Characteristics Of Airfoil Research Articles

A fractional derivative aerodynamic model at high angles of attack

A fractional derivative aerodynamic model is put forward based on Grünwald-Letnikov fractional derivative in this paper. In order to express the hysteresis property of aerodynamic coefficients, a fractional derivative state-space equation is developed from Goman’s differential equation. A fast and high-accuracy calculation method of Grünwald-Letnikov fractional derivative is proposed. Then, the model is demonstrated by several experiments data from literatures. The simulation results show that the presented fractional derivative aerodynamic model can preferably express the nonlinear unsteady aerodynamic characteristics of airfoils and aircrafts. The proposed modelling framework is meaningful to the designation of flight and control system.

A Shear-Sliding Rigid-Flexible Coupled Skin Variable-Sweep Wing Design and Heat-Fluid-Structure Multifield Coupling Analysis

The variable-sweep wing is very attractive for cross-speed domain aircraft. The shear-sliding rigid-flexible coupled skin variable-sweep wing and its associated mechanism are designed and optimized. The variable-sweep wing has smooth continuous deformation and rigid-flexible coupling features. The calculation model of the sliding skin patch segmentation strategy is established, and the aerodynamic characteristics of the two-dimensional airfoil before and after the deformation of the wing skin are analyzed. According to the deformation characteristics of sliding skin, the configuration of the associated mechanism is determined, and the kinematic characteristics of the reference points of each skin are calculated. The kinematic simulation verifies the force of the mechanism model at the joint of skin surfaces during the deformation process. Considering the aerodynamic heat at supersonic speed, the heat transfer, heat distribution, and structural thermal modes between the flow field and the skin are calculated based on the finite element method. The dynamic characteristics of the swept wing with different flight speeds and different morphologies are analyzed. The natural frequencies are found to be reduced by about 30% to 50% compared to cold models at supersonic speeds. Based on the results of the thermal fluid-solid coupling calculation, the skeleton structure of the swept wing is optimized, and the skeleton structure with 25% mass reduction and better performance is obtained.

Effect of Adjacent Blade Oscillation on the Forces on A Blade of a Compressor Cascade

The current trend of aircraft engines is one towards attaining high isentropic efficiency while minimizing its weight. This leads to a state where the blades are highly loaded and consequently susceptible to vibrations. High cycle fatigue caused as a result of such self-excited flutter or forced vibration due to defects in the air stream are detrimental to the engine. An understanding of the onset of instabilities is essential to predict their occurrences to avoid a catastrophic failure during operation or costly redesign during the development phase. The critical parameters in turbomachine aeroelasticity are the reduced frequency and the interblade phase angle. The damping of the system is known to be a function of the phase difference between the blade forces and the blade motion. In the present study, a linear cascade of five blades is considered to understand the effect of harmonically varying boundary conditions. The second and fourth blades of the cascade are subjected to torsional oscillation by an external mechanism. The third blade, considered as the reference, is stationary and instrumented. The unsteady pressure along the reference blade surface is measured simultaneously with the loads acting on the blade. The unsteady pressures are measured using a multi-sensor pressure scanner by multiplexing and the loads are measured using a five-channel strain gage balance. The blade displacement is determined from the integrated accelerometer signal mounted on an oscillating blade. The experiments are conducted at a low-subsonic speed and multiple oscillation frequencies. The cascade is set at zero incidence and four stagger angles. The effect of inter-blade phase angle is included as the oscillation of the walls adjacent to the reference blade. The phase difference between the harmonic motion of the neighboring walls and the pressure and load signals on the reference blade is related to the damping characteristics of the reference blade. The variation in damping is studied for the range of blade motion phase difference angles and reduced frequencies. The effect of the phase difference between the oscillating blades is seen to strongly affect the damping characteristics of the reference airfoil.

Numerical Analysis on The Effects of Stagger, Thickness, and Curvature on The Propulsion of Tandem Airfoil

The study of the aerodynamics of flapping airfoils is crucial to understand the flight of natural flyers and its potential applications in developing micro air vehicles and wind/water turbine blades. There has been much research on the aerodynamics of flapping wings recently, but there is only a little research relating to the tandem airfoil. Therefore, this study is conducted to determine the aerodynamic characteristics of the tandem airfoil at Re = 100000, typical of insect flight. The tandem airfoil is plunging and pitching harmonically. This study numerically analyzes the effects of stagger, thickness, and curvature on tandem airfoil propulsion. The effects of stagger are studied using NACA 0012, while the effects of thickness are analyzed on NACA 0012, 0015, 0020 and 0030. The simulations to study the effects of curvature are conducted using NACA 0030. The optimum distance of the stagger is X/c = 2.5, but the propulsive efficiency of tandem NACA 0012 is still smaller than two single NACA 0012 airfoils. For the most optimum thickness at 30% of the chord length, the propulsive efficiency of tandem NACA 0030 is higher than two single NACA 0030 airfoils. Meanwhile, the most optimum curvature is 0% because the increase in curvature of the airfoil reduces propulsive efficiency.

Experimental and Numerical Analysis of Incompressible Flow over an Iced Airfoil

Determining the aerodynamic characteristics of iced airfoil is an important step in aircraft design. The goal of this work is to study experimentally and numerically an iced airfoil to assess the aerodynamic penalties associated with presence of ice on the airfoil surface. Three iced shapes were tested on NACA 0012 straight wing at zero and non-zero angles of attack, at Reynolds No. equal to (3.36*105). The 2-D steady state continuity and momentum equations have been solved utilizing finite volume method to analyze the turbulent flow over a clean and iced airfoil. The results show that the ice shapes affected the aerodynamic characteristics due to the change in airfoil shape. The experimental results show that the horn iced airfoil consumes more power than the other shapes of ice, its value was (44.4W). The horn iced shape has the worst effect on the airfoil than the other shapes. The present results are compared with previously reported results; it is found there is a very good agreement between them. A comparison between the experimental and computational results of the presented work were pursing the same behavior.

Numerical Simulation of the Aerodynamic Characteristics of NACA0012 Airfoil Based on Operational Parameters

This study investigated the performance of symmetric airfoils of type NACA0012 numerically under different operating conditions. It has been assumed that the study involves steady state, non-compressive, and turbulent flows. The operating fluid was air. The effect of Reynolds number and angle of attack on lift and drag coefficients, pressure distribution, and velocity distribution was investigated. ANSYS FLUENT has been used to solve the numerical model by using continuity equations, Navier-Stokes equations, and the appropriate K-ω SST perturbation model. This study shows a clear difference between the pressure coefficient of the lower and upper surfaces of the airfoil at high Reynolds numbers, indicating higher lift at high Reynolds numbers. As the maximum stall angle of the airfoil NACA0012 is 14° after which it decreases significantly, a direct relationship was observed between lift and drag coefficients and angle of attack.

Prediction of Static Characteristics of Hydrodynamic Air Foil Bearing Considering Contact and Friction Between Foils

Abstract The elastohydrodynamic model of hydrodynamic air foil bearing has been built to study the influence of rotor speed, the friction coefficient between bearing components, load and other parameters on the foil displacement of hydrodynamic air bearing under steady-state conditions. The static characteristics of hydrodynamic air foil bearing are predicted by using the numerical simulation method. The results show that the radial displacement of the foil is the smallest at both ends of the bearing and the largest at the middle of the bearing, while the top foil changes gently along the width of the bearing away from the maximum pressure. After increasing the rotating speed, the maximum fluid pressure improves and the action position shifts, and the increase of rotating speed has a significant impact on the maximum pressure. Improving the friction coefficient µ2 between the bump foil and the bearing sleeve has different effects on the displacement of the foil. When µ1 is 0.1, by promoting µ2, the transverse displacement of the top foil at the pressure peak increases by 20.9%, the longitudinal displacement is reduced by 8.9%, and the transverse displacement and the maximum longitudinal negative displacement of the bump foil are decreased by 53.2% and 31.7%, respectively. Furthermore, the longitudinal displacement of bump foil at the fixed end has been reduced by increasing the load, and the relative size of the friction coefficient between the components affects the size and direction of the foil displacement at the same load.

Aeroelastic analysis of membrane airfoils and flexible-chord airfoils with trailing-edge flaps

This paper studies the static and dynamic aeroelastic characteristics of membrane airfoils and flexible-chord airfoils (deformable airfoils) with the emphasis on the effects of a trailing-edge (TE) flap which is a novel topic. Two modeling approaches are presented; the first method is the Rayleigh–Ritz method, and the second method is the finite element method which is an efficient method to study the TE flap effects. The two models are presented in the Laplace domain which enables the transient response analysis. The models adopt the potential flow aerodynamics based on the Prandtl–Glauert thin-airfoil theory and the Theodorsen’s unsteady theory. The airfoils are assumed to have small deformations, so linear structural models are used. The effect of the airfoils’ flexibilities on the static aeroelastic characteristics and the dynamic responses due to step and harmonic TE flap inputs is presented through a parametric study.

Multidisciplinary design of aircraft wing for multiregime purposes

In this paper optimization process of the geometrical design of the wing is described. The goal is to minimize the aerodynamic drag at a requested lift in the cruise regime and thus reduce the fuel consumption. The second goal is to ensure the requested landing regime of the aircraft. Both cases are solved under the wing structural and weight considerations. As a fast design computational tool, a lifting line theory is used. It is moreover supplemented by non-linear aerodynamic airfoil characteristics to provide more accurate results of aerodynamic drag of the wing. These airfoil data were calculated with the CFD and enables to take significant accuracy between low and high-fidelity method which is verified in previous work. The list of requirements is set for aircraft for 40 passengers with a range of 2,500 km at a speed of 438 km/h. As the baseline the L-610 aircraft is selected. Optimized wing geometry in verified in cruise and landing regime/configuration with CFD solver. From the calculation of the weight of the wing and CFD results, the flight performance is calculated for the desired flight mission.

Experimental research on effect of zonal heating airfoil about boundary layer flow and heat transfer

The anti-icing of aircraft and large wind turbines, where the wall temperature is higher than the fluid temperature, can significantly alter the flow evolution characteristics of the boundary layer. Local heating strategies for the manifold state need to be designed based on the changing characteristics of the flow velocity and temperature field in order to precisely control the heat supply and reduce inefficient energy consumption. In order to obtain accurate heat transfer characteristics of the airfoil’s boundary layer flow, it is necessary to refine the measurement of the boundary layer characteristics during flow and heat transfer. In this paper, wind tunnel experiments are carried out on the NACA2412 model with full surface’s zonal electric heating. The wall surface is equipped with a built-in heater and the temperature of the wall surface is obtained through the corresponding temperature sensor. By studying layer characteristics of the four heated regions, namely the laminar flow region near leading edge, the laminar flow destabilisation region, the transition region and the fully turbulent flow region, and comparing them with the boundary layer characteristics of the unheated airfoil, the effects of the presence of heat sources in different regions on the stability of the flow field and the spatial heat transfer pattern are revealed. The results show that heating in the laminar and turbulent zones maintains the stability of the flow field to a greater extent and achieves better heat transfer strength, while heating in the unstable zone brings forward the turbulence and heating in the fully turbulent zone intensifies the flow separation at the trailing edge of the airfoil. This study can be used as a reference for the design of efficient anti-icing systems on full wing surfaces.

Experimental investigation of the interaction between a curved-surface jet and the mainstream on an airfoil at Mach 8

The accumulation of aerodynamic heat at the rudder shaft of a hypersonic vehicle will reduce the vehicle's aerodynamic performance. This paper proposes a trailing-edge curved-surface jet with longitudinal characteristics to solve this problem. We used high-speed photography and force measurement techniques in the experiment. The results show that the interaction between the expansion wave formed by the curved surface jet and the hypersonic flow will generate an oblique shock wave and finally form a unique flow structure. The oblique shock wave in the new flow structure is the key to realizing the rudderless flight, and it can linearly control the pitching characteristics of the hypersonic airfoil. That is, it can linearly control the attitude of the model. The diffusion angle of the jet has a significant influence on this oblique shock wave. Experiments show that the dimensionless parameter pressure ratio PR and the jet diffusion angle roughly present a linear relationship. Therefore, there is approximately a linear relationship between PR and the flow control effect of the curved-surface jet. When the PR is within 90∼250, the curved-surface jet can increase the pitching moment coefficient by 0.033∼0.132. The dynamic mode decomposition results show that expansion wave, jet instability, oblique shock wave, and boundary layer are the dominant factors affecting the new flow structure. This paper proposes a new theoretical model to reveal the flow control effect and the physical mechanism of the curved-surface jet. The results provide an experimental and theoretical basis for realizing rudderless hypersonic vehicles.

Active control of airfoil turbulent boundary layer noise with trailing-edge blowing

Large Eddy Simulation (LES) and Ffowcs Williams-Hawkings acoustic analogy are performed to study the effect of trailing-edge blowing on airfoil self-noise. Simulations were conducted using a National Advisory Committee for Aeronautics 0012 airfoil at zero angle of attack and a chord-based Reynolds number of 4 × 10 5. The aerodynamic and aeroacoustic characteristics of the baseline airfoil were thoroughly verified by comparison with previous numerical and experimental data. The noise reduction effects of continuous and local blowing with different blowing ratios and blowing momentum coefficients were compared. A maximum noise reduction of 20 dB was achieved via trailing-edge blowing and the noise reduction mechanisms of the two blowing methods were discussed. The LES results show a pair of recirculation bubbles in the airfoil wake which are suppressed by trailing-edge blowing. As the blowing vortices convect into the wake, they stretch and stabilize the shear flows from airfoil surfaces. Instantaneous vorticity and root mean square velocity fluctuations are also weakened. There is a decrease in the spanwise coherence and an increase in the phase difference, which contribute to noise reduction. It is concluded that the suppression of turbulence fluctuations in the near wake is the main mechanism of noise reduction for airfoil trailing-edge blowing.

Numerical Simulations of the Adverse Effects of Rain on Airfoil And Rotor Aerodynamic Characteristics

There is a significant interest in improving the performance of rotors under adverse operating conditions. However, there is a very limited understanding of the performance implications on two-dimensional (2D) airfoils and rotor blades under adverse effects of rainfall. Furthermore, the fundamental physical phenomena causing the loss in performance are not clearly understood. In this study, low-fidelity models are first developed to rapidly estimate the water layer formation on 2D airfoils and assess the resulting impact on lift and drag characteristics. The low-fidelity simulations are also useful to obtain quick estimates of water layer thickness as a function of liquid water content and droplet diameter. Subsequently, computational fluid dynamics studies for 2D airfoils and a small-scale rotor in hover are done to obtain more accurate estimates of the effects of rain on airfoil performance and match test data where available. Higher fidelity parametric studies for various airfoils were conducted by varying angles of attack, the liquid water content in the rain droplets, and the droplet diameters to capture trends in performance degradation. The resulting trends match the trends from the test data reasonably well. The higher fidelity airfoil loads are subsequently used within a classical combined blade element-momentum model to assess the loss of performance attributable to rain for a small-scale rotor. The present studies indicate a significant loss in thrust production, a rise in the power requirement, and a reduction in the figure of merit for small-scale rotors caused by rain.

Experimental study on transition of dynamic airfoil in pitching oscillation

The transition characteristics of dynamic airfoil have significant effects on the aerodynamic performance of wind turbines, helicopter rotor blades, jet engine compressor blades, etc. The time domain and time-frequency domain characteristics of transition on a NACA0012 airfoil during its pitching oscillation were experimentally studied using wall pressure measurement technology with high time accuracy in this paper. The variable slip window technology was used to detect the transition position, and the proper orthogonal decomposition (POD) method and wavelet analysis were combined to perform the time-frequency analysis. In the gradual forward movement of the transition, the low-frequency instability is gradually enhanced by the main flow and the inverse pressure gradient, and significantly submerges the high-frequency fluctuated feature. The higher order moments of the wall pressure during dynamic airfoil transition deviate significantly from the Gaussian characteristics, which is caused by the low-frequency instability and high-frequency burst. The POD method is able to distinguish low-frequency instability from the high-frequency feature. The reduced frequency had significant effects on the transition. With the increase of the reduced frequency, the hysteresis effect of the transition became more and more significant, and the frequency component of transition was more concentrated and the energy was stronger.

Numerical study on the water entry of two-dimensional airfoils by BEM

Hydrodynamics of the traditional wedges, cylinders, and cones entering water have been heavily studied. However, the hydrodynamic characteristics of airfoils are practically unknown; the problem is inspired by the recently widely developed fixed-wing unmanned aerial-underwater vehicle, which can fly in the air, cruise in water and frequently enters and exits free water surface. In this study, the hydrodynamic characteristics and fully nonlinear free surface deformation for the water entry of airfoils have been investigated by the time domain boundary element method. First, convergence study based on the NACA0012 airfoil is considered. The time step and element size are adjusted, and the results show that the free surface elevation and pressure distribution agree well with those obtained through Reynolds-averaged Navier–Stokes equations. The results show that the higher the entry velocity, the greater the peak hydrodynamic force. Furthermore, the higher thickness ratio causes greater added mass. Gravity and velocity are found to significantly influence the hydrodynamic behavior, including the time-varying force, while thickness ratio has a great impact on added mass and pressure.

Dynamic stall characteristics of wind turbine airfoil in sand-wind environment

Although the traditional dynamic stall has been well studied, the effect of sand particle on dynamic stall characteristics is seldom considered in the previous studies. Therefore, a research about dynamic stall of the S809 airfoil is accomplished under a sand-wind environment. The unsteady CFD method and the discrete phase model (DPM) are adopted in this research to simulate the dynamic stall characteristic of the S809 airfoil. The influence of different sand particle diameters and different particle concentrations on airfoil dynamic stall characteristics is studied respectively. The simulated results indicate that the maximum lift coefficient and drag coefficient with particle diameter of 10 μm decrease about 2.18% and 2.52% respectively compared with that of the clear air. Meanwhile, the maximum lift coefficient decreases about 6.93% for the case of particle concentration with 62.6 g/m3. The simulated results also indicate that the lift coefficient and drag coefficient decreasing are enlarged with particle concentration increasing. This tendency indicated that the efficiency of a wind turbine would be reduced in sand storm weather.

Numerical investigation of flow control using plasma actuator to improve aerodynamic characteristics of a pitching airfoil

Numerical investigation of flow control using plasma actuator to improve aerodynamic characteristics of a pitching airfoil

The effects of geometry parameters on the aerodynamic performance of CFJ airfoil used by a STOL transport

With the purpose of investigating the effects of geometry parameters of CFJ (Coflow jet) device on the aerodynamic characteristics of the supercritical bacj airfoil used by a STOL transport, we have carried out a computational analysis of CFJ airfoil with different values of injection slot size and location under the low-speed condition. The results show that the lift coefficient decreases gradually with decreasing stall angle, when the injection slot size is increased. When α=8°, with increasing injection slot size, the velocity of blowing jet decreases with decreasing power consumption and increasing aerodynamic effectiveness. Further, with the injection slot shifted towards the downstream direction, the α value corresponding to the maximum effective lift-drag-ratio increases with increasing maximum lift coefficient.

Numerical study of the aerodynamic characteristics of airfoil with high-lift devices

The subject matter of this article is the aerodynamic profile of the wing with high-lift devices in the aircraft transport category. When high-lift devices are released, the aerodynamic flow of the wing changes significantly, this changes the stress-strain state of the wing. This relates not only to an increase in lift force due to a change in the curvature of the wing and an increase of the wing area, but also due to a change of the position of the center of pressure relative to the chord of the wing. The goal is to study the influence of wing high-lift devices on the aerodynamic characteristics of the profile during take-off, cruise, and landing cases using numerical methods. The obtained data will be used to determine the loads on the wing in various flight cases. The task is to determine the aerodynamic coefficients of lift and drag forces, changing the position of the pressure center during flight cases: take-off, cruise, and landing. The aerodynamic profile b737c-il was used in the analysis. The single-slot slat and double-slots flap were used in the analysis model. The numerical methods with the CAE system ANSYS Fluent were used. The solver models k-epsilon and transition SST were used for comparison. The use of numerical methods in the process of designing aircraft structures is widely used to accurately determine the aerodynamic parameters of the wing in various flight cases. The following results were obtained: the dependence of the lift coefficient on the angle of attack, the lift coefficient on the drag coefficient, and the position of the center of pressure along the chord of the profile for cruise, take-off, and landing flight cases. Conclusion. The scientific novelty of the results obtained is as follows: the use of numerical methods for determining the aerodynamic characteristics of a wing with high-lift devices in particular, determining the dependence of the position of the center of pressure relative to the chord and at different angles of attack. The obtained results will be used to determine the load on the wing, in particular the distributed load on the slats and flaps, to clarify the torque moment in the wing section where high-lift devices are used.

An experimental study of icing distribution on a symmetrical airfoil for wind turbine blade in the offshore environmental condition

For offshore installations in high-latitude regions, such as offshore wind turbines, ice accretion sometimes occurs on the blade surface due to cold and humid environments or splashed seawater. Hence, a potential hazard exists for the wind turbine. Icing destroys the aerodynamic characteristics of the blade airfoil and increases operational and maintenance fees. In this paper, icing tests of blade airfoils under offshore icing conditions are carried out. An icing wind tunnel is built by combining a conventional wind tunnel with a naturally low temperature in winter. A blade segment with NACA0018 airfoil is selected, while the effects of salinity, temperature, and wind speed on the icing area, the thickness of ice, and the icing scope on the blade surface are tested and analyzed. Experimental results show that the icing area and the thickness of ice both increase linearly with icing time. Salinity can decrease the icing area, and the thickness of ice compared to non-salinity conditions but has a minor effect on the icing scope. The icing scope is mainly in the range of −20%-20% at the relative position of the blade chord. Research findings lay an experimental foundation for in-depth exploration of the icing characteristics of an offshore wind turbine.