Showing papers on "Leading edge published in 1983"

The evolution of Tollmien-Schlichting waves near a leading edge

Abstract: The method of matched asymptotic expansions is used to study the generation of Tollmien-Schlichting waves by free-stream disturbances incident on a flat-plate boundary layer. Near the leading edge, the motion is governed by the unsteady boundary-layer equation, while farther downstream it is governed (to lowest order) by the Orr-Sommerfeld equation with slowly varying coefficients. It is shown that there is an overlap domain where the Tollmien-Schlichting wave solutions to the Orr-Sommerfeld equation and appropriate asymptotic solutions of the unsteady boundary-layer equation match, in the matched-asymptotic-expansion sense. The analysis explains how long-wavelength free-stream disturbances can generate Tollmien-Schlichting waves of much shorter wavelength. It also leads to a set of scaling laws for the asymptotic structure of the unsteady boundary layer.

Membrane insertion at the leading edge of motile fibroblasts.

Abstract: We are concerned with the mechanisms involved in the directed migration of eukaryotic cells. Previously we found that, inside cells at the edge of an experimental wound, the Golgi apparatus and the microtubule-organizing center were rapidly repositioned forward of the nucleus in the direction of subsequent cell migration into the wound. This repositioning was proposed to serve the purpose of introducing new membrane mass at the leading edge of the cell, by directing Golgi apparatus-derived vesicles bound for the plasma membrane to that edge. We now provide evidence to support this proposal. Cultured fibroblastic cells at the edge of a wound were infected with a temperature-sensitive mutant (0-45) of vesicular stomatitis virus. It is known that the G-protein, an integral membrane protein of the virus, is synthesized and remains in the rough endoplasmic reticulum at the nonpermissive temperature, but when the infected cells are shifted to the permissive temperature, the G-protein moves through the Golgi apparatus to the plasma membrane. By immunofluorescence microscopy, we here show that the first appearance of the G-protein at the cell surface corresponds to the leading edge of the motile cell. These observations are incorporated into a coherent scheme for the mechanisms involved in cell migration.

The fluid mechanics of slender wing rock

Abstract: The limit cycle oscillation in roll of very slender delta wings the so called wing rock is caused by asymmetric vortex shedding from the wing leading edges and not by vortex burst The breakdown or burst of the leading edge vortices of a delta wing can lead to static instability with associated roll divergence Vortex burst however can never be the cause of wing rock because it has a dynamically stabilizing effect on the roll oscillations Consequently slender wing rock is only realized for delta wings with more than 74 deg leading edge sweep in which case vortex asymmetry occurs before vortex breakdown A careful analysis of available experimental data reveals the fluid mechanical process that generates slender wing rock A simple analytic method is formulated by which the experimentally observed limit cycle amplitude in roll can be predicted provided that the static aerodynamic characteristics are known e g from static tests

Momentum Transport by a Line of Cumulonimbus

Abstract: The vertical transport of horizontal momentum normal to a line of cumulonimbus observed during GATE on 14 September 1974 is against the vertical momentum gradient, contrary to the predictions of mixing-length theory. Data from repeated aircraft passes normal to the line's axis at heights from 0.15 to 5.5 km are used to document the flux and determine its source. The flux is concentrated in roughly a 25 km wide “active zone” just behind the leading edge of the line, in kilometer-scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces. The fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic, resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical, with the clouds at the surface well ahead of those aloft. Evaluation of the terms in the momentum-flux generation equation confirms that the above process, reflected by the velocity-buoyan...

Assessment of quantitative methods for 2-dimensional echocardiography.

Abstract: Several 2-dimensional echocardiographic (2-DE) methods were tested in vitro for accuracy of linear and cross-sectional measurements and in vivo for left ventricular (LV) volume reconstruction. With 2-DE instrument settings at low and high gains and with precise in vitro calibrations, we studied myocardial slice thickness (3.0 to 10.0 mm). The 2-DE myocardial thickness was measured by leadingtrailing, trailing-leading, and leading-leading methods. Regression analysis of 2-DE versus direct measurements yielded excellent correlations for all 3 methods (r > 0.985), with interobserver variability 0.970), and low interobserver variability (< 4%) for the inner edge and leading edge methods, but the leading edge method was the most accurate (1.3 to 2.5% error). In vivo LV volumes in 7 anesthetized dogs were compared with 2-DE and cineangiography. Good correlations (r = 0.92) were obtained, but the inner edge method underestimated angiographic volume, whereas the leading edge method reduced the magnitude of underestimation. Thus, the leading edge method for 2-DE is most accurate not only for linear and cross-sectional measurements of the myocardium, but also for application to in vivo LV volumes.

Changes in cell shape and actin distribution induced by constant electric fields

Abstract: The development of motility in cultured cells is usually associated with a polarization of the cell shape. In particular, the leading edge of the cell is extended into a lamella which acts as a locus for the elaboration of cell processes and for the formation of cell-substrate contacts and, at the opposite end, retraction fibres often extend beyond the trailing edge of the cell. The alignment of microfilament bundles (stress fibres) along the direction of migration and the presence of a band of actin at the leading edge of the cell suggest an involvement of this protein in the motile process. The direction of growth and orientation of various cell types in tissue culture can be influenced by externally applied d.c. electric fields but the effect of the field on cellular motile activities is unknown. Here we describe a galvanotropic response of cultured Xenopus epithelial cells. At a field strength of 5 V cm-1 these cells elongate perpendicularly with respect to the field. The anodal side of the cell retracts and both the ends and cathodal edge become active in the extension of ruffling lamellipodia. In parallel with the change in the cell axis, stress fibres are oriented perpendicularly to the field, and a band of actin is associated with the lamellae at the cathodal edge and at the ends of the cell.

The evolution of Tollmien-Schlichting waves near a leading edge. II - Numerical determination of amplitudes

Abstract: In the first part of this investigation, Goldstein (1983) has shown that the amplitude of the spatially growing Tollmien-Schlichting wave generated by a time-harmonic free-stream disturbance is related to the coefficient multiplying the lowest-order asymptotic eigensolution of the unsteady boundary-layer equation. In the present study, a numerical solution of the unsteady boundary-layer equation is used to relate the amplitude of the asymptotic eigensolution, and consequently of the Tollmien-Schlichting wave, to that of the imposed free-stream disturbance for the special case of a uniformly pulsating stream. It is pointed out that the ideas of this study can be extended to other, more complex bodies and free-stream oscillations.

The effect of a leading-edge slat on the dynamic stall of an oscillating airfoil

Abstract: The dynamic stall characteristics of a slatted airfoil were investigated experimentally on a 2-ft-chord airfoil oscillating in pitch at M = 0.2 for a range of reduced frequency and mean angle of oscillation. The slat produced a flow that remained attached to the airfoil for angles well above those normally attained by the retreating blade of a helicopter during high speed flight. The dynamic stall vortex usually associated with these flight conditions was completely eliminated for all angles under 30 deg. Instantaneous surface pressure, lift, and pitching moment data are presented as a function of incidence throughout the oscillation cycle; a detailed analysis of instantaneous boundary-layer flow behavior for the various test conditions is included.

Apparatus and method for wrapping a plastic label around a container

Abstract: Apparatus and methods are disclosed for a high speed production line in which a container is wrapped with a plastic label comprising a foam polystyrene layer, there being means to move a leading edge of the label to the periphery of a rotating vacuum drum, means to apply methylene chloride to the underside of the foam layer to form finite areas on the leading label edge and a finite area on the trailing edge. The finite areas have therein a rapidly solidifying tacky solution of the foam polymer in methylene chloride, the tacky viscous solutions rapidly solidifying to form an adhesive bond. The solvent-applied label is quickly moved to a label wrapping station where it is wrapped around a container, the finite areas on the leading edge tacking the label to the container, and the finite area on the trailing edge forming a cohesive bond on the seam formed by the overlapped label ends.

Self-adjusting wind power machine

Abstract: A machine for economical recovery of wind power employs a self-adjusting mass-balanced aerodynamic blade weathervaning freely around a lengthwise pitching axis forward of its aerodynamic center, and an aerodynamic roller in its leading edge, spun at high RPM by a motor. The roller controls aerodynamic performance to high levels of efficiency at high lift coefficients, employing novel roller/airfoil profiles. For ship propulsion, the self-adjusting blade with roller stopped is like a furled sail, and with the blade held angling to the wind with roller spinning is like a large, efficient, easily controlled sail. On a horizontal axis wind turbine, the self-adjusting blade is continuously held to an efficient angle of attack by centrifugal lift-increasing pitching moments balancing aerodynamic lift-decreasing pitching moments. The blade whirls steadily despite fluctuations of wind speed and direction, reducing stresses, and preventing structural damage or loss of efficiency. Gyroscopic blade teetering moments are neutralized by mass-balance counter-spin, using a single blade with a balancing stub, on a teetering pivot at the mill shaft. A teetering pivot at the top of the mast and horizontal tail surfaces complete an overall dynamic stress relief system. Sensors monitor operating conditions, control roller speed and move centrifugal mass positions for optimum power output.

Centrifugal pump for liquids containing solid material

Abstract: A centrifugal pump for liquids containing solid material, the impeller of which has two or several vanes. In a bottom projection the leading edge (3) of the impeller (1) vane (2) is curved backwards in relation to the rotating direction of the impeller. The angle between the leading edge (3) and the outer edge (5) is obtuse in a meridian and a bottom projection. The outer end (10) of the leading edge of the vane is positioned behind a shoulder (9) provided with grooves (11), which cooperates with the vanes of the impeller. The form of the leading edge causes the fibres and the sticks to be conveyed towards the point of the vane where they are crushed by the combined effect of the groove and the vanes.

Aeroelastic control flap

Abstract: Auxiliary aeroelastic control flaps arranged on the leading edge of an aircraft's wings at or near the wing tips and ahead of the ailerons for actuation under control of the pilot. The aeroelastic control flaps operate with the ailerons to induce supplementary aerodynamic force to augment the effectiveness of lateral and directional control during high stress manuevers at high dynamic pressures, but do not rely on wing sensors such as accelerometers coupled with a computer for automatic operation.

Passive drag control of airfoils at transonic speeds

Abstract: An airfoil for transonic speeds includes a porous top surface extending from a location about 50 to 60% of the chord length from a leading edge of the airfoil to a location about 80 to 90% of the chord length from the leading edge. A cavity is defined under the porous surface in the airfoil which has a depth of from 0.05 to 0.2% of the chord length. The porosity of the porous surface is chosen to be from 1 to 3% of the total airfoil surface and may be variable. The presence of the porous surface and cavity decrease airfoil drag at transonic speeds by providing a pathway between a high pressure area downstream of a shock wave formed on the airfoil at transonic speeds to a low pressure area within a bubble on the airfoil upstream of the shock wave.

Sliding sheets: lubrication with comparable viscous and inertia forces

Abstract: A rigid plane thin sheet is sliding steadily at speed U close to a plane wall, in a fluid of kinematic viscosity v. The sheet is infinitely wide and is of length L in the direction of motion, and its leading edge is a distance h0 [Lt ] L from the wall. A solution is sought for arbitrary finite values of R = Uh20/νL. In the limit as e = h0/L→0, the problem reduces to that of solving the boundary-layer equation in the gap region between sheet and wall, and this is done here both by an empirical linearization, and by direct numerical methods. The solutions have the property that they reduce to those predicted by lubrication theory when R is small, and to those predicted by an inviscid small-gap theory when R is large. Special attention is paid to the correct entrance and exit conditions, and to the location of the centre of pressure.

Magnetic head air bearing slider

Abstract: A self-loading magnetic head air bearing slider is formed with a taper across the full width at its leading edge. The air bearing slider has two rails along its sides and a recess between the rails. The structure of the rails is preferably flared to provide an improved pressure profile thereby to allow fast liftoff from a disk surface.

On the time required to reach fully developed flow in pulsed supersonic free jets

Abstract: A new and simple model is presented for estimating the minimum pulse duration (‘‘valve open time’’) required for a pulsed nozzle to produce a supersonic beam comparably ‘‘cold’’ to that obtained from a continuous source. The model is based on the notion that cooling will be complete if the leading edge of the beamlet reaches the terminal temperature prescribed by the steady state flow equations before the sound wave created at the back of the pulse by the nozzle’s closing catches up with the leading edge. The times predicted from this model for reasonable stagnation conditions are all ≲10 μs.

Analysis of airfoil leading-edge separation bubbles

Abstract: A local inviscid-viscous interaction technique was developed for the analysis of low speed airfoil leading edge transitional separation bubbles. In this analysis an inverse boundary layer finite difference analysis is solved iteratively with a Cauchy integral representation of the inviscid flow which is assumed to be a linear perturbation to a known global viscous airfoil analysis. Favorable comparisons with data indicate the overall validity of the present localized interaction approach. In addition numerical tests were performed to test the sensitivity of the computed results to the mesh size, limits on the Cauchy integral, and the location of the transition region.

Effects of Free Convection Currents and Mass Transfer on Flow Past a Vertical Oscillating Plate

Abstract: An exact analysis of the flow caused by an oscillating vertical plate in the presence of free-convection currents and foreign mass has been presented. Solutions have been derived by Laplace-transform technique. Velocity profiles and leading edge effects have been shown for different gases present in air. During the course of discussion, the effects of Gr (Grashof number), Gm (modified Grashof number), Sc (Schmidt number), on the flow have been discussed. It has been observed that at all small values of Sc, transition from conduction to convection exists but at large values of Sc, such a transition is not present.

Leading edge flap system for aircraft control augmentation

Abstract: Traditional roll control systems such as ailerons, elevons or spoilers are least effective at high angles of attack due to boundary layer separation over the wing. This invention uses independently deployed leading edge flaps 16 and 18 on the upper surfaces of vortex stabilized wings 12 and 14, respectively, to shift the center of lift outboard. A rolling moment is created that is used to control roll in flight at high angles of attack. The effectiveness of the rolling moment increases linearly with angle of attack. No adverse yaw effects are induced. In an alternate mode of operation, both leading edge flaps 16 and 18 are deployed together at cruise speeds to create a very effective airbrake without appreciable modification in pitching moment. Little trim change is required.

Nacelle/wing assembly with wake control device

Abstract: In a wing and nacelle combination, where the nacelle is positioned below and forwardly of the wing leading edge, a wake control device to control a turbulent wake which is formed at the upper forward lip portion of the nacelle. This wake control device comprises a forward vortex generating portion to create a vortex which travels over the leading edge of the wing, and also a fence located at the middle third of the nacelle to control boundary layer air and thus properly locate the wake control vortex.

Improvements in wind turbine having a wing-profiled diffusor

Abstract: Arrangement for wind turbines which comprise not only a rotor (2) which can be caused to rotate about a shaft by a flow of air moving essentially in the direction of the shaft from an inlet side towards an outlet side, but also an annular body (1) enclosing the rotor in a concentric fashion, said body exhibiting on its intended inlet side an inlet having an inner boundary edge in connection with which the rotor is arranged and which makes the transition on the outlet side of the annular body to a front, inner boundary for an outlet which widens out in the direction of the flow and which is terminated by means of a rear, outer boundary edge (19). The transverse profile of the annular body (1) corresponds to a wing profile, of which the rounded leading edge (7-9) forms the inlet, of which the pointed trailing edge (19) forms the outer boundary edge of the outlet, which is situated radially outside said front edge, of which the flatter side (6) forms the inlet face of the ducting and extends from the outer boundary edge (22) of the inlet rearwards and outwards as far as the outer boundary edge (19) of the outlet, and of which the curved side (16-18) forms the outlet.

Container with solid plastic label and method of applying the label

Abstract: The present invention provides, without the drawbacks accompanied by the use of hot melt adhesives, an attractive, easily recycled labelled container, the solid polymer label, on its underside that is adjacent the container when applied, being provided with a finite area on its leading edge and a finite area on its trailing edge, by applying thereto a solvent for the polymer in each of the finite areas, the finite areas comprising a viscous tacky solution of the polymer in the solvent, the solidifying solution being sufficient to tack and bond the label to container during wrapping. After the label is wrapped around the container, the bond between the container and label becomes weaker as the solidifying solution hardens so that later the label can be easily and cleanly stripped from the container for recycling.

Cooling fan for internal combustion engine

Abstract: A cooling fan to be located between an internal combustion engine and a radiator and rotatingly driven from a rotational shaft of the engine. The fan includes a plurality of blade elements radially projecting from a boss portion and a cylindrical ring formed at the outer ends of the blade elements coaxially with the boss portion. In each blade element, a base line, which is drawn through a base point located on a chord of blade between leading and trailing edges of the blade element at a distance of 40% from the leading edge in percentage to the length of the chord, describes a straight or moderately curved line from the inner to the outer end of the blade element, which is inclined rotationally forward of a radial line passing through the base point at the inner end of the blade element. This fan construction produces air flows containing axial and radial components of velocity to increase the air flows through the radiator irrespective of the existence of the internal combustion engine on the downstream side of the fan. Maximum air flow is obtained by projecting the trailing edge of the outer end of each blade element from the trailing edge of the above-mentioned ring by a length corresponding to 1/3 of the chord length of the outer blade end.

Unsteady Aerodynamics and Gapwise Periodicity of Oscillating Cascaded Airfoils

Abstract: Tests were conducted on a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blades along the leading edge plane of the cascade and over the chord of the center blade. The pressure data were reduced to Fourier coefficient form for direct comparison and were also processed to yield integrated loads and, particularly, the aerodynamic damping coefficient. In addition, results from two unsteady theories for cascaded blades with nonzero thickness and camber were compared with the experimental measurements. The three primary results that emerged from this investigation were: (a) from the leading edge plane blade data, the cascade was judged to be periodic in unsteady flow over the range of parameters tested, (b) as before, the interblade phase angle was found to be the single most important parameter affecting the stability of the oscillating cascade blades, and (c) the real blade theory and the experiment were in excellent agreement for the several cases chosen for comparison.

Microwave phase shifting device

Abstract: An improved phase shifting device for varying the phase of the standing wave in a hollow rectangular waveguide is provided which is particularly applicable to microwave cooking appliances. A metallic septum is constructed at the end of the waveguide remote from the microwave source which extends inwardly into the waveguide from the adjacent waveguide end wall parallel to the narrow walls of the waveguide and electrically connects the broad walls of the waveguide, thereby dividing the waveguide into two sub-waveguides, each of which exhibits a cut-off characteristic at the operating frequency. The leading edge of the septum provides a short circuit termination reference point for the waveguide. The moving parts comprise a pair of dielectric plugs, each of which is received in a respective one of the sub-waveguides for selective movement in tandem from a reference position completely within the sub-waveguides to one or more phase shifting positions in which the plugs extend forward of the septum leading edge toward the microwave source. The shift in the phase of the standing wave varies linearly with the extent of forward displacement of the plugs relative to the septum leading edge. The plugs are selectively moved in tandem relative to the reference position in the sub-waveguides to provide the desired phase shift.

Leading edge flap and boundary layer control system

Abstract: The invention is a leading edge flap and boundary layer control system for an aircraft wing having a substantially sharp leading edge. The system comprises the wing 10 incorporating a spanwise slot 26 having front and rear guide walls 28, 30. A guide member 44 is rotatably mounted in the wind movable from a retracted position to an extended position. A flap segment 54 is rotatably mounted to the guide member 44 and is movable from a retracted position to an extended position in conjunction with the guide member 44. The flap segment incorporates an aerodynamic surface adapted to form an aerodynamic extension of the leading edge 16 of the wing 10 and, furthermore, cooperating with the guide member 44 to form a smooth transition inlet to the front guide wall 28 of the slot 26. Actuators 66, 72 are provided to actuate the guide member 44 and flap segment 54 from their retracted positions to their extended positions. A door member is rotatably mounted to the rear wall of the slot moveable from an extended position to a retracted position. An actuator 90 is provided to move the door member 62 to the retracted position where it forms a portion of the rear wall 30 of the slot 26. Thus, during normal flight conditions the sharp leading edge and smooth aerodynamic contour is maintained. For landing and takeoff purposes, the flap segment 54 and guide member 44 are extended and the door member 62 is retracted producing an aerodynamic extension of the leading edge and a smooth entrance to the slot is provided for energizing the boundary layer near the leading edge.

Turbo-machine blade

Abstract: Turbo-machine blade, including: a continuously curved profile contour having convex curved leading edge, suction side and trailing edge regions, and a concave curved pressure side region; the leading edge section being formed of a first ellipse section and a second ellipse section adjacent the first ellipse section; the suction side region being formed of a first circle section adjacent the second ellipse section and a first parabola section of a first second-order parabola being adjacent the first circle section; the trailing edge region being formed of a second circle section adjacent the first parabola section; and the pressure side region being formed of a third circle section adjacent the first ellipse section and a second parabola section of a second second-order parabola being disposed between the second circle section and the third circle section.