Showing papers on "Leading edge published in 1993"

An aerodynamic model for flapping-wing flight

Abstract: A design-oriented model for the unsteady aerodynamics of a flapping wing has been developed using a modified strip theory approach. Within this constraint, vortex-wake effects are accounted for as well as partial leading edge suction and post stall behaviour. Also, the contributions of sectional mean angle of attack, camber, and friction drag are added, which allows this model to be used for the calculation of the average lift, as well as the thrust, power required, and propulsive efficiency of a flapping wing in equilibrium flight. An example of such calculations is presented in the performance prediction of a mechanical flying pterosaur replica.

On the aerodynamics of birds’ tails

Abstract: The aerodynamic properties of a bird’s tail, and the forces produced by it, can be predicted by using slender lifting surface theory. The results of the model show that unlike conventional wings, which generate lift proportional to their area, the lift generated by the tail is proportional to the square of its maximum continuous span. Lift is unaffected by substantial variations in tail shape provided that the tail initially expands in width along the direction of flow. Behind the point of maximum width of the tail the flow is dominated by the wake of the forward section. Any area behind this point therefore causes only drag, not lift. The centre of lift is at the centre of area of the part of the tail in front of the point of maximum width. The moment arm of the tail, about its apex, is therefore more than twice the moment arm of a conventional wing about its leading edge. The drag of the tail is a combination of induced drag proportional to lift, and profile drag proportional to surface area. Induced drag can be halved by drooping the outer tail feathers to generate leading edge suction. This may be used for control, particularly in slow flight when both wings and tail are generating maximum lift. The slender lifting surface model is very accurate at angles of attack below about 15°. At higher angles of attack vortex formation at the leading edge can stabilize the flow over the tail and thereby generate increased lift by a detached vortex mechanism. Asymmetry in the orientation of the leading edges with relation to the freestream (either in roll, yaw or caused by asymmetry in the planform) is amplified in the flow field and leads to large rolling and yawing forces that could be used for control in turning manoeuvres. The slender lifting surface model can be used to examine the effect of variations in tail shape and tail spread on the aerodynamic performance of the tail. A forked tail that has a triangular planform when spread to just over 120° gives the best aerodynamic performance and this may be close to a universal optimum, in terms of aerodynamic efficiency, for a means to control pitch and yaw. However, natural selection may act to optimise the performance of the tail when it is not widely spread. The tail is normally only widely spread during manoeuvres, or at low speeds, selection may act to improve the efficiency of the tail when it is spread to only a relatively narrow angle - for example to maximize the bird’s overall lift to drag ratio - the optimum shape at any angle of spread is that which gives a straight trailing edge to the tail. This will always give a slightly forked planform, but fork depth will depend on how widely the tail is spread when selection acts, and this depends on the criteria for optimization under natural selection. A forked tail is more sensitive to changes in angle of attack and angle of spread, than other tail types. Forked tails are more susceptible to damage than other tail morphologies, and suffer a greater loss of performance following damage. Forked tails also confer less inherent stability than any other type of tail. Aerodynamic performance may not be an im portant optimization criterion for birds that fly in a cluttered environment, or do not fly very much. Natural selection, under these conditions, may favour tails of other shapes. The aerodynamic costs of sexually selected elongated tails can be predicted from the model. These predictions can be used to distinguish between the various models for the evolution of elongated tails. Elongated graduated tails and pintails could have evolved either through a Fisherian or H andicap mechanism. The evolution of long forked tails can be initially favoured by natural selection, the pattern of feather elongation seen in sexually selected forked tails is predicted by the Fisher hypothesis (Fisher 1930) but not by any of the other theories of sexual selection.

Dual capacitor biphasic defibrillator waveform generator employing selective connection of capacitors for each phase

Abstract: An implantable defibrillator/cardioverter which generates a biphasic defibrillation/cardioversion waveform including a pulse generator comprising two capacitors and a pair of switches for connecting the capacitors in parallel during a first phase and in series during a second phase. The first phase has a small "tilt" between the leading edge voltage and the trailing edge voltage. The second phase has a leading edge voltage which is approximately twice the trailing edge voltage of the first phase.

Coolable airfoil structure

Abstract: A coolable airfoil (10) having a plurality of spanwisely extending passages is disclosed. Various construction details are developed to increase the cooling effectiveness of the internal structure and decrease the need for cooling air. In one particular embodiment, a leading edge passage (56) has film cooling air flowing over the passage to shelter the passage from the hot working medium gases. This sheltered cooling air is then mixed with heated cooling air from a tortuous passage (84, 92) flowing through the mid-chord region (68) of the blade. In one embodiment, the coating air is supplied to a chordwisely extending tip passage (74) to cool the airfoil tip region and is mixed in the passage (74).

Leading edge section and asymmetric twisting in the wings of flying butterflies (insecta, papilionoidea)

Abstract: Summary Insect wings are mounted on hinges, restricting the extent to which their bases can be supinated for the upstroke. The forewings of many insects therefore include devices that allow the distal part of the wing to twist relative to the base under aerodynamic loading in the upstroke, but restrict such twisting in the downstroke where the effect would be detrimental. In the broad forewings of butterflies, this asymmetric resistance to aerodynamic twisting seems to be a consequence of the curved section of the leading edge. The wing can be modelled as a cantilevered, thin cambered plate. Torsional tests on the forewings of four butterfly species and on a paper wing of curved section confirm the effect. Differences between the results for the four species appear to f it their morphological and kinematic differences. The nature of the mechanism is outlined.

Measurements of Circulation and Vorticity in the Leading-Edge Vortex of a Delta Wing

Abstract: The present cross-wire measurements of the flowfield above a 75-deg flat-plate delta wing have yielded distributions of velocity, axial vorticity, and circulation which exhibit strongly conical behavior upstream of the breakdown region and away from the apex and trailing edge regions. The conical character of these properties is most pronounced over the central portion of the planform, away from the apex and trailing-edge regions. This behavior is further documented by the roughly linear increase in vortex strength with distance from the apex over the forward area of the wing.

Control of vortices on a delta wing by leading-edge injection

Abstract: This experimental investigation addresses the control of flow past a half-delta wing at high angle of attack. Application of steady blowing, steady suction, or alternate suction-blowing in the tangential direction along the leading edge of the wing can retard substantially the onset of vortex breakdown and stall. The most effective period of the alternate suction-blowing is on the order of one convective time scale of the flow past the wing. As a result of this type of control, the vortex structure in the crossflow plane is modified from a fully stalled condition to a highly coherent leading-edge vortex. This transformation to a restabilized vortex is represented by instantaneous velocity fields, streamline patterns, and vorticity contours

Observational test of hot flow anomaly formation by the interaction of a magnetic discontinuity with the bow shock

Abstract: The formation of a hot flow anomaly (HFA) observed near the Earth's bow shock appears to be due to the interaction between the bow shock and an impinging discontinuity in the upstream plasma Recent single-particle and 2D hybrid numerical studies have suggested that such an interaction will produce an HFA only if the motional electric field in the ambient plasma points toward the discontinuity, thereby focusing shock-reflected ions into it We perform a test of this electric field orientation for a set of nine HFA events observed by the ISEE spacecraft and described previously in the literature Under the assumption that the discontinuities were tangential, the predicted electric field orientation is found on at least one side of all nine observed HFAs (on the trailing edge of seven and the leading edge of five, and on both sides of three events) Further, there is evidence that asymmetries in the observed magnetic field signatures are related to the orientation of the motional electric field The events in which the electric field points toward the discontinuity on both sides tend to be those with fairly symmetric flanking magnetic field enhancements

Phase shifter for fine tuning a microwave applicator

Abstract: A phase shifter for shifting the phase angle of microwaves traveling in a waveguide of a microwave circuit. The phase shifter includes a dielectric plate which has first and second parallel surfaces, a distal edge, a proximate edge, a leading edge, and a trailing edge where each of the edges defines the outer bounds of the first and second parallel surfaces. The dielectric plate is shaped like a parallelogram lacking any right angles and is made of a microwave low loss dielectric material such as polystyrene or polytetrafluoroethylene. The height of the dielectric plate is less than one half the height of the waveguide side wall and the length is less than one guide wavelength long. The phase shifter fine tunes a resonating microwave circuit and provides approximately three-quarters of an inch adjustment of microwave circuit length.

Gas turbine vane

Abstract: A vane for the turbine section of a gas turbine has an airfoil portion with leading edge, center and trailing edge portions. The leading edge portion is attached to the center portion by a dove tail joint that allows the leading edge portion to slide in the radial direction with respect to the center portion while preventing movement in the axial and circumferential directions, thereby eliminating thermal stresses created by differential thermal expansion between the leading edge portion and the remainder of the vane. An opening in the vane inner shroud that is normally sealed by a closure plate allows the leading edge portion to be readily replaced in the event of damage. The leading edge portion may be formed from a ceramic material and need not be supplied with cooling air.

Air bearing slider with relieved rail ends

Abstract: A self-loading slider supports a transducer proximate a rotating disc. The slider includes a slider body having a leading edge, a trailing edge and first and second side edges. First and second side rails are positioned along the first and second side edges, respectively. The first and second side rails form coplanar air bearing surfaces. A cross rail extends between the first and second side rails to form a negative pressure cavity between the cross rail, the trailing edge and the first and second side rails. First and second trailing edge reliefs are formed within the first and second side rails, respectively. Each relief extends into a portion of the side rail from the negative pressure cavity, at the trailing edge to form first and second rail end portions adjacent the first and second side edges. The first and second rail end portions extend the air bearing surfaces to the trailing edge of the slider.

Experimental Study on the Three-Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part I—Velocity and Pressure Fields

Abstract: Experimental results from a study of the three-dimensional flow in a linear compressor cascade with stationary endwall at design conditions are presented for tip clearance levels of 1.0, 2.0, and 3.3 percent of chord, compared with the no-clearance case. In addition to five-hole probe measurements, extensive surface flow visualizations are conducted. It is observed that for the smaller clearance cases a weak horseshoe vortex forms in the front of the blade leading edge. At all the tip gap cases, a multiple tip vortex structure with three discrete vortices around the midchord is found. The tip leakage vortex core is well defined after the midchord but does not cover a significant area in traverse planes. The presence of the tip leakage vortex results in the passage vortex moving close to the endwall and the suction side.

Atraumatic needle for lumbar puncture

Abstract: An elongated, hollow spinal needle that is less prone to causing postdural puncture headache by having a modified, pencil-like point with a rounded shoulder at the juncture between the modified, pencil-like point and the body of the spinal needle. A side port is formed in the hollow needle at a position adjacent the rounded shoulder. The leading edge of the side port is located not more than 1.5 times the external diameter of the hollow needle from the tip of the pencil-like point to reduce the bending moment between the tip and the side port. The cross sectional area of the side port is configured to be equal to or incrementally larger than the cross sectional area of the lumen of the hollow needle.

Experimental Study on the Three-Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part II—The Tip Leakage Vortex

Abstract: An analysis of the experimental data of a linear compressor cascade with tip clearance is presented with special attention to the development of the tip leakage vortex. A method for determining the tip vortex core size, center position, and vorticity or circulation from the measured data is proposed, based on the assumption of a circular tip vortex core. It is observed that the axial velocity profile passing through the tip vortex center is wakelike. The vorticity of the tip vortex increases rapidly near the leading edge and reaches its highest values at a short distance downstream, from which it gradually decreases. In the whole evolution, its size is growing and its center is moving away from both the suction surface and the endwall, approximately in a linear way

Steam and air cooling for stator stage of a turbine

Abstract: The second-stage nozzles include a plurality of stator vanes 10 having first, second, third, fourth and fifth passages 40, 42, 44, 46 and 48, respectively, for cooling the vanes. The first and fourth passages have a steam inlet along an outer sidewall 14 and a junction box 70 along the inner sidewall 12 for returning steam to the second passage 42. The third passage 44 has a contour corresponding to the contour of the leading edge and impingement steam is directed through openings in a partition 52, cooling the leading edge. Steam flows from the third passage 44 directly into the return passage 42 and also into a channel 64 for cooling the inner sidewall 12. Cooling air flows through fifth passage 48 radially inwardly through the inner sidewall 12 into a cavity 72 in the diaphragm 32 for flow axially outwardly into wheel cavities 86 and 88.

Vertical takeoff and landing (VTOL) flying disc

Abstract: A flying disc capable of vertical takeoff, hovering, or powered horizontal flight. The aircraft configuration comprises a circular disc-like airfoil-shaped wing structure having a convex upper surface and a concave lower surface with a leading edge and a trailing edge. At least one thrust-producing unit is attached at each of the leading and trailing edges, respectively. A plurality of other thrust-producing units are mounted symmetrically about the circular wing structure. Each thrust-producing unit has attached thereto a thrust deflector assembly for angularly adjusting the thrust produced by the thrust-producing unit, thereby allowing the aircraft to fly both vertically and horizontally. A substantial volume of helium gas is stored encompassing the inner upper hull of the aircraft, thereby giving the flying disc greater lift capacity. The outer skin of the upper surface consists essentially of a plurality of solar panels for delivering power to a multiplicity of devices.

Leading Edge Separation Bubbles on Turbomachine Blades

Abstract: Results are presented for separation bubbles of the type that can form near the leading edges of thin compressor or turbine blades. These often occur when the incidence is such that the stagnation point is not on the nose of the aerofoil. Tests were carried out at low speed on a single aerofoil to simulate the range of conditions found on compressor blades. Both circular and elliptic shapes of leading edge were tested. Results are presented for a range of incidence, Reynolds number, and turbulence intensity and scale. The principal quantitative measurements presented are the pressure distributions in the leading edge and bubble region, as well as the boundary layer properties at a fixed distance downstream, where most of the flows had reattached. Reynolds number was found to have a comparatively small influence, but a raised level of free-stream turbulence has a striking effect, shortening or eliminating the bubble and increasing the magnitude of the suction spike. Increased free-stream turbulence also reduces the boundary layer thickness and shape parameter after the bubble. Some explanations of the processes are outlined

Orbitting nip plural mode sheet output with faceup or facedown stacking

Abstract: In a system of transporting sheets in an output path of a copier or printer to a sheet stacking area with opposing first and second sheet feeding rollers forming a sheet transporting nip engaging the leading edge of a sheet, while producing a relative orbital motion of the opposing rollers to progressively pivot the nip and thereby change the angular direction of motion of the leading edge of the sheet, plural mode selectable operation of this pivotal motion is provided. There is a selection between faceup and facedown stacking of the sheets by one selectable orbital motion of the nip. This selected orbital motion pivots the nip by greater than 90 degrees with the sheet's leading edge held in the nip, so that subsequently, the leading edge of the sheet is moving in a direction substantially different from the direction of motion of the leading edge when the leading edge first entered the nip, and the sheet is inverted. Another selectable orbital motion of the nip pivots the nip to feed the sheet into a separate area for further sheet processing. Another selectable orbital motion of the nip pivots the nip in the opposite direction to feed the sheet into a top stacking tray. Other selectable movements of the same orbiting nip unit can provide other output selections, such as a duplexing or highlight color sheet return, all without requiring any moving gates or baffles, and with positive sheet control.

Turbine vane assembly with integrally cast cooling fluid nozzle

Abstract: A gas turbine engine having a turbine vane assembly including an integrally cast cooling fluid nozzle (86) is disclosed. Various construction details are developed which disclose a cooling fluid nozzle including a flow passage (108) having an exit (112) and a wall means (114). In one embodiment, the wall means includes an angled leading edge (118) which mates with a circumferentially adjacent trailing edge (122) of an adjacent wall means. The leading edge is tapered such that in a most open position of the turbine vane assembly the leading edge and the trailing edge circumferentially align. In a most closed position of the turbine vane assembly, the angled leading edge aligns with the trailing edge such that a step down is created in the circumferentially directed flow of the sealed cavity. The plurality of wall means thereby produce a waterfall arrangement within the sealed cavity to reduce the windage losses.

Air bearing magnetic head sliders.

Abstract: The air bearing surface (ABS) of a head slider is formed with configured rails and leading edge tapers. In implementations of the invention, two side rails extend only partially from leading edge tapers to the slider trailing edge. The inner edges of each side rail are formed with at least two opposing angles so that at least two rail sections vary in width along the length of the rail. Each side rail is shaped with an oblique angle to reduce the rail width and a reverse angle to form the sections of differing widths. The leading edge side tapers may be angled for control of pitch stiffness of the slider. In one embodiment of the invention, a third center rail extends from a center taper to the slider trailing edge where the transducer is located. In another embodiment, a short center pad is provided at the trailing edge. In an alternative design, only two side rails are used without a center rail or pad. The ABS geometries disclosed herein include angled rail sections that provide controlled pitch and constant flying height during transducing operation in a disk drive.

Interferometric investigations of compressible dynamic stall over a transiently pitching airfoil

Abstract: The compressible dynamic stall flowfield over a NACA 0012 airfoil transiently pitching from 0 to 60 deg at a constant rate under compressible flow conditions has been studied using real-time interferometry. A quantitative description of the overall flowfield, including the finer details of dynamic stall vortex formation, growth, and the concomitant changes in the airfoil pressure distribution, has been provided by analyzing the interferograms. For Mach numbers above 0.4, small multiple shocks appear near the leading edge and are present through the initial stages of dynamic stall. Dynamic stall was found to occur coincidentally with the bursting of the separation bubble over the airfoil. Compressibility was found to confine the dynamic stall vortical structure closer to the airfoil surface. The measurements show that the peak suction pressure coefficient drops with increasing freestream Mach number, and also it lags the steady flow values at any given angle of attack. As the dynamic stall vortex is shed, an anti-clockwise vortex is induced near the trailing edge, which actively interacts with the post-stall flow.

Hinge fairings for control surfaces

Abstract: A new hinge fairing design for control surfaces such as ailerons, elevators, and rudders. By staggering the two curved hinge fairings, one mounted to the fixed airfoil and the other to the leading edge of the control surface, a curving load path is opened up that allows installation of hinge fittings and actuators without having to make cut-outs in the curved fairings. This principle makes it possible to keep the control surface faired and sealed over its entire span and during its entire motion range. This improves the effectiveness of the control surface. The principle of the present invention is applicable to trailing edge control surfaces of subsonic and supersonic airplanes and is of particular benefit for hinged leading edge flaps on a supersonic commercial transport.

Three-dimensional boundary-layer instability and separation induced by small-amplitude streamwise vorticity in the upstream flow

Abstract: We consider the effects of a small-amplitude, steady, streamwise vorticity field on the flow over an infinitely thin flat plate in an otherwise uniform stream. We show how the initially linear perturbation, ultimately leads to a small-amplitude but nonlinear cross flow far downstream from the leading edge. This motion is imposed on the boundary-layer flow and eventually causes the boundary layer to separate. The streamwise velocity profiles within the boundary layer become inflexional in localized spanwise regions just upstream of the separation point. The flow in these regions is therefore susceptible to rapidly growing inviscid instabilities.

Light weight steam turbine blade

Abstract: A steam turbine blade is provided in which the geometry of the blade airfoil is configured to reduce the weight of the blade while maintaining adequate thermodynamic performance. The blade has a high camber angle to increase its stiffness and an airfoil portion having pressure and suction surfaces. The curvature of the portion of the pressure surface between the base and 75% blade height has a point of inflection in an area adjacent the leading edge so that the curvature switches sign. The curvature upstream of the point of inflection is concave, while the curvature downstream of the point of inflection is convex.

Cooled turbo-machine vane

Abstract: A turbo-machine vane having a plurality of internal cavities for the flow of a cooling fluid, and a plurality of openings through the outer wall of the vane for communicating the internal cavities with the outside of the vane. Two rows of openings are provided in the leading edge of the vane, one row on each side of the central line of the leading edge end extending parallel with the central line, and each opening of each row is oriented to direct cooling fluid which flows through it from the interior of the vane away from the central line relative to the rows.

Micro-grooved heat transfer wall

Abstract: A gas turbine engine hot section component such as a turbine blade or vane having an airfoil is provided a non-film cooled portion of a heat transfer wall having a hot surface and a plurality of longitudinally extending micro-grooves disposed in the portion of the wall along the hot surface in a direction parallel to the direction of the hot gas flow. The depth of the micro-grooves is very small and on the order of magnitude of a predetermined laminar sublayer of a turbulent boundary layer. The grooves are sized so as to alter the boundary layer thickness near the leading edge of the airfoil to reduce heat transfer from the hot gas flow to the airfoil near the leading edge. In one embodiment the micro-grooves are about 0.001 inches deep and have a preferred depth range of from about 0.001 inches to 0.005 inches and which are square, rectangular, or triangular in cross-section and the micro-grooves are spaced about one width apart.

High-efficiency, supersonic aircraft

Abstract: A supersonic flight aircraft having a longitudinally forwardly extending axis in the direction of flight, and a wing (11, 12) comprising a wing (11, 12) extending generally laterally relative to the axis, and having a leading edge (13, 14) angled forward or rearwardly relative to a normal to the axis at an angle (Μ), and the wing (11, 12) having a maximum thickness (t); the angle (Μ) and thickness (t) characterized in that in supersonic flight conditions, the forwardmost shock wave produced in association with the wing (11, 12) extends generally along or rearwardly of the leading edge (13, 14) whereby laminar airflow conditions are maintained over the leading edge (13, 14) and adjacent the surface of the wing (11, 12).

Supersonic aircraft and method

Abstract: A supersonic aircraft having highly swept subsonic leading edge portions of the wings provided with boundary layer control suction slots. When the airplane is operating at high angles of attack under circumstances where noise is objectionable, air is drawn in through the suction strips to alleviate separated air flow and substantially eliminate (or at least alleviate) vortices that would otherwise develop over the upper wing surface. This improves the L/D ratio and permits the engines to be at a lower power setting, thus alleviating noise. There are shown a double delta planform configuration, and an arrow plan form configuration. Also, the boundary layer control suction can be used in conjunction with laminar flow control suction.