Showing papers on "Leading edge published in 1985"

The discrete vortices from a delta wing

Abstract: Introduction: The Classical View T HE flow over delta wings at an angle of attack is dominated by two large bound vortices that result from the flow separation at the leading edge. The classical view of these vortices is sketched in Fig. la and has been discussed by Hoerner and Borst among others. With a sharp leading edge at an angle of attack a, the flow is separated along the entire leading edge forming a strong shear layer. The shear layer is wrapped up in a spiral fashion, resulting in the large bound vortex as sketched. These vortices appear on the suction surface and increase in intensity downstream. The low pressure associated with the vortices produces an additional lift on the wing, often called nonlinear or vortex lift, which is particularly important at large angles of attack. As sketched in Fig. la, small secondary vortices also appear on the wing near the points of reattachment as a result of the strong lateral flow toward the leading edge.

Attached cavitation and the boundary layer: experimental investigation and numerical treatment

Abstract: Attached cavitation on a wall with continuous curvature is investigated on the basis of experiments carried out on various bodies (circular and elliptic cylinders, NACA 16 012 foil). Visualization of the boundary layer by dye injection at the leading edge shows that a strong interaction exists between attached cavitation and the boundary layer. In particular, it is shown that the cavity does not detach from the body at the minimum pressure point, but behind a laminar separation, even in largely developed cavitating flow. A detachment criterion which takes into account this link between attached cavitation and boundary layer is proposed. It consists of connecting a cavitating potential-flow calculation and a boundary-layer calculation. Among all the theoretically possible detachment points, the actual detachment point is chosen to be the one for which the complete calculation predicts a laminar separation just upstream. This criterion, applied to the NACA foil, leads to a prediction which is in good agreement with experimental results.

Plasmoid-associated energetic ion bursts in the deep geomagnetic tail: properties of the boundary layer

Abstract: Energetic (>35 keV) ion bursts in the deep geomagnetic tail associated with the passage of 37 plasmoids are examined using data from the energetic particle anisotropy spectrometer (EPAS) instrument on ISEE 3. These bursts can usually be divided into four distinct phases: (1) strongly tailward streaming ions observed in the lobe for a few minutes prior to plasmoid entry, commencing ∼25 min after geomagnetic substorm onset; (2) the plasmoid interval, when the energetic ions have a broader tailward angular distribution arising from convection with the plasmoid; (3) the “post-plasmoid” plasma sheet, where more strongly tailward streaming ions are observed in the plasma sheet on field lines disconnected from the earth at the substorm neutral line; and (4) a strongly tailward streaming ion population extending into the lobe for a few minutes after exit from the plasma sheet. We concentrate here on the streaming ion “boundary layers” observed in the lobe at the leading and trailing edges of these bursts. In a majority of these layers, a clear dawn-dusk gradient anisotropy and energy dispersion are evident at the leading edge, and a similar gradient anisotropy with “reverse” dispersion is evident at the trailing edge. It is shown however that the dispersion at onset is not consistent with simple time of flight from a near-earth neutral line or from a neutral line retreating tailward during substorm recovery. Instead, observations of 90° pitch angle ions with a time resolution of 16 s are used to infer that the ion onset is due to a layer of energetic ions expanding outward from the tail center plane and engulfing the spacecraft. At the trailing edge of the burst, this layer contracts back across the spacecraft toward the center plane. Mean expansion and contraction speeds are 94±74 km s−1 and 99±100 km s−1 respectively, with boundary layer thicknesses of ∼3 RE. From these observations, it is concluded that the expansion of the ion layer is caused predominantly by the ion layer being swept across the spacecraft by the arrival of the plasmoid in the deep tail, contributing ∼60 km s−1 to the expansion speed, rather than by a thickening of the region of lobe field lines disconnected at the substorm neutral line which expands at ∼35 km s−1. The energy dispersion at the leading edge can be reconciled with a near-earth neutral line in this case. Using this dispersion and the measured expansion speed of the layer, the electric field along the near-earth substorm neutral line is deduced. Values derived from layer expansions and contractions are both ∼0.4 mV m−1, equivalent to ∼110 kV across a ∼40-RE tail width.

Evidence of Kelvin Waves in California's Marine Layer and Related Eddy Generation

Abstract: Evidence suggests that an internal solitary Kelvin wave exists in the marine layer along California. The marine layer is lifted over the central coast by a weak cyclonic circulation. This “bump,” initially 850 m high, moves to the north along the coast at 6 m s−1. The undisturbed layer depth is 100–200 m thick. The crest height of the wave decreases to 500 m farther north. Winds under the raised marine layer are southerly. The leading edge of the wave is easily followed by satellite as the thickened marine layer is marked by overcast stratus. A greatly curved offshore leading edge indicates that nonlinear effects are important. Offshore scale in the overcast is about 300 km in the south and 50 km in the north. Surface pressure gradient alongshore is closely related to the marine layer depth. The surface wind shifts when the leading and trailing edge of the wave passes. Northerly wave progression ceases at the sharp bend formed by Cape Mendocino. At this time, a vortex is formed in the marine laye...

High strength fan.

Abstract: A fan (10) in which the root-to-tip net blade (16) skew angle (Ab) (either forward or rearward) is less than 1/2 of the blade (16) spacing; in a first radially inward region of the blade (16), the blade (16) is rearwardly skewed as indicated by the leading edge skew angle (Ae); in a second region radially outward of the first region, the leading edge skew angle indicates a forward skew.

Propulsive wing with inflatable armature.

Abstract: A very light wing, configured like a spherical segment, is intended to be used in the traction and lift of various loads. The wing includes a leading edge and a trailing edge and an inflatable armature covered by a flexible envelope. The surfaces of the wing are configured in the shape of an aircraft wing profile and the edges of the wing curve in two planes. The leading and trailing edges of the wing are oriented to intersect near the tips of the wing, and each of the tips of the wing receives a control rope via an adjusting plate. The control rope is passed through a pulley mounted on a craft to be displaced by a person through a harness. The wing can be used in sliding sports, yachting and gliding.

On Tollmien-Schlichting Wave Generation by Sound

Abstract: It is well known that acoustic disturbances incident upon the boundary layer may cause Tollmien-Schlichting waves. An intense generation of these waves is observed in local inhomogeneities of the flow [1]. To investigate this phenomenon we shall consider a two-dimensional gas flow about a flat plate directed along a free-stream flow (fig.1). The free-stream velocity U∞ is taken to be subsonic with M < 1. Introduce cartesian coordinates x′, y′ aligning their origin with the plate leading edge and orienting x′ along the plate surface. Denote velocity vector components in this coordinate system by u′ and v′, density by p′, and viscosity coefficient by μ′ . Let the gas under consideration have an adiabatic constant r and its thermodynamic state be described by the Clapeyron equation.

Total pressure loss in vortical solutions of the conical Euler equations

Abstract: A technique for the solution of the conically self-similar form of the Euler equations is described. Solutions for the flow past a flat-plate delta wing at angle of attack are presented. These solutions show strong leading edge vortices with large total pressure losses in the cores. A study of the effects of various computational parameters on the total pressure loss is made. An explanation for the cause of the total pressure loss is presented. It is shown to be consistent with the results for both a quasi-one-dimensional model problem and the conically self-similar flow past the flat-plate delta wing.

Displacement measuring device utilizing an incremental code

Abstract: A displacement measuring device, using an incremental code, which includes a coding member (22) resting on the object (21) to be measured and having a coding section for generating such signals that a sensing element can discriminate the signals as 0 or 1, sensing means (25A, 25B) disposed to sense the coding section of the coding member for producing sensed signals in response to the displacement of the coding member (22), and rectangular wave-converting circuits (27A, 27B) for receiving and converting the sensed signal into rectangular wave signals. A clock pulse generator (28) is provided in the device for generating a clock pulse with a higher repetition-frequency than the repetition-frequency of the sensed signal. An edge detector (29) receives the clock pulse from the clock pulse generator (28) and the rectangular wave-signal from the rectangular wave-converting circuits (27A, 27B) and then delivers, as an output pulse, the clock pulse substantially coincident with at least one of the leading edge and the trailing edge of the rectangular wave-signal. A counter (30) counts the output pulses from the edge detector and a display (31) indicates the counted value. With such an arrangement, an incremental displacement measurement can be made without a differentiating circuit and an averaging circuit.

Dynamics of vorticity fronts

Abstract: Vorticity fronts can form in a shear flow as the result of fast patches of fluid catching up with slower ones. This process and its consequences are studied in an inviscid two-dimensional model consisting of piecewise uniform-vorticity layers. Calculations using the method of contour dynamics for ‘intrusive’ initial states indicate that the leading edge of the front evolves into a robust structure whose propagation speed can be accounted for by a simple shock-joining theory. Behind the leading edge several different effects can occur depending upon the relative amplitude of the intrusion. These effects include lee-wave generation with possible wave breaking and folding of the front. A critical value of the frontal slope, above which wave breaking occurs, is suggested.

Temperature detection system for use on film cooled turbine airfoils

Abstract: Improved temperature detection system for use on film cooled turbine airfoils having a showerhead assembly with a series of parallel slots defined in the leading edge of an airfoil, each slot having a multiplicity of film flow ports exiting therefrom. A plurality of sensor assemblies are affixed to the airfoil showerhead and are couplable via electrodes to electronic sensing equipment for establishing the gas flow temperature.

Axial flow compressor surge margin improvement

Abstract: The casing 28 of an axial flow compressor for a gas turbine engine is provided with a plurality of axially extending circumferentially spaced slots 30 in its internal cylindrical surface 32 adjacent the tips of at least one row of blades 26. A benefit in both stall margin improvement and a reduction in efficiency deficit may be achieved by positioning the leading edge of the slot 30 such that it leads the leading edge 30(a) of the blade 26 by an amount termed the overhang A or by reducing the closed to open ratio m/M of the slots 30. A further reduction in efficiency deficit may be achieved by combining the overhang A which individually gave the best stall margin improvement with a slot closed to open ratio m/M somewhat higher than the value which individually gave the best stall margin improvement.

Experiments on the stability of crossflow vortices in swept-wing flows

Abstract: Experiments are conducted which demonstrate the feasibility of creating crossflow vortices in a flat-plate flow. A swept leading edge and contoured wind-tunnel walls produce a strong pressure gradient and a typical swept-wing flow on the plate. Detailed three-dimensional measurements, made within the boundary layer using hot-wire anemometry, are supplemented with different flow-visualization techniques. Data are presented on the mean flow characteristics as well as on the behavior of the crossflow vortices. Comparisons are made with theoretical flow-field and stability calculations.

Transverse driving bodies, particularly airplane wings

Abstract: This invention relates to a transverse driving body, particularly an aircraft wing, the wing comprising a wing tip extending basic parts of the wing in the span direction for the purpose of increasing the aspect ratio, the wing tip being of triangular design with a sweptback leading edge, and the profile camber of each of the wing tip increasing at least over a portion of the extension thereof from a basic wing part to the wing tip.

Low pressure drop modular centrifugal moisture separator

Abstract: A modular separating unit for separating a liquid from a gas-liquid mixture, comprising an annular riser tube, a hub coaxial with and located within the riser tube, four curved blades mounted between the hub and the riser tube, an annular downcomer tube surrounding the riser tube, and an orifice ring having an outer diameter smaller than the inner diameter of the riser tube and located adjacent the outlet end of the riser tube. The leading edge and leading surface of each blade, which are disposed adjacent the inlet end of the riser tube, are contained in a plane parallel to the initial direction of flow of the gas-liquid mixture. The trailing edge and trailing surface of each blade are contained in a plane which is at an angle of approximately 37° to a plane perpendicular to the axis of the hub. The projections of the leading edge of one blade and the trailing edge of an adjacent blade onto a plane perpendicular to the axis of the hub form an angle of approximately 22.5°.

On the abrupt turbulent reattachment downstream of leading-edge laminar separation

Abstract: A theoretical investigation of unsteady marginal separations, in a classical unsteady boundary layer, is described. This suggests that the nonlinear properties of such separations may be largely responsible, at least initially, for the central features often observed experimentally in the abrupt turbulent reattachment of eddies that follow laminar separation near the leading edges of aerofoils. The theory reduces the local flow problem to the solution of a nonlinear integro-partial differential equation for the unknown scaled skin friction, which is also proportional to the decrement in displacement locally. Numerical solutions followed by linear and nonlinear analysis show that all short-length small disturbances are unstable whenever reversed flow occurs; but for sufficiently confined initial conditions the instabilities accumulate in such a way that a breakdown is forced after a finite time. In the nonlinear breakdown a double structure arises near the point of collapse, with an effective ‘shock’ taking the flow abruptly from the reversed sense just upstream to the forward sense just downstream. This predicted shock forms the suggested possible link with the sudden transition and turbulent reattachment of laminar eddies in practice, at rounded leading edges. Discussions of the turbulence effects, of the related phenomenon of dynamic stall, of other instabilities present, and of the theoretical repercussions of the work are presented also.

Local heat-transfer measurements on a large scale-model turbine blade airfoil using a composite of a heater element and liquid crystals

Abstract: Local heat transfer coefficients were experimentally mapped along the midchord of a five-time-size turbine blade airfoil in a static cascade operated at room temperature over a range of Reynolds numbers. The test surface consisted of a composite of commercially available materials: a mylar sheet with a layer of cholesteric liquid crystals, that change color with temperature, and a heater sheet made of a carbon-impregnated paper, that produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat transfer coefficients were mapped over the airfoil surface. The local heat transfer coefficients are presented for Reynolds numbers from 2.8 x 10 to the 5th power to 7.6 x 10 to the 5th power. Comparisons are made with analytical values of heat transfer coefficients obtained from the STANS boundary layer code. Also, a leading edge separation bubble was revealed by thermal and flow visualization.

The effect of surface contamination on thermocapillary flow in a two-dimensional slot. Part 2. Partially contaminated interfaces

Abstract: We consider the flow driven by a thermally induced surface stress in a fluid held in a shallow two-dimensional slot, and show that, for low Maragoni number, the extent of surface stagnation due to the presence of a non-diffusing surfactant depends on a single parameter E, the elasticity number defined in Part 1 of this analysis (Homsy & Meiburg 1984). For situations in which the adsorbed species are insufficient to result in a fully covered surface, we find that the interface is either clean and subject to constant stress, or contaminated and no-slip. There is a region in which one type of surface is replaced by the other. The Wiener–Hopf technique is used to obtain an analytic expression for the stream function in the vicinity of the leading edge of the stagnant surface in the limit of creeping flow. This result shows that the flow dies off under the stagnant surface at a distance of the order of the depth of the fluid, in a series of vortices of exponentially decreasing magnitude.

High time resolution plasma wave and magnetic field observations of the Jovian bow shock

Abstract: High time resolution (60 ms) Voyager magnetometer and plasma wave measurements of a strong (fast Mach number 16), quasi-perpendicular Jovian bow shock reveal an abrupt change in the plasma wave spectrum at the leading edge of the shock foot. Upstream electron plasma waves terminate at the leading edge, and are replaced by a lower-frequency broadband spectrum of ion-acoustic-like waves, which terminates at the main shock ramp. The clear association with the foot region of the lower frequency component suggests that it is generated by reflected ions. If the upstream plasma waves are generated by an escaping electron heat flux, their termination at the leading edge suggests that electrons are heated by the low-frequency waves in the shock foot.

Leading edge slat/anti-icing system and method for airfoil

Abstract: A leading edge/anti-icing assembly for an airfoil comprising a leading edge slat having a nose section defining a heat exchange chamber. Anti-icing air directed into the heat exchange chamber flows rearwardly through the slat so as to have a deicing function, and is then discharged in a rearward direction from the trailing edge of the slat. Thus, the anti-icing air not only performs an anti-icing function over the upper surface of the slat, but also contributes to anti-icing over the upper surface portion of the main wing rearwardly of the trailing edge of the slat.

Gas turbine air cooling blade

Abstract: PURPOSE:To contrive to uniformize the temperature distribution by a structure wherein return flow passages of cooling fluid in the interior of a blade are provided independently at the blade concave side and at the blade convex side. CONSTITUTION:A return flow passage, to and through which cooling air is supplied and circulated, is divided into two passages or a blade convex side passage and a blade concave side passage along the camber line of a blade. In addition, cooling air supplying ports 21 and 22 are arranged at the positions, which have higher heat transfer coefficients on the outer peripheral surface of the blade. Further, the cooling air passing through the blade convex side passage is flowed in the direction moving from the leading edge to the trailing edge of the blade while the cooling air passing through the blade concave side passage is flowed in the direction moving from the trailing edge to the leading edge of the blade or both the cooling airs are flowed in the directions opposing to each other. Thus, the temperature distributions along the blade convex side surface and blade concave side surface can be uniformized.

Biased leading edge slat apparatus

Abstract: YAn aircraft leading edge slat is biased when at an extended location toward a first position wherein the trailing edge of the slat is a predetermined distance from the wing upper surface. The slat is pivotable to a second position, when aerodynamic forces acting on the wing overcome the biasing force, wherein the slat trailing edge is pivoted upward and forward, and the distance between the slat trailing edge and the wing upper surface is increased. The slat is retracted and extended by a drive track which is supported inside the wing by upper rollers located chordwise within the wing cavity, a lower front roller, and a pair of roller rings rotatably mounted at opposite sides of a rotary actuator pinion gear. The pinion gear engages the drive track and moves the slat between the extended and retracted positions.

Vortices incident upon a leading edge: instantaneous pressure fields

Abstract: A mixing-layer flow formed by merging of high- and low-speed streams leads to successive generation of vortices of the same sense that impinge upon a leading edge. Distortion of each incident vortex, secondary-vortex shedding, and 'sweeping’ of flow about the tip of the edge are related to the instantaneous pressure fields via simultaneous flow visualization and pressure measurement. The instantaneous pressure fields are interpreted as downstream travelling waves along the upper and lower surfaces of the edge; in turn, these wavelike pressure variations are linked to the visualized vortex patterns adjacent to each surface. Near the tip of the edge, where rapid flow distortion occurs, the pressure fields are non-wavelike; on the lower surface of the tip, negligible streamwise phase variations of fluctuating pressure are associated with secondary shedding there, while on the upper surface there is a phase jump. This jump can be as large as π when the incident vortex impinges directly upon, or passes just below, the tip of the edge. Downstream of this near-tip region, the wavelike pressure fields show short and long wavelengths on the lower and upper surfaces respectively. These wavelengths, in turn, differ substantially from the wavelength of the incident-vortex instability. Irrespective of the transverse location of the incident vortex with respect to the leading edge, maximum pressure amplitude always occurs at the tip of the edge; it takes on its largest value when the scale of secondary shedding from the tip of the edge is most pronounced. Moreover, the fact that the net force on the edge scales with tip-pressure amplitude underscores the crucial role of the local flow distortions in the tip region.

Cooling scheme for combustor vane interface

Abstract: The turbine vane (22) of a gas turbine engine immediately downstream of the combustor is maintained at a cool temperature by judiciously directing cooling air at the stagnation point ahead of the vane's leading edge (30) at the juncture of the vane's airfoil section and platform (32).

Flow Past a Suddenly Heated Vertical Plate

Abstract: An analysis is presented for steady free-convection flow past a semi-infinite vertical flat plate at large Grashof numbers. If it is assumed that the wall temperature varies as a power of the distance from the leading edge of the plate, then the governing equations can be reduced to a set of ordinary differential equations by the use of a similarity variable. Numerical and asymptotic solutions of these equations are given. The unsteady approach to these solutions are also investigated by considering the impulsive heating of the plate. If the temperature increases along the length of the plate, numerical solutions are presented which match the large- and small-time solutions. However, no matching of these limiting solutions has been achieved where the temperature decreases along the length of the plate. An asymptotic solution, which is valid at large values of time, is also given. For all the temperature distributions at the plate that are considered in this paper the disturbance from the leading edge of the plate travels fastest within the boundary layer. The unsolved problem, in which the temperature is impulsively increased to a constant value, is a special case of the problem considered here.

Aerodynamic device with reversible flexible and lowerable concavity for the propulsion by the force of the wind

Abstract: Device for producing the concavity of a thick profiled sail and making it reversible and remotely controllable to pass through all aerodynamic profiles comprising a rotatable mast (1), at least six assemblies sliding on the mast, each comprising a leading edge profile (3) provided with an inflatable part (4), and a mechanism (2) having two flexible battens (5) arranged symmetrically on either side. The trailing edge or rear end of the battens is controlled by a system of crow feet and sheet arms (6). The device is intended particularly for the propulsion of boats.

Generation of Crossflow Vortices in a Three-Dimensional Flat-Plate Flow

Abstract: Experiments are conducted which demonstrate the feasibility of creating crossflow vortices in a flat-plate flow. A swept leading edge and contoured wind-tunnel walls produce a strong pressure gradient and a typical swept-wing flow on the plate. Detailed three-dimensional measurements, made within the boundary layer using hot-wire anemometry, are supplemented with different flow-visualization techniques. Comparisons are made with theoretical flow-field and stability calculations.