Showing papers on "Airfoil published in 1971"

Airfoil and Bridge Deck Flutter Derivatives

Abstract: The writers compare the flutter phenomena of the suspension bridge and the airfoil and employ a free-oscillation experimental method to measure model bridge flutter coefficients analogous to airfoil flutter coefficients. They employ the airfoil as a check on the experimental method, both as a theoretical backdrop and to test out the nature of aerodynamic oscillatory forces under exponentially modified motion. A short catalogue of bridge deck flutter coefficients is then experimentally obtained and presented covering a range of bridge deck forms. Detailed results are described to account for a number of phenomena observed in the wind tunnel and in the field.

Calculation of plane steady transonic flows

Abstract: Transonic small disturbance theory is used to solve for the flow past thin airfoils including cases with imbedded shock waves. The small disturbance equations and similarity rules are presented, and a boundary value problem is formulated for the case of a subsonic freestream Mach number. The governing transonic potential equation is a mixed (elliptic-hyperbolic) differential equation which is solved numerically using a newly developed mixed finite difference system. Separate difference formulas are used in the elliptic and hyperbolic regions to account properly for the local domain of dependence of the differential equation. An analytical solution derived for the far field is used as a boundary condition for the numerical solution. The difference equations are solved with a line relaxation algorithm. Shock waves, if any, and supersonic zones appear naturally during the iterative process. Results are presented for nonlifting circular arc airfoils and a shock free Nieuwland airfoil. Agreement with experiment for the circular arc airfoils, and exact theory for the Nieuwland airfoil is excellent.

Air foil and bridge deck flutter derivatives

Abstract: THE FLUTTER PHENOMENA OF THE SUSPENSION BRIDGE IS COMPARED TO THE AIRFOIL. A FREE-OSCILLATION EXPERIMENTAL METHOD IS USED TO MEASURE MODEL BRIDGE FLUTTER COEFFICIENTS ANALOGOUS TO AIRFOIL FLUTTER COEFFICIENTS. THE AIRFOIL IS EMPLOYED AS A CHECK ON THE EXPERIMENTAL METHOD, BOTH AS A THEORETICAL BAKCDROP AND TO TEST OUT THE NATURE OF AERODYNAMIC OSCILLATORY FORCES UNDER EXPONENTIALLY MODIFIED MOTION. A SHORT CATALOGUE OF BRIDGE DECK FLUTTER COEFFICIENTS WAS EXPERIMENTALLY OBTAINED AND COVERS A RANGE OF BRIDGE DECK FORMS. DETAILED RESULTS ARE DESCRIBED TO ACCOUNT FOR A NUMBER OF PHENOMENA OBSERVED IN THE WIND TUNNEL AND IN THE FIELD. /AUTHOR/

Analysis of transonic airfoils.

Abstract: A finite difference scheme for the analysis of transonic airfoils at off-design conditions is described It is the ultimate goal of the investigations to avoid expensive wind tunnel tests by combining the mathematical techniques in a procedure for designing supercritical airfoils so that they will be effective over a wider range of angles of attack and Mach numbers A mathematical method is considered for computing two-dimensional transonic flows past a prescribed profile The method can provide accurate results for a comparison with a known shockless regime The approach gives also data of engineering reliability concerning the location and the strength of shocks at off-design conditions

The Computation of Transonic Flow Through Two-Dimensional Gas Turbine Cascades

Abstract: Steady transonic flow through two-dimensional gas turbine cascades is efficiently predicted using a time-dependent formulation of the equations of motion An integral representation of the equations has been used in which subsonic and supersonic regions of the flow field receive identical treatment Mild shock structures are permitted to develop naturally without prior knowledge of their exact strength or position Although the solutions yield a complete definition of the flow field, the primary aim is to produce airfoil surface pressure distributions for the design of aerodynamically efficient turbine blade contours In order to demonstrate the accuracy of this method, computed airfoil pressure distributions have been compared to experimental resultsCopyright © 1971 by ASME

Unsteady Airfoil Stall, Review and Extension

Abstract: Unsteady airfoil stall in incompressible flow, including pitch rate induced accelerated flow effect on leading edge and trailing edge stall

Tip vortices: Velocity distributions

Abstract: Hot-wire anemometer measurements of streamwise magnitudes and normal velocity components of wing tip vortex

Contribution to methods for calculating the flow about thin lifting wings at transonic speeds: Analytic expressions for the far field

Abstract: The problem of determining the small-disturbance flow about two-dimensional airfoils at transonic speeds has been successfully treated by the process of matching a numerical solution of the near field to analytic expressions for the far field. The three-dimensional problem, it would appear, can be treated in a similar way with the aid of algorithms adapted to high-speed and high-capacity computers. The far-field potential for both lifting and nonlifting three-dimensional wings at transonic speeds is developed herein for a subsonic free stream. This potential could be used for a three-dimensional-wing computation similar to the computation made for the two-dimensional wing.

High lift leading edge device

Abstract: The retractable leading edge wing flap has a skin surface with tapered thickness in order that it can more easily assume the desired nonuniform degree of curvature when the flap is in its extended position. Through the inherent resilency of the flap skin surface material in combination with an actuating mechanism having a minimum of operating elements, the surface of the flap is provided with a variable contour thereby producing a variable camber to the flap panel and likewise to the wing airfoil section that is in combination therewith. More specifically, the flap extension and retraction mechanism operates in a chordwise plane and requires a maximum of five links to produce the desired result. Further, the actuating mechanism operates to position the flap panel relative to the fixed wing leading edge so as to vary the wing airfoil section aerodynamic flow characteristics by changing the total overall amount of effective wing camber. For the landing condition, the arrangement of the linkage mechanism produces an angular relationship of the flap chord plane relative to the wing chord plane such that the overall aerodynamic affect is a greater airfoil section camber at said landing condition than at the take off condition. Also, the arrangement of the linkage mechanism for the landing condition is such that the leading edge wing flap is extended further forward from the relatively fixed leading edge of the main wing section in addition to being spaced away from the wing leading edge, to form an aerodynamic slot; whereas, at the take off position the movable flap section and wing leading edge are in abutment relation thereby forming a substantially continuous upper surface without the slot.

Gust Loading on a Thin Aerofoil

Abstract: A closed-form expression is derived which gives an approximate solution to the lift generated on a two-dimensional thin aerofoil in incompressible flow with a normal velocity component of the form exp [ i ( ωt – x x + y y )]. The inaccuracy of the solution when compared with other published work is compensated by the simplicity of the final expression, particularly if the result is required for the calculation of the sound power radiated by an aerofoil in a turbulent flow.

Theoretical and experimental aerodynamics of the sailwing

Abstract: The sailwing is a unique type of semiflexible foldable wing. A brief description of its construction, basic properties, and some past research, is used to introduce an analytical and experimental study of its aerodynamic characteristics. Emphasis is placed on an approximate structural analysis which treats the nonlinear behavior of the sail deflection. Twodimensional flexible airfoil theory and Prandtl lifting-line theory are used to establish the aerodynamic loading. The results allow prediction of the induced tensions, the nonlinear life curve, induced drag, and aeroelastic divergence of the sail chordwise deflection mode. Selected experimental results are presented for comparison with the theory, along with a brief discussion of the implications of the study regarding flight vehicle applications of the sailwing.

Analysis of the flow past a shockless lifting airfoil in design and off-design conditions

Abstract: A shockless lifting airfoil designed for shockless inviscid flow at M∞ = 0. 75 with CL = 0. 63 was tested at high Reynolds numbers up to 27 X 10σ in design and off-design conditions. The experimental results are compared against theoretical results, showing in general good agreement.

Dynamic Stall Simulation Problems

Abstract: Dynamic airfoil stall simulation in wind tunnels, considering pitch rate, Reynolds number, oscillation and test equipment effects

Semi-rigid airfoil for airborne vehicles

Abstract: The present invention relates to a semi-rigid airfoil for use with airborne vehicles and capable of being folded and/or warped. The airfoil includes a rigid spar defining a leading edge and a cable defining the trailing edge with the root end thereof secured to the fuselage of the vehicle and the other end to a tip truss structure, with a flexible material forming top and bottom airfoil surfaces. Means are also provided for twisting portions of the airfoil about an axis extending through the root end, and means for pivoting the spar to fold against the fuselage.

Airfoil shape for flight at subsonic speeds

Abstract: An airfoil having an upper surface shaped to control flow accelerations and pressure distribution over the upper surface and to prevent separation of the boundary layer due to shock wave formulation at high subsonic speeds well above the critical Mach number. A highly cambered trailing edge section improves overall airfoil lifting efficiency.

Flexible airfoil for compressor

Abstract: The inlet guide vanes for a turbine compressor are constructed of thin flexible material and mounted in a manner to be selectably formed into a desirable airfoil shape and camber angle by suitable control means.

Jet wing with multiple thrust augmentors

Abstract: The invention relates to an aircraft with VTOL or STOL operational capability. In accordance with the invention, the wing, or airfoil contour, is provided with a plurality of spanwise extending slots or ducts having inlet and outlet openings in the suction and pressure surfaces respectively of the wing. The slot openings are normally closed by spanwise extending flaps which fair into the airfoil contour and when the slots are open cooperate therewith to form individual thrust augmenting ducts. A large number of primary nozzles are provided for injecting high pressure air, derived for example from the bypass air of a conventional turbofan engine, into the ducts. The injected air is delivered as individual jets moving downward in the direction from the suction to the pressure surface of the airfoil and inducing a flow of ambient air from above the wing to mix with the primary air from the jets. The increased mass flow from the thrust augmentor ducts will give rise to vertical thrust or lift which may be of the order to twice the thrust which would have been produced by the primary air alone. The flaps on at least the suction surface are individually operable both as to magnitude and rate of displacement so as to provide for varying conditions of flight operation.

The Use of a Laser Doppler Velocimeter in Supersonic Flow

Abstract: : Results are presented for an experimental program which investigated the application of an LDV technique in supersonic flows. This paper presents an analysis of the behavior of light-scattering particles in rapidly accelerating or shock decelerated flows, an evaluation of particle production techniques and the results of several velocity measurements. Measurements included the velocity distribution along the nozzle centerline and flow over a diamond airfoil in a Mach 3 tunnel and velocity profiles for a turbulent boundary layer in a Mach 4.8 facility. It is demonstrated that LDV measurements can be made consistently with errors of less than five percent if the particle lag is considered. (Author)

Power-on channel wing aerodynamics

Abstract: A theory is developed for lift developed by semicircular channel wings with a pusher propeller at the trailing edge. The theory assumes that the lift on the inside (or top) of a channel airfoil can be determined by using standard airfoil pressure coefficient data but with an effective freestream velocity and an effective freestream static pressure equal* to those values just in front of the propeller plane. The lift on the outside (or bottom) of a channel airfoil is assumed to be the same as that calculated by present-day standard methods. Good correlation was found between the theory and wind-tunnel and flight- test data. Both the theory and test data indicate extremely large values of lift coefficient can be obtained with channel wings. Nomenclature A = area of propeller disk Ae = streamtube area of infinity c = wing chord length Ci = lift coefficient/unit span Cu = ideal lift coefficient/unit span CL = power-on lift coefficient, L/qmS CL* = unpowered lift coefficient, L/qmS CT = thrust coefficient,-T/qmA L = lift m = mass flow rate n = number of engines P = power p = pressure T — thrust/engine Tc = thrust coefficient, nT/qmS q = dynamic pressure, JpF2 R = channel radius S = total horizontal projected wing area Sc = horizontal projected channel wing area, 2 Re V = velocity x = distance from leading edge along chord line a. — angle of attack a = average sectional angle of attack in the channel /*7T/2 = COS"1 I COSO! COS = COS~1[a Cota]^, = 0 J o

Wind-tunnel investigation of effects of trailing-edge geometry on a NASA supercritical airfoil section

Abstract: Wind-tunnel tests have been conducted at Mach numbers from 0.60 to 0.81 to determine the effects of trailing-edge geometry on the aerodynamic characteristics of a NASA supercritical airfoil shape. Variations in trailing-edge thicknesses from 0 to 1.5 percent of the chord and a cavity in the trailing edge were investigated with airfoils with maximum thicknesses of 10 and 11 percent of the chord.

Airfoil for aircraft

Abstract: An airfoil for fixed and rotary wing aircraft comprising a continuous upper surface that joins with a generally planar portion of the under surface at the leading edge to form the apex of a wedge-like airfoil section that extends toward and terminates abruptly in advance of the trailing edge.

Analysis of a Circulation Controlled Elliptical Airfoil

Abstract: : The effect of trailing edge blowing on the circulation around an airfoil section is considered theoretically. The analysis is self-contained in that specification of the ambient conditions, flight conditions, and blowing conditions gives the sectional lift and drag coefficients on the prescribed airfoil section. The method of solution is an iterative one, and involves the matching of an assumed sectional lift coefficient with the sectional lift coefficient calculated from the actual pressure distribution over the body in the presence of trailing edge blowing. In order to obtain the pressure on the wall in the wall jet region a full boundary layer analysis is required over the airfoil. The Karman-Pohlhausen integral method is used in the laminar region and the Nash and Hicks turbulent layer analysis is used in the turbulent region. Using the boundary layer properties on the upstream side of the wall jet, along with conservation of mass and momentum relations through the mixing zone, a new wall jet profile is found at the downstream end of the potential core. The wall jet region is then analyzed using integral methods including entrainment. The analysis represents an extension to the calculation method proposed by Kind, and reconfirms the feasibility of obtaining high lift coefficients with relatively low blowing rates. (Author)

Numerical calculation of transonic flow about two-dimensional airfoils by relaxation procedures

Abstract: Compressible transonic flow about two dimensional airfoils, developing inviscid nonlinear potential equations by relaxation procedures

Development and application of a method for predicting rotor free wake positions and resulting rotor blade air loads. Volume 1: Model and results

Abstract: Rotor wake geometries are predicted by a process similar to the startup of a rotor in a free stream. An array of discrete trailing and shed vortices is generated with vortex strengths corresponding to stepwise radial and azimuthal blade circulations. The array of shed and trailing vortices is limited to an arbitrary number of azimuthal steps behind each blade. The remainder of the wake model of each blade is an arbitrary number of trailing vortices. Vortex element end points were allowed to be transported by the resultant velocity of the free stream and vortex-induced velocities. Wake geometry, wake flow, and wake-induced velocity influence coefficients are generated by this program for use in the blade loads portion of the calculations. Blade loads computations include the effects of nonuniform inflow due to a free wake, nonlinear airfoil characteristics, and response of flexible blades to the applied loads. Computed wake flows and blade loads are compared with experimentally measured data. Predicted blade loads, response and shears and moments are obtained for a model rotor system having two independent rotors. The effects of advance ratio, vertical separation of rotors, different blade radius ratios, and different azimuthal spacing of the blades of one rotor with respect to the other are investigated.

Unsteady airfoil stall and stall flutter

Abstract: Unsteady airfoil stall characteristics using static data input for predicting stall flutter boundaries of space shuttle wing