inserted within the frame of the smart structures’ design philosophy. Mechanic (whether compliant or kinematic), actuation and sensor systems, together with all the other devices necessary for its proper working, are embedded into the body envelope. After the successful experiences, gained inside the SARISTU (SmARt Intelligent Aircraft STrUctures) project where an adaptive trailing edge was developed with the aim of compensating the weight variations in a medium-size commercial aircraft (for instance, occurring during cruise), the team herein exploits the defined architecture in the wing of a typical airfoil, used on high-altitude long-endurance aircraft such as the Global Hawk. Among the peculiarities of this kind of aerial vehicle, there is the long endurance, in turn, associated with a massive fuel storage (approximately around 50% of the total weight). A segmented, finger-like, rib layout is considered to physically implement the transition from the baseline airfoil to the target configurations. This article deals with an extensive estimation of the possible benefits related to the implementation of this device on that class of planes. Parametric aerodynamic analyses are performed to evaluate the effects of different architectural layouts (in-plane geometry extension) and different shape envelopes (namely, the rotation boundaries). Finally, the expected improvements in the global high-altitude long-endurance aircraft performance are evaluated, following the implementation of the referred morphing device.

Effect of Stall Strip Position, Size and Geometry on the Lift Coefficient of NACA 001 Aerofoil

This study aims to determine the optimum position and geometry of stall strips (SS) to control sudden fall of lift in wind turbine blades. The type of airfoil used in this study is NACA 0015 with 150 mm of chord length. Total of five positions, two geometries and three sizes of SS configurations are simulated by using Ansys Fluent software. For position configuration, SS of size 2 mm is placed on the apex (POS-1), and on the upper and lower surfaces at distance of 0.65 mm (POS-4 and POS-2 respectively), and 2.45 mm (POS-5 and POS-3), respectively, from the leading edge. The shapes tested are dome and equilateral triangle. The results show that the addition of SS as a method of controlling sudden loss of lift decreases the maximum lift coefficient. Attachment of SS at the lower surface of the airfoil did not bring any significant effect to the lift and stall characteristics; while for the upper surface it reduces the sudden fall of lift but at the cost of big reduction in maximum lift coefficient. The optimum position and geometry of SS are POS-1 and triangle shape. Increasing in size of SS shows positive effect in control stalling effect.

NACA 0021 익형 유동장의 수치해석적 연구

A primary benefit of flight at high angle-of-attack conditions is to be able to reduce the speed of flight and maneuvers, which can enhance the capability of sensing and obstacle avoidance for a small UAV. The flight at high angle-of-attack conditions, however, is easy to be beyond stall which is characterized by substantial flow separation over an airfoil. Current numerical analysis was conducted on the capabilities of three representative turbulence models to predict the aerodynamic characteristics of a typical airfoil at angle-of-attack conditions. The investigation shows that these turbulence models provide good comparison with experimental data for attached flow at moderate angle-of-attack conditions. Calculation by current turbulence models are, however, not appropriate at high angle-of-attack conditions with flow separation.

Wind Tunnel Evaluation on the Performance of Blown Airfoil

This study investigated the performance of blown airfoil. Two types of blown airfoil were developed. The integrated parts of the airfoils were investigated in the subsonic wind tunnel to study the aerodynamic forces. Each airfoil was implemented with a blower at different locations on the upper surface and was tested in the wind tunnel, with different Reynolds numbers, and with and without blower. The results showed that the airfoil with air blower produced a very significant additional 35% lift force compared to airfoil without air blower. The experimental result also exhibited 7% higher lift coefficient for air blower compared to numerical analysis.

A novel heuristic method for optimization of straight blade vertical axis wind turbine

In this research study it is aimed to propose a novel heuristic method for optimizing the VAWT design. The method is the combination of continuous/discrete optimization algorithms with double multiple stream tube (DMST) theory. For this purpose a DMST code has been developed and is validated using available experimental data in literature. A novel continuous optimization algorithm is proposed which can be considered as the combination of three heuristic optimization algorithms namely elephant herding optimization, flower pollination algorithm and grey wolf optimizer. The continuous algorithm is combined with popular discrete ant colony optimization algorithm (ACO). The proposed method can be utilized for several engineering problems which are dealing with continuous and discrete variables. In this research study, chord and diameter of the turbine are selected as continuous decision variables and airfoil types and number of blades are selected as discrete decision variables. The average power coefficient between tip speed rations from 1.5 to 9.5 is considered as the objective function. The optimization results indicated that the optimized geometry can produce a maximum power coefficient, 44% higher than the maximum power coefficient of the original turbine. Also a CFD simulation of the optimized geometry is carried out. The CFD results indicated that the average vorticity magnitude around the optimized blade is larger than the original blade and this results greater momentum and power coefficient.

Improved B-Spline Skinning Approach for Design of Hawt Blade Mold Surfaces

AbstractThe intricate 3D design of wind turbine blades has caused unwanted problems for blade designers and blade mold manufacturers. For example the cord length variation and twisting of airfoils, change of the airfoil type and the blade pre-bend can introduce major geometric complications. A novel method is suggested to improve 3D modeling of the blade mold surfaces as well as the required parting lines during the design process of the wind turbine blade. In the proposed algorithm, the blade leading edge surface is trimmed by parting lines calculated based on the blade silhouette while keeping G1 continuity of resulting surfaces. The Minimum Variation Surface (MVS) and strain energy fairing criteria approve that blade mold surfaces obtained by the developed method have better fairness compared to the surface created by the well-established design method. All programs are written in MATLAB and the final surfaces are converted into the standard IGES file format which is importable into any commercial CAD/CAM system.

Effect of constitutive model parameters on the aeroelastic behavior of an airfoil with shape memory alloy springs

The effects of the pseudoelastic hysteresis of shape memory alloy springs on the aeroelastic behavior of a typical airfoil section are numerically investigated for six different sets of alloy constitutive properties. A two-degree-of-freedom (namely, plunge and pitch) typical section is modeled. Shape memory alloy helical springs are considered in the pitch degree-of-freedom based on classical phenomenological models modified by the pure shear assumption. Tension–compression asymmetry and nonhomogeneous distributions of shear strain, shear stress and martensitic fraction in the cross-sectional area of the coiled shape memory alloy wire are considered. A linear model is used to determine the unsteady aerodynamic loads. Attractive alloy characteristics, which can enhance the aeroelastic behavior of the typical section at the flutter boundary and at the post-flutter regime, are identified and discussed in detail.

An Investigation Of Design And Modal Analysis Of The Different Material On Helicopter Blade

In aviation, wings and blades play a major role for flight control. The helicopter rotor blade in both the symmetric and asymmetric airfoil type using CATIA software, Composite materials are widely opted in manufacturing industry because of high strength to weight ratio, hence carbon epoxy and boron epoxy are chosen for the design consideration and also it is compared with aluminum material and using ANSYS software package, the static strength and the dynamic characteristics will be analyzed in three modes. The high stressed area is identified in the von misses stress technique. The analysis is carried out in the symmetric and asymmetric airfoil separately by altering the material and the results are compared for the better solution. Thus resonance in rotor can be avoided by using the proper selection of material by calculating the natural frequency.

Fan Response to Boundary-Layer Ingesting Inlet Distortions

The modeling capabilities of TURBO, an existing turbomachinery analysis code, have been extended to include the ability to solve the external and internal flow fields of a boundary-layer ingesting inlet. Flow solutions are presented and compared with experimental data for several high-Reynolds-number flows to validate the solver modifications. The upstream flowfield was coupled to a hypothetical compressor fan to present a fully developed distortion to the fan. Although the total pressure distortion upstream of the fan was symmetrical for this geometry, the pressure rise generated by the fan blades was not, because of the velocity nonuniformity of the distortion. Total pressure profiles at various axial locations are computed to identify the overall distortion pattern, how the distortion evolves through the blade passages and mixes out downstream of the blades, and where any critical performance concerns might be. Stall cells are identified that are stationary in the absolute frame and are fixed to the inlet distortion. Flow paths around the blades are examined to study the stall mechanism. Rather than a typical airfoil stall, it is observed that the nonuniform pressure loading in the radial direction promotes a three-dimensional dynamic stall. The stall occurs at a point of rapid incidence angle oscillation observed when a blade passes through a distortion and re-attaches when the blade sees more uniform flow outside the distortion.

Effect of steady airflow field on drag and downforce

The purpose of this study is to examine the effect of the steady airflow field of a rear spoiler on the coefficients of drag (CD) and downforce (CDF). The type of spoiler is suggested as a two-jointed arm model that mimics the flapping flight mechanism of the Canada goose. Computational fluid dynamics (CFD) technique was used for the steady airflow analysis of a vehicle implemented with various spoiler topologies. We evaluated CD and CDF due to the three types of airfoils and the five phases of each airfoil. We obtained the following conclusions from the results: (1) We found that the best cases for CD and CDF were the case of Phase 5 and symmetry airfoil, and the case of Phase 1 and reverse airfoil, respectively. (2) It is clear that CD becomes the largest at Phase 1 of the reverse airfoil, since the eddy magnitude at the rear of the vehicle is the largest, and CDF also becomes the largest during that phase, since the pressure distribution on the upper surface of the spoiler is very large. (3) As Phase 1 moves to Phase 5 in the same type of airfoil, it is advantageous for CD and disadvantageous for CDF, respectively.

Roughness effect on airfoil aerodynamic performance for land-yacht robot

The land-yacht robot presented in this paper aims at an Antarctic expedition which is driven by wing-sail. The wing-sail is composed by airfoil and surface roughness, which is one of the main factors affecting the aerodynamic performance of the airfoil. In order to improve the efficiency of the airfoil, stress analysis of the wing-sail and airfoil mechanism is researched and the type of airfoil is determined. For roughness size, equivalent particle roughness is introduced and a boundary layer flow separation model is a simulated roughness model. Then N-S equations and the S-A turbulence model are predicted airfoil aerodynamics in CFD (Computational Fluid Dynamics). When different sizes of a roughness strip are deposed on an airfoil surface, we obtain lift and drag coefficient, sensitive angle of attack of 6°, and 0.5 mm of sensitive roughness size. When roughness is arranged at different positions, we discover two sensitive positions, 10% chord length in suction surface and near trailing edge in pressure surface. Further analysis of the two sensitive positions in 10% chord length and aerodynamic is worse with the increasing roughness size. Near the trailing edge, there is a threshold of 0.7 mm. Lower than 0.7 mm, aerodynamics is improving; in contrast, it is worse. Finally, simulation results are verified by experiments. It shows that the predicted value conforms to the experiments and this research can provide a valuable reference for the mechanism of the land-yacht robot.

A New Method for Horizontal Axis Wind Turbine (HAWT) Blade Optimization

Iran has a great potential for wind energy. This paper introduces optimization of 7 wind turbine blades for small and medium scales in a determined wind condition of Zabol site, Iran, where the average wind speed is considered 7 m /s. Considered wind turbines are 3 bladed and radius of 7 case study turbine blades are 4.5 m, 6.5 m, 8 m, 9 m, 10 m, 15.5 m and 20 m. As the first step, an initial design is performed using one airfoil (NACA 63-215) across the blade. In the next step, every blade is divided into three sections, while the 20 % of first part of the blade is considered as root, the 5% of last the part is considered as tip and the rest of the blade as mid part. Providing necessary input data, suitable airfoils for wind turbines including 43 airfoils are extracted and their experimental data are entered in optimization process. Three variables in this optimization problem would be airfoil type, attack angle and chord, where the objective function is maximum output torque. A MATLAB code was written for design and optimization of the blade, which was validated with a previous experimental work. In addition, a comparison was made to show the effect of optimization with two variables (airfoil type and attack angle) versus optimization with three variables (airfoil type, attack angle and chord) on output torque increase. Results of this research shows a dramatic increase in comparison to initial designed blade with one airfoil where two variable optimization causes 7.7% to 22.27 % enhancement and three variable optimization causes 17.91% up to 24.48% rise in output torque .Article History: Received Oct 15, 2015; Received in revised form January 2, 2016; Accepted January 14, 2016; Available online How to Cite This Article: Mohammadi, M., Mohammadi, A. and Farahat, S. (2016) A New Method for Horizontal Axis Wind Turbine (HAWT) Blade Optimization. Int. Journal of Renewable Energy Development, 5(1),1-8. http://dx.doi.org/10.14710/ijred.5.1.1-8

Grid Quality and Resolution Effects for Aerodynamic Modeling of Ram-Air Parachutes

This work provides an overview of the grid quality and resolution effects on the aerodynamic modeling of ram-air parachute canopies. The computational-fluid-dynamics simulations of this work were performed using the Cobalt flow solver, which is a three-dimensional code, but it was run in a two-dimensional mode for canopy sections with open and closed inlets. Previous simulation results of these geometries showed that grid independence is achieved for the closed and open airfoils with grids containing around half a million and 2 million cells, respectively. Previous grids were either hybrid with prismatic layers near the walls or multiblock structured using algebraic grid generators. The results presented in this work show that grid independence of both geometries can be achieved with much coarser grids. These grids, however, were generated with good smoothness, wall orthogonality, and skewness qualities. The results show that the grid quality value is mainly related to the grid smoothness and does not depend on the grid skewness or the wall orthogonality. Although a smooth grid improves the quality value, and therefore the solution convergence, it does not always lead to an accurate solution. For example, the unstructured grids with anisotropic cells near the wall have very good grid quality; however, they have the worst accuracy among all grids considered because of the poor skewness at the walls. The results also showed that, in comparison to the closed inlets, the open geometry solutions are less sensitive to the initial grid spacing and number of constant spacing layers at the outside airfoil walls. Finally, the open inlet solutions do not change with the inside airfoil grid resolution and type.

Lift and drag in two-dimensional steady viscous and compressible flow

This paper studies the lift and drag experienced by a body in a two-dimensional, viscous, compressible and steady flow. By a rigorous linear far-field theory and the Helmholtz decomposition of the velocity field, we prove that the classic lift formula $L=-{\it\rho}_{0}U{\it\Gamma}_{{\it\phi}}$, originally derived by Joukowski in 1906 for inviscid potential flow, and the drag formula $D={\it\rho}_{0}UQ_{{\it\psi}}$, derived for incompressible viscous flow by Filon in 1926, are universally true for the whole field of viscous compressible flow in a wide range of Mach number, from subsonic to supersonic flows. Here, ${\it\Gamma}_{{\it\phi}}$ and $Q_{{\it\psi}}$ denote the circulation of the longitudinal velocity component and the inflow of the transverse velocity component, respectively. We call this result the Joukowski–Filon theorem (J–F theorem for short). Thus, the steady lift and drag are always exactly determined by the values of ${\it\Gamma}_{{\it\phi}}$ and $Q_{{\it\psi}}$, no matter how complicated the near-field viscous flow surrounding the body might be. However, velocity potentials are not directly observable either experimentally or computationally, and hence neither are the J–F formulae. Thus, a testable version of the J–F formulae is also derived, which holds only in the linear far field. Due to their linear dependence on the vorticity, these formulae are also valid for statistically stationary flow, including time-averaged turbulent flow. Thus, a careful RANS (Reynolds-averaged Navier–Stokes) simulation is performed to examine the testable version of the J–F formulae for a typical airfoil flow with Reynolds number $Re=6.5\times 10^{6}$ and free Mach number $M\in [0.1,2.0]$. The results strongly support and enrich the J–F theorem. The computed Mach-number dependence of $L$ and $D$ and its underlying physics, as well as the physical implications of the theorem, are also addressed.

Numerical Simulation and Modeling of Unsteady Flow Around an Airfoil. (Aerodynamic Form)

During this work, we simulated an unsteady flow around an airfoil type NACA0012 using the Fluent software. The objective is to control the code on the one hand and on the other hand the simulation of unsteady flows. By simulating an unsteady flow Reynolds number (Re = 6.85 * 106) and Mach number (M = 0.3), we have the flowing with a grid (mesh) adequate numerical results and experimental data are in good agreement. To represent the results of the simulation we have validated by comparing the values of aerodynamic coefficients with those of experimental data. Keywords: Unsteady flow; Fluent; a single equation model; NACA0012.