Showing papers on "Leading edge published in 1980"

A laboratory model of an atmospheric mesofront

Abstract: Consideration is given to the leading edge of a well-defined flow of dense air without significant condensation, such as occurs at a thunderstorm outflow or a sea-breeze front. Explanation of the front is proposed in terms of a gravity (density) current formed by the denser air. Observations of such flows are related both to laboratory gravity current heads in which head, tail and calm wind conditions are simulated and to a simple, theoretical gravity current model based primarily on a momentum balance. Good agreement is found between the atmosphere, laboratory and analytical results. The mean flow in the gravity current behind the head is greater than the velocity of the head, a result of mixing between the two fluids. This mixing nearly all occurs at the leading edge of the current. The excess height of the head of the gravity current is interpreted as the mixing region at the leading edge, and this mixed fluid lays down a stable layer above the following gravity current. In the laboratory the effect of a headwind is to flatten the profile of the raised head at the front and to reduce its rate of advance by about three-fifths of the value of the opposing flow.

Heat-transfer in flow past a continuous moving plate with variable temperature

Abstract: A study of thermal boundary layer on a continuously moving semi-infinite flat plate, whose temperature varies as Axn, where A is a constant and x is measured from the leading edge of the plate, has been presented. Similarity solutions have been derived and the resulting equations are integrated numerically. It has been observed that the value of the Nusselt number increases with increasing n.

Laminar Separation, Transition, and Turbulent Reattachment near the Leading Edge of Airfoils

Abstract: The laminar separation, transition, and turbulent reattachment near the leading edge of a cylindrical noseconstant thickness airfoil model were investigated using a low-turbulence, low-speed smoke wind tunnel. The locations of separation, transition, and reattachment were obtained from smoke flow photographs and surface oil flow techniques for chord Reynolds numbers from about 150,000 to 470,000. These visual data combined with static pressure distributions delineate the effects of angle of attack, flap deflection angle, and chord Reynolds number on the separation bubble characteristics. The data concerning the length of the laminar and turbulent portions of the bubble agree with the empirical prediction methods for short bubbles.

Numerical lifting line theory applied to drooped leading-edge wings below and above stall

Abstract: A numerical iterative solution to the classical Prandtl lifting-line theory, suitably modified for poststall behavior, is used to study the aerodynamic characteristics of straight rectangular finite wings with and without leading-edge droop. This study is prompted by the use of such leading-edge modifications to inhibit stall/spins in light general aviation aircraft. The results indicate that lifting-line solutions at high angle of attack can be obtained that agree with experimental data to within 20%, and much closer for many cases. Therefore, such solutions give reasonable preliminary engineering results for both drooped and undrooped wings in the poststall region. However, as predicted by von Karman, the lifting-line solutions are not unique when sectional negative lift slopes are encountered. In addition, the present numerical results always yield symmetrical lift distributions along the span, in contrast to the asymmetrical solutions observed by Schairer in the late 1930's. Finally, a series of parametric tests at low angle of attack indicate that the effect of drooped leading edges on aircraft cruise performance is minimal.

Method and replacement member for repairing a gas turbine engine vane assembly

Abstract: A gas turbine engine air cooled vane assembly which includes inner and outer platform members and an airfoil member therebetween is repaired by removing from the vane assembly a vane assembly segment comprising at least a portion of the leading edge wall, a portion of the airfoil body wall and a portion of at least one platform member connected with the leading edge wall. The vane assembly segment is removed along a preselected path which, during operation of the vane assembly in a gas turbine engine, experiences relatively low mechanical stresses. A replacement member of substantially the same type of material and of a size and shape which matches the removed vane assembly segment is placed into registry with the vane assembly and then metallurgically bonded to the vane assembly.

The Nonlinear Equatorial Kelvin Wave

Abstract: Using the method of strained coordinates, a uniformly valid approximation to the nonlinear equatorial Kelvin wave is derived. It is shown that nonlinear effects are negligible for the Kelvin waves associated with the Gulf of Guinea upwelling. The Kelvin waves involved in El Nino, however, are significantly distorted both in shape and speed. The leading edge is smoothed and expanded rather than steepened, but the trailing edge will form sharp fronts and eventually break.

Wing mechanics and take-off preparation of Thrips (Thysanoptera).

Abstract: 1.All of the wing fringe cilia of Thrips physapus , except those along the hindwing leading edge, pivot in elongated sockets which lock them into two positions. 2. The wings lie parallel over the abdomen when not in use, with the cilia locked in the closed position at an angle of 15-20° to the wing axis. The closing of the fringes prevents entanglement of the trailing edge cilia and lateral projection of the forewing leading edge cilia. 3. During flight the cilia are locked in the open position, doubling the wing area. The locking force is stronger than the combined aerodynamic and inertial forces on the cilia. 4. The fringes are opened by abdominal combing and closed by tibial combing. 5. The same morphological features are found in other members of the sub-order Terebrantia. Parallel wings at rest are characteristic of this suborder, and the collapsible fringe system is viewed as an effective method for parking the wings. 6. The fringes of the sub-order Tubulifera are not collapsible. The wings overlap on the abdomen at rest and a similar parking problem does not arise.

Wing leading edge slat

Abstract: A wing leading edge slat actuation and positioning system, wherein a slat panel is connected to one end of an extensible track member which is supported and guided at its other end, by rollers mounted to fixed structure in the leading edge section of the wing. The actuation and positioning system comprises a unified drive and a programming mechanism which is connected to the slat panel and functions to combine an aerodynamic slot opening or closure operation with a slat extension drive mechanism. The unified drive and programming mechanism comprises a contoured camtrack somewhat in the shape of an S-camtrack and having a roller follower which is connected to a link and drive arm; and this combination allows synchronization of slat actuation with programming control of slat angle-of-deflection and aerodynamic slot opening or closure.

Stretch wrapping apparatus with mechanical closure

Abstract: A spiral wrapping apparatus provided with a mechanical closure device is used to tie the leading and trailing edges of a film web which have been overwrapped around a plurality of vertically stacked units to form a unitary package. The leading edge of material from the film dispenser is held by a clamp mechanism to a turntable. As the turntable is rotated to wrap the load, the wrapping material is stretched and the trailing end of the material is formed into a rope-like configuration which is carried on the mechanical closure device to a position adjacent the clamped leading end of material with the leading and trailing ends then being tied together. The turntable clamp mechanism releases the leading end of the film web, extends away from the edge of the turntable and clamps the trailing end of the material web behind the tie point at which time the trailing end is severed by a cutter device between the tie point and the clamp mechanism, allowing the tied ends of the wrap to be carried forward toward the wrapped load by the memory of the stretch material seeking its original state. The turntable clamp mechanism then is transported back toward the turntable edge drawing with it the new leading end of material with which to begin the next wrapping cycle.

Air cooled hollow vane construction

Abstract: To improve cooling and simplify construction the cavity of a hollow airfoil is divided into separate longitudinally extending pressure and suction side compartments each of which extend from the leading edge to the trailing edge portion of the airfoil for providing cooling air to their respective sides of the airfoil. Air enters one compartment from one end of the airfoil and is closed at its opposite end. Air enters the other compartment from the end opposite the inlet end of the first compartment and is closed at its other end. In a preferred embodiment a tubular insert provides the dividing wall between the compartments and forms a plenum within the suction side compartment from which cooling air is directed against the suction-side wall through impingement cooling holes in the insert.

Vane fairing for inertial separator

Abstract: A permanently fixed fairing is provided extending across the air duct coinciding with the opening in the air duct to the air intake of a gas turbine engine. The fairing is in the form of an airfoil vane with a high pressure concave surface and a low pressure convex surface extending between the leading edge and trailing edge of the fairing and shaped such that the leading edge portion of the fairing is in the direction of the longitudinal axis of the air duct while the trailing edge portion of the fairing is in the direction of the air intake of the engine such that the fairing will divert air into the intake. A deflecting flap is hinged to the wall of the duct in a first position for a non-icing mode whereby the flap is clear of the air duct and in a second position whereby the trailing edge of the flap is adjacent the leading edge of the fairing during an icing mode.

Method and apparatus for determining position.

Abstract: Position sensing apparatus comprises generating means (12) for generating a beam of radiation; rotation means (24) for rotating the beam about a vertical axis to define a horizontal reference plane, the beam having a sectional shape (for example "V" shape or "X" shape) such that a leading edge and a trailing edge are straight and diverge away from the reference plane; two radiation sensors (38, 40) spaced a known vertical distance apart; and means (30, 32, 44, 46) for determining the distances between the leading and trailing edges at the positions along those edges which pass across each sensor. The vertical distance of each sensor from the horizontal reference place and the distance of the sensors from the axis of rotation can then be determined.

Two Aspects of Cavitation Damage in the Incubation Zone: Scaling by Energy Considerations and Leading Edge Damage

Abstract: This study focused on two aspects of the cavitation damage problem, namely an energy approach to the scaling of cavitation damage in the incubation zone and damage near the leading edge of a test model The damage to the surface of the models was in the form of small indentations in which no material was removed For a wide range of velocities namely 149 to 593 m/s the rate of pit formation per unit area in the maximum damage zone increased by the sixth power of velocity Furthermore it is shown that the damage rate versus velocity data are in good agreement with three other investigations The volumes of the pits were found to increase by the fifth power of velocity A relationship between the volume of a pit and the cavitation bubble collapse energy absorbed was developed The damage to the leading edge was felt to be due to the reentrant jet striking the leading edge of the cavity creating a short term pressure rise causing the collapse of any cavitation bubbles in this area

Experimental studies of the laminar separation bubble on a two-dimensional airfoil at low Reynolds numbers

Abstract: The laminar separation, transition and turbulent reattachment near the leading edge of a two-dimensional NACA 663-018 airfoil were investigated using a low speed, smoke visualization wind tunnel. Lift and drag force measurements were made using an external strain gauge balance for a chord Reynolds number range of 40,000 to 400,000. An extensive flow visualization study was performed and correlated with the force measurements. Experiments were also conducted with distributed surface roughness at the leading edge and external acoustic excitation to influence the development of the airfoil boundary layer. This study delineates the effects of angle of attack and chord Reynolds number on the separation bubble characteristics and airfoil performance

Flow augmenters for vertical-axis windmills and turbines

Abstract: A windmill is disclosed, the windmill including a vertical shaft mounted for rotation about its longitudinal axis, a number of blades spaced circumferentially around the longitudinal axis, and being disposed generally parallel to the axis of rotation of the vertical shaft, and supporting arms extending radially outwardly from the vertical shaft for supporting the blades. The windmill also includes a first member connected to an upper end of one of the blades and defining a first surface having a leading edge with respect to the direction of movement of the blade and a trailing edge rearward of the leading edge, the leading edge being lower than the trailing edge. The first surface also includes an inside lateral edge and an outer lateral edge spaced radially outwardly from the inside lateral edge, the inside lateral edge being higher than the outer lateral edge. A second member is connected to the lower end of the blade and defines a second surface, the second surface having a leading edge with respect to the direction of movement of the blade and a trailing surface rearward of the second surface leading edge, the second surface leading edge being higher than the trailing edge. The second surface also includes an inside lateral edge and an outer lateral edge spaced radially outwardly from the second surface inside lateral edge, the second surface inside lateral edge being lower than the second surface outside lateral edge.

Estimation of wing nonlinear aerodynamic characteristics at supersonic speeds

Abstract: A computational system for estimation of nonlinear aerodynamic characteristics of wings at supersonic speeds was developed and was incorporated in a computer program. This corrected linearized theory method accounts for nonlinearities in the variation of basic pressure loadings with local surface slopes, predicts the degree of attainment of theoretical leading edge thrust, and provides an estimate of detached leading edge vortex loadings that result when the theoretical thrust forces are not fully realized.

Stability of the Boundary Layer on a Swept Wing with Wall Cooling

Abstract: Linear stability theory was used to examine the propagation of laminar instabilities in the leading edge region of a transonic swept wing with wall cooling. The condition of real group velocity ratio on the eigenvalue computation was examined for the case of crossflow instabilities. When temporal theory was used, this condition resulted in a single wave of maximum amplification. When spatial theory was used, and for a limited range of angles of wavegrowth direction, the growth rate in the direction formed by the real ratio of the group velocities and the direction itself were insensitive to the orientation of the wavegrowth. It was found that wall cooling has a stabilizing effect on crossflow disturbances, but the stabilization is mild compared to the stabilizing effect that wall cooling has on Tollmien-Schlichting waves.

Airframe Noise Reduction Studies and Clean-Airframe Noise Investigation

Abstract: Acoustic wind tunnel tests were conducted of a wing model with modified leading edge slat and trailing edge flap. The modifications were intended to reduce the surface pressure response to convected turbulence and thereby reduce the airframe noise without changing the lift at constant incidence. Tests were conducted at 70.7 and 100 m/sec airspeeds, with Reynolds numbers 1.5 x 10 to the 6th power and 2.1 x 10 to the 6th power. Considerable reduction of noise radiation from the side edges of a 40 deflection single slotted flap was achieved by modification to the side edge regions or the leading edge region of the flap panel. Total far field noise was reduced 2 to 3 dB over several octaves of frequency. When these panels were installed as the aft panel of a 40 deg deflection double slotted flap, 2 dB noise reduction was achieved.

Turbulence Modeling for Unsteady Transonic Flows

Abstract: Conditionally sampled, ensemble-averaged velocity measurements, made with a laser velocimeter, were taken in the flowfield over the rear half of an 18% thick circular arc airfoil at zero incidence tested at M = 0.76 and at a Reynolds number based on chord of 11 x 10(exp 6). Data for one cycle of periodic unsteady flow having a reduced frequency f of 0.49 are analyzed. A series of compression waves, which develop in the early stages of the cycle, strengthen and coalesce into a strong shock wave that moves toward the airfoil leading edge. A thick shear layer forms downstream of the shock wave. The kinetic energy and shear stresses increase dramatically, reach a maximum when dissipation and diffusion of the turbulence exceed production, and then decrease substantially. The response lime of the turbulence to the changes brought about by the shock-wave passage upstream depends on the shock-wave strength and position in the boundary layer. The cycle completes itself when the shock wave passes the midchord, weakens, and the shear layer collapses. Remarkably good comparisons are found with computations that employ the time-dependent Reynolds averaged form of the Navier-Stokes equations using an algebraic eddy viscosity model, developed for steady flows.

Self loading slider for magnetic recording heads

Abstract: A slider for flying a magnetic head on a fluid bearing above moving magnetic recording media is disclosed in which a fluid bearing surface includes a generally planar fluid support surface extending generally transverse to the direction of movement of the media, a ramped leading edge and a cavity having a generally spherical surface formed in the fluid support surface and spaced from the leading edge thereof. A method of making such a slider is also disclosed.

Leeward flow over delta wings at supersonic speeds

Abstract: A survey was made of the parameters affecting the development of the leeward symmetric separated flow over slender delta wings immersed in a supersonic stream. The parameters included Mach number, Reynolds number, angle of attack, leading-edge sweep angle, and body cross-sectional shape, such that subsonic and supersonic leading-edge flows are encountered. It was seen that the boundaries between the various flow regimes existing about the leeward surface may conveniently be represented on a diagram with the components of angle of attack and Mach number normal to the leading edge as governing parameters.

Paravane with automatic depth control

Abstract: A paravane includes an elongated fuselage; a wing section of spaced wing bers attached to an intermediate portion of the fuselage; stabilizer fins for maintaining the paravane lined-up with the direction of tow; a depth control flap positioned adjacent the wing section and having a pivot axis extending closely adjacent to the towing point; and depth control means for controlling the position of the control flap. The wing members have a straight leading edge portion, a straight trailing edge portion and a curved intermediate portion wherein the wing members are arranged such that the chord lines extend at oblique angles with the longitudinal axis of the fuselage and such that the resultant hydrodynamic lift force vector acting on the wing section passes through the tow point.

Studies of leading-edge thrust phenomena

Abstract: A study of practical limitations on achievement of theoretical leading-edge thrust has been made and an empirical method for estimation of attainable thrust has been developed. The method is based on a theoretical analysis of a set of two-dimensional airfoils to define thrust dependence on airfoil geometric characteristics and arbitrarily defined limiting pressures, an examination of two-dimensional airfoil experimental data to provide an estimate of limiting pressure dependence on local Mach number and Reynolds number, and employment of simple sweep theory to adapt the method to three-dimensional wings. Because the method takes into account the spanwise variation of airfoil section characteristics, an opportunity is afforded for design by iteration to maximize the attainable thrust and the attendant performance benefits. The applicability of the method was demonstrated by comparisons of theoretical and experimental aerodynamic characteristics for a series of wing-body configurations. Generally, good predictions of the attainable thrust and its influence on lift and drag characteristics were obtained over a range of Mach numbers from 0.24 to 2.0.

Stability of the Boundary Layer on a Swept Wing with Wall Cooling Spyridon

Abstract: Linear stability theory was used to examine the propagation of laminar instabilities in the leading edge region of a transonic swept wing with wall cooling. The condition of real group velocity ratio on the eigenvalue computation was examined for the case of crossflow instabilities. When temporal theory was used, this condition resulted in a single wave of maximum amplification. When spatial theory was used, and for a limited range of angles of wavegrowth direction, the growth rate in the direction formed by the real ratio of the group velocities and the direction itself were insensitive to the orientation of the wavegrowth. It was found that wall cooling has a stabilizing effect on crossflow disturbances, but the stabilization is mild compared to the stabilizing effect that wall cooling has on Tollmien-Schlichting waves.

Studies of Leading-Edge Thrust Phenomena

Abstract: A study of practical limitations on achievement of theoretical leading-edge thrust has been made and an empirical method for estimation of attainable thrust has been developed. The method is based on a theoretical analysis of a set of two-dimensional airfoils to define thrust dependence on airfoil geometric characteristics and arbitrarily defined limiting pressures, an examination of two-dimensional airfoil experimental data to provide an estimate of limiting pressure dependence on local Mach number and Reynolds number, and employment of simple sweep theory to adapt the method to three-dimensional wings. Because the method takes into account the spanwise variation of airfoil section characteristics, an opportunity is afforded for design by iteration to maximize the attainable thrust and the attendant performance benefits. The applicability of the method was demonstrated by comparisons of theoretical and experimental aerodynamic characteristics for a series of wing-body configurations. Generally, good predictions of the attainable thrust and its influence on lift and drag characteristics were obtained over a range of Mach numbers from 0.24 to 2.0.

Filter bucket for a flight conveyor

Abstract: An improved filter bucket for a flight conveyor having two sides and a bottom with an integral rake edge. Numerous equally spaced apart arcuately curved wires are fixed to and supported by longitudinally extended cross bars in a grid fashion to form the generally concave bucket bottom interior surface. The wires extend beyond the cross bar at the leading edge of the bucket to form a rake edge for engaging and retaining material conveyed. Perforated sides with numerous holes formed therethrough of diameter equal to the bottom grid spacing wires provide for a uniform filtering action filtering action through the bottom and sides of the bucket.