Symmetrical Aerofoil Research Articles

Aerofoil optimization using SLSQP and validation using numerical and analytical methods

Aircraft design optimization is one among the research enriched topic in the aerospace industry, with enhancing aircraft performance, safety, and efficiency numerous being the prime focus areas. The work done demonstrates the application of the Sequential Least Squares Programming (SLSQP) technique over a symmetrical aerofoil “NACA 0012” to improve its aerodynamic performance. The optimized aerofoil is validated using Design and Analysis Tools for Composite Aircraft (DATCOM) and Computational Fluid Dynamics (CFD) methods. The study focuses on optimizing the performance of a symmetric aerofoil, where drag minimization is crucial, subject to list constraints, such as in the design of fuel-efficient aircraft. The results reveal, the optimized aerofoil has a significant reduction in drag coefficient of closer to 11 % between 8° and 10° compared to the initial design. The validation using DATCOM and CFD methods confirms the accuracy and usefulness of the optimization results. Validation error values are found to be negligible when compared to the optimization data, coming in at 5.7% and 6.5% for DATCOM and CFD, respectively. The paper highlights that the SLSQP technique is efficient and reliable optimization method for designing high-performance aerofoils.

Computational study of a conceptual re-entry vehicle's aerodynamic characterization at Mach number-2

Re-entry vehicles are becoming an important topic of study in recent times due to the interest of many countries in space endeavor. They are incorporated with double-delta wings having many profiles, different strake and wing swept angles. A conceptual re-entry vehicle having a double delta wing with NACA0020 symmetrical aerofoil at the top surface and the reflex aerofoil at the bottom is studied. Here, the main objective is to examine the effect of viscosity on the aerodynamic characteristics of the vehicle by varying the angle of attack from 10°to 50°at a free stream Mach number of 2. The steady-state Reynolds Averaged Navier-Stokes equations with Spalart-Allmaras turbulence model and Euler equations are solved using ANSYS Fluent for examining the contribution of the viscous term on flow past the re-entry vehicle. The non-dimensional coefficients of lift, drag, pressure, Mach number, and density gradients obtained from both the models are compared. It is observed that the coefficients of lift and drag obtained from Euler simulations differed significantly from the Spalart-Allmaras turbulence model at all angle of attacks. The maximum value of lift coefficient is seen at 40°in Euler simulation and it appeared at 35°in Spalart-Allmaras model. Both the models have predicted the zones of attached flow, separated flow, leading-edge vortices and the shock pattern over the vehicle. But the flow transition and vortex breakdown are observed earlier in Spalart-Allmaras model compared to inviscid simulations. It suggested that the viscosity and fluctuation in the upstream flow has a significant role in the aerodynamic characteristics of re-entry vehicles.

Investigation of Airfoil Design and Analysis

Abstract: In this project “Aerofoil Design and Analysis” an attempt has made to make a complete study on lift and drag coefficient of various aerofoil sections using CFD. The primary goal of this project is to learn and analyse the aerodynamic performance of wings. The objective of this study is to improve aerofoil design using the software CATIA, And Fluent Analysis using the software ANSYS. Aerofoil is a principal part of any airplane construction. How much lift force and drag force is sufficient to balance the weight of the plane is decided by the aerofoil. Aerofoils are basically divided into two categories - they are Asymmetrical and Symmetrical aerofoils. Based on their drag and lift coefficient’s variation with angle of attack, stall angle of attack and magnitude of the coefficients they are divided. Here the NACA aerofoil is modified by adding dimples on the upper half of the wing and compared with the simple one. The comparison is made on different speed and pressure on the wing and the coefficient of lift and drag.

Near-Stall Modelling of a Pitching Airfoil at High Incidence, Mach Number and Reduced Frequency

The prediction accuracy of aeroelastic stability in fans and compressors depends crucially on the accuracy of the underlying aerodynamic predictions. The prevalent approach in the field solves the unsteady Reynolds-averaged Navier—Stokes equations in the presence of blade vibration. Given the unsteady, three-dimensional and often separated nature of the flow in the regimes of aeroelastic interest, the confidence in URANS methods is questionable. This paper uses the simple test case of a pitching symmetric aerofoil with a sharp leading edge to illustrate the challenges of aeroelastic modelling. It compares coupled numerical simulations against time-resolved experimental measurements. The unsteady aerodynamic response of the pitching blade and its dependency on tip-clearance flow and time-averaged incidence angle are analyzed. The results indicate that differences in the unsteady aerodynamics between different numerical approaches close to stall can have a significant impact on local aerodynamic damping. Furthermore, for the chosen test case there is a strong correspondence between the local quasi-steady and unsteady behaviour which weakens, but is still present, towards stall.

On the Incipient Indicial Lift of Thin Wings in Subsonic Flow: Acoustic Wave Theory with Unsteady Three-Dimensional Effects

Enhanced approximate expressions for the incipient indicial lift of thin wings in subsonic potential flow are presented in this study, featuring explicit analytical corrections for the unsteady downwash. Lifting-line and acoustic-wave theories form the basis of the method, within an effective synthesis of the governing physics, which grants a consistent generalised framework and unifies previous works. The unsteady flow perturbation consists of a step-change in angle of attack or a vertical sharp-edged gust. The proposed model is successfully evaluated against numerical results in the literature for the initial airload development of elliptical and rectangular wings with a symmetric aerofoil, considering several aspect ratios and Mach numbers. While nonlinear downwash and compressibility terms demonstrate marginal (especially for the case of a travelling gust), both linear and nonlinear geometrical effects from a significant taper ratio, sweep angle or curved leading-edge are found to be more important than linear downwash corrections (which are crucial for the circulation growth at later times instead, along with linear compressibility corrections). The present formulae may then be used as a rigorous reduced-order model for validating higher-fidelity tools and complex simulations in industrial practice, as well as for estimating parametric sensitivities of unsteady aerodynamic loads within the preliminary design of aircraft wings in the subsonic regime.

Performance Improvement of Subsonic aircraft wing by Dimple Effect

Improving lift and drag ratio is the most important parameter that helps to improving the aerodynamic efficiency of the wing Vortex generators are used to delay flow separators for higher angle of attacks. Simple on surface of body tend provide vortex to delay flow separators and make boundary layer attached with the surface. NACA 0018 symmetrical aerofoil is considered for analysis of dimple in various position on the wing like leading edge, middle of the wing and end of the wing to predict optimum position. In that dimple in middle of the wing shows good improvement in delaying the flow separation this improves the lift to drag ratio compared to other position of the wing.

Numerical and structural investigation of flow past a helical axis wind turbine

The present work is about designing a helical axis wind Turbine and testing its performance of both numerical and static structural analysis. NACA 0018 symmetric aerofoil is used as a turbine blade to modelling the vertical 3 bladed axis wind turbine rotor is tilted to an angle of 60 degrees, so as to get better performance of turbine. This paper deals, Numerical investigation of Helical Axis Wind Turbine (HAWT) with three blades has been carried out by means of both the numerical simulation and static structural analysis. The turbine performance can be observed by the span wise pressure distribution and velocity distribution, stress distribution and also observed that HAWT generated a power, which is an average power output incremental of 6.75 percent than precedes.

Effect of ground on the shape optimisation of a symmetric aerofoil at low angles of attack

Numerical investigation on the aerodynamic characteristics of an optimised NACA0012 aerofoil in-ground effect (IGE) has been performed. Gradient-based shape optimisation was carried out using the ANSYS® 19.0 Adjoint Solver to augment lift over drag ratio (L/D) by at least 10%, at various heights and angles of attack. SST k-ω turbulence model was chosen for the simulations, after its validation for out-of-ground effect (OGE) and performing wind tunnel tests for IGE. While the desired target of 10% increase in the performance parameter was easily achieved through optimisation at low angles of attack (α < 6°), the frozen turbulence assumption in Adjoint Solver limited large shape alterations at higher angles of attack. Upper surface of the aerofoil had larger changes from original camber when compared to the lower surface. Also, the optimised profiles had significant modifications towards x/c ≥ 0.8. This signifies the suitability of trailing edge morphing for such applications.

Effect of ground on the shape optimisation of a symmetric aerofoil at low angles of attack

Numerical investigation on the aerodynamic characteristics of an optimised NACA0012 aerofoil in-ground effect (IGE) has been performed. Gradient-based shape optimisation was carried out using the ANSYS® 19.0 Adjoint Solver to augment lift over drag ratio (L/D) by at least 10%, at various heights and angles of attack. SST k-ω turbulence model was chosen for the simulations, after its validation for out-of-ground effect (OGE) and performing wind tunnel tests for IGE. While the desired target of 10% increase in the performance parameter was easily achieved through optimisation at low angles of attack (α < 6°), the frozen turbulence assumption in Adjoint Solver limited large shape alterations at higher angles of attack. Upper surface of the aerofoil had larger changes from original camber when compared to the lower surface. Also, the optimised profiles had significant modifications towards x/c ≥ 0.8. This signifies the suitability of trailing edge morphing for such applications.

CFD Simulation for Turbulent Flow Past NACA4412 Aerofoil

The complex fluid dynamics of different flow situations at low Reynolds number for natural flying objects like birds and insects, needs to be clearly understood for arriving at an optimum design for sizes ranging from the small man-made ones to very large size high speed commercial aircrafts or the fighter aircrafts. Airfoil performance at low Reynolds numbers impacts the performance of a wide range of systems. Computational Fluid Dynamics (CFD) tools have been around for a couple of decades now. With the superfast growth of computing power, speed and accuracy of these mathematical tools have improved to a considerable extent. However, any CFD simulation employing turbulence models needs to be validated against reliable and accurate measurement data obtained from wind tunnels. The present work focuses on 2D numerical simulation of turbulent flow past a symmetric NACA4412 aerofoil, using C- grid topology, for a Reynolds number of 1 million and 3 million. The computation uses the CFD code RANS3D, an implicit, pressure-based finite volume type Reynolds averaged Navier-stokes solver in generalized non-orthogonal curvilinear coordinates.

A numerical study on choosing the best configuration of the blade for vertical axis wind turbines

Detailed studies on wind turbines have been attracting increasing attention in recent years in order to save fossil resources and protect the environment. Vertical axis wind turbines (VAWTs) are not as popular as horizontal axis wind turbines (HAWTs) because of their relatively low efficiency. Based on CFD approaches, this paper studies the influence of the aerofoil’s maximum camber as well as its position along the chord on the performance of the VAWT. During this process, a Kriging model is established to reflect the functional relationship between the design variables and the power coefficient of the VAWT and the numerical samples of the blade configuration for this model are accessed by the Latin Hypercube Sampling approach. The influence of the aerofoil’s thickness is studied based on the two-dimensional symmetrical NACA 4 digits aerofoils. In addition, based on a three-dimensional numerical model, this paper investigates the influence of the blade’s configuration along the spanwise direction on the blade’s power coefficient and the flow characteristics around it. The current results show that the straight blade with a symmetrical aerofoil has the best power efficiency. Also, the thickness of the NACA0018 aerofoil is the most suitable for the operating conditions investigated.

Recurrence analysis of surface pressure characteristics over symmetrical aerofoil.

We study the surface pressure data exhibiting the underlying dynamical behavior of the flow transition over the upper surface of the aerofoil by using recurrence quantification analysis (RQA). In this study, NACA 2415 aerofoil subjected to a turbulent inflow of TI=8.46% at various angles of attack ranging from α=0° to 20° with an increment of 5° corresponding to Re=2.0×105 is considered. We show that the values of recurrence quantification measures effectively distinguish the underlying dynamics of time series surface pressure data at each port, which proves RQA as an effective tool in accurately predicting the flow transitions.

Experimental study of the effects of turbine solidity, blade profile, pitch angle, surface roughness, and aspect ratio on the H‐Darrieus wind turbine self‐starting and overall performance

AbstractNew and comprehensive time‐accurate, experimental data from an H‐Darrieus wind turbine are presented to further develop our understanding of the performance of these turbines with a particular focus on self‐starting. The impact of turbine solidity, blade profile, surface roughness, pitch angle, and aspect ratio on the turbine's performance is investigated, parameters that are thought to be critical for small‐scale VAWT operation, particularly when operating in the built environment. It is demonstrated clearly that high turbine solidity is beneficial for turbine self‐starting and that the selection of a thick, symmetrical aerofoil set at a low, negative pitch angle () is better than a cambered foil. Increased blade surface roughness is also shown to improve a turbine's self‐starting capability at low tip speed ratios and with high turbine solidity and the associated flow physics are discussed. Finally, it was confirmed that blade span has a significant impact on turbine starting. This paper contributes to the understanding of the turbine characteristics during the starting period and provides clear guidance and validation cases for future design and research in order to promote and justify the wider application of this wind turbine configuration.

Improve Performance of Wing Plan by Gettingnd of the Boundary Layer Control Using Electric System

The amount of drag produced significantly depends on shape of the airfoil. These implementation concerns the lift and drag analysis of three different profiles of airfoils, which are symmetrical aerofoil (NACA 0015, NACA0012) and cambered aerofoil (NACA 4415) have different volume. NACA0015 is provided with perforated tube fixed at 75% from the leading edge for suction. Electrical control system used to control the suction operation the three different types of objected has been tested at a sub-sonic wind tunnel and experimental data has been obtained at different Reynolds’s number and angle of attack. The three airfoils (symmetrical NACA 0015, NACA0012 and cambered with NACA 4415) tested at (00, 50, 100, 150 and 180) angles of attack. All the three objects tested at Re (1.72, 2.9,4, 5.2 and 6.3 x105). The cambered airfoil has been given least drag among than all the airfoils. The drag force of all test model are decreased when the value of Reynolds number are increased and NACA 4415 exhibit less drag and high lift in comparison with other models that used in this study. Suction technique is more active at lower values of Re –number.

Dynamic stall control on a vertical axis wind turbine aerofoil using leading-edge rod

Abstract The installation of a small rod in front of the leading edge of the symmetrical aerofoil as a passive control approach was proposed to control the dynamic stall of the Darrieus vertical-axis wind turbine (DVAWT). The flows around original NACA 0018 aerofoil and that with a rod were extensively simulated by solving the unsteady Reynolds-averaged Navier-Stokes equations with an SST k-ω turbulent model to investigate the effect of the rod on the dynamic stall control of the aerofoils undergoing Darrieus pitching motions. Numerical simulation results reveal that the counter-rotating vortices shedding from the rod continuously transmit kinetic energy into the boundary layer of the aerofoils. This mechanism prevents the formation of dynamic stall vortex and eliminates the flow separation of the aerofoils at large angles of attack. Parameter studies show that the diameter of the rod and the gap between the rod and aerofoil play an important role in stall control and performance improvement of the aerofoil. With the aid of the leading-edge rod, up to 210.9% relative increment of average tangential force coefficient for oscillating aerofoil and 42.1% relative increment of power coefficient for a two-bladed DVAWT were achieved at a tip speed ratio of 2.

Negative lift characteristics of NACA 0012 aerofoil at low Reynolds numbers

Numerical investigations on the flow over NACA 0012 aerofoil are carried out to provide better understanding of the unusual lift characteristics exhibited by this aerofoil at low Reynolds numbers. Computations are carried out at Re = 10,000–100,000, for different values of angles of attack and freestream turbulence intensity. There exists a narrow range of these parameters where the net circulation around this symmetrical aerofoil is negative, leading to the generation of negative lift at positive angles of attack. Different flow regimes are identified and physical explanations are given for this unusual behaviour of negative lift, and the influence of different flow parameters is discussed.

A study of the coarse water droplets formation in the nozzle

The paper introduces the experimental results of the droplets formation for three different aqueous solutions. The new wind tunnel was built to study water droplets atomization from liquid films at high speed flow similar to that found in steam turbines. Liquid atomization is a widely studied problem for sprays and generally in the field of aerosol research. A similar phenomenon occurs in steam turbines but mainly with undesirable effects, the formed droplets from the film (coarse droplets) have a negative effect on the reliability and efficiency of the turbines due to the erosion and corrosion by the droplets impact on the leading edges of the blades. The new wind tunnel is equipped with classical pressure and temperature measurement systems for the determination of the initial condition in the settling chamber and measurement of the static pressure along the nozzle with a known profile. The photogrammetric method and light scattering are used to measure the diameter distribution of the droplets. The liquid film is made with an aqueous solution supplied on the symmetrical aerofoil NACA 0008. Different aqueous solutions were studied for different liquid surface tension effects.

The effect of aerofoil camber on cycloidal propellers

PurposeThis paper aims to investigate the impact of aerofoil camber on the performance of micro-air-vehicle-scale cycloidal propellers.Design/methodology/approachFirst, experiments were conducted to validate the numerical methodology. After that, three turbulent models were compared to select the most accurate one. Then, 2D numerical simulation was carried out on 11 aerofoils with different cambers, including five cambered aerofoils, one symmetrical aerofoil and five inverse cambered aerofoils. The inverse cambered aerofoils are symmetrical about the chord line to the corresponding cambered ones.FindingsThe cycloidal propeller with large cambered aerofoil gives the lowest hovering efficiency, but with symmetrical aerofoil or small inverse cambered aerofoil shows the highest. Also, blades with large cambered aerofoil display high performance at the upper part of its trajectory, while with symmetrical aerofoil or the inverse cambered aerofoil have their best at the lower part. In addition, intensified downwash can be observed in the rotor cage for all cases. When a blade runs through the top-left part of its circle path, all cases display the feature of deep dynamic stall. When the blade travels through the nadir of its path, the actual angle of attack is close to zero due to the strong downwash. Furthermore, there exits intensified blade-vortex interaction induced by the preceding blade for large cambered aerofoils at the lower-right part of its trajectory.Practical implicationsThis paper develops a new cycloidal propeller which is more efficient than the one already present.Originality/valueThis paper discovers that the aerofoil camber is a vital design parameter in the performance of cycloidal propeller, and the authors expect that the rotor with deformable aerofoil on camber would achieve much higher efficiency.

Upstream shear-layer stabilisation via self-oscillating trailing edge flaplets

The flow around a symmetric aerofoil (NACA 0012) with an array of flexible flaplets attached to the trailing edge has been investigated at Reynolds numbers of 100,000–150,000 using high-speed time-resolved particle image velocimetry (HS TR-PIV) and motion tracking of the flaplets’ tips. Particular attention has been made on the upstream effect on the boundary layer evolution along the suction side of the wing, at angles of attack of 0^circ and 10^circ. For the plain aerofoil, without flaplets, the boundary layer on the second half of the aerofoil shows the formation of rollers as the shear-layer rolls-up in the fundamental instability mode (linear state). Proper orthogonal decomposition analysis shows that non-linear modes are also present, the most dominant being the pairing of successive rollers. When the flaplets are attached, it is shown that the flow-induced oscillations of the flaplets are able to create a lock-in effect that stabilises the linear state of the shear layer, whilst delaying or damping the growth of non-linear modes. It is hypothesised that the modified trailing edge is beneficial for reducing drag and can reduce aeroacoustic noise production in the lower frequency band, as indicated by an initial acoustic investigation.

Free Dry Vibration of Low-Aspect-Ratio Cantilever Wing: SemiAnalytical and Numerical Analysis With Experimental Verification

The free vibration of a low-aspect cantilever wing is studied by semianalytical, numerical, and experimental means. The wing is modeled as a two-way tapered, hollow Kirchhoff's plate, with the chord-wise section as symmetrical NACA0018 aerofoil. The chord length and the thickness taper from root to tip, over the span. The semianalytical approach is based on Galerkin's method, which includes the modal superposition of two orthogonal beam modeshapes (free-free beam in chord-wise direction and cantilever beam in span-wise direction). The free vibration is also studied numerically using ANSYS. The results have been compared with an experimental study, performing the dry impact hammer test. A model scale wing has been constructed from a 3-mm-thick metal sheet, with a length-scale ratio of 1:10. Comparative studies have been done among the three methods. The feasibility of modeling a low-aspect-ratio wing as a plate has been investigated. 1. Introduction Lifting surfaces commonly occur in engineering structures: fans, steam and gas turbine blades, impeller blades, wind turbine blades, helicopter fans, airplane wings, marine propeller blades, marine rudders and skegs, and other control surfaces like hydrofoils and wings in high-speed marine crafts. The lifting surface is typically a cantilever, with one edge welded to the main structure (root), and the other end free (tip). The span-wise geometry is tapered, for greater strength at the root and lighter weight at the tip. The chord-wise cross section is an aerofoil, which acts as a lifting surface to the incoming flow at varying angles of attack. The aspect ratio of the lifting surface, i.e., the ratio of the span length to the mean chord length, may vary from 0.4 to 0.6 in a turbine blade to 12 to 15 in an airplane wing/wind turbine. This work focuses on a low-aspect-ratio lifting surface, whose usual span-to-chord ratio is 1.5–2.