Airfoil Profile Research Articles

Dynamic behaviour of pretwisted metal matrix composite blades

In this first attempt, a unified, consistent and accurate numerical solution is obtained for the dynamic behaviour of a metal matrix composite (MMC) blade. The MMC blade is made of Titanium (Ti6Al4V) and reinforced with Silicon Carbide (SiC) fibers. The present nonlinear formulations take into account airfoil profile of the blade, profile pretwist angle, fiber orientation, reinforcement volume fraction, coupling of bending and torsional displacement fields, and centrifugal stiffening. Three aspects of the work are considered. The first is concerned with the development of a unified approach to describe the blade’s dynamic behaviour. The second with the determination of the effective properties of the MMC blade using micromechanical homogenisation. The third with the discretization of the displacement field and its treatment using Gaussian quadrature. The developed model is used to examine the effect of angle of pretwist, blade thickness, fiber volume fraction and fiber orientation on the dynamic response of the blade. The results reveal that a significant increase in the natural frequencies of the blade can be obtained with the reduction of its weight as a result of the SiC reinforcement. They also show that the bending and torsional natural frequencies are governed by the pretwist angle.

Airfoil profile reconstruction from unorganized noisy point cloud data

Abstract Airfoil blades are typically inspected in sections to verify their conformance to the geometric tolerances specified on their nominal design. To maintain the accuracy of geometric error evaluation, in particular, for the position and orientation errors of the airfoil sections, sectional airfoil profiles should be reconstructed from the inspection data points. This paper presents a new method to automatically reconstruct the airfoil profile from unorganized noisy sectional data points of 3D scanned blades. A three-step airfoil profile reconstruction approach is presented. First, the algorithm thins the scattered set of sectional data points by projecting them onto the local curves fitted to them. For this purpose, a recursive weighted local least-squares scheme is proposed to fit local curves within the measurement uncertainty constraint of inspection data. Then, to order the thinned set of data points, the profile polygon is generated and imperfect nodes are modified by evaluation of the angular deviation of edges. Finally, a closed nonperiodic B-spline curve is fitted to the thinned and ordered set of data points to construct the smooth airfoil profile. A series of case studies have been carried out to demonstrate the effectiveness of the proposed airfoil profile reconstruction method. Implementation results have demonstrated that the proposed method is accurate and robust to noise. In addition to blade inspection, other applications such as repair and adaptive machining of aero-engine blades can equally benefit from the proposed method for automatic airfoil profile reconstruction.

A multi-objective airfoil shape optimization study using mesh morphing and response surface method

Here, a distinct procedure was adopted to optimize the shape of the NACA 0012 airfoil profile for Reynolds number, Mach number, and angle of attack equal to 2e6, 0.15, and 10.24 deg, respectively. The airfoil shape was appropriately parameterized, and mesh morphing tools were used to bypass the remeshing process. Computational fluid dynamic (CFD) simulations were carried out for all combinations of selected parameters. Response surfaces were constructed for the drag and lift coefficients of the airfoil based on several statistical criteria. Subsequently, the Pareto front was used to solve the multi-objective optimization problem. Eventually, three single-objective types of optimization problems were studied. A 10 % reduction in drag coefficient was estimated for the drag minimization problem, a 22 % improvement in lift coefficient was found in case of lift maximization problem, and a 6 % reduction in drag coefficient was determined in the lift constrained drag minimization problem.

Aerodynamic Performance Optimization of Multiple Slat Airfoil based on Multi-Objective Genetic Algorithm

In this work, the optimization for the optimum position of the secondary slat was investigated with an emphasis on enhancing the aerodynamic performance. The method adopted here merges the computational fluid dynamic (CFD) technique with the response surface method. The multi-objective genetic algorithm was used for the optimization of the positioning of the secondary slat, and the Pareto ranking was done using a non-dominated sorting method. In CFD analysis, the Reynolds average Nervier–Stokes equation is solved using the k-ω shear stress transport model which is very popular due to its accuracy. The obtained numerical result for the primary airfoil NACA 2415 and the airfoil with a single slat is validated with the experimental data. The NACA 22 airfoil profile is selected to serve as a slat to impediment the separation of boundary layer and enhance airfoil characteristics. The addition of slat at the leading edge of the primary slat increases the overall aerodynamic performance of the configuration and enhances the stall angle from 12o to 22o. Further, the addition of slat significantly reduces the boundary layer thickness as a result delays the separation to a higher angle of attack. The method used in this work can be employed as a valuable tool for positioning optimization of the secondary slat at the leading edge of the primary slat of the airfoil.

Aerodynamic shape optimization of wind turbine blades for minimizing power production losses due to icing

Ice formation on a wind turbine alters the airfoil profiles of the blades and causes degradation in the aerodynamic performance of the wind turbine and the resulting power production losses. Since the blade profile plays a significant role in the icing of a blade, power production losses due to icing can be minimized by optimizing the blade profile against icing. In this study, blade profiles are optimized in order to minimize power production losses. A Gradient based aerodynamic shape optimization method is developed together with the Blade Element Momentum method and an ice accretion prediction tool in order to minimize the power production losses of horizontal axis wind turbines under various icing conditions. In an optimization study performed for the Aeolos-H 30 kW and NREL 5 MW wind turbines exposed to icing conditions up to 1 h, the power loss due to icing is reduced by about 4%.

Aerodynamics Analysis of a Slotted A4412 Wind Turbine Airfoil Using CFD / Case Two

The static pressure, dynamic pressure and velocity magnitude are important parameters and have a strong influence on airfoil lift force. In this paper a slotted NACA4412 airfoil profile is considered for analysis by using the commercial code ANSYS-FLUENT 14.5® at an inlet boundary condition of different approaching wind velocities for various airfoil angles of attack in the range 0?to 24?. Renormalized group (RNG) k-? turbulence model with enhanced wall function is used for the analysis due its’ wide usage in the aerodynamic industry. Variations of the physical properties like static pressure, dynamic pressure and velocity magnitude are plotted in form of contours and/or vectors. The main aim of the research is to find out a method to enhance the efficiency of the selected airfoil and its’ workability in a wide range of low and high wind speeds which might make it suitable for installation and operation in different climates.This feasibility of enhancing the lift is and/or minimizing the drag is done by CFD on a series of independently modified NACA4412 airfoils. The current one is called Case 2. The analysis output of Case 2 is not encouraging. It does not show any improvement in NACA4412 airfoil efficiency and therefore it is classified as (obsolete).

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

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

Numerical Investigation of the Effect of Changing the Thickness of Airfoils used in Wind Turbines on the Lift to Drag Ratio

In this paper, the effect of changing the thickness of the airfoils on the lift and drag coefficients and lift to drag ratio for three types of airfoils is presented. The study was done by making a 2D simulation by using the commercial software ANSYS FLUENT 2019R1. The airfoils that were selected for the simulation were the NREL S830, SG6043, and SD7062. In order to study the effect of changing the thickness of airfoils on the aerodynamic characteristics, the thickness of NREL S830, SG6043, and SD7062 airfoils was increased and decreased by 20%. The method used to increase and decrease the thickness was done by modifying the coordinates of the upper and lower curves of the baseline airfoils in the y-direction. The simulation was done using the Spalart Allmaras turbulence model for low wind speed (5m/s) and a wide range of attack angles (from 0 to 15 degrees). The aerodynamic characteristics, which are the lift and drag coefficients, lift to drag ratio, and the optimum angle of attack, are presented in this study. It was concluded that reducing the thickness to 20% leads to a remarkable increase in the lift to drag ratio while increasing the thickness leads to a decrease in the lift to drag ratio. It was also concluded that reducing thickness will not always lead to maximizing the lift coefficient but will always reduce the drag coefficient. It was also found that for wind turbines operating in low wind speed regions, the SG6043 airfoil profile is the most suitable as it showed a good aerodynamic performance at low wind speed.

Aerodynamic Investigation of Morphing Wing UAV with Adjustable Slotted Airfoil Configuration

Aviation has wide aspects to challenge and discover, the ability to land and take off at slow speed, sudden increase in drag for short runway landings. This paper puts forth the solution by the use of adjustable multi slots configuration of an airfoil. In this case, the slots extend from the wing leading edge to trailing edge. This causes change in the chord, thereby changing the camber of unsymmetrical airfoil. An investigation was made to determine and compare the aerodynamic characteristics of multi slotted adjustable airfoil with unmorphed unsymmetrical airfoil at varied speeds and Angle of Attack (AoA). There are three slots distanced equally along the airfoil. The extension of these slots increases the chord length by 10% of total chord. The slotted and unslotted airfoil profile are then studied using computational fluid dynamics of external flow over a body. The flow simulation is done at 10m/s, 20m/s, 30m/s, 40m/s and 50 m/s flow velocity and at 0, 3, 6, 9 ,12, 15 AoA. The results were obtained for each case and the values for base and slotted model were compared. It was found that lift of slotted model is slightly higher than base model at low flow velocity. It was also seen that the use of slots at high speed causes a large amount of drag. This increased drag factor can be used in UAV’s as spoilers during landing or for landing at shorter runways at lower speed, allowing a sudden decrease in aircraft speed and also to glide at a steeper angle over obstruction.

Shape effect of thickness of the NREL S815 profile on the performance of the H-rotor Darrieus turbine

With the aim of improving the performance of vertical axis wind turbines, in this article, the flow field and aerodynamic performance of an H-rotor Darrieus turbine are computed using computational fluid dynamics. Specifically, the power coefficient (Cp) of different airfoil profile thicknesses was evaluated as a function of tip-speed ratios (TSRs) and wind speed. Four different thicknesses of the NREL S815 airfoil were evaluated, and the TSR was varied from 0.6 to 2.25 using wind speeds of 6 and 8 m/s. As a result, the power coefficient (Cp) was calculated for each airfoil and the different tip-speed ratios. It was found that for each airfoil profile, the Cp increases when the airfoil thickness and the TSR rise, until reaching a maximum, then the Cp decreases in spite of larger thickness or TSRs. After comparing the performance of each airfoil profile, the Cp is improved 14.96% for 19.2% thicker airfoils, using a TSR of 1.725 and a wind speed of 8 m/s.

Numerical Study on Flow and Noise Characteristics of a NACA0018 Airfoil with a Porous Trailing Edge

In this paper, the effects of porous trailing edge on airfoil aerodynamic and aeroacoustic characteristics are investigated. In order to reduce the airfoil trailing edge noise and in the mean while to minimize the negative influence on aerodynamic performance, a new filling method is proposed such that porous medium is only used in the suction side half of the trailing edge which is more sensitive to the noise generation. The Large Eddy Simulation (LES) for flow and Ffocws-Williams and Hawkings (FW-H) methods for acoustics are used. At a Reynolds number of 2.63×105 and various angles of attack, the NACA0018 airfoil profile with 20% chords porous trailing edge is studied under two porous configurations, namely a fully-porous and a suction-side-porous trailing edge types. The results show that the flowfield of the porous airfoils are also influenced due to the presence of the porous medium. The noise radiation from the newly proposed porous airfoil achieves a noise reduction of 4.3dB at an angle of attack α=0°, and 4.07dB at an angle of attack α=2°. On the other hand, the loss of lift force is about 0.8%-1.5% in the angle of attack range of 0~10°.

Features of Use of Rapid Prototyping Technology in the Manufacture of Wax Models of GTE Turbine Blades

The paper presents the main results related to the peculiarities of using 3D printing technology and methods of rapid prototyping in the manufacture of wax models of blades of a GTE turbine. The main design solutions that must be used in the design of a blade blank are presented in detail: the total shrinkage coefficient, equidistant rolling of the airfoil profile, allowance along tract surfaces, radial fillets, and a number of others. The results of control of geometric dimensions of the turbine blade blanks at the corresponding stages of the technological process showed deviations from the nominal value within the tolerance range for the executable dimensions, and the statistical information from the measurement of an experimental batch of wax models of blade blanks showed stability of the silicone tooling and ability to manufacture a series of wax models of the blades in the amount of 100 pieces when using one mold.

Design and Fabrication of a Novel Window-Type Convection Device

Global warming, climate change, and ever-increasing energy demand are among the pressing challenges currently facing humanity. Particularly, indoor air conditioning, a major source of energy consumption, requires immediate improvement to prevent energy crises. In this study, various airfoil profiles were applied to create a window-type convection device that entrains air to improve convection between indoor and outdoor airflows and adjust the indoor temperature. How the geometric structure of the convection device affects its air entrainment performance was investigated on the basis of various airfoil profiles and outlet slit sizes of the airflow multiplier. The airfoil profiles were designed according to the 4-digit series developed by the National Advisory Committee for Aeronautics. The results revealed that airfoil thickness, airfoil camber, and air outlet slit size affected the mass flow rate of the convection device. Overall, the mass flow rate at the outlet of the convection device was more than 10 times greater than at the inlet, demonstrating the potential of the device to improve air convection. To validate these simulated results, the wind-deflector plate was processed using the NACA4424 airfoil with a 1.2 mm slit, and various operating voltages were applied to the convection device to measure the resulting wind speeds and calculate the corresponding mass flow rates. The experimental and simulated results were similar, with a mean error of <7%, indicating that the airfoil-shaped wind-deflector plate substantially improved air entrainment of the convection device to the goal of reduced energy consumption and carbon emissions.

2-D modelling of effect of free-stream turbulence on trailing edge vortex

Vorticity causes many adverse effects on the area near the surface, both on moving (turbine blade) and fixed objects. Therefore, this study attempts to investigate the effects of free-stream turbulence on trailing edge vortex on the NACA 0015 airfoil profile. This research was conducted using two-dimensional numerical simulations. To determine the interaction of vortex and free stream turbulence, two variations of turbulent intensity were given, namely 0.5% and 4.6% with Reynolds number of 1.6 x 105. The k-ε turbulence model was used in the current study. The angle of attack of the flow towards the airfoil was varied from 0° to 25° in conditions of increase and decrease in the horizontal position of the airfoil. The result was found that there is an agreement between the simulation and the experiment result. Increased turbulent intensity can delay the stall condition, the stall process begins to be observed after the 12° attack angle at 0.5% turbulent intensity while at turbulent intensity 4.6% the stall process was found after the 15° attack angle. From a velocity streamline, it was found that an increase in turbulent intensity can inhibit vortex growth.

Numerical investigation of leading edge noise reduction on a rod-airfoil configuration using porous materials and serrations

A lattice-Boltzmann method has been employed to study the aeroacoustics and aerodynamics of airfoils equipped with leading edge treatments, namely the porous leading edge and leading edge serrations. The present study aims to identify the differences in noise reduction mechanisms between the two treatments. Within the context of turbomachinery applications, the airfoils undergo aerodynamic excitation due to the impingement of turbulent wake shed by an upstream rod. Two airfoil profiles are considered: NACA 0012 and NACA 5406; the latter mimics geometrical features and aerodynamic loading distribution of the outlet-guide vane in a turbofan test rig. Simulations are carried out at a freestream Mach number of 0.22, corresponding to Reynolds number based on the rod diameter of 48 000. The serrations are designed to follow a sinusoidal planform shape, whereas the porous leading edge is based on a Ni-Cr-Al metal-foam with homogeneous and isotropic properties. It is found that the porous leading edge attenuates noise by dampening surface pressure fluctuations due to the reduced blockage effect compared to the solid one. Differently, the leading edge serrations promote destructive interference of noise sources along the span. When applied against turbulent inflow with tonal characteristic, such as that induced by the impingement of Kàrmàn vortex street in the rod wake, the latter is more effective. On the other hand, both treatments are found to produce similar broadband noise reduction. When comparing aerodynamic performances, it is found that under a lifting condition, cross-flow is present through the porous material which results in lift reduction and drag increase. A serrated porous leading edge is then proposed to combine the benefits of the two leading edge treatments. This results in optimal noise reduction performances and lower aerodynamic penalty with respect to the fully porous leading edge.

Horizontal axis wind turbine modelling and data analysis by multilinear regression

Abstract. The modelling of each horizontal axis wind turbine (HAWT) differs due to variation in operating conditions, dynamic parameters, and components. Thus, the choice of profiles also varies for specific applications. So for the better choice of profiles, the wind turbine performance is analysed for different parameters and working conditions. The efficiency of HAWTs mainly depends on the blade, which in turn is related to the profile of the blade, blade orientation, and tip size. Hence, the main aim of the present work is to evaluate the performance of HAWTs for three different blade tip sizes and six different blade twist angles for three major NACA (National Advisory Committee for Aeronautics) airfoils. A statistical analysis is also carried out to find the influence of different performance parameters such as drag, lift, vorticity, and normal force. The static design parameters are considered based on the available literature. A three-bladed offshore HAWT is adopted as the research object in the study. Data visualization using star glyphs and sunray plots is performed, along with multilinear regression analysis. From the multilinear regression analysis and reliable empirical correlations, it is known that drag coefficient and lift coefficient parameters have less significance in contrast to the other parameters which have more significance in the regression model. The different results obtained in terms of parametric coefficients provide an effective way to generate appropriate airfoil profiles for given HAWTs. Thus, the study helps to achieve better turbine performance, and it serves as a benchmark for future studies on HAWTs.

An automated higher order meshing for NACA0018 airfoil design using subparametric transformation

A novel higher order meshing around the airfoil design by using finite simple triangle elements has been presented in this paper. An automated meshing has been performed by linear to sextic order (n = 1, 2, 3, 4, 5 and 6) simple triangle elements using MATLAB code. The subparametric transformation approach has been implemented in the present accurate and efficient meshing. Linear, quadratic, cubic, quartic, quintic and sextic order triangle shaped elements are been utilized to discretize the area near the airfoil shape. An itemized extraction of the edge information, nodal coordinates, the total number of discretized elements and the triangle indices has been carried out from the present meshing. A NACA0018 airfoil design of 18% thickness of max camber is under consideration for the present work. Meshing is executed with the MATLAB code AirfoilHOmesh2d .m by implementing simple changes based on the present 4-digit NACA0018 airfoil profile. The accuracy of an eminent linear mesh generator scheme presented by Gilbert Strang and Persson has been proved and verified. Present work has extended these eminent linear meshing scheme by utilizing subparametric transformation on higher order triangular elements. The algorithm of meshing with higher order has been explained in detail and represented in flowchart form in the Appendix. The data extracted from the meshing can offer a simplified approach to optimize the airfoil shape, for the study of flow around the airfoil in fluid dynamics and the analysis of adverse effects on its external surface in aerospace applications. The advanced higher order meshing is beneficial for the optimization of any symmetric airfoil resulting a better economical fuel usage in the aircraft.

Enhancing CFD predictions in shape design problems by model and parameter space reduction

In this work we present an advanced computational pipeline for the approximation and prediction of the lift coefficient of a parametrized airfoil profile. The non-intrusive reduced order method is based on dynamic mode decomposition (DMD) and it is coupled with dynamic active subspaces (DyAS) to enhance the future state prediction of the target function and reduce the parameter space dimensionality. The pipeline is based on high-fidelity simulations carried out by the application of finite volume method for turbulent flows, and automatic mesh morphing through radial basis functions interpolation technique. The proposed pipeline is able to save 1/3 of the overall computational resources thanks to the application of DMD. Moreover exploiting DyAS and performing the regression on a lower dimensional space results in the reduction of the relative error in the approximation of the time-varying lift coefficient by a factor 2 with respect to using only the DMD.

Airfoil profile surface drag reduction characteristics based on the structure of the mantis shrimp abdominal segment

To reduce the drag of fluid on a surface, the parameterized structure of the mantis shrimp abdominal segment was analyzed to design the airfoil profile, and a calculation model was established based on the biological characteristics of the mantis shrimp. By using a numerical simulation method, the change in the viscous sublayer and drag reduction of the biological surface under different flow velocities and with different numbers of airfoil profiles was analyzed, and the mechanism of the drag reduction of the biological airfoil profile was revealed. The results show that the biological surface with airfoil profiles exhibited a better drag reduction effect. With an increase in airfoil profile numbers, the drag reduction rate first decreased and then increased. When the flow velocity was 10 m/s and the number of airfoil profiles was 5, the drag reduction rate exhibited the largest value of 15.33%. This result showed that the biological airfoil profile could affect the structure of the wall turbulent boundary layer and diminish the velocity gradient of the boundary layer, which finally changed the interaction pattern between the fluid and wall. In addition, the vortex cushioning effect was created to change the friction between the fluid and the wall into a rolling friction with a lower friction coefficient, thus reducing the shear stress on the wall, which achieved drag reduction.

Computer-Aided Design of Die Tooling for Large Parts of Airfoil Profiles Made of Aluminum Alloys

The paper describes the computer-aided design system developed for design of die tooling of large parts of airfoil profiles made of aluminum alloys. The system is characterized by a high degree of unification and integration. The paper gives a special focus on the analysis of a design object and the structure of information support of this system.