Showing papers on "Leading edge published in 1978"

Flow around a circular cylinder near a plane boundary

Abstract: The flow around a circular cylinder placed at various heights above a plane boundary has been investigated experimentally. The cylinder spanned the test section of a wind tunnel and was aligned with its axis parallel to a long plate and normal to the free stream. It was placed 36 diameters downstream of the leading edge of the plate and its height above the plate was varied from zero, the cylinder lying on the surface, to 3·5 cylinder diameters. The thickness of the turbulent boundary layer on the plate at the cylinder position, but with it removed from the tunnel, was equal to 0·8 of the cylinder diameter. Distributions of mean pressure around the cylinder and along the plate were measured at a Reynolds number, based on cylinder diameter, of 4·5 × 104. Spectral analysis of hot-wire signals demonstrated that regular vortex shedding was suppressed for all gaps less than about 0·3 cylinder diameters. For gaps greater than 0·3 the Strouhal number was found to be remarkably constant and the only influence of the plate on vortex shedding was to make it a more highly tuned process as the gap was reduced. Flow-visualization experiments in a smoke tunnel revealed the wake structure at various gap-to-diameter ratios.

Lift Enhancement by an Externally Trapped Vortex

Abstract: A theoretical study is made of the performance capabilities of a lift concept that utilizes a spanwise vortex over the upper surface of the wing. The vortex is generated by a vertical flap near the leading edge of the wing and maintained by suction through orifices in endplates at the wingtip. The analysis approximates the three-dimensional flow field with a two-dimensional configuration that is mapped by conformal transformation into the flow about a circle. Theoretical solutions for a range of flap and orifice configurations predict that section lift coefficients up to around 10 can be achieved. It is concluded that such a lift concept is applicable to STOL aircraft if the vortex can be adequately stabilized and if the endplate suction can be generated efficiently.

Unsteady flow in a supersonic cascade with subsonic leading-edge locus

Abstract: Linearized theory is used to predict the unsteady flow in a supersonic cascade with subsonic axial flow velocity. A closed-form analytical solution is obtained by using a double application of the Wiener-Hopf technique. Although numerical and semianalytical solutions of this problem have already appeared in the literature, this paper contains the first completely analytical solution. It has been stated in the literature that the blade source should vanish at the infinite duct resonance condition. The present analysis shows that this does not occur. This apparent discrepancy is explained in the paper.

Cooled rotor blade

Abstract: A cooled rotor blade is constructed having a cooling passage extending from the root and through the airfoil shaped section in a serpentine fashion, making several passes between the bottom and top thereof; a plurality of openings connect said cooling passage to the trailing edge; a plurality of compartments are formed lengthwise behind the leading edge of the blade; said compartments having openings extending through to the exterior forward portion of the blade; and sized openings connect the cooling passage to each of the compartments to control the pressure in each compartment.

Influence of debris dent on EHD lubrication

Abstract: Film thickness measurements associated with a debris dent have been made with interferometry under static and dynamic conditons. The presence of a debris dent alters the shape of the inlet region so that the local film thickness at the leading edge of the dent can become substantially lower than the trailing edge. The pressure modifications associated with these local elastohydrodynamic (EHD) effects are in line with the frequent occurrence of surface initiated fatigue spalls originating at the trailing edge of debris dents. The effectiveness of the EHD mechanism in reducing the stress concentrations at the shoulders of the dent is related to inlet dimensions and dent size.

Fixed geometry self starting transverse axis wind turbine

Abstract: This invention relates to a fixed geometry self starting wind turbine having a blade rotatable about a vertical axis. The blade is of a wide streamlined cambered airfoil shape and has a forward portion that includes a well rounded leading edge and thickness distribution that is conducive to high lift to drag ratios and having a high drag characteristic in reversed flows. The concave curvature of this camber line of said airfoil is directed to the rotational axis. The wide blade in combination with the well rounded leading edge, camber and airfoil thickness gives the turbine improved self-starting characteristics and causes the turbine to have improved acceleration characteristics through the intermediate speed range and up to full operating speed.

Aircraft wing drooping leading edge device

Abstract: A drooping leading edge device is provided in which the leading edge structure that droops is pivotally mounted, by a single pivot inside the wing, upon the front spar structure of the wing and is of substantially constant shape. A gap which would otherwise open up between the upper skin of the main part of the wing and the upper skin of the leading edge structure, when the leading edge droops, is filled by an upper flexible skin section secured to the main part of the wing and extending forward first into contiguity with the rear edge of the upper skin of the leading edge structure and then inside said leading edge structure. At the underneath of the wing, a rear flexible portion of the lower skin of the leading edge device extends back to meet the forward edge of the lower skin of the main part of the wing. When the leading edge droops, the profile of the upper flexible skin section is controlled by links inside the structure which are hinged at their upper ends on the upper flexible skin section and at their lower ends on inner structure of the leading edge device.

On transient sliding motion

Abstract: Summary. Two kinds of transient sliding motion under a case of idealized dry friction are studied. One concerns uni-directional slip at constant propagation velocity along a strip of constant length in the propagation direction. The other regards extensional slip along a strip expanding symmetrically with constant velocity. The former kind involves one leading and one trailing edge, whereas the latter involves two leading edges. At a leading edge there must be a region of tearing, where sliding is initiated, and at a trailing edge a region of healing, where sliding ceases. The finiteness of these regions follows from the requirement of bounded strains. In the linearized treatment chosen, the edge processes are described by a modulus of tearing and a modulus of healing, both being characteristics of the material. Relations between the applied remote stress, the extension of the sliding region, the amount of slip, the slip propagation velocity and the rate of energy dissipation are given.

Variable twist leading edge flap

Abstract: A leading edge flap system for the tapered wing of an aircraft and more particularly, the spanwise flap segments and their linkage mechanism allow a relatively large leading edge bullnose member to be extended and unfolded out from a wing cavity. Each of the spanwise flap segments is supported from the leading edge of the wing by a pair of linkage mechanisms which are spaced apart spanwise and attached towards each spanwise end portion of the flap segment. The spanwise spaced apart linkage mechanisms are interconnected by a torque tube which is rotated through a fixed number of degrees by an actuator. By altering the geometry of the linkage mechanism, a differential motion is applied between the spanwise ends of the flap segment to torsionally twist the panel in a spanwise direction thereby varying the flap deflection angle spanwise.

System for detecting heart pacemaker pulses

Abstract: A system is disclosed for accurately providing a signal or signals indicative of the relatively sharp leading edge and the relatively attenuated trailing edge of a pulse and in particular of a pulse applied by a heart pacemaker to a patient's heart. The system of this invention functions to distinctly detect each of the relatively fast rising leading edge and the relatively slow rising trailing edge, while preventing a premature detection of the trailing upon the attenuated or drooping portion of the pacing pulse therebetween.

Propulsion system for a V/STOL airplane

Abstract: A propulsion system for an airplane to permit it to achieve vertical and/or short take-offs and landings. The propulsion system is integrated into a wing/nacelle unit and includes a thrust vectoring system. A separate flow turbofan engine is mounted in each wing/nacelle unit. A system of three flaps is located at the rear of each wing/nacelle unit for deflecting the turbofan engine exhaust downward, rearward, or any angle in between. These three flaps are arranged to provide a main thrust nozzle in the horizontal flight position without any additional flaps between them. One flap is located at the wing/nacelle upper surface trailing edge. Two slots are provided at the leading edge of this flap. The upper forward most slot is provided as an exit nozzle for the engine turbine exhaust, which is shrouded from the fan exhaust. The second of these two slots removes a portion of the high energy fan exhaust from the fan discharge duct and ejects it over the flap upper surface. The other two flaps are positioned such that, in the horizontal position they are both aligned with the wing/nacelle lower surface and in the vertical position, one is aligned with the wing/nacelle lower surface and the other is aligned with the wing/nacelle upper surface. When the flaps are in the vertical position, the aft most slot in the upper flap and a slot formed between the upper flap and the lower aft flap provide a means of improving the turning efficiency of the fan exhaust stream.

Aerodynamic drag-reducing shield for mounting on the front of a cargo carrying compartment of a road vehicle

Abstract: An aerodynamic drag-reducing shield for mounting on the front of a trailer or truck box, has a front surface contour defined by a series of semi-ellipses, the minor axes of the ellipses tapering off towards the upper rear edge of the shield at such rate that in profile the shield has a part-elliptical leading edge.

Counter-rotating vortices generator for an aircraft wing

Abstract: A device for enhancing the lift capability of an aircraft wing is characterized by at least one forwardly projecting finger member mounted on the leading edge of the wing. The finger generates counter-rotating vortices, each in contact with the other, trailing backwardly across substantially the entire upper surface of the wing behind the fingers as the airflow moves upwardly and around the lateral edges of the finger. As the counter-rotating vortices trail backwardly over the upper surface of the wing, a blockage effect is created and the airflow patterns across the wing are modified to produce an increase in lift.

Estimation of leading-edge thrust for supersonic wings of arbitrary planform

Abstract: A numerical method for the estimation of leading edge thrust for supersonic wings of arbitrary planform was developed and was programmed as an extension to an existing high speed digital computer method for prediction of wing pressure distributions The accuracy of the method was assessed by comparison with linearized theory results for a series of flat delta wings Application of the method to wings of arbitrary planform, both flat and cambered, is illustrated in several examples

Control of withdrawal of flat items individually from a stack

Abstract: During the successive discharge and conveyance, along a conveying path, of items of mail from a stack by a continuously driven conveying device and an externally controllable removal member arranged to transport successive items from the stack to the region of action of the conveying device, the desired spacing between each pair of successive items is established automatically as a function of the length of that item of such pair which is the leading item on the conveying path such that for a leading item whose length exceeds a predetermined length value, the next succeeding item is transported from the stack when the distance between the trailing edge of that leading item and the leading edge of the next succeeding item reaches a given first spacing value, and for a leading item whose length is less than the predetermined length value, the next succeeding item is transported from the stack when the distance between the leading edge of that leading item and the leading edge of the next succeeding item reaches a given second spacing value.

Smoke and fire shield damper

Abstract: A combination smoke and fire shield damper comprising a line of blades each of which is so supported for rotation in a surrounding frame that the blades are swingable about parallel axes to open or close an opening in the frame, in which the blades are provided with "opened-out" trailing edges so that the leading edge of each blade interlocks with the trailing edge of an adjacent blade when the blades are in their fully-closed positions.

Axial flow fan with auxiliary blades

Abstract: An axial flow fan having auxiliary blades which includes a hub rotatably supported and driven by a drive source, a plurality of fan blades extending radially outwardly from the hub and at least one auxiliary blade projecting from an outer part on a suction and/or pressure surface of the fan blade and extending in the chord-length direction in such a manner that the leading region of the auxiliary blade is located nearer to the central axis of the fan than the trailing region thereof. A supplementary angle θ 0 of an angle formed between a chord line connecting to a leading edge and a trailing edge of the outer auxiliary blade and a reference line decided by the shape or operation of the fan blade has the relation; 5°≦θ 0 ≦40°. A supplementary angle θ N of an angle formed between a chord line connecting to a leading edge and a trailing edge of the inner auxiliary blade and a reference line decided by the shape or operation of the fan blade also has the relation; 18°≦θ n ≦50°. The axial flow fan serves to produce a strong radial flow by auxiliary blades of the optimum positional relation as described and improves the aerodynamic performances of the fan such as the air flow rate, efficiency and noise level.

Measurements of noise produced by flow past lifting surfaces

Abstract: Wind tunnel studies have been conducted to determine the specific locations of aerodynamic noise production within the flow field about various lifting-surface configurations. The models tested included low aspect ratio shapes intended to represent aircraft flaps, a finite aspect ratio NACA 0012 wing, and a multi-element wing section consisting of a main section, a leading edge flap, and dual trailing edge flaps. Turbulence was induced on the models by surface roughness. Lift and drag were measured for the flap models. Hot-wire anemometry was used for study of the flap-model vortex roll-up. Apparent noise source distributions were measured by use of a directional microphone system, located outside the tunnel, which was scanned about the flow region to be analyzed under computer control. These distributions exhibited a diversity of pattern, suggesting that several flow processes are important to lifting-surface noise production. Speculation concerning these processes is offered.

Apparatus for obtaining useful work from wave energy

Abstract: An apparatus and method for obtaining useful work from or with waves includes a buoyant body having a leading edge and a trailing edge, and a convex upper surface extending between the leading and trailing edges. The upper surface is configured with a gradually sloping shape from the leading edge toward the trailing edge and terminates at the trailing edge in a sharply oppositely sloping surface, whereby the circular or orbital motion of water particles in waves is converted by the upper surface to linear flow of the water particles, and waves traveling across the surface from the leading to the trailing edge are not damped or extinguished by backwash of waves from the trailing edge toward the leading edge. Upstanding structures on the upper surface define open-ended venturi-shaped water flow channels across the upper surface which increase the velocity of the linear flow of water across the upper surface, and water-driven devices are disposed in the water flow channels to obtain work from the accelerated linear flow of water. The buoyant body floats at the surface of the body of water, with the upper surface of the buoyant body disposed beneath and substantially parallel to the surface of the water, and the configuration of the buoyant body is such that it undergoes both pitching and heaving motion as waves move therepast. Devices may be attached to the buoyant body and/or positioned therewithin to obtain work from the pitching and heaving motion of the buoyant body.

Vertical axis type wind power turbine

Abstract: Wind power turbines are largely divided into vertical axis type wind power turbines and propeller type (horizontal axis type) wind power turbines. The present invention discloses a vertical axis type wind power turbine. The airfoil of blades in this vertical axis type wind power turbine is formed in such manner that, denoting a proper position on the airfoil chord line as a camber reversing position, a camber having a downward convex curvature is given between said position and a leading edge and a camber having an upward convex curvature is given between said position and a trailing edge so as to be a mean line and a rational thickness distribution is given to this mean line. This vertical axis type wind power turbine is formed by keeping the spanwise direction of the above mentioned blade parallel with a vertical rotary axis and fitting a plurality of blades at regular intervals at a distance to the vertical rotary axis through respective supporting arms.

Flight investigation of insect contamination and its alleviation

Abstract: An investigation of leading edge contamination by insects was conducted with a JetStar airplane instrumented to detect transition on the outboard leading edge flap and equipped with a system to spray the leading edge in flight. The results of airline type flights with the JetStar indicated that insects can contaminate the leading edge during takeoff and climbout. The results also showed that the insects collected on the leading edges at 180 knots did not erode at cruise conditions for a laminar flow control airplane and caused premature transition of the laminar boundary layer. None of the superslick and hydrophobic surfaces tested showed any significant advantages in alleviating the insect contamination problem. While there may be other solutions to the insect contamination problem, the results of these tests with a spray system showed that a continouous water spray while encountering the insects is effective in preventing insect contamination of the leading edges.

Method for steering an aircraft

Abstract: The present aircraft steering method makes use of additional lift gained byontrolling the separating of vortical flows from the leading edges of the wings for the purpose of controlling the aircraft about its pitch axis, its roll axis, and its yaw axis. The vortical flows are selectively or differentially separated from the leading edge of the wings by raising or lowering leading edge flaps and/or blowing a flowing medium over the wing surfaces substantially in parallel to the leading edge.

Wing with improved leading edge for aircraft

Abstract: A thin, high performance swept wing of the tapered type with an improved leading edge characterized by a first portion that extends from near the wing root at a fixed radius to a transition point where twice the fixed radius does not exceed about 100.6 percent of wing thickness at about 5 percent of the local chord at the transition point, and a second leading edge portion extending from the transition point to the wing tip that has a radius expressed in percent of local chord which does not exceed that percent of local chord at the transition point. Winglets are optionally provided in combination with the wing with improved leading edge to provide in combination, improved aircraft performance.

Impeller of a centrifugal blower

Abstract: In an impeller of a centrifugal blower of the backward type having a relatively large blade inlet width as contrasted with the diameter of the impeller, blades are each shaped, as seen from the axial direction of a rotary shaft, in a concave curve with respect of rotation of the impeller, each of the blades has a larger inlet diameter on the shroud plate side than on the hub plate side, and each of the blades has a leading edge shaped, in a meridional plane, in a smooth convex curve directed radially inwardly of the impeller. By these structural features, it is possible to bring the inlet blade angle into agreement with the inlet relative flow angle at each point of the leading edge of each blade and to reduce the rate of a reduction in the velocity of flow on the shroud plate side. Thus separation of the flow from blade surfaces and production of noise caused thereby can be prevented, and a sufficiently large blade area to achieve high efficiency can be obtained, so that a loss of load on the blade surfaces can be avoided and a higher pressure coefficient than in conventional impellers can be obtained. Each blade can be developed in a plane, and its leading edge can be in the form of a circular arc centered on a side edge of the blade either on the hub plate side or on the shroud plate side. Thus the impeller is hydrodynamically advantageous and easy to fabricate.

Some observations on the mechanism of aircraft wing rock

Abstract: A pressure scale model of Northrop F-5A was tested in NASA Ames Research Center Eleven-Foot Transonic Tunnel to simulate the wing rock oscillations in a transonic maneuver. For this purpose, a flexible model support device was designed and fabricated which allowed the model to oscillate in roll at the scaled wing rock frequency. Two tunnel entries were performed to acquire the pressure (steady state and fluctuating) and response data when the model was held fixed and when it was excited by flow to oscillate in roll. Based on these data, a limit cycle mechanism was identified which supplied energy to the aircraft model and caused the Dutch roll type oscillations, commonly called wing rock. The major origin of the fluctuating pressures which contributed to the limit cycle was traced to the wing surface leading edge stall and the subsequent lift recovery. For typical wing rock oscillations, the energy balance between the pressure work input and the energy consumed by the model aerodynamic and mechanical damping was formulated and numerical data presented.