Aerodynamic Performance Of Airfoil Research Articles

Study on influence of turbulence intensity on blade airfoil icing mass & aerodynamic performance

Wind is an emerging renewable energy resource, but more useful in cold regions. With the increasing threat of climate change and global warming, the unpredictability of wind energy patterns has been affected. With continual threats from extremes and uncertainties, icing on wind turbines has been noted to grow affecting aerodynamic performance. The effect of turbulence intensity at its impact on aerodynamic performance was numerically done using ANSYS Fluent and FENSAP ICE software. Conditions considered for the study included turbulence intensities, median volume diameter (MVD), liquid water content (LWC), angle of attack, and ambient temperature for 180 min. The study's conditions aimed at providing a wide range of effects covering the in-cloud icing and freezing drizzle. The mass of ice increased with an increase in LWC when it increased from 0.05 g/m3 to 0.3 g/m3, and MVD with 1000 μm compared to 40 μm, but when temperature decreased led to an increase from −1 °C to −15 °C. Increasing the angle of attack led to reduced aerodynamic performance with stall angle occurring at α = 0–18°. An increase in the turbulence intensity from 0.01 % to 50 % resulted in decreased CL/CD.

Airfoil aerodynamic performance prediction using machine learning and surrogate modeling

In recent times, machine learning algorithms have gained significant traction in addressing aerodynamic challenges. These algorithms prove invaluable for predicting the aerodynamic performance, specifically the Lift-to-Drag ratio of airfoil datasets, when the dataset is sufficiently large and diverse. In this paper, we delve into an exploration of five machine learning algorithms: Random Forest, Gradient Boosting Regression, Decision Tree Regressor, AdaBoost Algorithm, and Linear Regression. These algorithms are scrutinized within the context of various train/test ratios to predict a crucial aerodynamic performance metric—the lift-to-drag ratio—for different angle of attack values. Our evaluation encompasses an array of metrics including R2, Mean Square Error, Training time, and Evaluation time. Upon analysis, the Random Forest Method, with a train/test ratio of 0.2, emerges as the frontrunner, showcasing superior predictive performance when compared to its counterparts. Conversely, the Linear Regression algorithm distinguishes itself by excelling in training and evaluation times among the algorithms under scrutiny.

The Effect of Riblets on the Aerodynamic Performance of NACA 0018 Airfoil

In this numerical study, riblets on the airfoil were utilized to enhance the aerodynamic performance of NACA0018 airfoil. Riblets of identical height and base length are strategically placed on the suction surface of the airfoil with varying spacing ratios along the flow direction (x) and chord length (c), specifically x/c = 0.3 and 0.7. Four distinct riblet airfoil models are subjected to computational fluid dynamics (CFD) analysis within an angle of attack range from 0° to 21° at a Reynolds number of Re=1×105. The obtained results are systematically compared with the performance of the plain airfoil. Numerical analyses reveal the significant influence of the spacing ratio on flow control and the overall aerodynamic performance of the airfoil, establishing a direct relationship with riblet spacing. The presence of riblet structures is observed to increase the lift coefficient, concurrently delaying the stall angle up to 19°. Notably, the ribbed structures effectively mitigate the interaction between the laminar separation bubble and trailing edge separation, leading to a reduction in turbulent kinetic energy values.

Numerical Analysis of Gurney Flap Impact on NACA 4415 Airfoil Aerodynamics Performance

Improving airfoil aerodynamic performance is an essential aspect of aerodynamic technology. The use of passive flow control is one way to enhance the aerodynamic performance of the airfoil. The influence of using gurney flaps as passive flow control was explored through the CFD approach employing the RANS control equations with the k-epsilon turbulence model. The airfoil model utilized in this investigation was the NACA 4415 operating at a Reynolds number of 1×106. This study explored three different variations of flap height, namely 0.5%, 1%, and 2% of chord length. The outcomes showed that adding gurney flaps showed quite positive results in increasing the lift and drag performance of NACA 4415. An airfoil with a 0.5%c height flap has an average percentage increase in Cl of 12%, followed by a height flap of 1%c, which is 23%, and a percentage Cl of 37% for a height flap of 2%c. Meanwhile, each variation in height flap affected the increase in Cd. A height flap of 0.5%c increased Cd with an average percentage of 2%, while a height flap of 1%c increased the percentage of Cd by 4% and 6% for a height flap of 2%c. Moreover, visualization of fluid flow with pressure and velocity contours given at AoA 12º to determine the effect on the increase in Cland Cd in NACA 4415.

Numerical Study on Glaze Ice Accretion Characteristics over Time for a NACA 0012 Airfoil

Ice accretion on wind turbine blades can significantly impact their aerodynamic performance, increasing additional load and reducing power generation. This paper utilizes numerical simulation to predict the cross-section at the blade tip of a small wind turbine and study the ice accretion process and aerodynamic characteristics of the airfoil. The research investigates the dynamic characteristics of ice accretion on NACA 0012 airfoil, as well as the influence of dynamic icing at different angles of attack and airflow velocities on the lift coefficient of the airfoil. The findings show that ice accretion leads to a more significant decrease in the lift coefficient of the airfoil at angles of attack of 8° and 12°. From 0 min to 30 min, the decrease rate of the lift coefficient is up to 48% and 46.2%, respectively. The aerodynamic performance of airfoil at 70 m/s deteriorates the most severely and the reduction degree of the lift coefficient can exceed 23.2%. These results may supply guidance for wind turbine anti-icing solutions.

Moving wall effect on normal shock wave–turbulent boundary layer interaction on an airfoil

Purpose This paper aims to describe a proposal for an innovative method of normal shock wave–turbulent boundary layer interaction (SBLI) and shock-induced separation control. Design/methodology/approach The concept is based on the introduction of a tangentially moving wall upstream of the shock wave and in the interaction region. The SBLI control mechanism may be implemented as a closed belt floating on an air cushion, sliding over two cylinders and forming the outer skin of the suction side of the airfoil. The presented exploratory numerical study is conducted with SPARC solver (steady 2D RANS). The effect of the moving wall is presented for the NACA 0012 airfoil operating in transonic conditions. Findings To assess the accuracy of obtained solutions, validation of the computational model is demonstrated against the experimental data of Harris, Ladson & Hill and Mineck & Hartwich (NASA Langley). The comparison is conducted not only for the reference (impermeable) but also for the perforated (permeable) surface NACA 0012 airfoils. Subsequent numerical analysis of SBLI control by moving wall confirms that for the selected velocity ratios, the method is able to improve the shock-upstream boundary layer and counteract flow separation, significantly increasing the airfoil aerodynamic performance. Originality/value The moving wall concept as a means of normal shock wave–turbulent boundary layer interaction and shock-induced separation control has been investigated in detail for the first time. The study quantified the necessary operational requirements of such a system and practicable aerodynamic efficiency gains and simultaneously revealed the considerable potential of this promising idea, stimulating a new direction for future investigations regarding SBLI control.

Sensitivity Analysis of an Unsteady Flow Around a Pitching Airfoil

Various ways to control the loads and thus the output of the wind turbine by pitching the blades and by controlling the rotational speed already exist. However, adverse pressure gradient leading to flow separation at the trailing edge, with relatively high angles of attack (AOA) due to blade-pitching motion, largely affects the airfoil aerodynamic performance. This work presents the results of a numerical study of the unsteady flow around a pitching FFA-W3-301 airfoil at a Reynolds 1.6 × 106 using OpenFOAM®, as obtained by first performing 2D Unsteady Reynolds-Averaged Navier- Stokes (URANS) simulations whereby the flow characteristics are simulated by the shear stress transport (SST) k − ω model and Spalart-Allmaras (SA). The influence of various parameters on the numerical results is investigated, namely y+, computational grid resolution, dynamic mesh technique, time step and turbulence model. Integral aerodynamic forces and detailed flow patterns are compared with experimental measurements presented in the literature. A range of angles of attack, including early stalls, are examined. For best-performing parameters, an adequate refinement close to the wall was imperative in order to match experiments, especially during the upstroke motion of the airfoil, while for the downstroke phase, some differences still appeared. The agreement was greatly improved by using a 2.5D hybrid RANS-LES approach with enhanced delayed-Detached Eddy Simulation (DES) capabilities.

Optimized design of wind turbine airfoil aerodynamic performance and structural strength based on surrogate model

Though offshore wind turbines have great potential for applications in ocean energy harvesting, their subject to complex unsteady aerodynamic loads. To obtain wind turbine airfoils with both aerodynamic performance and structural strength, an airfoil optimization method was proposed by adding the torsion constant to the objective function under the premise of improving the lift-to-drag ratio. The optimization method characterizes the airfoil geometric profile by using Class/Shape function transformation (CST) parameterization. The airfoil aerodynamics and the structural properties were solved by the computational fluid dynamics (CFD) method and Matlab program, respectively. To reduce the number of CFD calculations, a Kriging surrogate model was established. The combination of an optimized Latin hypercube sampling method and expected improvement (EI) points infill criteria is to improve surrogate modeling efficiency. The NREL 5 MW wind turbine blade was used as the research object. The NACA64618 with 18% relative thickness, the DU91-W2-250 with 25% and the DU97-W-350 with 35% were optimized by assigning different weights to aerodynamic and structural objectives based on airfoil position in the blade. The results showed that the aerodynamic performance of the optimized airfoils was improved. Subsequently, the three optimized airfoils were replaced in the same positions of the blade for lay-up design. The blade structural properties were calculated by finite element method (FEM) and it found that the blade torsion angle was reduced, which indicated that adding structural objectives in the airfoil optimization could enhance the blade structural performance.

Active flow control on airfoils by reinforcement learning

Active flow control is a widespread practice for airfoil aerodynamic performance enhancement. Within active flow control, reactive strategies are very effective, but the adequate design of these strategies is often complex. This study proposes a reactive control strategy based on a Reinforcement Learning (RL) agent to effectively govern the motion of a rotating flap implemented on a NACA0012 airfoil. With this objective, first different Computational Fluid Dynamics (CFD) simulations are conducted to gather data about the tested case. Then, a numerical model based on Artificial Neural Networks (ANN) is developed to model the discussed case. Finally, the RL agent is trained and tested under different conditions. The results show that the trained RL agent is able to provide a fast and reliable response for every tested condition, setting the adequate position of the flap and obtaining an appropriate aerodynamic performance of the airfoil for all the tested conditions. In comparison with the optimum conditions, the absolute error in the position of the flap set by the agent is below 2.2 ° for all the angles of attack, resulting in an aerodynamic performance very close to the optimum, being only 0.39%–3.05% lower, depending on the case.

Airfoil Optimisation at Ultra-Low Reynolds Number

In recent times micro-air vehicles are utilised for various civilian and military applications. Because of their small size and low flight speeds they fly in the low Reynolds number (Re) regime. At such low Re the aerodynamic characteristics, most importantly the lift-to-drag ratio (Cl/Cd), are deteriorated. An improvement in (Cl/Cd) can lead to enhanced vehicle performance. The aerodynamic improvements can be achieved by optimising the wing profile geometry. In the present paper, optimisation of an airfoil is done to maximise (Cl/Cd) at Re = 1000. The upper and lower surfaces of a modified NACA 2408 airfoil are parametrised using the Akima interpolation method. The fixed-direction set method is used in optimising the airfoil aerodynamic performance with six control points each on the upper and lower surfaces. A corrugated airfoil, with a trapped vortex within it, is obtained as a result of this optimisation. Further, optimisation is carried out only on the upper surface of the corrugated airfoil with flat lower surface by increasing the number of control points from six to ten. (Cl/Cd)max is 3.718 for the baseline airfoil, while the final optimal airfoil resulted in (Cl/Cd)max of 4.670, a 25.6 % increase.

Aerodynamic performance of a characteristic airfoil at low-Reynolds number and transonic flow under Mars sand-containing environment

The propeller tip of an unmanned aerial vehicle on Mars operates at a low-Reynolds number (Re = 1–5 × 104) and transonic velocity range (Ma = 0.7–1.2). Generally, this implies flow separation and shock waves in the flow field. Furthermore, the impact of Martian atmospheric sand particles significantly affects the aerodynamic performance, and numerical simulations of this issue have received increasing attention recently. Aimed at a characteristic airfoil, the study of a low-Reynolds number transonic flow and the influence of sand-containing flow on airfoil aerodynamic performance were analyzed in this study. The discrete phase model was adopted to simulate the two-phase flow considering Re = 8100–56 800 and Ma = 0.2–1.4. The results indicate that, compared with the atmospheric environment on Earth, the low-pressure atmosphere on Mars can delay the generation of the surface shock wave of the airfoil as well as alter the shock wave structure, significantly increasing the lift-to-drag ratio at high subsonic velocities (Ma = 0.6–0.8). Moreover, due to the weak compressive wave generated at the separation position, the low-pressure atmosphere weakens the strength of the trailing-edge oblique shock wave and reduces the drag when Ma = 0.9–1.4. Compared with a sand-free environment, sand-containing flow can affect the separation and transition positions of laminar separation bubbles, in addition to alter the shock wave structure. At different Mach numbers, the lift and drag of the airfoil first increased and then decreased as the sand particles flowed in the horizontal direction during the entire process of particles entering and exiting the airfoil flow field.

Design & analysis of NACA 0012 airfoil with circular dent of 30 mm depth on upper surface

This research paper presents the design and analysis of a NACA 0012 airfoil with a circular dent of 30 mm depth on its upper surface. The objective of this study is to investigate the effect of the dent on the airfoil's aerodynamic performance. The airfoil's geometry was modeled using a CAD software, and a CFD analysis was carried out using the ANSYS Fluent software to evaluate the airfoil's lift and drag coefficients. The results showed that the airfoil's performance was affected by the presence of the dent, with a decrease in lift and increase in drag. However, the airfoil's stall behavior was not significantly affected by the dent.

Numerical Simulation of Flow Over Airfoil and Its Optimization

Airfoils are one of the most important factors in determining an airplane’s ability to fly. As such, their optimization holds important ramifications for the continual need to improve airplane performance. In this paper, the optimization of airfoil design is explored through numerical computational fluid dynamics. This paper first investigates the effects of Angle of Attack on airfoil lift/drag ratios, which is shown to have a significant influence on the performance of airfoils. Then, the effects from thickness are explored, and it is found that the influence of thickness is highly dependent on the specific shape of airfoil. In addition, in order to further improve airfoil aerodynamic performance, a type of modified airfoil with an additional tip is developed and simulated. The results indicate that airfoils with additional tips can perform better, but only with the proper combination of tip parameter values. For example, the modified airfoil with a tip of 0.03 L length at a 25° tip angle bested that same airfoil without an additional tip. Finally, it is found that the Backpropagation machine-learning algorithm, when trained with prior simulation data, can quickly predict lift and drag coefficients of airfoils. The results in this paper could facilitate the further optimization of airfoil design.

Study on design characteristics of airfoil pressure distribution for low Mach number general aircraft

This paper studies several problems that may exist in the aerodynamic design of low Mach number general aircraft, and discusses the design characteristics of the pressure distribution of some related airfoils while part of the characteristics is verified by a multi-point laminar airfoil design case. Firstly, several issues which exist in the aerodynamic design of low Mach number general aircraft, such as relatively large zero-lift drag coefficient, high stall performance requirements, and large variation range of Reynolds number, are discussed and analyzed. Then, to address these issues, the paper extracts some useful design features that are beneficial to the airfoil aerodynamic performance from the study on the design characteristics of the pressure distribution of several turbulent flow airfoils and laminar flow airfoils that are designed for low Mach number general aircraft. Finally, by considering the typical design conditions of a light multi-purpose single-turboprop-engine general aircraft, including the cruise, climb and stall conditions, a multi-point laminar airfoil optimization is offered by using the GAW-1 airfoil as the baseline. The optimized foil has a 9.6 improvement in the lift-to-drag ratio of the cruise condition, a 16.3 improvement in the lift-to-drag ratio of the climb condition but a 0.115 decrease in the maximum lift coefficient of the stall condition. The results show that the requirements from the cruise, climb and stall conditions are contradictory to some degree in the considering multi-point optimization case, and the designers should deal with this trade-off carefully based on the features of the low Mach number general aircraft.

Pix2Pix and Deep Neural Network-Based Deep Learning Technology for Predicting Vortical Flow Fields and Aerodynamic Performance of Airfoils

Traditional computational fluid dynamics (CFD) methods are usually used to obtain information about the flow field over an airfoil by solving the Navier–Stokes equations for the mesh with boundary conditions. These methods are usually costly and time-consuming. In this study, the pix2pix method, which utilizes conditional generative adversarial networks (cGANs) for image-to-image translation, and a deep neural network (DNN) method were used to predict the airfoil flow field and aerodynamic performance for a wind turbine blade with various shapes, Reynolds numbers, and angles of attack. Pix2pix is a universal solution to the image-to-image translation problem that utilizes cGANs. It was successfully implemented to predict the airfoil flow field using fully implicit high-resolution scheme-based compressible CFD codes with genetic algorithms. The results showed that the vortical flow fields of the thick airfoils could be predicted well using the pix2pix method as a result of deep learning.

Comparison of Flow Topology Between Major Groups of Airfoil with Vortex Shedding

The effect of vortex behavior on airfoil aerodynamic performance has been widely debated for many years, and many research studies have been conducted to examine the relationship. This paper highlights the in-depth study of flow topological processes on major airfoil groups with vortex shedding. It considers various typeof corresponding geometriesincludingsymmetrical, asymmetrical, thick, and thin airfoilsin order to showthe differences in flow topology. The study also emphasized the behavior of separationbubbles, vortex shedding and reattachment points. The use of a commercial CFD softwarefor the studygave reliable resultswithinan adequate length of time. The vortex shedding wassuccessfully highlighted either physically or hypothetically. The separation bubble was relatively easier to be identified in all cases of airfoil of interest. The evolution of separation bubble captured by the topology in the case of Eppler169 was the unique, and involved the break of reattachment point.

Experimental Study on the Effect of Porous Media on the Aerodynamic Performance of Airfoils

Porous media has potential applications in fluid machinery and in aerospace science and engineering due to its excellent drag-reduction properties. We carried out experimental time-resolved particle image velocimetry (TR-PIV) research, laying porous media with different pore densities on the suction side of an airfoil in the low-turbulence recirculation wind tunnel of Nanjing University of Aeronautics and Astronautics to study the effects and mechanisms of porous media on airfoil aerodynamic performance. We also used a smooth airfoil model in the experiment for comparison. Comparing the aerodynamic forces, pressure distributions, and the airfoil’s suction side flow field, we found that the porous media with different pore densities had different effects on the airfoil’s aerodynamic performance. Although the porous media with 20PPI (pores per inch) increased the pressure drag and reduced the airfoil lift, it considerably reduced the friction drag, thus significantly improving the airfoil’s aerodynamic force. The flow visualization results indicated that, although the porous media with 20PPI reduced the circulation of flow velocity around the suction side of airfoil, it also destroyed the vortex structure, broke the low-frequency large-scale vortex into a high-frequency granular vortex, inhibited the amplitude of vortex fluctuation, reduced the shear stress on the airfoil surface, weakened the vortex energy of different modes, and accelerated the vortex’s spatio-temporal evolution.

Prediction and optimization of airfoil aerodynamic performance using deep neural network coupled Bayesian method

In this paper, we proposed an innovative Bayesian optimization (BO) coupled with deep learning for rapid airfoil shape optimization to maximize aerodynamic performance of airfoils. The proposed aerodynamic coefficient prediction model (ACPM) consists of a convolutional path and a fully connected path, which enables the reconstruction of the end-to-end mapping between the Hicks–Henne (H–H) parameterized geometry and the aerodynamic coefficients of an airfoil. The computational fluid dynamics (CFD) model is first validated with the data in the literature, and the numerically simulated lift and drag coefficients were set as the ground truth to guide the model training and validate the network model based ACPM. The average accuracy of lift and drag coefficient predictions are both about 99%, and the determination coefficient R2 are more than 0.9970 and 0.9539, respectively. Coupled with the proposed ACPM, instead of the conventional expensive CFD simulator, the Bayesian method improved the ratio of lift and drag coefficients by more than 43%, where the optimized shape parameters of the airfoil coincide well with the results by the CFD. Furthermore, the whole optimization time is less than 2 min, two orders faster than the traditional BO-CFD framework. The obtained results demonstrate the great potential of the BO-ACPM framework in fast and accurate airfoil shape optimization and design.

Numerical study on flow characteristics of airfoil with bionic micro-grooves

Three airfoil models with bionic micro-grooves were developed to investigate the effect of the bionic micro-grooves on the airfoil flow field and aerodynamic performance. Large eddy simulation (LES) was used to predict the flow field around the airfoil. The Re were 1.6 × 105 and 2 × 105, and the angle of attack was 6°. The results show that all three airfoils reduce the velocity gradient at the airfoil suction surface near the wall and the energy loss in the boundary layer. The area of the recirculation zone of the H1 and H2 airfoils is significantly reduced. However, when the Re is 1.6 × 105, the area of the recirculation zone of the H3 airfoil increases. The aerodynamic performance of all three airfoils was improved. When the Re is 1.6 × 105, the aerodynamic performance of the H1 airfoil is improved most significantly, and the drag reduction rate reaches 16.41%. When the Re is 2 × 105, the aerodynamic performance improvement of H2 is the most obvious, and the drag reduction rate reaches 17.45%. In order to achieve the best drag reduction effect, the position of the bionic micro-grooves should gradually approach the wing's tail with the increase of Re.

Direct numerical simulation of transitional flow past an airfoil with partially covered wavy roughness elements

We perform direct numerical simulation of flow past the NACA (National Advisory Committee for Aeronautics) 0012 airfoil with partially covered wavy roughness elements near the leading edge. The Reynolds number Rec based on the freestream velocity (U0) and airfoil chord length (C), and the angle of attack (AoA) is fixed, i.e., Rec=5×104, AoA=10°. The leading edge roughness elements are characterized by streamwise sinusoidal-wave geometry that is uniform in the spanwise direction with fixed height, whereas varying wave numbers (k) from 0 to 12. Based on the validation of the smooth baseline case (k = 0), the roughness effects on the aerodynamic performance are evaluated in terms of the lift and drag coefficients. The drag coefficient decreases monotonically with k, while the variation of the lift coefficient with k is similar to the “drag crisis” phenomenon observed in cylinder flows. The sharp variations of lift and drag coefficients from k = 6 to 8 indicate that k = 8 is a critical case, beyond which massive separation occurs and almost covers the airfoil's suction side and dominates the airfoil aerodynamic performance. To further reveal the underlying mechanism, the flow structures, pressure, skin friction coefficients, shear layer transition onset, and boundary layer separation are quantified to investigate the roughness effects. The roughness elements strongly modify the separation behavior, whereas they have little effect on the transition onset. The unsteady interactions and convections of separation bubbles downward the trailing edge also change the wake evolution. Based on the scaling of the asymmetric wake profiles, we find that the wake defect is gently decreasing with k, but the increase in the wake width is much stronger. This scaling analysis gains a better insight into the roughness effects on the momentum deficit flow rate, which confirms the drag mechanism with different roughness wave numbers.