Showing papers on "Leading edge published in 1987"

Method and apparatus for information recording and reproduction of a pit-shape-forming optical recording type

Abstract: A method and an apparatus for recording and reproducing information for use with an optical disk apparatus in which a pit edge recording method is used. According to the pit edge recording method, the leading edge and the trailing edge of a hole pit or a record domain generated during a recording operation are dealt with as information. During the recording, the recording pulse width and the recording power are corrected, and during the reproduction, the variation in the edge position is corrected.

Scattering of electrons by intense coherent light.

Abstract: We report the first direct observation of electron inelastic scattering from the pondermotive potential of an intense laser pulse in vacuum. Electrons gained up to 0.2 eV when scattered from the temporal leading edge of a 1064-nm (1.165 eV), 140-psec laser pulse, and lost comparable amounts of energy when scattered from the trailing edge. When directed to the most intense part of the pulse, they were deflected out of the beam.

Lift-curve characteristics for an airfoil pitching at constant rate

Abstract: This paper reports the results of wind-tunnel studies of dynamic stall for an NACA 0015 airfoil pitching about the midchord at a constant rate. Time-varying pressure readings from 16 locations on the airfoil were collected and used to determine the lift, pressure-drag, and moment coefficients as functions of angle of attack for 100 test cases, covering 20 dynamic airspeed/pitch rate combinations. The dynamic-stall effects of the change (from steady flow) in the angle of attack at which separation occurs at the quarter chord and the change in the angle of attack at which stall occurs were extracted from these data and found to collapse onto a nondimensional pitch rate given by the chord times the pitch rate divided by two times the freestream velocity. The results showed that relatively slow pitch rates had dramatic effects on both the delay of stall and the magnitude of the maximum lift coefficient. The nondimensional rate is a measure of the speed of the leading edge divided by the speed of the freestream; it was found that nondimensional rates of less than 0.03 more than doubled the maximum coefficient of lift. The reduced data also clearly indicate that quarter-chord separation is systematically linked to dynamic stall.

Experimental study of shock wave interference heating on a cylindrical leading edge

Abstract: An experimental study of shock wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet at Mach numbers of 6.3, 6.5, and 8.0 is presented. Stream Reynolds numbers ranged from 0.5 x 106 to 4.9 x 106 per ft. and stream total temperature ranged from 2100 to 3400 R. The model consisted of a 3" dia. cylinder and a shock generation wedge articulated to angles of 10, 12.5, and 15 deg. A fundamental understanding was obtained of the fluid mechanics of shock wave interference induced flow impingement on a cylindrical leading edge and the attendant surface pressure and heat flux distributions. The first detailed heat transfer rate and pressure distributions for two dimensional shock wave interference on a cylinder was provided along with insight into the effects of specific heat variation with temperature on the phenomena. Results show that the flow around a body in hypersonic flow is altered significantly by the shock wave interference pattern that is created by an oblique shock wave from an external source intersecting the bow shock wave produced in front of the body.

Aerothermodynamics of transatmospheric vehicles

Abstract: A transatmospheric vehicle (TAV) using airbreathing propulsion requires a long acceleration period within the denser part of the atmosphere to reach orbital speed. The long flight time, coupled with the need for a low-drag configuration, results in severe heating of parts of the vehicle. The ascent peak stagnation point and wing leading edge equilibrium wall temperatures are about 3500 K and 2500 K, respectively, likely requiring some form of mass addition cooling. The corresponding temperatures during entry are 1000 K lower. The vehicle windward centerline temperatures are more moderate, with values peaking around 1300 K during both ascent and entry. Therefore, radiative cooling should be effective over large areas of the vehicle. The windward centerline heat loads during entry are comparable to those for low acceleration ascent trajectories. However, ascent heat loads for the stagnation point and the wing leading edge are about three times higher than those during entry. For comparison, the entry heat load for the TAV's stagnation point is about three times higher than the value for Shuttle. Therefore the ascent heat load at the TAV's stagnation point exceeds the Shuttle's entry value by an order of magnitude.

A potential based panel method for the analysis of marine propellers in steady flow

Abstract: : A surface panel method suitable for the analysis of marine propellers is developed and applied to various geometries to demonstrate its effectiveness. A reliable pressure distribution around a marine propeller, especially near the leading edge of the blade, is obtained. Hub effects are naturally included by distributing panels on the hub surface. Detailed study of the flows at the trailing edge near the tip suggests a pressure Kutta condition, which requires the pressures of the last panels at the trailing edge be equal. Due to the nonlinear aspect of the pressure Kutta condition, an iterative process is employed. An efficient approximation of the ultimate wake is achieved by replacing it with a sink disk a the beginning of the ultimate wake. The sample geometries include an ellipsoid at zero angle of attack, a circular planform wing, a rectangular planform wing with varying sweep angles, a wing-body configuration, a long axisymmetric duct, and a marine propeller. Calculated pressure distributions around the wing-body configuration are in excellent agreement with the experimental data. Calculated thrust and torque for the propeller agree well experimental results.

Separation control over an airfoil at high angles of attack by sound emanating from the surface

Abstract: Active control by sound emanating from a narrow gap in the vicinity of the leading edge of a symmetrical airfoil is used to study the influence of sound on the pressure distribution and the wake at high angles of attack The results from experiments conducted at a Reynolds number based on the chord of 35,000 show that, with injection of sound at twice the shedding frequency of the shear layer, the region of separation becomes drastically reduced The shear layer is found to be very sensitive to sound excitation in the vicinity of the separation point The excitation sufficiently alters the global circulation to cause an increase in lift and reduction in drag Furthermore, experimental results describing stall and post-stall conditions compare well with the limited data available and indicate that stall is delayed by sound injection into the separated region

Characteristics of ejections in turbulent channel flow

Abstract: Quantitative measurements of the structure of ejections from the wall region have been made using conditional-sampling techniques. Discrete ejections from a burst event were identified using fluorescent-dye flow visualization simultaneously with streamwise, u, and normal, v, velocity measurements. These velocity measurements, at y+ = 15, were conditionally sampled based on different phases of the ejection event. Features of the ejection which were educed from the conditional sampling were found to be very sensitive to the phase alignment. Results showed that ejections were characterized by a rapid deceleration at the leading edge followed by a strong positive velocity gradient at the trailing edge. An intense second-quadrant uv spike occurred immediately following the leading edge. This uv peak was highly correlated with a positive peak in the v velocity. The first ejection which occurred in a burst was found to be significantly more intense than the following ejections. Many characteristics of bursts which have been obtained from previous conditional-sampling studies were found to correspond to different phases of the ejection event.

The effect of thin film variations and transverse curvature on the shape of fingers in a Hele–Shaw cell

Abstract: The steady‐state shape of a finger penetrating into a viscous fluid that fills the gap between two closely spaced parallel plates is examined. Boundary conditions that take into account variations in the thickness of the thin film and both transverse curvature (across the gap) and lateral curvature (along the interface edge) are applied at the leading edge of the interface. These interface conditions, derived from local solutions in the vicinity of the interface edge, depend on μUn/T, where μ is the viscosity of the original fluid, Un is the normal velocity of the interface edge, and T is the interfacial tension. They also depend on e/R, where e=b/a≪1 is the ratio of gap width to cell width and aR is the lateral radius of curvature. The problem is solved by conformally mapping the domain to a circle. By expanding the solution in terms of analytic functions and satisfying the boundary conditions, the shape of the interface edge and finger width λ are determined. The agreement between numerical and experime...

Sliding cover for truck bed

Abstract: A sliding cover assembly is provided primarily for a truck cargo bed. The sliding cover assembly is mounted on the top edge of the side walls of the cargo bed and includes a plurality of longitudinal, arcuate parallel-disposed rotatably interconnected slats which slide on a low friction surface within the guide means attached to the side walls of the cargo bed. The sliding cargo assembly further includes a lockplate attached to the leading edge of the sliding cover which secures the cover to the tailgate of the cargo bed.

Heat transfer in triangular channels with angled roughness ribs on two walls

Abstract: Leading edges of internally cooled gas turbine engine airfoils are often cooled convectively by flow through triangular cross-sectioned passages containing roughness ribs on two of their three sides. The roughness augments heat transfer coefficients and thereby increases the ability of the cooling air to cool the airfoil leading edge. Ribs are normally placed on the two sides of the passage that constitute forward sections of the airfoil pressure and suction surfaces, and the third side, a cooling passage divider or internal bulkhead, is usually left smooth. The present study is an experimental investigation of developing local convection heat transfer in triangular ducts with square ribs at various rib angles, orientations, and pitch-to-diameter ratios on two of the three channel walls in conjunction with a smooth third wall. Stream-wise development of spanwise-averaged Nusselt numbers is presented for both rough and smooth walls, along with typical spanwise variations. Results were obtained for...

Baldwin-Lomax factors for turbulent boundary layers in pressure gradients

Abstract: References Lan, C. E. and Hsu, C. H., "Effects of Vortex Breakdown on Longitudinal and Lateral Directional Aerodynamics of Slender Wings by the Suction Analogy," AIAA Paper 82-1385, 1982. Brown, C. E. and Michael, W. H., "Effects of Leading Edge Separation on the Lift of a Delta Wing," Journal of Aeronautic Science, Vol. 21, 1954, pp. 690-694. Smith, J. H. B., "A Theory of the Separated Flow from the Curved Leading Edge of a Slender Wing," A.R.C. RM 3116, 1959. Werle, H., "On Vortex Bursting," ONERA-NT-175, 1971. Wentz, W. H. and Kohlman, D. L., "Wind Tunnel Investigations of Vortex Breakdown on Slender Sharp-Edged Wings," NASA-CR98737, 1967. Zohar, Y. and Er-El, J., "The Effects of Vortex Breakdown on the Aerodynamic Characteristics of Delta Wings," Technion, Israel Institute of Technology, Aeronautical Research Center, Rept. 0-236, 1984.

On the structure of a turbulent spot in a heated laminar boundary layer

Abstract: An artificially generated turbulent spot was investigated experimentally in a heated boundary layer using a rake of mini-thermocouples. Simultaneous temperature traces were used to determine the spot's leading and trailing edge characteristics. The measurements on the centerline of the plate at a constant velocity and variable streamwise positions provided a Rex range of 2.45–12.6 x 105. At one axial station the free stream velocity was varied and off-axis measurements were obtained.

Method of adhering labels to containers

Abstract: We have disclosed a method of applying a plastic label to a container wherein a label is severed from the strip of polymer label material. A hot melt adhesive is applied to an area along the leading edge of the label and a solvent of the polymer is applied to an area along the trailing edge of said material to form a tacky solution. The label is then applied to a container so that when heat shrunk, the tacky solution solidifies and the hot melt adhesive crystalizes to release its grip on the container.

Temperature and pressure probe

Abstract: A pressure and temperature measuring probe with a low drag, airfoil shaped cross section includes a longitudinally extending pressure cavity adjacent the leading edge and a separate longitudinally extending temperature cavity immediately downstream thereof. Longitudinally spaced apart passages extend downstream from their inlets at pressure measuring stations along the leading edge and intersect the pressure cavity. At temperature measuring stations along the leading edge passages extend downstream adjacent the pressure cavity to intersect the temperature cavity and direct a high velocity flow of gases over a thermocouple junction disposed within the temperature cavity. Stagnation devices at the leading edge reduce gas velocity to zero at the passage inlets.

Method and apparatus for deicing a leading edge

Abstract: An airfoil deicer and method for deicing an airfoil wherein the deicer has an outer skin having an elevated modulus of elasticity and a means for introducing a small deflection into the outer skin thereby creating substantial chord-wise tension in the outer skin, the deflection being induced in less than 0.250 seconds. In the method of deicing, the deflection is induced periodically and being completed within a time span of about 0.250 seconds to remove accumulations of ice as thin as 0.06 centimeters.

Tilting pad thrust bearing with optimized tilt axis location

Abstract: A tilting pad thrust bearing in which the sector-shaped pads are supported on individual disks. A runner runs on top of the pads. The disks have a spherical element projecting from their bottoms. The elements make tangential contact with a stationary support ring and the pads and disks tilt about an axis on which the point of tangency lies. The tilt axis of each pad is located at 70% to 80% of the length of an arc extending from the leading edge to the trailing edge of the pad midway between the radially outermost and innermost edge of the pad.

Vertical velocities and dynamical balances in Gulf Stream meanders

Abstract: A triangular array of current meter moorings was deployed within the cyclonic flank of the Gulf Stream in the South Atlantic Bight from September 1981 to April 1982. Using velocity and temperature data and the nondiffusive heat equation, a time series of vertical velocity was derived. A mean vertical velocity of −0.013 cm s−1 and standard deviation of 0.078 cm s−1 were obtained. To better understand the subsurface structure of Gulf Stream meanders, the time series of horizontal and vertical velocities and temperature were examined at times when events were passing through the array. The flow along the trailing edge of a Gulf Stream meander and within the leading portion of a cold core frontal eddy was found to have an upward component (positive w), while that within the trailing portion of the frontal eddy and along the leading edge of a meander had a downward component (negative w). Using the horizontal and vertical velocity time series, cross-stream and along stream momentum balances were calculated. The downstream flow was found to be in geostrophic balance. In contrast, the Coriolis and nonlinear terms were found to contribute equally to the determination of the cross-stream flow.

Airfoils with leading edge pockets for reduced heat transfer

Abstract: A gas turbine engine airfoil leading edge includes depressions therein longitudinally spaced apart and centered on stagnation points. The depressions stay filled with relatively stationary air during engine operation and reduce the heat load at the leading edge, which is primarily cooled by an internal supply of cooling fluid.

Dynamic stall due to unsteady marginal separation

Abstract: A theoretical investigation into the next stage of dynamic stall, concerning the beginnings of eddy shedding from the boundary layer near an aerofoil's leading edge, is described by means of the unsteady viscous-inviscid interacting marginal separation of the boundary layer. The fully nonlinear stage studied in the present paper is shown to match with a previous weakly nonlinear regime occurring in the earlier development of the typical eddy from its initially slender thin state. Numerical solutions followed by linear and nonlinear analysis suggest that with confined initial conditions the strong instabilities in the present unsteady flow tend to force a breakdown within a finite time. This leads on subsequently to an unsteady predominantly in viscid stage where the eddy becomes non-slender, spans the entire boundary layer and its evolution then is governed by the Euler equations. This is likely to be followed by the shedding of the eddy from the boundary layer. © 1987, Cambridge University Press. All rights reserved.

Apparatus for milling metal powder to produce high bulk density fine metal powders

Abstract: Apparatus for milling metal powder in a mill is disclosed which comprises a central shaft, the top of which is rotatably mounted to rotating apparatus, bottom stirrer(s), attached to the bottom edge of central shaft, upper stirrer(s), attached above the point of attachment of the bottom stirrer(s), and two or more primary stirrers, upper ends of which are attached to outer edge(s) of the upper stirrer(s) and the bottom ends attached to bottom edge(s) of the bottom stirrer(s). The bottom stirrer has a downward sloping leading edge with a first angle formed by a first plane extending along this edge to a second plane extending along the bottom of the mill, this angle being 10° to 90°, the first angle being that between those faces of the first and second planes within which the bottom stirrer sits. The distance between the bottom of the mill and the lowest point of the downward sloping leading edge is equal to or less than the distance between the bottom of the mill and the other points on the bottom edge of the bottom stirrer. The upper stirrer has an upward sloping leading edge, with a second angle formed by a third plane extending along this edge to a fourth plane parallel to the top of the mill and above the upper stirrer(s), this angle being 10° to 90°, the second angle being that between those faces of the third and fourth planes within which the upper stirrer sits. The distance between the fourth plane and the uppermost point of the upward sloping leading edge is equal to or less than the distance between the fourth plane and the other point(s) on the top edge of the upper stirrer(s).

Aircraft stall-spin entry deterrent system

Abstract: A system for deterring subsonic airplane stall-spin entry wherein a highly swept wing tip mounted lifting surface panel 18 (FIGS. 1-3) is attached to the tip of a main wing panel 14 and provides a stabilizing vortex lift to the aircraft at an angle of attack slightly greater than the normal angle of attack used in climbing flight. This vortex lift enhances roll damping at high angles of attack and serves to prevent airplane stall-spin entry. FIG. 4 shows an alternate form of the invention wherein the wing tip mounted lifting surface panel 48 is provided with a forward highly swept leading edge. For sharp leading edges a leading edge sweep for the wing tip mounted lifting surfaces is approximately forty-five degrees while, for blunt leading edge surfaces, a greater degree of sweep is employed to generate the vortex lift.

Experimental study of the velocity field on a delta wing

Abstract: An experimental study of the leading edge vortices on delta wings at large angles of incidence is presented. A combination of flow visualization, seven-hole pressure probe surveys and laser velocimeter measurements were used to study the leading edge vortex formation and breakdown for a set of delta wings. The delta wing models were thin flat plates with sharp leading edges having sweep angles of 70, 75, 80, and 85 degrees. The flow structure was examined for angles of incidence from 10 to 40 degrees and chord Reynolds numbers from 85,000 to 640,000. Vortex breakdown was observed on all the wings tested. Both bubble and spiral modes of breakdown were observed. The visualization and wake survey data shows that when vortex breakdown occurs the core flow transforms abruptly from a jet-like flow to a wake-like flow. The result also revealed that probe induced vortex breakdown was more steady than the natural breakdown.

Housing for an axial compressor

Abstract: A housing for an axial compressor is disclosed having an inner and outer wall surrounding the compressor rotor, the walls being joined by a number of flexible connecting rods, connecting lugs and a connecting block. An outer surface of the inner wall has circumferentially extending corrugation and the rods are attached thereto at peaks in the corrugation. The flexible connecting rods are located in alignment with a leading edge and a trailing edge of stator vanes which extend from an inner surface of the inner wall. The housing may be cast as an integral, one piece element and subsequently subdivided into arcuate segments to facilitate attachment to the compressor.

Gas turbine engine airfoil

Abstract: A rotor blade for a gas turbine engine includes an airfoil that extends in span between a root and a tip region. A leading edge and a trailing edge of the airfoil section extend between a chord line of the airfoil. A sweep angle is defined at the leading edge of the airfoil section, and a dihedral angle is defined relative to the chord line of the airfoil section. The sweep angle and the dihedral angle are localized at the tip region of the airfoil section.

A Study of the Leading Edge Vortex and Tip Vortex on Prop-Fan Blades

Abstract: An oil flow visualization study was conducted on the blades of a counterrotating prop-fan model, the CRP-X1. A kink in the oil streaks was interpreted as an indication of the leading edge vortex reattachment line. The leading edge vortex was found to be on the lower surface for cases with negative leading edge loading and on the upper surface for cases with positive leading edge loading. For most cases, the leading edge vortex merged with a tip vortex. The results presented here represent the first systematic study of this phenomenon.

Angle mount header

Abstract: There is disclosed a light emitting device which includes a header and an angle stripe light emitting diode. The header has a longitudinal axis and a forward mounting surface. The forward mounting surface includes a leading edge portion which extends perpendicular to the longitudinal axis. The mounting surface further includes a trailing alignment edge portion which extends rearwardly from the leading edge portion at a predetermined compensating angle. The light emitting diode is affixed in electrical and heat transfer relation to the mounting surface of the header such that the emitting facet is aligned with the trailing alignment edge portion of the header. The trailing alignment edge portion compensates for the offset angle that light is emitted from a stripe light emitting diode.

Slender delta wing at high angles of attack - A flow visualization study

Abstract: The flow past a delta wing of aspect ratio one is examined at angles of attack ranging from 25 deg to 90 deg. On the basis of detailed observations of the flow in a water channel, using laser-induced fluorescence, four angle of attack flow regimes are identified, in addition to the well known regime of a stable pair of leading edge vortices. These are: a regime where the two leading edge vortices break down independently, primarily into the spiral form; a regime where spiral and bubble breakdowns alternate periodically on the two sides of the wing, accompanied by an antisymmetric motion in the chordwise direction of the two points of breakdown; a regime where a single streamwise vortex springing from the wing apex alternates in sign at irregular intervals; and finally, a regime dominated by a wake bubble and the relatively small scale vortices arising from the instability of its boundary.

Self-sharpening mower blade

Abstract: A blade for a rotary mower comprising an elongated, flat metallic member having first and second ends and a central aperture for mounting the member on a shaft for rotation in a cutting plane, each of the first and second ends having a leading cutting edge and a trailing cutting edge, the leading cutting edge being formed on a downturned portion of a leading edge of the metal member when the member is rotating in the cutting plane and the trailing cutting edge being formed on an upturned portion of an edge opposite the leading edge, the downturned portion being angled between 15 and 45 degrees with respect to the cutting plane. The blade may include air dams formed on upper and lower surfaces, respectively, of the member parallel to and coterminous with the cutting edges. In another form, the blade may have first and second end portions forming extensions oppositely directed from a central portion, each of the end portions being angularly oriented with respect to the cutting plane, cutting edges being formed on the end portions, the cutting edges being defined by the angular orientation of the end portions with the cutting plane.

Simulated airline service experience with laminar-flow control leading-edge systems

Abstract: The first JetStar leading edge flight test was made November 30, 1983. The JetStar was flown for more than 3 years. The titanium leading edge test articles today remain in virtually the same condition as they were in on that first flight. No degradation of laminar flow performance has occurred as a result of service. The JetStar simulated airline service flights have demonstrated that effective, practical leading edge systems are available for future commercial transports. Specific conclusions based on the results of the simulated airline service test program are summarized.