Basic Airfoil Research Articles

INVESTIGATION OF AERODYNAMIC PERFORMANCE OF A NACA 0021 AIRFOIL MODIFIED WITH CAVITY

In this paper, an experimental investigation was conducted to investigate the effect of cavity on the NACA 0021 airfoil at low Reynolds number. The force measurement and smoke-wire flow visualization experiments were conducted in a low-speed open suction wind tunnel with a test section of 57cm×57cm×100 cm at a Reynolds number of 5.0×104 and 1.0×105. Two different airfoil models produced for the experiments such as base and cavity models. The diameter and location of the cavity was chosen as 0.08C and 80% x/C, respectively. The maximum lift coefficient of the cavity modified airfoil was increased about 6% for both positive and negative angles of attack compared to base airfoil at Reynolds number of 1.0×105. The cavity modified airfoil showed higher lift coefficient values at negative attack angles when compared to base airfoil at Reynolds number of 5.0×104.

Stall characteristics of wavy leading-edge airfoil in subsonic and transonic airflows

Based on the bioinspired wavy leading-edge, the stall characteristics of the NACA0012 airfoil are optimized. In this paper, the semicircle plus line segment is used to obtain the wavy leading edge. The aerodynamic forces of the airfoil are measured by a high-precision balance, and the detailed flow features of the airfoil are obtained by the oil flow tests. Then, combined with numerical simulation, the optimization mechanism is obtained. The operating conditions are as follows: Mach number ranging from 0.4 to 0.8, and angle of attack ranging from −4° to 25°. The results show that in high speed airflows, compared with the basic airfoil, the lift coefficient of the wavy leading-edge airfoil does not decrease sharply with the increase of the angle of attack, and the drag coefficient of the wavy leading-edge airfoil is similar to the basic airfoil; among the three types of airfoils studied, the larger wavy leading-edge feature size has better aerodynamic characteristics; combined with the numerical simulation results, it can be seen that the stall mechanism of airfoils varies at different Mach numbers. The wavy leading-edge generate streamwise vortex. The streamwise vortices increase energy transport in the boundary layer. Therefore, the separation zone moves toward the trailing edge of the airfoil, and the stall characteristics of the airfoil are optimized.

Analyzing the aerodynamic characteristics of eroded wind turbine blades

The study investigates the influence of erosion over the leading edge of S809 series airfoil and its impact on the aerodynamic performance of wind turbine blades. The research work determines how erosion affects the performance of wind turbine blades at an angle of attack varying from 0° to 45° for the fixed Reynolds number of 2.1 x 105. To analyse the flow characteristics, the average pressure acting around the surface of the airfoil is scanned with the aid of 20 pressure taps. The time series pressure of 10,000 samples at each point has been collected. The roughness is introduced at the leading edge of the airfoil and measures 0.1% of the total chord at the top and bottom surface, respectively. Six different intensities of roughness are introduced and tested. The base airfoil, as well as roughed surface airfoil, is compared and the results are discussed. The aerodynamic parameters like lift, drag, and pressure coefficients are included. The estimated data suggests the erosion that occurs on the wind turbine blade surface alters the flow pattern and the aerodynamic properties of the wind turbine blades. Collectively, the experiment on analysing the eroded surface possibly taking place over the wind turbine blade surface affects the lift parameter with a considerable increment in drag. However, the roughness allows the airflow to remain fixed with the airfoil surface, favouring the concept of extending the stall.

NUMERICAL INVESTIGATIONS ON THE DYNAMIC BEHAVIOUR OF A 2-DOF AIRFOIL WITH APPLICATION IN ENERGY HARVESTING SYSTEM

This article presents the basic airfoil model with two degrees of freedom - the semi-rigid model, where its forced vibrations were considered, and the exciting force is the aerodynamic force, including its periodic changes, that is, gusts. Since the phenomenological model under study has a coupled form, its versions after decoupling are presented, which has an impact on the results of the final research. The airfoil model presented in this way was shown from the application side in the system of a simple energy harvester based on a deformable beam with piezoelectric elements. The result of the simulation tests is a preliminary analysis of the possibility of using the airfoil as a vibration generator for the energy harvesting system. Along with the application of the mechanical part, a numerical simulation of the electrical part was also implemented, related to the transformation of the voltage generated by piezoelectric elements into a constant voltage signal with a connected receiver with power consumption similar to the Atmega microcontroller with battery charging.

Investigation of a Newly Developed Slotted Bladed Darrieus Vertical Axis Wind Turbine: A Numerical and Response Surface Methodology Analysis

Abstract In the past few years, wind energy became the most reliable and clean energy source throughout the world. This research broadly has focused on the 2D design of the conventional (without slot) wind turbine blades as well as slotted airfoil blades for places having a low power density of wind. For vertical axis wind turbines, optimum airfoil design plays a vital role in the aerodynamic efficiency of the wind turbine. To get better aerodynamic efficiency, a feasible airfoil criterion of selection, played an important role in the chosen blade design. In this paper, the conventional NACA0018 profile without slots and slotted airfoil profile is selected for measuring the turbine blade performance. The geometry of the computational domain has been created using the solid works software and the computational investigation has been performed using the computational fluid dynamics (CFD) solver ansys fluent 2020 R2 with the help of the shear stress transport (SST k–ω) turbulence model. The simulations are conducted initially with base airfoil and then varying the different structures of slots. After introducing slots in the base airfoil, efficiency was increased in terms of lift coefficient (Cl) and power coefficient (Cp) by 2.32% and 17.94%, respectively at the angle of attack of 15 deg. The results indicate that slotted airfoils have a better lift coefficient and power coefficient compared to an airfoil without a slot. The best turbine operating parameters were found to be 14.82 deg of angle of attack, 1.73 coefficient of lift, and 2.99 tip speed ratio (TSR) by using the response surface methodology (RSM). At these optimal settings, the best Cp response was 0.406. A field experiment was carried out to verify the modeling-optimization outcomes, and the results were within 7% of the model projected results. Thus, this type of slotted airfoil designed for a vertical axis wind turbine (VAWT) can be used to harness wind energy potential more efficiently.

Effect of turbulence intensity on aerodynamic characteristics of extended trailing edge airfoil

PurposeThis paper aims to study the extended trailing edge airfoil for a range of angle of attack at different intensities of turbulence.Design/methodology/approachIn this paper, an experimental study on NACA 0020 airfoil with thin extended trailing edge modification of amplitude of h = 0.1c, 0.2c and 0.3c at the Reynolds number of 2.14 × 105 are tested. The research was carried out for an angle of attack ranging from 0° = α = 35° for the turbulence intensity of 0.3%, 3%, 5%, 7% and 12%. From the experimental readings, the surface pressures are scanned using a Scanivalve (MPS2464) pressure scanner for a sampling frequency of 700 Hz. The scanned pressures are converted to aerodynamic force coefficient and the results are combined and discussed.FindingsThe airfoil with the extended trailing edge will convert the adverse pressure gradient to a plateau pressure zone, indicating the delayed flow separation. The CL value at higher turbulence intensity (TI = 12%) for the extended trailing edge over perform the base airfoil at the post-stall region. The maintenance of flow stability is observed from the spectral graph.Practical implicationsA thin elongated trailing edge attached to the conventional airfoil serves as a flow control device by delaying the stall and improving the lift characteristics. Additionally, extending the airfoil's trailing edge helps to manage the performance of the airfoil even at a high level of turbulence.Originality/valueDistinct from existing studies, the presented results reveals how the extended trailing edge attached to the airfoil performs in the turbulence zone ranging from 0.3% to 12% of TI. The displayed pressure distribution explains the need for increasing trailing edge amplitude (h) and its impact on flow behaviour. The observation is that extended trailing edge airfoil bears to maintain the performance even at higher turbulence region.

Experimental study of the effect of a slat on the aerodynamic performance of a thick base airfoil

Abstract. There is continuous effort to try and improve the aerodynamic performance of wind turbine blades. This experimental study focusses on the addition of a passive slat on a thick airfoil typically used in the inboard part of commercial wind turbine blades. Nine different slat configurations are considered, with both a clean and tripped main airfoil. The results are compared with the performance of the airfoil without slat, as well as the airfoil equipped with vortex generators. It is found that, when the airfoil is clean, the increase in lift-to-drag ratio due to the presence of a slat is larger than when vortex generators are used. This is also true for the tripped airfoil but only at small angles of attack. As expected, in all configurations, the presence of the slat delays flow separation and stall. Finally, for a clean airfoil and small angles of attack, the slat decreases the lift-to-drag ratio of the main airfoil only. By contrast, as the angle of attack increases, it seems that the slat changes the flow field around the main airfoil in such a way that its lift-to-drag ratio becomes larger than for the airfoil without slat. These effects are less pronounced when the airfoil is tripped. This work helps to better understand the role of a slat in improving the aerodynamics of blade sections. It can also be used to validate simulation tools in the field.

Modeling and implementation of a novel amphibious robot with multimode motion

PurposeThe purpose of this paper is to introduce the modeling and implementation of a novel multimode amphibious robot, which is used for patrol and beach garbage cleaning in the land–water transition zone.Design/methodology/approachStarting from the design idea of multimode motion, the robot innovatively integrates the guiding fin and wheel together, is driven by the same motor and can achieve multimodal motion such as land, water surface and underwater with only six actuated degrees of freedom. The robot dispenses with the transmission mechanism by directly connecting the servo motor with a reducer to the actuator, so it has the characteristics of simplifying the structure and reducing the quality. And to the best of the authors' knowledge, the design of the robot can be considered the minimal configuration of amphibious robots with the same locomotion capabilities.FindingsBased on the classical assumptions of underwater dynamics analysis, this paper uses basic airfoil theory to analyze the dynamics of the robot’s horizontal and vertical motions and establishes its simplified dynamics model. Also, the underwater motion of the robot is simulated, and the results are in good agreement with the existing research results. Finally, to verify the feasibility of the robot, a prototype is implemented and fully evaluated by experiments. Experimental results show that the robot can reach the maximum speed of 2.5 m/s and 0.3 m/s on land and underwater, respectively, proving the effectiveness of the robot.Originality/valueThe robot has higher work efficiency with the powerful multimode motion, and its simplified structure makes it more stable while costing less.

Effects of leading edge slat on the aerodynamic performance of low Reynolds number horizontal axis wind turbine

The present study considers the use of a slat near the leading edge of an airfoil to delay or completely cancel separation and thus improves the performance of small wind turbines, in addition to lowering the cost of the blade by reducing the used material. Flow around the S809 airfoil with a slat is numerically simulated using ANSYS 2019 R1 (CFD) program. The present work concentrates on two geometrical parameters namely the location of the slat relative to the base airfoil and the chord size of the slat. Relative to the total chord length of the main airfoil, a slat with a chord length 10% is located at range of distances +3.6% to +10.8% in y direction, slat located at 9% shows the best lift coefficient. To study the effect of slat size, slat sizes range from 5% to 12.5% are numerically investigated, slat size 7.5% shows the best lift coefficient and attached flow over the airfoil for a wide range of angles of attack. The improvement is achieved with the same total chord length with 12% saving of material which corresponds to 6% of the total cost of the turbine.

Improving the power coefficient of the Darrieus vertical axis wind turbine with the aid of morphing airfoils

With the advent of smart materials in recent years, the aviation industry and airfoils have undergone many changes. Research into the use of smart materials in aircraft wings to increase their performance and then the use of smart materials in wind turbine airfoils has begun. In this study, computational fluid dynamics and URANS equations for a three-bladed Darrieus wind turbine equipped with a morphing airfoil was used to determine the optimum blade cross-section. 250 airfoils were generated by random control points, in Gambit software, they were unstructured and generated as a sliding mesh then they were simulated in 2D Ansys using the k-ω SST turbulence model and PISO algorithm. Control points and power coefficient were used for Artificial Neural Network (ANN)training and the Genetic Algorithm(GA) was used to optimize the power coefficient. In this study, the base airfoil is NACA0015. The results of that have been very effective. For the first case (Determine the optimal cross-section of the turbine at a full round) the power coefficient of Darrieus wind turbine with the optimal cross-section increased by 42%, and the blade section(airfoil) was also drawn. For the second case(Determine the optimal cross-section in each of the four zones of the rotor), the most efficient sections(airfoils) in four-zone were obtained, increasing the turbine power coefficient by 60% was the result of this optimization.

Experimental study on the effect of bionic flap parameters on airfoil aerodynamic performance

The effects of bionic flap on airfoil performance were experimentally studied to provide theoretical support for the application of the bionic flap in aeronautical engineering. Seven kinds of bionic flaps were used to study the effects of the key flap parameters, including the flap angle, length, shape, and position, at a Reynolds number of Re = 0.8 × 106. At small angle of attacks (AoAs), the drag and pitching moment increased and the lift reduced when using the bionic flap. While at high AoAs, the lift increased and the drag reduced, which improved the airfoil stall characteristics. The configuration of deflection bionic flap had the smallest initial AoA for improving the airfoil stall characteristics in the seven kinds of bionic flaps. More than eight degrees of the effective AoA range for improving lift characteristics could be achieved. The maximum lift coefficient could be increased by 3.9%. Additionally, the control mechanisms of the flap under different flow conditions (attached flow and separated flow) were deeply studied. In the attached flow, the effective camber and thickness of the basic airfoil could be changed by the flap, resulting that the flow around the airfoil was affected, which in turn affected the Cl and the slope of the lift line. In the separated flow, the flap affected the flow around the airfoil by controlling the development of the trailing edge separation vortex. These research results confirmed the aerodynamic mechanisms for the formation of double layered feathers when birds land, and provided insight into application of bionic flaps in aeronautical engineering.

Flow separation control using the cetacean species nose design

Most of the flow separation control devices used in the aircraft wing are effective at high angles of attack, and adversely affect the performance of the wing at low angles of attack. In flight mission, the cruise phase takes major portion than the take-off and landing. Therefore, the flow separation control devices installed on wing may reduce the performance of the aircraft in total flight mission. A bio-inspired passive flow control method is used by introducing leading edge modification. The leading edge modification inspired by the cetacean species (Porpoise) has been analyzed on NACA2412 and NACA66215 airfoils at different subsonic speed using 2D analysis. The effect of the spanwise location and extent of these leading edge modifications is analyzed using a three-dimensional numerical investigation. The porpoise nose design (shorter length and medium depth i.e. depth — 2.25 % of chord, nose length — 0.75 % chord, and nose diameter — 2 % chord) delay the flow separation and improves the aerodynamic efficiency up to the critical Mach number. After critical Mach number, the shock wave formation affects the porpoise nose performance and shows similar flow behavior as base airfoil. A finite wing with a porpoise nose design of full spanwise length showed the better aerodynamic efficiency than base wing model. This rigid design improves aerodynamic performance of a wing without major structural modification.

Highly Flexible Wind Turbine Blades Utilizing Corrugated Surface Hinges

An anthropomorphic wind turbine blade was the suggested design that had a flexure hinge at root, middle, and tip regions. The inter-distances of the flexure hinges follow the Fibonacci sequence and resembled the natural finger through binding. Therefore, the present study designs various corrugated flexure hinges. NACA0012 is chosen as the basic airfoil for designing the corrugated flexure hinges with different geometrical profiles and leading edges. The designs are based on morphing technology and the main geometrical parameters of the corrugation, the pitch distance along the span and the height, are inspired by tubercles of the whale flippers. The study uses the finite element method to define the significant strength characteristics of each design flap-wise, edge-wise, torsional stiffness, and buckling resistance in order to assign the best fit corrugation profile for each region of the blade.

Influence of Basic Airfoil Layout on Aerodynamic Characteristics of Forward-swept Wing

When the swept angle of the wing varies, the parameters such as the aspect ratio of the forward-swept wing aircraft and the relative speed of the cross-section airfoil relative to the incoming flow will change, which will play a great influence on the aerodynamic characteristics of the wing. Based on this purpose, this paper explores the impact of the oblique angle of the basic airfoil on the aerodynamic performances of the forward-swept wing. Firstly, the wing models of the upright and oblique basic airfoil were established, meanwhile the one-equation Spalart-Allmaras turbulence model and CFD technique were used for numerical simulation calculation. The change law of the aerodynamic characteristics of the wing with the fundamental airfoil upright and tilted are compared and analyzed when the swept angle varies.

Numerical Investigation of The Effect of Airfoil Trailing Edge Inflation at low Reynolds Number

To investigate the effect of airfoil shape design on aerodynamics of the airfoil, a new modified airfoil shape design is introduced in this paper. Thick symmetrical NACA 0021 airfoil is used as base model in this study that the trailing edge end curvature was altered in design shape to be inflated to have 25%, 50% and 100% scaled of the leading-edge curvature at the same cord length and same maximum thickness data. Numerical investigation, using shear-stress transport kω-SST turbulence model, is performed to study the effect of airfoil trailing edge inflation on the aerodynamic characteristics at low Reynolds Number. The base airfoil model, NACA0021, is validated numerically and shows a good agreement with previous experimental results. The results show that the new modified airfoil with 100% inflation delays the flow separation to higher angle of attack and increases the maximum lift coefficient about 40% compared with the base NACA0021 airfoil.

Design Optimization and Investigation of Aerodynamic Characteristics of Low Reynolds Number Airfoils

This study aims to develop a simple and efficient design optimization methodology for the low Reynolds number airfoils. XFOIL is used as an aerodynamic solver while modeFRONTIER workflow is employed for the design optimization purpose. The airfoil SG6043 is used as the reference airfoil for optimization due to its common applications when long-endurance characteristics are desired. A simple design optimization methodology with the integration of XFOIL in the modeFRONTIER workflow environment is proposed in this study. The proposed “software integration methodology” demonstrated up to 10% improvement in the optimization parameter which makes it more efficient by reducing the optimization time and steps without unnecessary user intervention which are the limitations conventionally associated with the optimization process. The optimization results are further compared with the results of the numerical simulations. The use of the transition-sensitive turbulence model allowed the evaluation of the behavior of the laminar separation bubble for different angles of attack, observing that it shifts towards the leading edge and has its length reduced as the angle of attack increases. The newly generated airfoil exhibits improved aerodynamic characteristics as compared to the base airfoil. The optimized airfoil can be used in the applications of UAVs as well as in general aviation. Further validation of the airfoil using wind tunnel testing is recommended and planned.

Multidisciplinary research method for designing and selection of bio-inspired profiles in the conceptual designing stage

A multidisciplinary research method was employed with the intention to create a series of bio-inspired flattened airfoils, observe their aerodynamic characteristics, and analyse their applicability to small devices or to designs of high-speed trains, within the shortest period in the conceptual stage. A research specimen of a kingfisher, selected for biomimicry, was examined with the following methods: visual inspection, analysis of photographs, manufacturing quality control measurement with a 3D laser scanner, and microscopy. A basic multi-arc-line profile, re-engineered from the overlapped specimen shape data and based on the observations, was used for designing a series of seven derived airfoils. The aerodynamic characteristics of the bio-inspired airfoils were obtained with the panel methods at low and moderate subsonic speeds, while the small transonic difference method was used in the high-subsonic speed range. Basic and ellipse-like airfoils produce higher total drag at low and moderate velocities and higher forebody drag in the high-subsonic range when compared to derived and parabola-like airfoils. The obtained critical Mach numbers are in the range from 0.76 to 0.78, where three bionic airfoils show values equal to or smaller than the values of ellipse- and parabola-like airfoils. The profile with the shortest bio-inspired relative chord has a higher critical Mach number value than the parabola-like profile. The sonic lines above these profiles appear at close positions. The applied set of examination methods of the bio-inspired design is not time consuming and produces sufficiently good results in the conceptual stage. Therefore, a further development of unique and adjusted numerical methods and codes at pre-computational fluid dynamics run is encouraged, together with shape parameterization.

Fluid Force and Wake-Flow Characteristics of Basic Airfoils at Very-Low Reynolds Numbers

Fluid Force and Wake-Flow Characteristics of Basic Airfoils at Very-Low Reynolds Numbers

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

Aerodynamic Analysis of Active Trailing-Edge Flaps and Passive Surface Roughness on NACA 4412 Airfoil

The focus of this study is to understand the effect of the flow control mechanism on NACA 4412 airfoil. Two configuration of flow control method is used in this investigation. The first configuration is, airfoil with only the trailing-edge flap. This is the active flow control method. The trailing-edge flap can be deflected to various angle accordingly. The second configuration is a combination of, active trailing-edge flap with a passive surface roughness at the leading-edge of the airfoil. The surface roughness is expected to reduce the flow separation at the leading-edge of the airfoil. This is expected to enhance the aerodynamic performance of the airfoil. Both configuration 1 and configuration 2 was simulated and the results compared with the base airfoil without any flow control mechanism. Based on the results, airfoil with configuration 1 performed better compared to the base airfoil. Airfoil with configuration 2, performed well but not better than the airfoil with configuration 1. Upon further analysis, key patterns emphasise airfoil with configuration 2 could perform better if the roughness element parameters further optimised. This airfoil to be used for wind turbine applications.