Showing papers on "Leading edge published in 1992"

A new modelling of cavitating flows : a numerical study of unsteady cavitation on a hydrofoil section

Abstract: A new cavity model that can explain the interaction between viscous effects including vortices and cavitation bubbles is presented in this study. This model, which is named a bubble two-phase flow (BTF) model, treats the inside and outside of a cavity as one continuum by regarding the cavity as a compressible viscous fluid whose density changes greatly. Navier–Stokes equations including cavitation bubble clusters are solved in finite-difference form by a time-marching scheme, where the growth and collapse of a bubble cluster is given by a modified Rayleigh's equation. Computation was made on a two-dimensional flow field around a hydrofoil NACA0015 at angles of attack of 8° and 20°. The Reynolds number was 3 × 105. The experiments were also performed at the same Reynolds number for comparison. The computed results by the BTF cavity model can express the feature of cloud-type cavitation shed from the trailing edge of the attached cavities when the angle of attack is 8°. It shows the mechanism of cavitation cloud generation and large-scale vortices. The boundary layer separates at the cavity leading edge. Then it rolls up and produces the cavitation cloud. In other words, the instability of the shear layer may produce the cavitation cloud. When the angle of attack is 20°, the flow was fully separated from the leading edge of the hydrofoil and vortex cavitation occurs in the separated region. The BTF cavity model can also express the generation of such vortex cavitation and the effect of cavitation nuclei in the uniform flow.

The Role of Convectively Generated Rear-Inflow Jets in the Evolution of Long-Lived Mesoconvective Systems

Abstract: In this study, the structure of convectively generated rear-inflow jets and their role in the evolution of long-lived mesoconvective systems are investigated through an analysis of idealized three-dimensional simulations using a nonhydrostatic cloud model. Rear-inflow jets are generated within these systems in response to the upshear-tilting of the convective circulation, as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear. Within this framework, a wide range of rear-inflow strengths and structures are produced, depending on the magnitude of the ambient convective available potential energy (CAPE) and the vertical wind shear. In general, for environments characterized by weak-to-moderate vertical wind shear and weak-to moderate CAPE, the rear-inflow jet descends and spreads along the surface well behind the leading edge of the gust front, and the subsequent convective activity becomes weaker. However, for e...

The overshoot and equilibration of saltation

Abstract: Downwind of the leading edge of a saltating surface, the saltation process develops toward an eventual stream wise equilibrium. The nature of this development is investigated in a portable wind tunnel by measuring the vertically integrated streamwise flux Q of saltating sand grains as a function of distance x from the leading edge of the erodible surface, at wind speeds between 8 and 13 m s−1. It is found that Q(x) increases from zero at x = 0 to a maximum value at x around 7 m, before decreasing toward an eventual equilibrium value (about half the maximum value) when x is greater than about 15 m. These results are in qualitative agreement with two recent numerical simulations of the approach of saltation to equilibrium. The experiment indicates the minimum length of wind tunnel required for studying the saltation process in its equilibrium state, and the order of magnitude of the measurement errors if shorter tunnels must be used.

Unsteady flow past an airfoil pitching at a constant rate

Abstract: The unsteady flow past a NACA 0012 airfoil that is undertaking a constant-rate pitching up motion is investigated experimentally by the PIDV technique in a water towing tank. The Reynolds number is 5000, based upon the airfoil's chord and the free-stream velocity. The airfoil is pitching impulsively from 0 to 30 deg. with a dimensionless pitch rate alpha of 0.131. Instantaneous velocity and associated vorticity data have been acquired over the entire flow field. The primary vortex dominates the flow behavior after it separates from the leading edge of the airfoil. Complete stall emerges after this vortex detaches from the airfoil and triggers the shedding of a counter-rotating vortex near the trailing edge. A parallel computational study using the discrete vortex, random walk approximation has also been conducted. In general, the computational results agree very well with the experiment.

Effect of leading-edge geometry on boundary-layer receptivity to freestream sound

Abstract: The receptivity to freestream sound of the laminar boundary layer over a semi-infinite flat plate with an elliptic leading edge is simulated numerically. The incompressible flow past the flat plate is computed by solving the full Navier-Stokes equations in general curvilinear coordinates. A finite-difference method which is second-order accurate in space and time is used. Spatial and temporal developments of the the Tollmien-Schlichting wave in the boundary layer, due to small-amplitude time-harmonic oscillations of the freestream velocity that closely simulate a sound wave travelling parallel to the plate, are observed. The effect of leading-edge curvature is studied by varying the aspect ratio of the ellipse. Boundary layer over the flat plate with a sharper leading edge is found to be less receptive. The relative contribution of the discontinuity in curvature at the ellipse-flat-plate juncture to receptivity is investigated by smoothing the juncture with a polynomial. Continuous curvature leads to less receptivity. A new geometry of the leading edge, a modified super-ellipse, which provides continuous curvature at the juncture with the flat plate, is used to study the effect of continuous curvature and inherent pressure gradient on receptivity.

Effect of acoustic excitation on stalled flows over an airfoil

Abstract: The effect of acoustic excitation on poststalled flows over an airfoil, ie, flows that are fully separated from near the leading edge, is investigated The excitation results in a tendency toward reattachment, which is accompanied by an increased lift and reduced drag, although the flow may still remain fully separated It is found that with increasing excitation amplitude, the effect becomes more pronounced but shifts to a Strouhal number which is much lower than that expected from linear, inviscid instability of the separated shear layer

Distortion of a flat-plate boundary layer by free-stream vorticity normal to the plate

Abstract: A nominally uniform flow over a semiinfinite flat plate is considered. The analysis shows how a small streamwise disturbance in the otherwise uniform flow ahead of the plate is amplified by leading-edge bluntness effects and eventually leads to a small-amplitude but nonlinear spanwise motion far downstream from the leading edge of the plate. This spanwise motion is then imposed on the viscous boundary-layer flow at the surface of the plate - causing an order-one change in its profile shape. This ultimately reduces the wall shear stress to zero, causing the boundary layer to undergo a localized separation, which may be characterized as a kind of bursting phenomenon that could be related to the turbulent bursts observed in some flat-plate boundary-layer experiments.

Measurements in a leading-edge separation bubble due to a simulated airfoil ice accretion

Abstract: The separation bubble formed on an airfoil at low Reynolds number behind a simulated leading-edge glaze ice accretion is studied experimentally. Surface pressure and split hot-film measurements as well as flow visualization studies of the bubble reattachment point are reported. The simulated ice generates an adverse pressure gradient that causes a laminar separation bubble of the long bubble type to form. The boundary layer separates at a location on the ice accretion that is independent of angle of attack and reattaches at a downstream location 5-40 percent chord behind the leading edge, depending on the angle of attack. Velocity profiles show a large region of reverse flow that extends up from the airfoil surface as much as 2.5 percent chord. After reattachment, a thick distorted turbulent boundary layer exists. The separation bubble growth and reattachment are clearly seen in the plots of boundary-layer momentum thickness vs surface distance. Local minima and maxima in the boundary-layer momentum thickness development compare well with the shear layer transition point as indicated by the surface pressures and the reattachment point as measured from surface oil flow, respectively.

Excitation of unstable modes in a supersonic boundary layer by acoustic waves

Abstract: The acoustic excitation of the first and second boundary layer modes in the neighborhood of the sharp leading edge of a plate in a supersonic gas flow is analyzed.

Equatorial bubbles updrafting at supersonic speeds

Abstract: Plasma and electric field observations from two satellite encounters with equatorial plasma bubbles updrafting at velocities of about 2 km/s are presented. These large, upward velocities are consistent with an adaptation of Chandrasekhar's model for the motion of plasma blobs supported against gravity by a magnetic field. Vector magnetic field measurements, available during one of the bubble encounters show a perturbation of about 150 nT, directed radially outward from the earth, near the western wall of deepest plasma depletion. This magnetic variation is too large to be caused by simple shunting of the g x B current along the bubble's edge. Rather, it is Alfvenic in nature, radiating from a generator located near the magnetic equator, in the plasma outside the bubble's leading edge. A heuristic model of a depleted flux tube with constant circular cross section moving upward through a background plasma predicts most of the measurements' qualitative features.

Air bearing slider with relieved trailing edge

Abstract: A slider supports a transducer proximate a rotating disc. The slider includes a slider body having a leading edge, a trailing edge and first and second edges. First and second raised side rails are positioned along the first and second edges, respectively, to form a pair of air bearing surfaces. The first and second side rails each includes a trailing edge relief positioned adjacent the trailing edge. The trailing edge reliefs are recessed from the air bearing surfaces and are raised from the slider body. The trailing edge reliefs have depths which are suitable for forming subambient pressure regions at the trailing edge.

Negative pressure air bearing slider having an air bearing surface trailing a negative pressure cavity

Abstract: A negative pressure air-bearing slider supports a transducer proximate a rotating disc. The slider includes a slider body having a surface with a leading edge, a trailing edge, and a first and second side edges. First and second raised side rails are positioned along the first and second side edges, respectively. A raised cross rail is positioned near the leading edge and extends between the side rails. A negative pressure cavity trails the cross rail and is positioned between the side rails. The negative pressure cavity develops subambient pressure during flight. A raised island forms an air-bearing surface positioned at the trailing edge and between the side rails. The island has a forward edge which is raised from the negative pressure cavity and is recessed from the air-bearing surface to increase pressurization of the air-bearing surface. The air-bearing surface increases lift and slider flying height at the trailing edge at low disc speeds. At high disc speeds, the air-bearing surface has a diminished effect relative to an increased subambient pressure effect of the negative pressure cavity which provides a more even flying height over inner and outer data tracks on the disc surface.

Effects of a leading-edge fillet on the flow past an appendage-body junction

Abstract: Oil-flow visualizations and pressure and velocity measurements are presented to demonstrate the effects of a leading-edge fillet on the flow of a turbulent boundary layer past an idealized appendage-body function. The fillet, a large fairing in the corner between the appendage nose and body surface, modifies the flow in a way that is desirable in many applications. With the appendage at zero angle of attack, it eliminates leading-edge separation and thus the formation of a horseshoe vortex around the wing nose. It greatly improves the stability of the flow close to the junction and the nonuniformity of its wake

Combined support and seal ring for a combustor

Abstract: A combined support and seal ring supports the aft end of an annular combustor and provides a seal to contact the leading edge of the platform of the adjacent stator vane for sealing the cooling air from the gas path in a gas turbine engine.

Turbine airfoil including diffusing trailing edge pedestals

Abstract: A turbine airfoil having a cut-back trailing edge and a plurality of diffusing flow dividers upstream of the cut-back trailing edge is disclosed. Various construction details are developed which provide ejection of a diffusing film of cooling fluid over a cut-back trailing edge. In one particular embodiment, a turbine airfoil includes a plurality of radially spaced flow dividers extending between a pressure wall and a suction wall. Each flow divider includes a rounded leading edge, a pair of parallel sidewalls downstream of the leading edge, and a pair of converging sidewalls downstream of the parallel sidewalls. Adjacent sidewalls of adjacent flow dividers form flow channels having a constant area channel and a diffusing section. The diffusing section includes a covered portion upstream of the cut-back trailing edge and an uncovered portion extending over the cut-back trailing edge.

Numerical simulation of laminar and turbulent flows around rectangular cylinders

Abstract: By a finite volume method, laminar flows around bluff bodies with a rectangular cross-section of various width-to-height ratios from 0.2 to 10 and with a cross-section of a round leading edge and a square trailing edge have been computed on body-fitted curvilinear co-ordinates at Reynolds numbers of (1, 4, 7)×10 3 . Turbulent flows have also been computed by a standard κ-e turbulence model. Computed results are compared with experimental data at a Reynolds number of 10 3 and clearly show the effects of the shape of the bluff body on the aerodynamic characteristics

Control of leading-edge vortices on a delta wing

Abstract: The unsteady flow structure of leading-edge vortices on a delta wing has been investigated using new types of experimental techniques, in order to provide insight into the consequences of various forms of active control. These investigations involve global control of the entire wing and local control applied at crucial locations on or adjacent to the wing. Transient control having long and short time-scales, relative to the convective time-scale C/U(sub infinity), allows substantial modification of the unsteady and time-mean flow structure. Global control at long time-scale involves pitching the wing at rates an order of magnitude lower than the convective time-scale C/U(sub infinity), but at large amplitudes. The functional form of the pitching maneuver exerts a predominant influence on the trajectory of the feeding sheet, the instantaneous vorticity distribution, and the instantaneous location of vortex breakdown. Global control at short time-scales of the order of the inherent frequency of the shear layer separating from the leading-edge and the natural frequency of vortex breakdown shows that 'resonant' response of the excited shear layer-vortex breakdown system is attainable. The spectral content of the induced disturbance is preserved not only across the entire core of the vortex, but also along the axis of the vortex into the region of vortex breakdown. This unsteady modification results in time-mean alteration of the axial and swirl velocity fields and the location of vortex breakdown. Localized control at long and short time-scales involves application of various transient forms of suction and blowing using small probes upstream and downstream of the location of vortex breakdown, as well as distributed suction and blowing along the leading-edge of the wing applied in a direction tangential to the feeding sheet. These local control techniques can result in substantial alteration of the location of vortex breakdown; in some cases, it is possible to accomplish this without net mass addition to the flow field.

An Experimental Study of Subcooled Film Boiling on a Vertical Surface—Thermal Aspects

Abstract: Wall and liquid side heat fluxes near the leading edge of a vertical wall 6.3 cm wide and 10.3 cm high were measured during subcooled film boiling of water at 1 atm pressure. The heat flux from the interface into the liquid and temperature profiles in the liquid thermal layer were measured using real time holographic interferometry. The wall heat flux was measured with thermocouples embedded in a copper block, one face of which served as the heated wall. The role of the leading edge vapor layer, ripples, and large bulges in modifying the liquid side heat transfer is quantified.

Splicer tape system

Abstract: A splicer tape is provided for holding down the leading end portion of the outer layer of a new roll of web and for enabling the leading end portion of the new roll to be spliced to the trailing end portion of an active web. The tape contains an elongated strip of carrier material having inner and outer sides with the inner side of the strip having a first and second longitudinally extending section and preferably having an intermediate longitudinally extending section located between the first and second sections, said intermediate section being free of adhesive. A first adhesive is applied onto the first section and comprises a non-releasable adhesive which is to be applied against the leading end portion of the new roll. A second adhesive is applied onto the second section of the inner side of the carrier strip and comprises a releasable adhesive which is to be applied against the body of the new roll to hold the leading edge of the new roll down until the leading edge of the new roll is spliced to the trailing end portion of the active web whereupon the second adhesive releases from the body of the new roll without leaving any portion of the tape on the roll body. A third adhesive is applied on the outer side of the carrier strip and it comprises a non-releasable adhesive which is to be applied against trailing end portions from the active web during splicing.

An Experimental Study of Subcooled Film Boiling on a Vertical Surface—Hydrodynamic Aspects

Abstract: The aim of the present study is: (1) To determine the physical characteristics of the interfacial waves for different wall superheats and liquid subcoolings. (2) To determine the velocity field adjacent to the interface at different locations along the interface. Interface and liquid velocities near the leading edge of a vertical wall 6.3 cm wide and 10.3 cm high were measured during subcooled film boiling of water at 1 atm pressure. The interface and liquid velocities in the boundary layer adjacent to the interface were measured using the hydrogen bubble flow visualization method. Photographs taken from the front and side showed the existence of a finite vapor layer at the leading edge and the existence of ripples and large-amplitude waves (bulges) on the interface. The bulges and ripples did not slide on the interface but moved in unison with the interface. The wave amplitude and wavelength were also measured. For a given subcooling and wall superheat, the amplitude, the interfacial velocity, and the wavelength were found to attain an equilibrium value several millimeters downstream of the leading edge. The waves were highly nonlinear and the interface velocities, which are found to be governed by the wave amplitude, were much largermore » than those predicted from the smooth interface, laminar flow theory. Streamlines in the liquid were found to expand into the wave valleys. At the wave peaks the streamlines appeared to be clustered together and the measured interface velocity gradients were high. The overall picture is one of expansion in the wave valleys and contraction (of flow) at the wave peaks. The flow field in turn is found to affect the liquid side heat transfer in subcooled film boiling significantly.« less

Leading edge protection for fan blade

Abstract: A protection element containing a spring steel strip is bent to have a greater curvature than the curvature at the leading edge of a fan blade. This protection element is then fixed to the leading edge of the fan blade over an area of maximum erosion. Rubber or another elastomer can be extruded over the strip before or after it is fixed to the fan blade or the strip can incorporate an outer hardened layer to resist erosion. Attachment of the strip to the blade is advantageously accomplished using rivets or screws at spaced locations along the blade and at the leading edge of the blade.

Jet engine fan nacelle

Abstract: (57) [Summary] (Modified) [Purpose] To provide a jet engine fan nacelle that maintains the adhering flow while the engine is in a windmill state. The nacelle 32 includes a cylindrical air foil body 36 having an inner surface. A plurality of eddy-generating pieces 48 are provided on the inner surface of the nacelle, between the front edge of the nacelle body and the throat, and about the longitudinal axis of the nacelle. Place it within the rotation angle of 0 °. The eddy strips 48 act on the air flow to maintain a sticking flow around the leading edge 38 and along the outer surface of the nacelle body, thus preventing the air flow from being stripped from the outer surface resulting in an undesirable drag increase.

Tarpaulin deployment and retraction apparatus

Abstract: In summary, the present invention contemplates an improved tarpaulin deployment and retraction apparatus which includes a plurality of removable or permanent tracks installed at intervals over the load carrying compartment of a vehicle. A leading edge slider travels to and fro on the tracks under the influence of deployment/retraction mechanism. A ridgepole slider is towed to a mid-deployment position due to a latch on the ridgepole slider engaging a towing pin on the leading edge slider. Upon reaching the mid-deployment position, a de-coupling pin upon each of the tracks cooperates with a camming surface on the latch to disengage the ridgepole slider from the leading edge slider. The leading edge slider then is further urged to a fully deployed position. A leading edge pole, to which is attached the leading edge of a tarpaulin, is connected to the leading edge sliders on the tracks. As the sliders are urged into their deployed positions the tarpaulin is unfurled from its stowed position. A ridgepole connected to the ridgepole sliders creates a pitch in the deployed tarpaulin. Upon retraction, the tarpaulin is furled by the deployment/retraction mechanism. The furling action of the tarpaulin urges the leading edge slider towards a stowed position during which the leading edge slider comes in contact with the ridgepole slider. The respective pairs of sliders on each track are then further urged towards a fully retracted or stowed position.

Golf club shaft

Abstract: An improved aerodynamic golf club shaft is disclosed. The improved aerodynamic golf club shaft comprises a tube that has an exterior with a non-circular cross section. The golf club shaft may have an elliptical exterior cross section in one preferred embodiment. The golf club shaft has a leading edge that is on the half of the shaft aligned with the face of the golf club and a trailing edge on the half of the shaft aligned with the back of the club. A portion of the leading edge of the shaft has a smaller radius of curvature than the leading edge of a equivalently sized shaft having a circular cross section.

Heat Transfer and Turbulence in a Turbulated Blade Cooling Circuit

Abstract: The aerothermalperformance of a typical turbine blade three-pass turbulated cooling circuit geometry was investigated in a 10X plexiglass test model. The model closely duplicated the blade's leading edge, midchord, and trailing edge cooling passage geometries. Steady-state heat transfer coefficient distributions along the blade pressure side wall (convex surface) of the cooling circuit passages were measured with a thin-foil heater and a liquid crystal temperature sensor assembly. The heat transfer experiments were conducted on rib-roughened channels with staggered turbulators along the convex and concave surfaces of the cooling passages. Midchannel axial velocity and turbulence intensity measurements were taken by hot-wire anemometry at each passage end of the three-pass cooling circuit to characterize and relate the local thermal performance to the turbulence intensity levels

Pulse-shape dependence of stimulated-Brillouin-scattering phase-conjugation fidelity for high input energies.

Abstract: The shot-to-shot phase fidelity of a stimulated-Brillouin-scattering phase conjugator operated many times above threshold has been found to be very sensitive to the slope of the leading edge of the input pulse. For a pulse with a rising edge that is short relative to the acoustic lifetime of the stimulated-Brillouin-scattering medium, strong random fluctuations in the fidelity of the wave-front reversal are observed. However, by tailoring the leading edge of the pulse relative to the acoustic response time of the medium, good phase reproduction has been demonstrated for input energies of 100 times above threshold.

Cooled turbine guide vane

Abstract: A hollow turbine guide blade or vane is provided with three separate cooling circuits formed by virtue of two radial partitions extending the length of the blade within the cavity bounded by the outer wall of the blade and dividing the cavity into first, second and third ducts, and radial passages extending the length of the blade within the outer wall in the vicinity of the leading edge and the extrados face of the blade. The leading edge area is cooled by air flowing through the radial passages in this area and then through the first duct. The extrados face area is cooled by air flowing through the radial passages in this area and then through the second duct. The intrados face area is cooled by air flowing through the third duct. The first duct communicates with the outside of the blade through slits opening in the extrados face near the leading edge of the blade, and the second and third ducts each communicate with the outside of the blade through slits opening in the intrados face in the vicinity of the trailing edge.