Showing papers on "Airfoil published in 1981"

Aerodynamic characteristics of seven symmetrical airfoil sections through 180-degree angle of attack for use in aerodynamic analysis of vertical axis wind turbines

Abstract: When work began on the Darrieus vertical axis wind turbine (VAWT) program at Sandia National Laboratories, it was recognized that there was a paucity of symmetrical airfoil data needed to describe the aerodynamics of turbine blades. Curved-bladed Darrieus turbines operate at local Reynolds numbers (Re) and angles of attack (..cap alpha..) seldom encountered in aeronautical applications. This report describes (1) a wind tunnel test series conducted at moderate values of Re in which 0 less than or equal to ..cap alpha.. less than or equal to 180/sup 0/ force and moment data were obtained for four symmetrical blade-candidate airfoil sections (NACA-0009, -0012, -0012H, and -0015), and (2) how an airfoil property synthesizer code can be used to extend the measured properties to arbitrary values of Re (10/sup 4/ less than or equal to Re less than or equal to 10/sup 7/) and to certain other section profiles (NACA-0018, -0021, -0025).

Wingmill: An Oscillating-Wing Windmill

Abstract: This article describes an analytical and experimental investigation of a windmill which utilizes a harmonically oscillating wing to extract wind energy. In particular, the wing's span is horizontally aligned and the airfoil is a chordwise-rigid symmetrical section. The whole wing oscillates in vertical translation and angle-of-attack, with prescribed phasing between the two motions. A theoretical analysis was developed utilizing unsteady-wing aerodynamics from aeroelasticity and the results guided the design of a working model for wind-tunnel experiments. For the cases tested, theory and experiment compared favorably, and showed the wingmill to be capable of efficiencies comparable to rotary designs.

Two-dimensional aerodynamic characteristics of the NACA 0012 airfoil in the Langley 8 foot transonic pressure tunnel

Abstract: Data are presented for lift coefficients from near zero through maximum values at Mach numbers from 0.30 to 0.86 and Reynolds numbers of 3.0 x 10 to the sixth power with transition fixed. A limited amount of data is presented near zero and maximum lift for a Reynolds number of 6.0 x 10 to the sixth power with transition fixed. In addition, transition free data is presented through the Mach number range from 0.30 to 0.86 for near zero lift and a Reynolds number of 3.0 x 10 to the sixth power.

Dynamic Stall on Advanced Airfoil Sections

Abstract: : The dynamic stall characteristics of eight airfoils have been investigated in sinusoidal pitch oscillations over a wide range of two-dimensional unsteady flow conditions. The results provide a unique comparison of the effects of section geometry in a simulated rotor environment. Important differences between the various airfoils were observed, particularly when the stall regimes were penetrated only slightly. Under these circumstances, the profiles that stall gradually from the trailing edge appear to offer an advantage. However, all of the airfoils tended increasingly toward leading-edge stall when both the severity of dynamic stall and the free-stream Mach number increased. In all cases, the parameters of the unsteady motion appear to be more important than airfoil geometry for configurations that are appropriate for helicopter rotors. (Author)

A discrete vortex method for the non-steady separated flow over an airfoil

Abstract: A discrete vortex method was used to analyze the separated non-steady flow about a cambered airfoil. The foil flow modelling is based on the thin lifting-surface approach, where the chordwise location of the separation point is assumed to be known from experiments or flow-visualization data. Calculated results provided good agreement when compared with the post-stall aerodynamic data of two airfoils. Those airfoil sections differed in the extent of travel of the separation point with increasing angle of attack. Furthermore, the periodic wake shedding was analyzed and its time-dependent influence on the airfoil was investigated.

Design and experimental results for a flapped natural-laminar-flow airfoil for general aviation applications

Abstract: A natural-laminar-flow airfoil for general aviation applications, the NLF(1)-0416, was designed and analyzed theoretically and verified experimentally in the Langley Low-Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of the NASA low-speed airfoils with the low cruise drag of the NACA 6-series airfoils was achieved. The safety requirement that the maximum lift coefficient not be significantly affected with transition fixed near the leading edge was also met. Comparisons of the theoretical and experimental results show excellent agreement. Comparisons with other airfoils, both laminar flow and turbulent flow, confirm the achievement of the basic objective.

An Aerodynamic Analysis of Bird Wings as Fixed Aerofoils

Abstract: The aerodynamic properties of bird wings were examined at Reynolds numbers of 1-5 × 10 4 and were correlated with morphological parameters such as apsect ratio, camber, nose radius and position of maximum thickness. The many qualitative differences between the aerodynamic properties of bird, insect and aeroplane wings are attributable mainly to their differing Reynolds numbers. Bird wings, which operate at lower Reynolds numbers than aerofoils, have high minimum drag coefficients (0·03-0·13), low maximum lift coefficients (0·8-1·2) and low maximum lift/drag ratios (3–17). Bird and insect wings have low aerofoil efficiency factors (0·2-0·8) compared to conventional aerofoils (0·9-0·95) because of their low Reynolds numbers and high profile drag, rather than because of a reduced mechanical efficiency of animal wings. For bird wings there is clearly a trade-off between lift and drag performance. Bird wings with low drag generally had low maximum lift coefficients whereas wings with high maximum lift coefficients had high drag coefficients. The pattern of air flow over bird wings, as indicated by pressure-distribution data, is consistent with aerodynamic theory for aeroplane wings at low Reynolds numbers, and with the observed lift and drag coefficients.

Visualization of Transition in the Flow over an Airfoil Using the Smoke-Wire Technique

Abstract: The smoke-wire technique was used for visualization of the transition of the free shear layer associated with the laminar separation bubble of a NACA 663-018 airfoil section at low Reynolds number (Rec = 50,000120,000). The smoke-wire technique allows for the introduction of fine smoke streaklines into the flowfield through the electrical resistive heating of a very fine wire which has been coated with oil and which is located upstream from the leading edge of the airfoil section. Streakline data were collected using both high speed still and motion picture photography.

Double-multiple streamtube model for Darrieus in turbines

Abstract: An analytical model is proposed for calculating the rotor performance and aerodynamic blade forces for Darrieus wind turbines with curved blades. The method of analysis uses a multiple-streamtube model, divided into two parts: one modeling the upstream half-cycle of the rotor and the other, the downstream half-cycle. The upwind and downwind components of the induced velocities at each level of the rotor were obtained using the principle of two actuator disks in tandem. Variation of the induced velocities in the two parts of the rotor produces larger forces in the upstream zone and smaller forces in the downstream zone. Comparisons of the overall rotor performance with previous methods and field test data show the important improvement obtained with the present model. The calculations were made using the computer code CARDAA developed at IREQ. The double-multiple streamtube model presented has two major advantages: it requires a much shorter computer time than the three-dimensional vortex model and is more accurate than multiple-streamtube model in predicting the aerodynamic blade loads.

Low Reynolds number airfoil survey, volume 1

Abstract: The differences in flow behavior two dimensional airfoils in the critical chordlength Reynolds number compared with lower and higher Reynolds number are discussed. The large laminar separation bubble is discussed in view of its important influence on critical Reynolds number airfoil behavior. The shortcomings of application of theoretical boundary layer computations which are successful at higher Reynolds numbers to the critical regime are discussed. The large variation in experimental aerodynamic characteristic measurement due to small changes in ambient turbulence, vibration, and sound level is illustrated. The difficulties in obtaining accurate detailed measurements in free flight and dramatic performance improvements at critical Reynolds number, achieved with various types of boundary layer tripping devices are discussed.

Development of a linear unsteady aerodynamic analysis for finite-deflection subsonic cascades

Abstract: An unsteady potential flow analysis, which accounts for the effects of blade geometry and steady turning, was developed to predict aerodynamic forces and moments associated with free vibration or flutter phenomena in the fan, compressor, or turbine stages of modern jet engines Based on the assumption of small amplitude blade motions, the unsteady flow is governed by linear equations with variable coefficients which depend on the underlying steady low These equations were approximated using difference expressions determined from an implicit least squares development and applicable on arbitrary grids The resulting linear system of algebraic equations is block tridiagonal, which permits an efficient, direct (ie, noniterative) solution The solution procedure was extended to treat blades with rounded or blunt edges at incidence relative to the inlet flow

Rime ice accretion and its effect on airfoil performance

Abstract: A methodology was developed to predict the growth of rime ice, and the resulting aerodynamic penalty on unprotected, subcritical, airfoil surfaces. The system of equations governing the trajectory of a water droplet in the airfoil flowfield is developed and a numerical solution is obtained to predict the mass flux of super cooled water droplets freezing on impact. A rime ice shape is predicted. The effect of time on the ice growth is modeled by a time-stepping procedure where the flowfield and droplet mass flux are updated periodically through the ice accretion process. Two similarity parameters, the trajectory similarity parameter and accumulation parameter, are found to govern the accretion of rime ice. In addition, an analytical solution is presented for Langmuir's classical modified inertia parameter. The aerodynamic evaluation of the effect of the ice accretion on airfoil performance is determined using an existing airfoil analysis code with empirical corrections. The change in maximum lift coefficient is found from an analysis of the new iced airfoil shape. The drag correction needed due to the severe surface roughness is formulated from existing iced airfoil and rough airfoil data. A small scale wind tunnel test was conducted to determine the change in airfoil performance due to a simulated rime ice shape.

Mission Adaptive Wing System for Tactical Aircraft

Abstract: The aerodynamic cruise efficiency of the supercritical airfoil in the transonic range is well known. Adaptation of this technology to a multirole tactical aircraft system requiring Mach 2 + maximum speed and 7 + g maneuver capability is enhanced by airfoil modification capabilities. This paper describes the hardware design and development of a mission adaptive wing system utilizing smooth, variable camber leadingand trailing-edge mechanisms to optimize wing airfoil camber for all flight conditions. Development included design and manufacture of a full-scale wing test component to demonstrate system capability and reliability.

Variable camber leading edge mechanism with Krueger flap

Abstract: An actuating mechanism for variable camber leading edges of aerodynamic airfoils characterized by its rigidity and structural stability and which permits varying the camber of a flexible continuous airfoil skin through leading edge deflection angles ranging from on the order of 14° to on the order of 22° with reference to the wing box chord line without deployment of a Krueger flap and up to on the order of 32° with deployment of a Krueger flap; and, which permits varying the camber of a flexible continuous airfoil skin while maintaining a uniform, essentially constant curvature throughout the chordal extend of deflection for any given degree of deflection; yet, wherein: (a) the upper continuous flexible airfoil skin (i) is not required to provide load bearing support, (ii) is not subjected to chord-wise stress from movement of the actuating linkage, and (iii) is not subjected to localized stress resulting from non-uniform deflection; (b) the actuating linkage is contained entirely within the airfoil aerodynamic contour or airfoil envelope at all operating positions; (c) the actuating linkage may be readily employed with a wide range of conventional structural wing box configurations; and (d), which permits of deployment of either " slotted" Krueger flaps to meet operating requirements during take-off and landing operations or to function as an inflight speedbrake under both high speed and low speed flight conditions More specifically, the variable camber leading edge actuating mechanism comprises a simple 4-bar linkage arrangement which readily permits of incorporation of Krueger flaps actuated by a suitable torque tube extending span-wise through the deflectable leading edge of the airfoil

Coolable airfoil for a rotary machine

Abstract: A coolable airfoil 10 for rotary machines is disclosed. The airfoil has a passage 54 extending spanwisely through the leading edge region 26 of the blade. The passage has a plurality of trip strips 68 canted toward the direction flow. Each trip strip includes a vortex generator integrally formed with the trip strip which is spaced from the wall of the airfoil. In one embodiment, a plurality of trip strips each having an integral vortex generator are disposed in the passageway and at least one of the vortex generators is of greater height than the remaining vortex generators.

Moving surface boundary layer control for aircraft operation at high incidence

Abstract: The paper studies effectiveness of the moving-surface boundary-layer control on a NACA 63-218 (modified) two-dimensional wing used in the Canadair CL-84, a twin-propeller V/STOL design. Tests with rotating cylinder(s) at the leading edge of the airfoil and/or of the flap show the former to have a significant effect on the maximum lift, stall characteristics, and lift/drag ratio. On the other hand, the advantage gained by the presence of the rear cylinder is relatively small for the slotted flap configuration. The availability of a high value of lift suggests the approach velocity with this form of boundary-layer control is likely to be limited only by the lateraldirectional stability characteristics. The concept presents several possible applications including a mechanism for delaying the vortex-induced resonance of bluff bodies.

Calculation of Unsteady Transonic Flow over an Airfoil

Abstract: An implicit finite-difference solver for either the Euler equations or the "thin-layer" Navier-Stokes equations was used to calculate a transonic flow over the NACA 64A010 airfoil pitching about its one-quarter chord. An unsteady automatic grid-generation procedure that will improve significantly the computational efficiency of various unsteady flow problems is described. The calculated results for both inviscid and viscous flows at Mach number 0.8 over the airfoil oscillating with reduced frequency referenced to one-half chord, 0.2, are compared with experimental data measured in the Ames 11 x 11 ft Transonic Wind Tunnel. Nonlinear, unsteady effects of the flow on the surface pressure variations, shock-wave excursions, and overall airloads are examined. Good agreements between the results of computations and experiments were obtained. In the shock-wave region, however, the results of the viscous-flow computations showed closer agreement with the experimental data.

Utilization of wind energy

Abstract: A wind energy device comprising a first airfoil having a leading edge, a trailing edge and a tip, means supporting the airfoil above a surface, the airfoil being adapted, when traversed by a prevailing wind, to generate a vortex at its tip, an air deflector associated with the airfoil and arranged so as to deflect prevailing wind traversing the deflector into the vortex to augment the energy of the vortex, means to vary the orientation of the airfoil relative to the prevailing wind, and a rotary device located in the path of the vortex and adapted to be driven by the wind in the vortex.

An analytical approach to airfoil icing

Abstract: An analytical procedure has been developed to predict rime ice growth on unprotected airfoil sections and to evaluate the aerodynamic performance. A time stepping method is used in which: (1) water droplet trajectories are calculated, (2) a rime ice shape determined, (3) the flowfield around the iced airfoil is recalculated, and (4) the build-up process iterated upon until the desired icing time is reached. The performance of the iced airfoil shapes are then determined from existing analytic methods. Rime ice shapes determined in the NASA Lewis Icing Research Tunnel on a modified NACA 64 series airfoil agree well with the shapes predicted by the analytical method. Measured and predicted increases in drag due to the rime ice also agree favorably. A simplified scaling analysis is also presented and verified which provides the duplication of full scale results of rime ice accretions in small scale model tests.

Sound generated in a cascade by three-dimensional disturbances convected in a subsonic flow

Abstract: Discrete tone sound generation in a subsonic fan subject to three-dimensional disturbances is investigated. The analytical model used treats the fan rotor and stator as linear cascades of thin airfoils in a rectangular duct subject to a three-dimensional gust for which a complete aerodynamic theory already exists. The sound pressure can then be cast as the sum of a finite number of discrete sound waves (modes) the magnitude of which depends on an unknown function satisfying a singular integral equation. Similarity rules are derived to reduce the problem to that of a two-dimensional gust. Three-dimensional effects on the cut-off condition, the sound pressure, and the acoustic power are first investigated for each mode. The theory is then applied to noise generated by typical rotor-wake-defect and rotor-tip-vortex disturbances interacting with a stator.

Boundary-Layer Control on Wings Using Sound and Leading-Edge Serrations

Abstract: T study systematically examined the effect of leadingedge serrations, sound emitted from periodically spaced holes near the wing leading edge, and external sound upon the flow over two low-speed wings, one with camber (NACA 2412) and one without (NACA 0015). The main purpose of the study was to determine whether these techniques could be used to increase the lift coefficient of these wings. These techniques were all found to have a beneficial effect upon the aerodynamic properties of these airfoils. The first two techniques could be practically used to improve the low-speed lift and stall performance of light aircraft during takeoff and landing and could be used for stall/flutter suppression on rotor and propeller blades.

Bending-torsion flutter of a highly swept advanced turboprop

Abstract: Experimental and analytical results are presented for a bending-torsion flutter phenomena encountered during wind-tunnel testing of a ten-bladed, advanced, high-speed propeller (turboprop) model with thin airfoil sections, high blade sweep, low aspect ratio, high solidity and transonic tip speeds. Flutter occurred at free-stream Mach numbers of 0.6 and greater and when the relative tip Mach number (based on vector sum of axial and tangential velocities) reached a value of about one. The experiment also included two- and five-blade configurations. The data indicate that aerodynamic cascade effects have a strong destabilizing influence on the flutter boundary. The data was correlated with analytical results which include aerodynamic cascade effects and good agreement was found.

On the structure of turbulent wakes and merging shear layers of multielement airfoils

Abstract: The structure of the attached turbulent flow in the vicinity of a NACA 4412 airfoil equipped with a single-slotted flap was studied. The airfoil/flap configuration was tested at a Mach number of 0.06 and a Reynolds number of 1.3 x 10 to the 6th in a 7- by 10-Foot Wind Tunnel. Surface-pressure measurements were made on the main airfoil and on the flap. Detailed measurements, obtained using a high-spatial-resolution laser Doppler anemometer, were made of the mean velocity flow field and of the second-order statistical quantities (Reynolds stresses) in the boundary layers, wakes, and merging shear layers. The experimental observations are compared with theoretical predictions of pressure, mean velocity, and Reynolds stress.

Aileron system for aircraft and method of operating the same

Abstract: Two aileron assemblies at opposite ends of a wing. Each aileron assembly has an aileron airfoil member having a first stowed position for high speed flight, where aerodynamic contours of the airfoil member match those of the wing. Each aileron airfoil member has a second extended position forming a slot with the trailing edge of the wing. Each airfoil member is slide mounted to a track member which is in turn pivotally mounted to wing structure.

Low-Speed Aerodynamic Characteristics of a Small, Fixed-Trailing-Edge Circulation Control Wing Configuration Fitted to a Supercritical Airfoil

Abstract: : Excellent high-lift and cruise performance of a small, round, fixed circulation control wing (CCW) trailing edge fitted to a supercritical airfoil has been confirmed by subsonic wind tunnel investigations. This fixed-trailing- edge blown high-lift airfoil generates a negligible subsonic cruise drag penalty, but can generate a section lift coefficient near 7.0. This configuration is a significant improvement over the flight-proven A-6/CCW airfoil that had similar lift performance, but had a large trailing edge requiring mechanization for transition to cruise flight. Further, the large leading edge radius of the supercritical airfoil allows operating at high lift over a moderate angle-of-attack range. These results imply the feasibility of a mono-element airfoil with no moving components required for high lift; the transition from the cruise to the high-lift configuration is accomplished by blowing from a fixed slot. The favorable characteristics of both the cruise and high-lift airfoils are retained without compromise to either. (Author)