Showing papers on "Leading edge published in 1970"

Aquatic animal propulsion of high hydromechanical efficiency

Abstract: This paper attempts to emulate the great study by Goldstein (1929) ‘On the vortex wake of a screw propeller’, by looking for a dynamical theory of how another type of propulsion system has evolved towards ever higher performance. An ‘undulatory’ mode of animal propulsion in water is rather common among invertebrates, and this paper offers a preliminary quantitative analysis of how a series of modifications of that basic undulatory mode, found in the vertebrates (and especially in the fishes), tends to improve speed and hydromechanical efficiency.Posterior lateral compression is the most important of these. It is studied first in ‘pure anguilliform’ (eel-like) motion of fishes whose posterior cross-sections are laterally compressed, although maintaining their depth (while the body tapers) by means of long continuous dorsal and ventral fins all the way to a vertical ‘trailing edge’. Lateral motion of such a cross-section produces a large and immediate exchange of momentum with a considerable ‘virtual mass’ of water near it.In § 2, ‘elongated-body theory’ (an extended version of inviscid slender-body theory) is developed in detail for pure anguilliform motion and subjected to several careful checks and critical studies. Provided that longitudinal variation of cross-sectional properties is slow on a scale of the cross-sectional depth s (say, if the wavelength of significant harmonic components of that variation exceeds 5s), the basic approach is applicable and lateral water momentum per unit length is closely proportional to the square of the local cross-section depth.The vertical trailing edge can be thought of as acting with a lateral force on the wake through lateral water momentum shed as the fish moves on. The fish's mean rate of working is the mean product of this lateral force with the lateral component of trailing-edge movement, and is enhanced by the virtual-mass effect, which makes for good correlation between lateral movement and local water momentum. The mean rate of shedding of energy of lateral water motions into the vortex wake represents the wasted element in this mean rate of working, and it is from the difference of these two rates that thrust and efficiency can best be calculated.Section 3, still from the standpoint of inviscid theory, studies the effect of any development of discrete dorsal and ventral fins, through calculations on vortex sheets shed by fins. A multiplicity of discrete dorsal (or ventral) fins might be thought to destroy the slow variation of cross-sectional properties on which elongated-body theory depends, but the vortex sheets filling the gaps between them are shown to maintain continuity rather effectively, avoiding thrust reduction and permitting a slight decrease in drag.Further advantage may accrue from a modification of such a system in which (while essentially anguilliform movement is retained) the anterior dorsal and ventral fins become the only prominent ones. Vortex sheets in the gaps between them and the caudal fin may largely be reabsorbed into the caudal-fin boundary layer, without any significant increase in wasted wake energy. The mean rate of working can be improved, however, because the trailing edges of the dorsal and ventral fins do work that is not cancelled at the caudal fin's leading edge, as phase shifts destroy the correlation of that edge's lateral movement with the vortex-sheet momentum reabsorbed there.Tentative improvements to elongated-body theory through taking into account lateral forces of viscous origin are made in §4. These add to both the momentumandenergyof the water's lateral motions, but mayreduce the efficiencyof anguilliform motion because the extra momentum at the trailing edge, resulting from forces exerted by anterior sections, is badly correlated with that edge's lateral movements. Adoption of the ‘carangiform’ mode, in which the amplitude of the basic undulation grows steeply from almost zero over the first half or even two-thirds of a fish's length to a large value at the caudal fin, avoids this difficulty.Any movement which a fish attempts to make, however, is liable to be accompanied by ‘recoil’, that is, by extra movements of pure translation and rotation required for overall conservation of momentum and angular momentum. These recoil movements, a potentially serious source of thrust and efficiency loss in carangiform motion, are calculated in § 4, which shows how they are minimized with the right distribution of total inertia (the sum of fish mass and the water's virtual mass). It seems to be no coincidence that carangiform motion goes always with a long anterior region of high depth (possessing a substantial moment of total inertia) and a region of greatly reduced depth just before the caudal fin.The theory suggests (§5) that reduction of caudal-fin area in relation to depth by development of a caudal fin into a herring-like ‘pair of highly sweptback wings’ should reduce drag without significant loss of thrust. The same effect can be expected (although elongated-body theory ceases to be applicable) from widening of the wing pair (sweepback reduction). That line of development of the carangiform mode in many of the Percomorphi leads towards the lunate tail, a culminating point in the enhancement of speed and propulsive efficiency which has been reached also along some quite different lines of evolution.A beginning in the analysis of its advantages is made here using a ‘twodimensional’ linearized theory. Movements of any horizontal section of caudal fin, with yaw angle fluctuating in phase with its velocity of lateral translation, are studied for different positions of the yawing axis. The wasted energy in the wake has a sharp minimum when that axis is at the ‘three-quarter-chord point’, but rate of working increases somewhat for axis positions distal to that. Something like an optimum regarding efficiency, thrust and the proportion of thrust derived from suction at the section's rounded leading edge is found when the yawing axis is along the trailing edge.This leads on the present over-simplified theory to the suggestion that a hydromechanically advantageous configuration has the leading edge bowed forward but the trailing edge straight. Finally, there is a brief discussion of possible future work, taking three-dimensional and non-linear effects into account, that might throw light on the commonness of a trailing edge that is itself slightly bowed forward among the fastest marine animals.

Similarity rules for thin aerofoils in non-stationary subsonic flows

Abstract: Similarity rules are constructed for the load distributions induced on a thin two-dimensional wing at subsonic speeds by sinusoidal gusts whose wave fronts are at an angle to the leading edge of the wing. It is shown that these rules divide into two groups according to the value of a parameter dependent on the Mach number and the angle between the gust front and the wing. The similarity rules for each group relate all the members of the group to a simpler problem whose solution can be found by existing methods. The similarity between the two groups is also discussed in terms of the two methods of solution available and it is shown that each method of solution is applicable in all cases.

Two-Dimensional Transonic Wind Tunnel Tests of Three 15-Percent Thick Circulation Control Airfoils

Abstract: : Two relatively thin Circulation Control (CC) elliptic airfoils were tested subsonically to determine their characteristics as proposed helicopter rotor tip sections. These airfoils, employing tangential trailing edge (Coanda) blowing, had shown very promising transonic characteristics in previous tests. It was the purpose of the subonic retests to determine if these thin sections could generate low speed characteristics which would be equally impressive. Due to its more forward slot location, the 15-percent thick pure elliptic section displayed effective subsonic operation at positive angle of attack, reducing drag while producing lift coefficients up to 3.5. The rounded trailing edge configuration, with further aft slot and better Coanda deflection of the jet, generated lift coefficients up to 4.25 (with a preference for negative incidence), but experienced higher drag levels. As a result of the small nose radii and low test Reynolds number, both sections were limited in performance by leading edge separation. At a fixed momentum coefficient, variation in slot height indicated that better performance was obtained for reduced heights. This was due primarily to higher energy levels in the jet sheet, but the lower bound on slot height was limited by boundary layer building in very small nozzles. Comparison of both CC sections to the more conventional NACA 0012 blade section indicated far greater lift capabilities with circulation control. However, due to blowing power requirements, equivalent efficiency was less at positive incidence, than for the conventional section.

The Navier-Stokes solution for laminar flow past a semi-infinite flat plate

Abstract: A numerical solution joining Carrier and Lin's solution near the leading edge to the boundary layer solution at large distance of the leading edge is presented. The solution is valid for any Reynolds number. Results are given for the skin friction, the integrated skin friction, the displacement thickness, the pressure along the plate and the velocity ahead of the plate. The asymptotic value of the integrated skin friction agrees very well with the exact value. The displacement thickness is already different from zero for small distances ahead of the plate.

Boundary-layer displacement and leading edge bluntness effects on attached and separated laminar boundary layers in a compression corner. I - Theoretical study

Abstract: This paper describes a theoretical analysis of highly cooled attached and separated regions of shock wave-laminar boundary-layer interaction in the presence of strong streamwise pressure gradients generated by boundary-layer displacement effects at the leading edge. This method is an extension of an earlier analysis by Holden1'12 to conditions where the inviscid flow cannot be described by simple isentropic flow relationships, and where the boundarylayer upstream of the main interaction is subjected to a strong pressure gradient. The analysis is compared with measurements described in Part II of the study. For strong leading edge displacement effects (%z, > 1), the analysis predicts that highly cooled boundary layers in hypersonic flow will be supercritical; a supercritical-subcritical jump is therefore required to join the solution to the subcritical viscous layer at separation. An examination of the experimental measurements indicates that the supercritical-subcritical jump does not reflect a sudden and basic change in the flow mechanics of separation, but is an approximation necessary because the conventional boundary-layer equations cannot adequately describe the viscous interaction process leading to separation. For some high Mach number, low Reynolds number conditions, we were unable to obtain a unique solution, without recourse to experimental data, by locating a critical point in the throat region of the flow. As in the separated region, there is serious question whether the conventional boundary-layer equations can be used to adequately describe the mechanism of boundary-layer reattachment in these flows.

Method and apparatus for turbine blade cooling

Abstract: A method of cooling turbine blades of a fluid flow machine in which relatively low-temperature air is bled from a relatively high-pressure source and is split into at least two separate portions, one portion of which is fed to the leading edge of one or more of the blades of a turbine and the other portion of which is fed into one or more of the blades at a location rearwardly of the first portion.

Unsteady airfoil stall review and extension

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

Pickup bed cover

Abstract: This invention relates to an improved telescopable cover for truck beds and the like characterized by a transversely-spaced pair of generally channel-shaped tracks opening toward one another and shaped to define a gutter in the bottom thereof alongside a slot separating upper and lower rail-forming surfaces. Mounted in these rails are a plurality of interlocking slot-forming panels, all but the lead panel of which has a downturned flange along its leading edge, a downwardly and rearwardly sloping cam surface adjacent the trailing edge thereof and an upturned flange along the trailing edge positioned and adapted to lock in behind the downturned flange on the leading edge of the panel therebehind so as to form a chain. A continuation of the lower rail slopes downwardly and forwardly to produce a ramp down which the panels slide and stack atop one another as they leave the confines of the upper rail, become separated and enter a storage area. An upwardly and rearwardly sloping surface above the ramp engages the leading edges of each panel in turn and leaves them in a staggered stack such that the leading edge of each panel is offset to the rear of the corresponding edge of the panel therebeneath. The cam surfaces and upturned flanges on the trailing panel edges define troughs effective to conduct water to the gutters in the tracks where it is discharged onto the ground through suitable drains.

Leading edge flow by the Monte Carlo direct simulation technique

Abstract: The flow near the leading edge of a sharp flat plate is studied by means of a Monte Carlo molecular simulation. This technique consists of following, by digital computation, the motion of a representative set of molecules flowing past the body while collisions are computed by statistical sampling. Flowfield properties and plate surface fluxes are presented for a monatomic gas for several molecular models: hard spheres and point centers of inverse power repulsion. The gas-surface interaction law used was a prescribed mixture of diffuse and specular reflection. Mach number was varied from 5.5 to 29.2 and both insulated and cooled plates were studied. Plate length relative to the freestream mean free path was varied from 10 to 88. For the longer plates the flow over much of the plate is that for a semiinfinite plate. Comparisons are made between these results and experimental data.

Fluid dynamic lift generating or control force generating structures

Abstract: In a fluid dynamic structure having an outer wall or skin defining a fluid dynamic profile part of the outer wall is flexible and has movable support apparatus and power apparatus are provided for effecting movement of the support apparatus and the flexible part whereby the fluid dynamic profile of the structure is changed. The invention is applicable to the leading edge of an aircraft wing and also to auxiliary control surfaces such as flaps and ailerons.

Method of applying corrosion and mechanical protective coatings in form of tapes to a metal pipe

Abstract: A METHOD OF COATING A PIPE AND A PIPE COATED THEREBY, SAID METHOD COMPRISING THE STEPS OF PROGRESSIVELY SPIRALLY WINDING A CORROSION PROTECTIVE ADHESIVE COATED PLASTIC TAPE ONTO THE OUTER SURFACE OF THE PIPE WITH A SPIRAL OVERLAP, COVERING THE COATED PIPE BY PROGRESSIVELY WINDING A FILM THEREON WITH A PREDETERMINED OVERLAP, AND, AS THE FILM IS WOUND ONTO THE COATED PIPE, INTRODUCING AND DISTRIBUTING UNDER PRESSURE A HOT MELTED ADHESIVE INTO INTIMATE CONTACT WITH THE SURFACE OF THE MARGINAL PORTION OF THE TRAILING EDGE OF THE FILM AND THE SURFACES OF THE OVERLAPPED PORTION ALONG THE LEADING EDGE THEREOF AND OF THE PORTION OF THE TAPE IMMEDIATELY ADJACENT THE LEADING EDGE OF THE FILM.

Multi-channel particle separator

Abstract: A multi-channel particle separator for separating and removing foreign particles from engine inlet air is disclosed. The multichannel particle separator utilizes a plurality of concentric catching rings mounted in the air inlet passageway. The leading edge of each ring is mounted to the air swirl vanes. Each trailing or catching portion of the rings is connected with struts which serve as particle scavenge vanes and air deswirl vanes.

Gas contacting element leading edge and trailing edge insert

Abstract: A leading edge or trailing edge insert for use with a gas contacting blade or vane. The insert is a macrocomposite structure of metal and refractory material wherein wires in single crystal form pass through the refractory material and prestress the refractory material in compression.

Blade cooling liner

Abstract: A sheet metal liner for an internally air-cooled turbine blade is of generally airfoil shape and is spaced from the interior of the hollow blade by bosses extending from the blade wall. The liner is closed at its edge toward the trailing edge of the blade and is partially closed at its forward edge. At the forward edge, a row of nozzles to jet cooling air against the interior of the leading edge of the blade is defined by two strips of sheet metal bonded together having grooves etched into their abutting faces, which grooves are registered to define nozzles of converging configuration.

Automatic welting patch and liner assembler and sewing device therefor

Abstract: A device for turning over sequentially alternate garment components being transferred on a conveyor is disclosed which senses the presence of a garment component on the conveyor, raises and captures the leading edge of the garment component thereby permitting conveyor rollers covered with an elastomeric material to sweep the following edge of the garment component under its captured leading edge, and releases the captured leading edge of the garment component after an appropriate delay period.

Device for sonic boom reduction and improving aircraft performance

Abstract: Method and means for improving the performance of, and particularly for reducing the sonic boom produced by a supersonic aircraft, comprising the production of a jet stream of approximately equal pressure but higher Mach number than the ambient supersonic flow, which steam is directed below the wing leading edge to intercept and interact with the wing shock wave. The interaction weakens the wing shock and decreases its propagation velocity, so that the wing shock, which normally reinforces the leading nose shock at the ground, will be shifted aftward spatially and in time in the boom signature, and will be delayed in its arrival with respect to the leading nose shock at any fixed position on the ground. By thus altering the signature, both the peak overpressure and the positive impulse of the boom may be substantially reduced without affecting the lift in support of the aircraft. Indeed, proper use of the stream will increase the lift on the aircraft, permitting some decrease in the angle of attack in maintaining level flight, which further weakens the wing shock to add to the altering of the boom signature. Also, the increase in lift, occurring largely on the aft part of the wing, results in reduction in drag, aftward shift of the center of pressure, and increase in the aerodynamic efficiency factor or lift-to-drag ratio, so that the jet stream can be used to improve various aspects of aircraft performance. Supersonic aircraft equipped with the anti-boom means, and a particular feasible means for producing the antiboom jet using existing technology are described, along with particular alternatives for the manner of incorporating the means on existing supersonic transports.

High speed faired towing cable

Abstract: A low-drag underwater towing cable having a high stability at high towing speeds. The cable comprises an elongated hydrofoilshaped structure with a leading edge made from continuous unidirectional glass fibers bonded together and a trailing edge made from flexible material such as plastic, rubber, or the like. An elastomer impregnated cross-woven material covers and encloses the leading and trailing edge portions. Braided electrical conductors are led through the trailing edge at a predetermined location nearest the leading edge for preventing tension forces and for avoiding interference with trailing edge yielding properties.

Process for the production of turbine blades

Abstract: A turbine blade blank is roughly formed having a recess extending along at least a portion of the leading edge, and a hard alloy leading edge insert is also roughly formed to be commensurate in shape to the recess. The insert is then welded to the blade blank, the composite blade is then forged into final shape and heat treated.

Aerodynamic blade with high stiffness-to-weight ratio

Abstract: A flight blade or wing having a structural spar at its forward end comprising a solid forward-portion and an after-portion of low density construction, such as a sandwich construction of honeycomb, plastic foam, or balsa wood core and having a structural trailing edge pocket member to produce a blade of maximum stiffness and minimum weight by eliminating leading edge counterweights and reducing spar weight by substituting sandwich construction material for solid metal wall members in the spar after portion.

Ram air glide parachute

Abstract: An airfoil-shaped parachute having airflow channels formed below a top flexible canopy between ribs extending from the leading edge of the canopy toward its trailing edge. Suspension lines are secured to the lower edges of the ribs for supporting a payload. The airflow through the channels and the distribution of stress applied from the suspension lines, maintains the airfoil shape of the inflated parachute to sustain a controlled glide path for the payload.

Angle of attack indicating system

Abstract: An electronic angle of attack indicating system is provided which may be used, for example, to indicate the sail trim of a sailboat, or the angle of attack of an aircraft, or the like, so that the sail or the aircraft may be maintained at any preset attack angle. The system of the invention uses a pair of temperature sensitive devices, such as thermistors, which are mounted on either side of the leading edge of an airfoil, such as a sail or wing, and which sense the air flow differential on the opposite sides of the airfoil, by virtue of the resulting temperature differences. An electric indicating system coupled to the temperature sensitive devices indicates the existence of the air flow differential, so that the appropriate adjustments may be made to maintain the preset attack angle.

Structure of evolving ion-acoustic fronts in collisionless plasmas.

Abstract: Exact analytic solutions are obtained to the linearized, two‐species Maxwell‐Vlasov equations for the evolution of an initial step‐function density discontinuity in an initially neutral, collisionless plasma. These solutions have been evaluated numerically for hydrogen plasmas with starting temperature ratios 0 ≤ θ = Te/Ti ≤ 30, for times 0 ≤ τ = ωpit ≤ 100, and over distances into the original low‐density region 0 ≤ η = x/Ait ≤ 12, where Ai is the mean thermal speed of ions. For τ ≪ 1 both species simply free stream. By late times (τ ≳ 30) quasineutrality of the perturbation has been established, and it is found that: (1) the ion profiles for θ ≲ 1 exhibit the appearance of free streaming at an enhanced ion temperature, suggesting that the strong Landau damping usually attributed to the low‐θ limit might better be termed “ambipolar free streaming,” (2) for θ ≃ 5 they are self‐similar and monotonic with a steep leading edge near η = θ1/2 followed by a broad, arched trailing edge accounting for half the de...

Carpet-cutting apparatus and method

Abstract: A sloping edged-cutting blade is mounted in a horizontally moving carriage so as to effect a transverse cut on carpet and related materials from below. A pair of overheat mounted parallel combs hold the material on both sides of the cutting channel. The leading edge of the blade carrier is raised so as to push up on the material before the blade reaches the material.

Magnetically readable bar and code

Abstract: A code formed of bars having one type of bar for one piece of information and another type of bar for another piece of information with the bars being formed of magnetizable material and in which the ratio of the amplitude of the electromagnetic wave produced by the leading edges of both types of bars being moved past a character reading system is substantially increased by slanting or inclining the leading edge of one type of bar with respect to the movement while maintaining the leading edge of the other type of bar perpendicular to the movement.

Observation of Optical Nutation in an Active Medium

Abstract: An intense optical pulse at 10.6 \ensuremath{\mu}m, of rise time that is short compared with the inverse bandwidth of an active C${\mathrm{O}}_{2}$ medium in which it is amplified, has been observed experimentally to attain a sharpened leading edge and attenuated lagging edge. This is an effect attendant upon optical nutation in the C${\mathrm{O}}_{2}$ medium. Computer solutions are presented for comparison.

Effect of vortices on delta wing lee-side heating at Mach 6

Abstract: Off-centerline heating on lee surface of supersonic delta wing with separation and vortex initiation at leading edge

Experimental Model for High‐Speed Rarefied Flow over a Sharp Flat Plate

Abstract: A flow field survey has been made of the shock layer development on a flat plate, at M = 6, from just upstream of the leading edge to downstream of the merged layer. The electron beam fluorescence technique has been used to measure density profiles from which a comprehensive description of the flow field is constructed. Close to the leading edge the flow is near free molecular and can be described in terms of two effective mean free paths, as proposed by Hamel and Cooper. The results suggest that continuum flow is not established for a distance approximately four times the mean free path for the collision of a free stream molecule with a body molecule. An upstream disturbance occurs a few free stream static mean free paths ahead of the leading edge, although this was aerodynamically sharp.

Turbulent-boundary-layer heat-transfer and transition measurements with surface cooling at Mach 6

Abstract: Wall cooling effects on turbulent heat transfer and boundary layer transition for sharp leading edge flat plate at hypersonic speeds