Showing papers on "Leading edge published in 1972"

On the mechanism of dynamic stall.

Abstract: The sequence of events comprising dynamic stall of an airfoil is discussed, with emphasis on the role of the leading edge laminar separation bubble and shed vortex. A simple bubble model, based on a combination of theoretical and experimental investigations, is used to discuss the events prior to the shedding of the vortex, and provides the basis for a heuristic estimate of the delay in the occurrence of dynamic stall on a pitching airfoil. The evidence for the existence and dominant effect of the leading edge vortex on the dynamic stall required (but in most cases not presently available) for the prediction of the effects of stall on helicopter rotor blades are discussed. It is the intention of this paper to focus attention on the laminar separation bubble and the shed leading edge vortex as the dominant features of the dynamic stall mechanism in the hope of stimulating greater emphasis on these features in future dynamic stall research.

Aerodynamic effects of leading-edge serrations on a two-dimensional airfoil

Abstract: An investigation was conducted to determine the flow field and aerodynamic effects of leading-edge serrations on a two-dimensional airfoil at a Mach number of 0.13. The model was a NACA 66-012 airfoil section with a 0.76 m (30 in.) chord, 1.02 m (40 in.) span, and floor and end plates. It was mounted in the Ames 7- by 10-Foot Wind Tunnel. Serrated brass strips of various sizes and shapes were attached to the model in the region of the leading edge. Force and moment data, and photographs of tuft patterns and of oil flow patterns are presented. Results indicated that the smaller serrations, when properly placed on the airfoil, created vortices that increased maximum lift and angle of attack for maximum lift. The drag of the airfoil was not increased by these serrations at airfoil angles of attack near zero and was decreased at large angles of attack. Important parameters were serration size, position on the airfoil, and spacing between serrations.

Cooled vane or blade for a gas turbine engine

Abstract: A hollow cooled blade or vane for a gas turbine engine comprises a hollow leading edge portion given substantially unrestricted access to a source of cooling air and provided with film cooling holes to the blade outer surface, a hollow center portion with an air entry tube supplied with cooling air and apertured to cause the air to impinge on the blade inner surface, and a trailing edge portion having a sinuous passage for cooling air therein.

Impingement cooling performance in gas turbine airfoils including effects of leading edge sharpness

Abstract: An experimental study of the heat transfer characteristics of impingement into cavities which model the cooled leading edges of gas turbine engine airfoils is presented. The study includes both two-dimensional slot jets and single lines of evenly-spaced circular jets. For broad cylindrical cavities correlations are given for the maximum heat transfer rates attainable with optimum positioning of the jet nozzle with respect to the cooled surface. For elongated narrow cavities heat transfer rates relative to these maximum values are presented for a variety of cavity shapes.

Method for applying labels to containers

Abstract: Method and apparatus for continuous high speed application of labels to containers wherein the adhesive is applied to a predetermined location upon each of a succession of contains moved past a vacuum drum applying the leading edge of a label to each container at such location. The labels are successively cut from a strip by means ensuring continuous label movement and have an adhesive applied to a trailing edge thereof before application to containers. The containers are then moved to a discharge station where the labels are wrapped about the containers.

Bat wing structures important for aerodynamics and rigidity (Mammalia, chiroptera)

Abstract: From comparisons between bat wing structures and aerofoils and high-lift devices with known aerodynamic data, from the aeronautical literature, deductions are made regarding the function of some bat wing structures. Special arrangements in the hand wing add to rigidity and reduce the demands for powerful muscles and thick digits, thereby reducing the mass of the wing. 1. The anterior part of the wing, formed by the membrane parts anterior to the arm and third digit, is proportionally broad in megachiropteran bats as well as in many broad-winged microchiropteran bats. These parts can be lowered by the thumb and by pronation of the manus, and may together function as a leading edge flap. Leading edge flaps of aeroplanes permit, when lowered, higher angles of attack without separation, and thus higher lift coefficients. The leading edge in bats is very sharp, which increases the effectiveness of the leading edge flap. 2. The Reynolds number of bat wings lies in an interesting range, where the lift coefficient can be improved by induced turbulence of the boundary layer. The arm and digits, projecting markedly over the dorsal surface of the wing, and hair may function as turbulence generators. 3. The tension forces of the membrane on the digits have different effects upon the different digits, depending on the tautness of the surrounding membrane parts. The second digit and distal phalanx of the third digit are exposed mostly to bending in the membrane plane. The phalanges of the fourth and fifth digits are exposed to large dorsoventral bending. 4. Two arrangements add to relieving the distal part of the wing of large tension forces, thereby reducing the demand for a powerful extensor muscle of the distal phalanx (-ges) of the third digit: 1. The fourth and fifth digits act to alter the direction of tension. 2. By splitting the wing membrane in several parts by the digits, the second and third phalanges (the second in fruit-bats) of the third digit, which constitute the distal part of the wing's leading edge, are exposed to tension forces transformed from forces only from the nearest patagium. If the wing membrane would be outstretched only by one digit, as was the case in pterosaurs, the leading edge digit would have to resist the tension forces transformed from forces from the entire membrane posterior to the arm. 5. The fourth digit is angled in such a way that the proximal part of the membrane between the third and fourth digits is kept very taut, and the fourth metacarpophalangeal and interphalangeal joints are held very steady without any need of large muscular forces.

Shrink palletized process and apparatus

Abstract: This invention provides a process for making a high-strength unitary package, which has its generally vertically arranged portion overwrapped by a sheet of material of a type laminateable at its heat-shrinking temperature wherein an overlapped laminated seal is simultaneously formed between the leading and trailing edges of the sheet when the overwrapping sheet is also heat shrunk tightly against the package. Basically, the process comprises the steps of: placing a package on a support; locating a generally vertically arranged rolled-up sheet of a material of a type laminateable at its heat-shrinking temperature on dispenser means mounted for movement relative to the support; withdrawing a leading edge of the material from the dispenser and holding that leading edge against the package; moving the dispenser means relative to the support about a generally vertical axis and thereby causing a sufficient amount of the material to be dispensed from the dispenser means to overwrap the generally vertically arranged portion of the package and also provide a section of the material overlapping the leading edge; severing the overlapping section from the dispenser means and holding it to the package in a position overlapping the leading edge; and heating the overwrapped package to the heat-shrinking temperature of the material and thus simultaneously forming an overlapping laiminated seal between the leading edge and the overlapping section and also heat shrinking the overwrapped material tightly against the package. The present invention is also directed toward the product that is produced by this process and to certain apparatus which can be utilized to perform this process.

Effects of Leading-Edge Camber on Low-Speed Characteristics of Slender Delta Wings: Techniques and Tabulated Data

Abstract: Special tests to determine the importance of transition fixing and Reynolds number variation on forces produced by thin delta wings are discussed. Transition fixing was achieved by applying cement to models and sprinkling grit on wet adhesive. Strips were applied along lines emanating from the apex located along sixty-five percent semi-span rays. Tests were made with grit on both surfaces, upper surface only, lower surface only, and on clean surfaces. Reynolds number varied by testing at three dynamic pressures. Correspondence between dynamic pressure and Reynolds number based on the mean aerodynamic chord are shown. No significant changes are noted due to either Reynolds number variation or transition fixing, within the range of Reynolds numbers used for the test.

Centrifugal separator having axial-flow vortex generator

Abstract: In a centrifugal separator having a hollow cylindrical casing with coaxial inlet and outlet zones through which a particleladen medium is flowed, airfoil means is provided in the inlet zone for creating a vortex in the casing to separate the particles from the medium. The airfoil extends radially into the inlet zone and has a leading edge facing upstream and a tip located centrally in the flow stream. As the medium flows at a high velocity across the airfoil a vortex is generated downstream of the tip and in the casing. A layer of porous material lines the inside of the casing to capture the particles which are separated from the medium by the centrifugal action of the vortex. A continuous helical vane extends between the inlet and the outlet to channel the swirling fluid in a helix as it flows through the casing. In one embodiment, a venturi-shaped insert is provided in the casing and an axial-flow fan is provided in the outlet zone for inducing a draft in the inlet zone to maintain the velocity of the medium in the inlet zone at a sufficiently high level to ensure generation of a vortex.

Mass transfer to a rotating fluid: Part I. Transport from a stationary disk to a fluid in bödewadt flow

Abstract: Solutions are developed for mass transfer between a fluid undergoing solid body rotation and a coaxial disk which is located on a stationary infinite surface. The fluid mechanics corresponds to a laminar Bodewadt boundary layer. The overall mass transfer is dominated by the outer portion of the disk, a result of the high transfer rate associated with a leading edge. The concentration field near the axis of rotation extends to great axial distances as a long narrow plume. Approximate analytical solutions are given for each of these regions, and a numerical solution is provided for the entire concentration field.

Device for aiding the stacking of documents

Abstract: The present disclosure describes a technique for prevening collisions and jams of closely spaced documents, such as mail pieces which vary in size and weight, as they enter a stacking mechanism at high speed in a single file. Means are provided which are timed to impart a rotary motion about a vertical pivot point to each document as it approaches the stationary stack. Such motion insures that the leading edge of a succeeding document does not collide with the trailing edge of the preceeding document. Moreover, in a positive sense the leading edge of each document is caused to contact the previously stacked stationary document close to its leading edge, thereby eliminating the jamming of documents which might otherwise occur, particularly with documents having substantially different lengths.

Fiber blade with leading edge reinforcement

Abstract: This invention concerns a leading edge reinforcement for a fiber reinforced blade suitable for use in a gas turbine engine. The reinforcement comprises two strips of metal joined together at and adjacent to an edge which is shaped to form the leading edge of the blade. At least a part of the remaining portion of the metal strip serves for the attachment of the reinforcement to the blade.

Effects of leading-edge camber on low-speed characteristics of slender delta wings

Abstract: Wind-tunnel studies have been conducted to determine the effects of leading-edge camber on the low-speed aerodynamic characteristics of a thin, sharp-edge 74 deg delta wing. The results include force and moment measurements, pressure distributions, and flow visualization patterns determined from oil flow, tuft and water vapor observations. The study indicated that leading-edge camber near the apex is effective in controlling the pitch-up tendency of slender delta wings.

Experimental and Analytical Investigation of the Coolant Flow Characteristics in Cooled Turbine Airfoils

Abstract: The flow characteristics of turbine airfoil cooling system components were experimentally investigated Flow models representative of leading edge impingement, impingement with crossflow (midchord cooling), pin fins, feeder supply tube, and a composite model of a complete airfoil flow system were tested Test conditions were set by varying pressure level to cover the Mach number and Reynolds number range of interest in advanced turbine applications Selected geometrical variations were studied on each component model to determine these effects Results of these tests were correlated and compared with data available in the literature Orifice flow was correlated in terms of discharge coefficients For the leading edge model this was found to be a weak function of hole Mach number and orifice-to-impinged wall spacing In the impingement with crossflow tests, the discharge coefficient was found to be constant and thus independent of orifice Mach number, Reynolds number, crossflow rate, and impingement geometry Crossflow channel pressure drop showed reasonable agreement with a simple one-dimensional momentum balance Feeder tube orifice discharge coefficients correlated as a function of orifice Mach number and the ratio of the orifice-to-approach velocity heads Pin fin data was correlated in terms of equivalent friction factor, which was found to be a function of Reynolds number and pin spacing but independent of pin height in the range tested

Encapsulating sleeve for headstay of a sailboat

Abstract: The leading edge of a sail, particularly a jib sail of a sailboat, is supported along the length of a headstay by an encapsulating sleeve embracing the headstay and having a through slot along its rear edge through which the cloth at the leading edge of the sail extends. An elongated channel in the sleeve communicates with the aforesaid slot and is shaped to contain and restrainably engage the leading edge or luff of a jib sail, whereby the leading edge of the sail is slidably supported along its entire length within the aforesaid sleeve. The encapsulating sleeve is free to rotate on the headstay, thereby permitting the rotational movement of the leading edge of the sail about the headstay with directional changes of the sailboat and the wind.

Turbulent bursts and rings on a cone in helium at Me = 7.6.

Abstract: Review of data obtained on turbulent burst geometry and growth characteristics for cone boundary-layer transition in a helium wind tunnel at a boundary-layer edge Mach number (Me) of 7.6. Detailed data concerning turbulent spot geometry and downstream propagation velocities were obtained using a spark schlieren system with sequential spark capability. In one particular test evidence of a symmetrical turbulent burst ring was obtained; all other bursts developed in a singular random manner. Profiles of the apparent outer edges of the bursts were obtained, and the velocities of the leading and trailing edges of the bursts relative to the local velocity were determined. The velocities of the leading and trailing edges were found to be fairly consistent for each observation, with the leading edge of the burst traveling at about local edge velocity, while the trailing edge moved supersonically relative to local speed.

Apparatus for attaching a printing foil or master to the cylinder of a printing machine

Abstract: The present apparatus greatly facilitates the handling of the printing foil or sheet material of which a printing master is produced for use in printing machines such as office offset machines. The foil handling means include a first pair of rollers arranged inside a hollow foil cylinder for paying out a length of foil. First clamping means are provided for securing the leading edge of the foil to said cylinder. Second clamping means are provided for clamping down a portion of the foil which after severing becomes the trailing edge of the preceding master and the leading edge of the next following master. For this purpose the second clamping means are combined with severing means.

Some Recent MIT Research on Dynamic Stall

Abstract: OME recent research on airfoil dynamic stall by members of the MIT Aeroelastic and Structures Research Laboratory is summarized below. This work tentatively defines the boundary-layer flow processes during dynamic stall. The initial work investigated the forward movement of the laminar separation point of an unsteady laminar boundary layer during rapid changes of angle of attack.1 The separation mechanism considered is shown in Fig. 1. The boundary layer is laminar initially, separates when it encounters the adverse pressure gradient in the vicinity of the airfoil leading edge, becomes turbulent, and reattaches, forming a separation bubble. The analysis included the calculation of the potential flow and the computation of the laminar boundary layer. In the unsteady calculations, a Joukowsky airfoil having the same leading-edge radius as the NACA 0012 airfoil was considered. A plot of the movement of the laminar separation point forward over the airfoil upper surface as angle of attack is increased at various rates is shown in Fig. 2. It is seen that the laminar separation point reached the airfoil leading edge at an angle of attack of about 9° for all rates considered. This result is due to the large adverse pressure gradient near the leading edge at large angles of attack; the boundary layer for either the steady or unsteady case cannot overcome this large gradient and thus separates. Theoretical variation of the airfoil pitching axis location from the airfoil leading edge to the three-quarter chord point had negligible influence on the position of the laminar separation point for the typical rates and pitching axis locations considered, since the effect of pitching-axis location on the potential flow was small. One purpose of these calculations was the prediction of the unusual dynamic stalling behavior of the wing tested by Garelick.2 The wing tested had an NACA 0012 airfoil section, 5-in. chord and 42-in. span between side-walls, with

Stress wave emission defect location system

Abstract: The invention is a system for determining the location of defects in structures, using a suitable programmed computer, in which a number of transducers are placed at different locations in the structure to pick up the bursts of stress wave emission produced by the defects and to determine the location of the defects from the differences in the times of arrival of the burst at the various transducers, the arrival of each burst being determined by a peak level sensing circuit rather than by leading edge triggering, as used in previous systems

Dynamically induced fracture

Abstract: Expressions are presented for the stresses generated in the vicinity of a crack tip when a plane transient tension-stress wave, which is incident under an arbitrary angle, is diffracted by the crack. The effect of ductility effects on the combined Mode I and Mode II fractures is examined by assuming that yielding is restricted to a thin strip in the plane of the crack. Within this zone of yielding the normal stress in a certain defined direction is set equal to a yield stress of the material. It is shown that for a step-stress wave the leading edge of the zone of yielding initially moves at a constant speed, which is computed. The time for rupture at the trailing edge of the zone of yielding is also determined.

Rotor blade shear reinforcement

Abstract: Stiffness and shear resistance necessary for a helicopter rotor blade is provided by a first honeycomb cellular structure whose cells extend across the blade thickness and which structure spans at least that portion of the blade chord which includes the longitudinal boundary between a leading edge spar and a trailing edge skin section and a second honeycomb cellular structure joined to the trailing edge of the first structure of density less than the density of the first cellular structure. The front leading edge spar is joined to an upper trailing skin and a lower trailing skin which join at a trailing edge seam. The honeycomb sections are enclosed within the leading edge spar and a tapering chamber formed by the upper and lower skins.

Aircraft wing structure and method of assembly

Abstract: An aircraft wing comprising an upper shell and a lower shell secured together to form a complete wing. The wing is of metal construction particularly adapted for assembly on an automobile rivetting machine, the use of two pre-assembled shells providing the necessary access to both sides for the rivetting machine to operate. The upper shell includes the top skin, ribs, spars and leading edge assembled in accurate airfoil configuration, the lower shell comprising the lower skin with attached stiffeners conforming to the lower contour of the airfoil section. Assembly of the shells is made primarily by blind rivets with conventional solid rivets where accessible.

Control unit for minimizing water and power consumption in automatic film processors

Abstract: An automatic film processor is provided with a control system for inhibiting the drier heater and blower motor circuits unless film is being transported through the processor, to save electrical power, and to prevent wash water from flowing to waste except while film is being transported, in order to effect reduction of water consumption. The control system includes a pulse generator producing a train of pulses related to the rate of film transport through the processor; a film feed sensor for monitoring the presence or absence of a sheet of film at the input tray of the processor; a first counter, preferably taking the form of a slow integrator, which is activated by passage of the trailing edge of a sheet of film past the film feed sensor and which operates to count pulses from the transport pulse generator to produce an output signal operative to energize the drier heater and blower motor circuits and water solenoid for a period of time, determined by the transport speed and film length, sufficient to allow the trailing edge of the film to reach the catch tray at the output of the processor; and a second counter, preferably taking the form of a fast integrator, activated by passage of the trailing edge of the sheet of film past the film feed sensor for counting a series of pulses from the transport pulse generator and operative to indicate when a further sheet of film can be fed into the processor with constant trailing edge to leading edge space separation between the film sheets.

Computation of transonic flow about finite lifting wings.

Abstract: The results of Murman and Krupp (1971) are used to develop a procedure for computing a transonic flow about a finite lifting wing. A small disturbance equation describing the velocity potential of three-dimensional wings is solved in the process. The procedure is applied to a wing with a symmetric biconvex airfoil section in a zero-incidence subsonic flow, to a supersonic rectangular lifting wing with a sharp leading edge and to a subcritical nonlifting rectangular wing with a blunt leading edge.

Numerical Method for Hypersonic Internal Flow over Blunt Leading Edges and Two Blunt Bodies

Abstract: The steady-state solution of mixed subsonic-supersonic flow near a blunt leading edge in hypersonic internal flow and supersonic flow over two blunt bodies is obtained as an asymptotic solution of the unsteady equations of motion by a time-dependent method. The continuous flow region between the shock and the body is calculated by the method of finite differences and exact boundary conditions are applied using the two-dimensional, unsteady, method of characteristics. Numerical results are presented for two-dimensional and axisymmetric flows with a continuously curved shock and shock interacting at the axis of symmetry as Mach or regular interaction. The shock wave configuration is found to be dependent on freestreain Mach number, leading edge shape and bluntness. Theoretical calculations for inviscid, perfect gas are compared with experimental data, obtained in a hypersonic gun tunnel at a freestream Mach number of 8.33, for leading edge shapes of circular cross section.

Navigational and collision avoidance apparatus

Abstract: Marine surface radar processing equipment provides digitized target range pulses at a plurality of ranges, and includes target evaluation apparatus that comprises target leading edge signal means providing a target leading edge signal pulse at successive azimuths, and target trailing edge signal means providing a target trailing edge signal pulse at successive azimuths and initially separated in range from the target leading edge signal. The edge signal pulses describe a target envelope. The coincidence in range of a leading edge signal pulse and a trailing edge signal pulse provides a target envelope end recognition signal. The target evaluation apparatus further comprises discriminating means responsive to a maximum number of target leading edge signal pulses at successive azimuth intervals. The maximum number decreases at successively increasing ranges. The discriminating means discriminates between landmass targets of greater than a predetermined actual length in azimuth representing a maximum ship length, and possible ship targets of less than the predetermined actual length in azimuth. The discriminating means provides a discriminated target output signal responsive to possible ship targets of less than the predetermined length for display of ship targets with their speed and course vectors.