Aerodynamic Performance Of Airfoil Research Articles

Vortex Shedding and Aerodynamic Performance of Airfoil with Multiscale Trailing-Edge Modifications

An experimental investigation was conducted into the nature of the vortex shedding generated by truncated and nonflat serrated trailing edges of a NACA 0012 wing section as well as the aerodynamic performance of such trailing edges. In line with previous findings, the truncated trailing edge generates a significant amount of vortex shedding, while increasing both the maximum lift and drag coefficients, resulting in an overall reduction in the maximum lift-to-drag ratio compared to a plain NACA 0012 wing section. By decreasing the chevron angle of the nonflat trailing-edge serrations (i.e., by making them sharper), the energy of the vortex shedding significantly decreases, and the lift-to-drag ratios increase compared to a plain NACA 0012 wing section. Fractal/multiscale patterns made of scaled-down repetitions of these serrations were also investigated with a view to further improve performance. It was found that the energy of the vortex shedding increases with an increasing fractal iteration if the chevron is broad () but decreases for sharper chevrons (). It is believed that if is too big, the multiscale trailing edges are too far away from each other to interact and break down the vortex shedding mechanism. Fractal/multiscale trailing edges are also able to improve aerodynamic performance compared to the NACA 0012 wing section.

Fluid-Structure Coupling Effects on the Aerodynamic Performance of Airfoil with a Local Flexible Structure at Low Reynolds Number

Fluid-Structure Coupling Effects on the Aerodynamic Performance of Airfoil with a Local Flexible Structure at Low Reynolds Number

Modification of k-ω turbulence model for predicting airfoil aerodynamic performance

Predicting wind turbine S825 airfoil’s aerodynamic performance is crucial to improving its energy efficiency and reducing its environmental impact. In this paper, a numerical simulation on the wind turbine S825 airfoil is conducted with k-ω turbulence model at different attack angles. By comparing with experimental data, a new method of modifying k-ω model is proposed. A modifying function is proposed to limit the production term in ω equation based on fluid rotation and deformation. This method improves turbulent viscosity and decreases separating region when the airfoil works at large separating conditions. The predictive accuracy could be improved by using the modified k-ω turbulence model.

Numerical study of the S809 airfoil aerodynamic performance using a co-flow jet active control concept

A Co-Flow Jet (CFJ) active flow control concept is implemented on the S809 airfoil and numerically investigated by using an in-house code based on Reynolds-averaged Navier-Stokes equations and the Spalart-Allmaras turbulence model, aiming to systematically study the jet effect on the airfoil aerodynamic performance. The solver is validated by comparing the computed results with the baseline experiment measurement. The calculated aerodynamic force and moment coefficients agree fairly well with the experimental data, demonstrating the present solver can predict the attached as well as separated flows around the S809 airfoil with an acceptable precision. The CFJ jet-off geometry of S809 airfoil is simulated to study the jet channel effect on the baseline aerodynamic characteristic, showing that the jet channel could reduce the lift, increase the drag and cause an earlier abrupt stall at angle of attack (AoA) 16.24°. The CFJ jet-on geometry is elaborately studied at three jet momentum coefficient levels, showing that co-flow jet has a significantly positive effect in increasing lift, stall margin, and drag reduction. For the cases with jet momentum coefficients 0.12 and 0.18, the total drag even becomes negative. It is found that the drag from pressure and shear stress of CFJ airfoil is larger than that of baseline, and it is the negative mass-flow-produced drag that significantly reduces the total drag to be below zero. For cases in which AoA are below a critical value (e.g., 20.15° for the case with jet momentum coefficient 0.18), the power required to drive the jet flow decreases when AoA increases, demonstrating that the CFJ concept has an attractive advantage of minimum energy consuming. The present CFJ concept is proved to be a promising and effective active flow control method in the wind turbine application.

Effect of Relative Thickness on Improving Airfoil Aerodynamic Performance by Blunt Trailing-Edge Modification

Effect of Relative Thickness on Improving Airfoil Aerodynamic Performance by Blunt Trailing-Edge Modification

Numerical Analysis of Wind Turbine Airfoil Aerodynamic Performance with Leading Edge Bump

Aerodynamic performance improvement of wind turbine blade is the key process to improve wind turbine performance in electricity generated and energy conversion in renewable energy sources concept. The flow behavior on wind turbine blades profile and the relevant phenomena like stall can be improved by some modifications. In the present paper, Humpback Whales flippers leading edge protuberances model as a novel passive stall control method was investigated on S809 as a thick airfoil. The airfoil was numerically analyzed by CFD method in Reynolds number of 106and aerodynamic coefficients in static angle of attacks were validated with the experimental data reported by Somers in NREL. Therefore, computational results for modified airfoil with sinusoidal wavy leading edge were presented. The results revealed that, at low angles of attacks before the stall region, lift coefficient decreases slightly rather than baseline model. However, the modified airfoil has a smooth stall trend while baseline airfoil lift coefficient decreases sharply due to the separation which occurred on suction side. According to the flow physics over the airfoils, leading edge bumps act as vortex generator so vortices containing high level of momentum make the flow remain attached to the surface of the airfoil at high angle of attack and prevent it from having a deep stall.

Reynolds Number Effect on the Optimization of a Wind Turbine Blade for Maximum Aerodynamic Efficiency

AbstractBecause of the increase in wind rotor size, the Reynolds number of an airfoil profile can reach a very high value. The effect of the Reynolds number on the aerodynamic performance of airfoils is investigated, and its influence on the optimal design of a wind rotor aiming to maximize the power coefficient is discussed. Six airfoils are involved—four DU and two NACA6—as well as five Reynolds numbers varying from 106 to 107, which cover most commercial wind turbines. At a higher Reynolds number, all of the airfoils exhibit better performance, such as a higher lift coefficient, a lower drag coefficient, and a larger lift-to-drag ratio at a given angle of attack. The largest lift-to-drag ratio and the corresponding lift coefficient and angle of attack also change with the Reynolds number, which in turn affects both the performance and the optimal shape of a blade. The results show that a practical blade operating at a higher Reynolds number requires a duller shape with a greater twist angle, and has a ...

Influence of Flap Deflection Angle on Wind Turbine Airfoil with Trailing Edge Flaps

To improve the ability of capturing the wind energy of wind turbine and shorten the design period is of great importance to designing wind turbine blade. The article established S809 airfoil model with trailing edge flaps, The gap of the frontal subject and trailing edge flap adopt uniform gap structure, this structure will reduce the influence of the gap on aerodynamic characteristics.Using the k-ω Two equation turbulence model , the article calculated aerodynamic performance of S809 with 10% chord length trailing edge flaps under different deflecting angles. Results show that gap between the main body and trailing edge flap has little effect on airfoil aerodynamic performance, however, the deflection Angle of Trailing edge flap have great affect on airfoil aerodynamic performance, when deflection Angle of trailing edge flap is 14 ° degrees ,the lift-to-drag ratio is the largest.

Optimization of Nano-Rotor Blade Airfoil Using Controlled Elitist NSGA-II

The aerodynamic performance of airfoil at ultra-low Reynolds number has a great impact on the propulsive performance of nano rotor. Therefore, the optimization of airfoil is necessary before the design of nano rotor. Nano rotor blade airfoil optimization is a multi-objective problem since the airfoil suffers a wide range of Reynolds number which increases the difficulty of optimization. In this paper, the airfoil of nano rotor was optimized based on the controlled elitist Non-dominated Sorting Genetic Algorithm II (NSGA-II) coupling with the parameterization method of Class function/Shape function Transformation technique (CST) and the multi-objectives function processing method of statistical definition of stability. An airfoil was achieved with the thickness of 2% and the maximum camber of 5.6% at 2/3 of chord. Airfoil optimized exhibits a good aerodynamic performance at ultra-low Reynolds number according to the computational results. And comparisons were carried out between the performance of the rotor designed with airfoil optimized and that of the rotor designed with AG38 airfoil, which showed that the airfoil optimized was suitable for rotor design.

Modification of Spalart-Allmaras Turbulence Model for Predicting S825 Airfoil Aerodynamic Performance

In this paper, a 2-D numerical simulation of the wind turbine S825 airfoil is conducted with Spalart-Allmaras (SA) turbulence model at different attack angles. By comparing with experimental data, a novel method of modifying SA model is proposed. The key parameter in SA turbulence model is set with different values in the non-separating region and separating region divided by separating point respectively. This method improves the predictive accuracy of SA turbulence model when the airfoil works at stall conditions.

Modeling Multiresponse Surfaces for Airfoil Design with Multiple-Output-Gaussian-Process Regression

Response surfaces are frequently used in airfoil design due to less resource requirement compared with direct slow simulations. In many cases, multiple responses need to be modeled to achieve multiple objectives. Considering the correlations between multiple responses in modeling the nonlinear relationship between airfoil shapes and aerodynamic performance, the authors construct multiresponse surfaces for airfoil design with multiple-output-Gaussian-process-regression model. The authors simulate computational data to evaluate the prediction accuracy and stability of the multiple-output Gaussian process in airfoil design, compared with other popular alternative approaches, kriging, and backpropagation and radial-basis-function neural networks. In the experiments, response surfaces from the airfoil shapes, parameterized by the class/shape-function-transformation method, to lift, drag, and pitching-moment coefficients are constructed. The results indicate that the multiple-output Gaussian process receives higher prediction accuracy and stability in modeling multiresponse surfaces than other popular methods when there are significant correlations between responses.

High fidelity numerical simulation of airfoil thickness and kinematics effects on flapping airfoil propulsion

High-fidelity numerical simulations with the spectral difference (SD) method are carried out to investigate the unsteady flow over a series of oscillating NACA 4-digit airfoils. Airfoil thickness and kinematics effects on the flapping airfoil propulsion are highlighted. It is confirmed that the aerodynamic performance of airfoils with different thickness can be very different under the same kinematics. Distinct evolutionary patterns of vortical structures are analyzed to unveil the underlying flow physics behind the diverse flow phenomena associated with different airfoil thickness and kinematics and reveal the synthetic effects of airfoil thickness and kinematics on the propulsive performance. Thickness effects at various reduced frequencies and Strouhal numbers for the same chord length based Reynolds number (=1200) are then discussed in detail. It is found that at relatively small Strouhal number (=0.3), for all types of airfoils with the combined pitching and plunging motion (pitch angle 20°, the pitch axis located at one third of chord length from the leading edge, pitch leading plunge by 75°), low reduced frequency (=1) is conducive for both the thrust production and propulsive efficiency. Moreover, relatively thin airfoils (e.g. NACA0006) can generate larger thrust and maintain higher propulsive efficiency than thick airfoils (e.g. NACA0030). However, with the same kinematics but at relatively large Strouhal number (=0.45), it is found that airfoils with different thickness exhibit diverse trend on thrust production and propulsive efficiency, especially at large reduced frequency (=3.5). Results on effects of airfoil thickness based Reynolds numbers indicate that relative thin airfoils show superior propulsion performance in the tested Reynolds number range. The evolution of leading edge vortices and the interaction between the leading and trailing edge vortices play key roles in flapping airfoil propulsive performance.

잠열 전달이 일어나는 얇은 익형주위의 천음속 습공기 유동에서의 마하수와 익형 두께비의 영향

Once the condensation of water vapor in moist air around a thin airfoil occurs, liquid droplets nucleate. The condensation process releases heat to the surrounding gaseous components of moist air and significantly affects their thermodynamic and flow properties. As a results, variations in the aerodynamic performance of airfoils can be found. In the present work, the effects of upstream Mach number and thickness ratio of airfoil on the transonic flow of moist air around a thin airfoil are investigated by numerical analysis. The results shows that a significant condensation occurs as the upstream Mach number is increased at the fixed thickness ratio of airfoil(

Horizontal Axis Wind Turbine Numerical Simulation of Two Dimensional Angle of Attack

wind power is the most effective form of wind energy utilization, modern large-scale wind turbine with horizontal axis wind mainly. Horizontal axis wind turbine aerodynamic performance calculation of the wind turbine aerodynamics research hot spot, is a wind turbine aerodynamic optimization design and calculation of critical load. Horizontal axis wind turbine airfoil aerodynamic performance of the wind turbine operation characteristics and life plays a decisive role". Using Fluent software on the horizontal axis wind turbine numerical simulation, analysis of the United States of America S809NREL airfoil aerodynamic characteristics of different angles of attack numerical simulation, analyzes the different angles of attack in the vicinity of the pressure, velocity distribution. By solving the two-dimensional unsteady, compressible N-S equations for the calculation of wind turbine airfoil S809used the characteristics of flow around. N-S equation in body-fitted coordinate system is given, with the Poisson equation method to generate the C grid.

A Multi-Point Approach to Airfoil Shape Optimization

Airfoil design is essential for civil aircraft. A multi-point method is presented in this article to improve the aerodynamic performance of airfoil over a range of the flight envelope. This method combines computational fluid dynamics and numerical optimization. It comprises of three phases: 1) Airfoil shape parameterization method to develop candidate shapes. 2) Flow solver validation to calculate aerodynamic forces. 3) Searching for the optimized airfoil shape using the genetic algorithm. The major limitation of single-point design is the poor off-design performance. By basing the objective on a combination of the drag at three design points, the resulting overall performance can be improved with respect to the single-point result.

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a five-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.

Numerical Simulation on the Flow Control by Mounting Indented Gurney Flaps for a Wind Turbine

Numerical investigation of large thick and low Reynolds airfoil of wind turbines by mounting indented Gurney flaps was carried out. The influenced rules of the position of Gurney flaps on the aerodynamic performance of airfoil under same height of flaps were achieved, and the optimal position of Gurney flap was presented. At last, the mechanism of wind turbine performance controlled by Gurney flap was discussed. The results can provide the theoretical guidance and technical support to wind turbines control in practical engineering.

Unsteady numerical estimation of the aerodynamic loads of the Krueger flap

The aim of this paper is to study the unsteady aerodynamic interaction between a Krueger flap and a three-element airfoil using the finite volume method to solve the Unsteady Reynolds- Averaged Navier-Stokes equations. For a better understanding of this unsteady interaction, the Krueger flap is placed at different positions. Our results clearly show that the airfoil's aerodynamic performance and the pressure distributions are strongly influenced by the Krueger flap position.

Numerical Simulation of Gurney Flap on RAE-2822 Supercritical Airfoil

A two-dimensional steady Reynolds-averaged Navier–Stokes equation was solved to investigate the effects of a Gurney flap on RAE-2822 (Royal Aeronautical Establishment) supercritical airfoil aerodynamic performance. The heights ofGurneyflaps range from0.25 to 3%airfoil chord lengths. The incompressible/compressibleNavier–Stokes equations were used to simulate the flow structure around the airfoils in subsonic/transonic flows, respectively, with the Spalart–Allmaras turbulence model. In comparison with the clean airfoil, the Gurney flap can significantly increase the prestall lift and lift-to-drag ratio of an RAE-2822 airfoil at a small angle of attack. Nosedown pitching moment also increased with the Gurney flap height. At both takeoff-and-landing status and cruise phase, the aerodynamic performance of the airfoil was significantly improved byGurney flaps with the height below 1%airfoil chord length. In addition, the surface pressure distribution, wake flow velocity profile, and trailing-edge flow structure of the airfoil were illustrated, which helps to understand the mechanisms of the Gurney flap to improve RAE-2822 airfoil aerodynamic performance.

Research of Measurement Method of Two Dimensional Configuration Drag Test in Wind Tunnel in Case of High Lift

Computational fluid dynamics and wind tunnel test are two main technical means to examine the aerodynamic performance of airfoil and two-dimensional(2-D) configuration. Two dimensional wind tunnel tests use commonly wake flow field measurement to integrate for drag of airfoil or two-dimensional configuration, but the integral formulas are based on certain assumptions and of certain bounds of application. In this paper, based on Navier-Stokes equations numerical simulation and two dimensional wind tunnel testing, the drag measuring technique for high lift configuration in low speed wind tunnel is researched. Navier-Stokes equations is solved for the flow around a multi-element airfoil, the wake flow characteristics behind the multi-element airfoil and the assumptions for conventional drag measuring method are analyzed, then a new more precise drag formula for two dimensional wind tunnel test is put forward; Based on the simulation results of multi-element airfoil flow, it’s aerodynamic performance is obtained respectively by integrating the surface pressure and friction drag, and computing with the information of wake flow according to conventional and newly proposed drag calculation formulas, and the three results are compared to verify the accuracy of the new drag formula; The wind tunnel test is carried out to ascertain the accuracy of the new drag formula. It is shown from the results that in the high-lift case the conventional drag formula with the wake information is of many limitations and must be improved, and the new drag formula presented in this paper is more accurate because of consideration of the wake flow characteristics of airfoil or two-dimensional configuration.