Airfoil Camber Research Articles

공력음향학적 특성을 고려한 시로코 팬의 설계 방법

A design method of Sirocco fan is developed for constructing 3-D impeller and scroll geometries, and for predicting both the aerodynamic performance and the noise characteristics of the designed fan. The aerodynamic blading design of fan is conducted by blade angle, camber line determinations and airfoil thickness distribution, and then the scroll geometry of fan is designed by using logarithmic spiral. The aerodynamic performance of designed fan is predicted by the meanline analysis with flow blockage, slip and pressure loss correlations. Based on the predicted performance data, fan noise is predicted by two models for cutoff frequency and broadband noise sources. The present predictions for the performance and the noise level of actual fans are well agreed with measurement results.

Macro-Fiber Composite actuated simply supported thin airfoils

A piezoceramic composite actuator known as Macro-Fiber Composite (MFC) is used foractuation in the design of a variable camber airfoil intended for a ducted fan aircraft. Thestudy focuses on response characterization under aerodynamic loads for circular arc airfoilswith variable pinned boundary conditions. A parametric study of fluid–structureinteraction is employed to find pin locations along the chordwise direction that result inhigh lift generation. Wind tunnel experiments are conducted on a 1.0% thick, 127 mm chordMFC actuated bimorph airfoil that is simply supported at 5% and 50% of the chord.Aerodynamic and structural performance results are presented for a flow rate of15 m s − 1 and a Reynolds number of 127 000. Non-linear effects due to aerodynamicand piezoceramic hysteresis are identified and discussed. A lift coefficientchange of 1.46 is observed, purely due to voltage actuation. A maximum 2DL/D ratio of 17.8 is recorded through voltage excitation.

Aero-elastic behavior of a flexible blade for wind turbine application: A 2D computational study

This paper presents a computational study into the static aeroelastic response of a 2D wind turbine airfoil under varying wind conditions. An efficient and accurate code that couples the X-Foil software for computation of airfoil aerodynamics and the MATLAB PDE toolbox for computation of the airfoil deformation is developed for the aero-elastic computations. The code is validated qualitatively against computational results in literature. The impact of a flexibility of the airfoil is studied for a range of design parameters including the free stream velocity, pitch angle, airfoil thickness, and airfoil camber. Static aero-elastic effects have the potential to improve lift and the lift over drag ratio at off-design wind speed conditions. Flexibility delays stall to a large pitch angle, increasing the operating range of a flexible blade airfoil. With increased thickness the airfoil deformation decrease only linearly.

Heat transfer coefficient measurements on the pressure surface of a transonic airfoil

This paper presents steady-state recovery temperature and heat transfer coefficient measurements on the pressure surface of a modern, highly cambered transonic airfoil. These measurements were collected with a peak Mach number of 1.5 and a maximum turbulence intensity of 30%. We used a single passage model to simulate the idealized two-dimensional flow path between rotor blades in a modern transonic turbine. This set up offered a simpler construction than a linear cascade, yet produced an equivalent flow condition. We performed validated high accuracy (±0.2°C) surface temperature measurements using wide-band thermochromic liquid crystals allowing separate measurements of the previously listed parameters with the same heat transfer surface. We achieved maximum heat transfer coefficient uncertainties that were equivalent to similar investigations (±10%). Two key observations are the heat transfer coefficient along the aft portion of the airfoil is sensitive to the surface heat flux and is highly insensitive to the level of freestream turbulence. Possible explanations for these observations are discussed.

Unsteady Airfoil with Dynamic Leading- and Trailing-Edge Flaps

Unsteady Airfoil with Dynamic Leading- and Trailing-Edge Flaps

Back-scattering correction and further extensions of Amiet's trailing-edge noise model. Part II: Application

The analytical model of the trailing-edge noise of an airfoil derived in the first part of this study is assessed by first comparing the predictions with alternative analytical and numerical computations found in the literature. Comparisons are also made with experimental data. The data are either taken from the literature or collected in a series of new experiments run in open-jet anechoic wind tunnels. Several configurations have been investigated, ranging from a flat plate to symmetric and cambered, thick and thin airfoils, at various angles of attack triggering various flow regimes at different Reynolds numbers. The comparisons address the distribution of the far-field radiated noise both in frequency and radiation angle. The transfer function between the wall-pressure fluctuations in the vicinity of the trailing edge and the noise radiated in the far field is found experimentally to be roughly independent of the flow conditions encountered on the airfoil, as far as the mean flow remains attached. The good agreement of the present predictions with both the measurements and the alternative theories not only emphasises the relevance and accuracy of the model but also stresses the effect of the finite chord length in the noise generation and radiation mechanisms. Moderate airfoil camber and angle of attack are shown to be of secondary importance on the noise radiation, even though they fully determine the sources of the noise through the flow field. All comparisons make the model accurate enough provided precise flow data are available.

Mechanization of a High Aspect Ratio Wing for Aerodynamic Control

Investigations are conducted to mechanize a controlled spanwise-varying airfoil camber change for a high aspect ratio wing, resulting in optimized aerodynamic performance for a aircraft that changes weight by 50% over its mission. Mechanisms to achieve these shape changes are designed based on two separate design methodologies: a rigid body kinematics approach and a compliant mechanism approach. A framework for optimizing mechanisms based on each approach is presented. Differences between the approaches are illustrated through the design of a mechanism for a specific set of airfoil shapes. Mechanisms are evaluated based on the error in the shapes and on the energy efficiency of the systems.

Aerodynamics of a Flapping and Pitching Wing Using Simulations and Experiments

Computational fluid dynamics simulation results for a thin cambered plate airfoil, and flow visualization and force measurements from experiments conducted in water on a flapping-and-pitching thin flat-plate wing of semi-elliptic planform at low Reynolds numbers are reported. Time-varying force data, measured using a force transducer, provide a means to understand the mechanisms that lead to enhanced performance observed in insect flight compared with fixed-wing aerodynamics. Experimental uncertainties associated with low-level (∼1 N) fluid dynamic force measurements on flapping-and-pitching wings, including inertia effects, are addressed. A previously proposed pitching mode in which the leading-edge and trailing-edge switch roles to allow using cambered airfoils is shown to be feasible. A vortex-trapping model is proposed to explain the aerodynamic advantages of switching. The present results also support the authors' proposed idea that an optimum reduced flapping frequency might exist. The study has applications in micro air vehicle development.

Skin design studies for variable camber morphing airfoils

This paper identifies the desirable attributes of a flexible skin of a morphing wing. Thestudy is conducted using airfoil camber morphing as an example. The ideal flex-skin wouldbe highly anisotropic, having a low in-plane axial stiffness but a high out-of-plane flexuralstiffness. Reduced skin axial stiffness allows morphing at low actuation cost. However, forsome substructure and actuation designs, a lower limit on the skin’s in-plane axial stiffnessmay be required to prevent unacceptable global camber deformation under aerodynamicloads. High flexural stiffness prevents local deformation of skin sections betweensupports due to aerodynamic pressure loads, and avoids buckling of skin sectionsunder compression as the airfoil cambers under actuation force. For the cambermorphing application the strain levels in the flex-skin are not expected to exceedaround 2%. If the axial stiffness of the flex-skin is reduced significantly, it may benecessary to consider aerodynamic stiffness (negligible vis-à-vis structural stiffness forclassical airfoils) to accurately calculate deformation under loading. The approachfollowed in the study can be used to identify specifications for the skin and thenreverse engineer and design highly anisotropic composite skins that meet thespecifications.

Design Optimization of a Controllable Camber Rotor Airfoil

A conformable airfoil is proposed as an alternative to trailing-edge flaps used for active helicopter vibration reduction through high-frequency changes in camber. The design consists of several compliant mechanisms of predetermined topology that are placed serially within the airfoil along the chord, aft of the leading-edge spar. A shape optimization approach is used to design the compliant mechanisms, in which the objective is to maximize trailing-edge deflection while minimizing airfoil deflections due to aerodynamic loads. Solutions were obtained using a sequential linear programming method coupled with a finite element analysis. An optimized shape is predicted to achieve a trailing-edge deflection of ±6.0 mm or a ±4.6- deg equivalent flap deflection angle using the tip deflection objective. Results indicate that the deflection is dependent on the amount of passive material allowed and the objective function used. The aerodynamic loads are found to cause only small deformations in comparison with those caused by the actuation. Prototype fabrication and bench-top tests demonstrated that rotor airfoil camber is controllable using the proposed concept.

Design and testing of fixed‐wing MAVs

Design/methodology/approach – The MAV wing planform in this study was designed based on previous results and the need to reduce the weight of the MAV. The MAV had a wing planform with a 6 percent Gottingen‐329 camber airfoil, a 20° swept‐back leading edge and a straight trailing edge. The fuselage was designed to contain a motor, an electronic control system and a video camera with a built‐in transmitter. The battery was located outside the fuselage to trim the center of gravity and enable the battery to be changed easily when it has run out. Two exaggerated vertical stabilizers were installed to prevent the MAV from rolling. The materials, the power plant and the electronics used to fabricate the MAV herein were either the lightest or the smallest from that could be obtained off‐the‐shelf. Since, MAVs should be expendable, the cost was kept under US$250 (including the cost of an onboard video camera system, which costs US$170).

Aerodynamic performance of thin wings at low Reynolds numbers

PurposeThis study seeks to explore the aerodynamic performance of wings with different shapes at low Reynolds numbers.Design/methodology/approachThe airfoils of these wings are made from aluminum plates, and the maximum cord length and wingspan are 15 cm. Wings A to D are plates with 6 percent Gottingen camber but different wing planforms. The forward‐half sections of wings E and F are dragonfly‐like, whereas the rear‐half sections of wings E and F are flat and positively cambered, respectively. The aspect ratios of these wings are close to one, and the ratios of plate thickness to the maximum cord length are 1.3 percent. Experimental results indicate that the wings with Gottingen camber have a superior lift and lift‐to‐drag ratio, whereas the wings with dragonfly‐like airfoils perform well in terms of drag and pitch moment.FindingsThe aerodynamic measurements of the wings demonstrate that the wing with the Gottingen camber airfoil, a swept‐back leading edge and a straight trailing edge is suitable for use in micro aerial vehicle (MAV). An MAV is fabricated with this wing and the aerodynamic performance of the MAV is examined and compared with the bare wing data.Originality/valueThis study develops several criteria to the design of MAV‐sized wings. For example, the thickness ratio of airfoil must be small, usually less than 2 percent. Besides, the airfoil must be cambered adequately. Furthermore, a wing planform with a swept‐back leading edge and a straight trailing edge would be contributive to the successful flights of MAVs.

Design of Postbuckled Spinal Structures for Airfoil Camber and Shape Control

In this paper the use of shape definition schemes to design spinal structures for the control of deformable airfoils is examined. The aim is to find strcutures that, when suitably loaded, can be used to alter the aerodynamic properties of a cladding that forms the airfoil, thus obviating the need for flaps or ailerons. Morphing through different cambered airfoils to achieve aerodynamic performances for different maneurvers is then possible by exploiting a range of incremental nonlinear structural solutions. Further, by using structures that are acting in the postbuckling reginme, it is possible to obtain significant changes in shape with only modest changes in applied load. Results are formulated in terms of the aerodynamic properties of the morphed airfoils using a shape optimized beam as the spinal structure with fixed aerodynamic cladding.

Effect of Airfoil Aerodynamic Loading on Trailing Edge Noise Sources

A previous experimental investigation of the broadband self noise radiated by an industrial cambered controlled-diffusion airfoil embedded in an homogeneous flow at low Mach number has been extended to various aerodynamic loadings. The instrumented airfoil is placed at the exit of an open-jet anechoic wind tunnel, with a jet width of about four chord lengths. Sound is measured in the far field at the same time as the statistical properties of the wall-pressure fluctuations close to the trailing edge. A new set of mean wall-pressure data has been collected on this airfoil at a chord Reynolds number of 2.9 x 105, which provides some insight on the Reynolds-number effect. Two previously investigated flow regimes with different statistical behaviors are investigated by changing the angle of attack from 8 to 15 deg. They respectively correspond to the nearly separated boundary layer with vortex shedding at the trailing edge and to the turbulent boundary layer initiated by a leading-edge separation.

Aerodynamics of a Cambered Airfoil in Ground Effect

The flow characteristics over a NACA 4415 airfoil are studied experimentally at a Reynolds number of 2.4 • 105 by varying the angle of attack from 0 to 10° and ground clearance of the trailing edge from five percent of chord to eighty percent. The pressure distribution on the airfoil surface was obtained, velocity survey over the surface was performed, wake region was explored and lift and drag forces were measured. A strong suction effect was observed on the lower surface for angles of attack of 0 and 2.5° at small ground clearances. For the angle of attack of 0°, a separation bubble formed on the lower surface for the smallest ground clearance while for 2.5°, laminar separation occurred from the lower surface well ahead of the trailing edge. Increased suction was observed on the upper surface for small ground clearances. For the angle of attack of 10°, the flow on the upper surface could not withstand the adverse pressure gradient at small ground clearances and separated from the surface resulting in a loss of lift and an increase in drag.

Structure and Induced Drag of a Tip Vortex

The three-dimensional flow structure of a tip vortex in the near wake of both a rectangular, square-tipped NACA 0015 airfoil and a high-lift cambered airfoil was investigated by using a seven-hole pressure probe at Re = 2.01 x 10 5 . Lift-induced drag was computed based on vorticity and was compared with force-balance data. For both the airfoils tested, the vortex strength reached a maximum immediately behind the trailing edge and remained nearly constant up to two chord lengths downstream. As the airfoil incidence increased, the increase in the lift force resulted in a basically linear increase in the vortex strength and the peak values of the tangential velocity and vorticity, whereas the vortex radius did not appear to have a clear dependence on the vortex strength. Depending on the airfoil incidence, the core axial velocity could be wake-like or jet-like. The normalized circulation within the inner region of the nearly axisymmetric tip vortex exhibited a universal, or self-similar, structure. The NACA 0015 airfoil, however, possessed smaller tangential velocities but similar vortex core diameters compared to those of a cambered airfoil

Broadband Self Noise from Loaded Fan Blades

An experimental investigation and analytical modeling were conducted of the broadband self-noise radiated by an industrial cambered airfoil embedded in an homogeneous flow at low Mach number. The instrumented airfoil is placed at the exit of an open jet anechoic wind tunnel. Sound is measured in the far field at the same time as the statistical properties of the wall pressure fluctuations close to the trailing edge. Three different flows with different statistical behaviors are investigated by changing the angle of attack, namely, the turbulent boundary layer initiated by a leading-edge separation, the nearly separated boundary layer with vortex shedding at the trailing edge, and the laminar boundary layer with Tollmien‐Schlichting waves. The far-field spectrum is related to the spectrum and spanwise correlation length of the wall pressure fluctuations. Simple statistical models based on Howe’s theory and on an extension of the original Amiet’s theory show a good agreement with the experimental results. They provide helpful tools to predict the self-noise from subsonic fans in an industrial context.

Some practical issues in the computational design of airfoils for the helicopter main rotor blades

Very important requirement for the helicopter rotor airfoils is zero, or nearly zero moment coefficient about the aerodynamic center. Unlike the old technologies used for metal blades, modern production involving application of plastic composites has imposed the necessity of adding a flat tab extension to the blade trailing edge, thus changing the original airfoil shape. Using computer program TRANPRO, the author has developed and verified an algorithm for numerical analysis in this design stage, applied it on asymmetrical reflex camber airfoils, determined the influence of angular tab positioning on the moment coefficient value and redesigned some existing airfoils to include properly positioned tabs that satisfy very low moment coefficient requirement. .

Unsteady airload of an airfoil with variable camber

With the application of new materials and actuators an aerodynamic surface with variable geometry can be manufactured that offers the possibility of vibration and flutter suppression. For this purpose, the analytical solution for calculation of the unsteady airload on the airfoil with variable camber was derived for the incompressible potential flow. The calculated results were confirmed with a numerical time stepping method. In addition, the effects of the location of the maximum camber along the chord and the reduced frequency on the airload were analysed. The presented, computationally efficient solution written in frequency and time domain offers a possibility to design an active control of the airfoil camber for the purpose of vibration and flutter suppression.

Active Control of Separation on a Wing with Oscillating Camber

Introduction L OW-REYNOLDS-NUMBER effects are signiŽ cant in the aerodynamics of low-speed airfoils, aircraft intended to operate in low-density environments, and small-scale lifting surfaces such as insect and bird wings. Current aerodynamic applications includemicro-aerialvehicles and unmannedaerial vehicles, as well as aircraft operating at high altitudes or low-density atmospheres other than Earth’s. The primary difŽ culty with the operation of a wing at low Reynolds number is that the  ow over the suction surface encounters an adverse pressure gradient at a point at which the boundary layer is quite likely to still be laminar. Because a laminar boundary layer is incapable of negotiating any but the slightest adverse pressure gradient, the  ow will inevitably separate. The separated  ow then transitions to turbulence, entrains  uid, and reattaches to form a turbulent boundary layer. The resulting structure is the laminar separation bubble, which has been described by Lissaman.1 A number of different  ow-control approaches have been investigated to reduce separationand improve efŽ ciency at lowReynolds numbers. Continuous blowing and sucking have long been shown to havepronouncedeffects.More recently, intermittentblowing and sucking in the form of synthetic jets have shown their effectiveness and suggest the presence of optimum values in the range of frequency inputs, which can translate to other oscillatory inputs.3i5 Mechanical momentum transfer and acoustic excitation have also been explored. The approach presented herein employs an adaptive wing.6 Naturally, all practical wings are adaptive in the sense that they use actuators to alter lift coefŽ cient by changing effectiveproŽ le with a subsequentloss in efŽ ciency.A truly adaptivewing, however, refers to an airfoil, which can change its proŽ le to adapt optimally to  ow conditions. Similar concepts have been explored in the past, such as the snap-through airfoil, which changes local airfoil camber by moving a  exible portion of the pressure surface or the Defense AdvancedResearch Projects Agency “smart wing,” which uses torsional elements to twist the wing. Modern smart materials such as piezoelectricactuators offer great promise in the area of future stall