Showing papers on "Leading edge published in 2001"

Spanwise flow and the attachment of the leading-edge vortex on insect wings

Abstract: The flow structure that is largely responsible for the good performance of insect wings has recently been identified as a leading-edge vortex. But because such vortices become detached from a wing in two-dimensional flow, an unknown mechanism must keep them attached to (three-dimensional) flapping wings. The current explanation, analogous to a mechanism operating on delta-wing aircraft, is that spanwise flow through a spiral vortex drains energy from the vortex core. We have tested this hypothesis by systematically mapping the flow generated by a dynamically scaled model insect while simultaneously measuring the resulting aerodynamic forces. Here we report that, at the Reynolds numbers matching the flows relevant for most insects, flapping wings do not generate a spiral vortex akin to that produced by delta-wing aircraft. We also find that limiting spanwise flow with fences and edge baffles does not cause detachment of the leading-edge vortex. The data support an alternative hypothesis-that downward flow induced by tip vortices limits the growth of the leading-edge vortex.

Aerodynamic Flow Control over an Unconventional Airfoil Using Synthetic Jet Actuators

Abstract: Control of flow separation on an unconventional symmetric airfoil using synthetic (zero net mass flux) jet actuators is investigated in a series of wind tunnel tests. The symmetric airfoil comprises the aft portion of a NACA four-digit series airfoil and a leading edge section that is one-half of a round cylinder. The experiments are conducted over a range of Reynolds numbers between 3.1 × 10 5 and 7.25 × 10 5 . In this range, the flow separates near the leading edge at angles of attack exceeding 5 deg. When synthetic jet control is applied near the leading edge, upstream of the separation point, the separated flow reattaches completely for angles of attack up to 17.5 deg and partially for higher angles of attack. The effect of the actuation frequency, actuator location, and momentum coefficient is investigated for different angles of attack. The momentum coefficient required to reattach the separated flow decreases as the actuators are placed closer to the separation point. In some cases, reattachment is also achieved when the actuators are placed downstream of the stagnation point on the pressure side of the airfoil

Large-eddy simulation of boundary-layer separation and transition at a change of surface curvature

Abstract: Transition arising from a separated region of flow is quite common and plays an important role in engineering. It is difficult to predict using conventional models and the transition mechanism is still not fully understood. We report the results of a numerical simulation to study the physics of separated boundary-layer transition induced by a change of curvature of the surface. The geometry is a flat plate with a semicircular leading edge. The Reynolds number based on the uniform inlet velocity and the leading-edge diameter is 3450. The simulated mean and turbulence quantities compare well with the available experimental data. The numerical data have been comprehensively analysed to elucidate the entire transition process leading to breakdown to turbulence. It is evident from the simulation that the primary two-dimensional instability originates from the free shear in the bubble as the free shear layer is inviscidly unstable via the KelvinHelmholtz mechanism. These initial two-dimensional instability waves grow downstream with a amplification rate usually larger than that of TollmienSchlichting waves. Three-dimensional motions start to develop slowly under any small spanwise disturbance via a secondary instability mechanism associated with distortion of two-dimensional spanwise vortices and the formation of a spanwise peakvalley wave structure. Further downstream the distorted spanwise two-dimensional vortices roll up, leading to streamwise vorticity formation. Significant growth of three-dimensional motions occurs at about half the mean bubble length with hairpin vortices appearing at this stage, leading eventually to full breakdown to turbulence around the mean reattachment point. Vortex shedding from the separated shear layer is also observed and the 'instantaneous reattachment' position moves over a distance up to 50% of the mean reattachment length. Following reattachment, a turbulent boundary layer is established very quickly, but it is different from an equilibrium boundary layer.

An Experimental and Numerical Investigation Into the Mechanisms of Rotating Instability

Abstract: This paper reports on an experimental and numerical investigation aimed at understanding the mechanisms of rotating instabilities in a low speed axial flow compressor. The phenomena of rotating instabilities in the current compressor were first identified with an experimental study. Then, an unsteady numerical method was applied to confirm the phenomena and to interrogate the physical mechanisms behind them. The experimental study was conducted with high-resolution pressure measurements at different clearances, employing a double phase-averaging technique. The numerical investigation was performed with an unsteady 3-D Navier-Stokes method that solves for the entire blade row. The current study reveals that a vortex structure forms near the leading edge plane. This vortex is the result of interactions among the classical tip-clearance flow, axially reversed endwall flow, and the incoming flow. The vortex travels from the suction side to the pressure side of the passage at roughly half of the rotor speed. The formation and movement of this vortex seem to be the main causes of unsteadiness when rotating instability develops. Due to the nature of this vortex, the classical tip-clearance flow does not spill over into the following blade passage. This behavior of the tip-clearance flow is why the compressor operates in a stable mode even with the rotating instability, unlike traditional rotating stall phenomena.Copyright © 2001 by ASME

Air bearing facilitating load/unload of a magnetic read/write head

Abstract: An air bearing surface for use on a magnetic read/write head. The air bearing surface provides a stable flight profile while exhibiting exception load/unload characteristics through the use of a plurality of pads providing high pressure areas as well as a central cavity providing a sub-ambient pressure to counter the high pressure areas. The channel is set a predetermined distance from the leading edge of the air bearing, the predetermined distance being greater than with prior art designs. A channel extends from the leading edge to the cavity to allow airflow into the cavity. The channel and the set back of the cavity both act in conjunction to facilitate unloading of the air bearing by preventing excessive sub ambient pressures.

Perpendicular magnetic recording heads with write pole shaped to reduce skew effects during writing

Abstract: A writer for perpendicular recording on bilayer media with suppressed skew angle effect on the width of the recorded track is disclosed. The writer has a wide and flat trailing edge and a narrow leading edge. In a preferred embodiment, the pole has a trapezoidal cross-section. To suppress the skew effect on the width of the recorded track, the slope angle of the pole sides may be greater than the maximum skew angle in a drive.

Leading-edge receptivity of a hypersonic boundary layer on a flat plate

Abstract: Experimental investigations of the boundary layer receptivity, on the sharp leading edge of a at plate, to acoustic waves induced by two-dimensional and three- dimensional perturbers, have been performed for a free-stream Mach number M∞ = 5.92. The fields of controlled free-stream disturbances were studied. It was shown that two-dimensional and three-dimensional perturbers radiate acoustic waves and that these perturbers present a set of harmonic motionless sources and moving sources with constant amplitude. The disturbances excited in the boundary layer were measured. It was found that acoustic waves impinging on the leading edge generate Tollmien–Schlichting waves in the boundary layer. The receptivity coefficients were obtained for several radiation conditions and intensities. It was shown that there is a dependence of receptivity coefficients on the wave inclination angles.

Mobius combination of reversion and return path in a paper transport system

Abstract: An apparatus for processing a substrate on two sides. A substrate has a first edge as a leading edge in a process direction and a first side in a face-up orientation. In one embodiment, the apparatus comprises an input pathway for receiving the substrate from a substrate processing station, a station for processing the face-up side of the substrate, a reversion pathway for reverting the substrate and returning the reverted substrate to the input pathway. After reversion, a second side of the substrate is in the face up orientation and the first edge is the leading edge. A merge point merges the reverted substrate into the input pathway for processing the face-up side of the substrate in the print station.

Shape of a liquid front upon dewetting.

Abstract: The profile of a liquid front of a polymer film dewetting a solid substrate is examined by atomic force microscopy. The material removed from the substrate is accumulated in a rim next to the three-phase contact line. Theory predicts the leading edge of the rim profile to be a damped harmonic oscillation for a large class of systems. This is investigated experimentally for the first time, and we show that a non-Newtonian liquid behaves qualitatively different due to viscoelastic effects. It is pointed out that analysis of the rim shapes allows one to study quantitatively the rheological properties of complex fluids on a nanometer scale.

Edge-source acoustic Green's function for an airfoil of arbitrary chord, with application to trailing-edge noise

Abstract: Approximations are derived for the three-dimensional, time-harmonic acoustic Green's function whose normal derivative vanishes on the surface of an airfoil of finite thickness and chord for source locations in the neighbourhood of either the leading or trailing edge. The acoustic wavelength is assumed to be large relative to the airfoil thickness, but no restriction is placed on its magnitude relative to . A multiple scattering calculation is performed for high frequencies that involves an expansion in terms of the successive scattering of waves from the leading and trailing edges of the airfoil. The 'principal subseries' of the expansion is summed and shown to provide an excellent approximation for the Green's function when κ 0 ≥ 1, where κ 0 is the acoustic wavenumber. The solution is extended down to κ 0 = 0 by interpolation with the corresponding Green's function for an airfoil of acoustically compact chord. The results extend the single scattering approximation introduced by R. K. Amiet (AIAAJ. 12 1970), and are illustrated by application to the problem of trailing-edge noise generated by nominally steady, low Mach number flow past the airfoil. Experiments and numerical simulations of such flows often include acoustic frequencies that are sufficiently small that the usual assumption of trailing-edge noise theory, that the airfoil is semi-infinite, is not valid.

Computational Design and Experimental Evaluation of Using a Leading Edge Fillet on a Gas Turbine Vane

Abstract: With the desire for increased power output for a gas turbine engine comes the continual push to achieve higher turbine inlet temperatures. Higher temperatures result in large thermal and mechanical stresses particularly along the nozzle guide vane. One critical region along a vane is the leading edge-endwall juncture. Based on the assumption that the approaching flow to this juncture is similar to a two-dimensional boundary layer, previous studies have shown that a horseshoe vortex forms. This vortex forms because of a radial total pressure gradient from the approaching boundary layer.This paper documents the computational design and experimental validation of a fillet placed at the leading edge-endwall juncture of a guide vane to eliminate the horseshoe vortex. The fillet design effectively accelerated the incoming boundary layer thereby mitigating the effect of the total pressure gradient. To verify the CFD studies used to design the leading edge fillet, flow field measurements were performed in a large-scale, linear, vane cascade. The flow field measurements were performed with a laser Doppler velocimeter in four planes orientated orthogonal to the vane. Good agreement between the CFD predictions and the experimental measurements verified the effectiveness of the leading edge fillet at eliminating the horseshoe vortex. The flowfield results showed that the turbulent kinetic energy levels were significantly reduced in the endwall region because of the absence of the unsteady horseshoe vortex.Copyright © 2001 by ASME

Partial cavity flows. Part 2. Cavities forming on test objects with spanwise variation

Abstract: Partial cavitation forming on the vertex of a wedge and on the leading edge of a stationary hydrofoil was experimentally examined. The geometry of these test objects varied in the spanwise direction (i.e. three-dimensional test objects). Closed cavities formed on these test objects. The interface of the closed cavities curved smoothly to form a re-entrant jet at the cavity terminus, and the re-entrant flow was directed spanwise, thus preventing its impingement on the cavity interface. The cavity shape and the pressure gradients near the closure of the closed cavities were qualitatively similar to those predicted with the two-dimensional free-streamline theory. These cavities had a steady, laminar flow reattachment. The flow around the closed cavity was largely irrotational.

Single pole type recording head and magnetic storage apparatus

Abstract: A magnetic head for perpendicular recording without writing from the lateral sides of a main pole and without erasing data on adjacent tracks. A magnetic disk storage apparatus using the magnetic head. The lateral side of the main pole of a magnetic head for perpendicular recording may have an inverted tapered shape obtained by forming a groove as a track portion to an inorganic insulating layer and then forming a magnetic layer and then flattening the upper surface. A leading edge, a trailing edge, or both lateral edges of the magnetic head may be tapered. The taper may be either smooth and linear or curved in profile.

Unsteady aerodynamics of flap cove flow in a high-lift device configuration

Abstract: The unsteady flow around the flap cove region of a three-element high lift aerofoil configuration has been experimentally investigated using Particle Image Velocimetry (PIV) and Laser Doppler Anenometry (LDA). Measurements were carried out in the University of Southampton 3.5m x 2.5m and 2.1m x 1.7m wind tunnels on the two-dimensional National High Lift Programme (NHLP) model in typical landing configuration. The flow inside the flap cove resembles that of a leading-edge slat A strong shear layer separates from the cove lip and rolls-up downstream into a series of large, coherent vortices. These impinge on the main element surface and are seen to strike the leading edge of the flap. The effect of the flap gap stabilising the flow is seen in Reynolds stress and turbulent kinetic energy profiles within the flap cove. The wake of the main element trailing edge resembles a mixing layer, with little evidence of vortex shedding.

Analysis of Vortical Flow Field in a Propeller Fan by LDV Measurements and LES—Part I: Three-Dimensional Vortical Flow Structures

Abstract: Three-dimensional structures of the vortical flow field in a propeller fan with a shroud covering only the rear region of its rotor tip have been investigated by experimental analysis using laser Doppler velocimetry (LDV) measurements and by numerical analysis using a large eddy simulation (LES) in Part I of the present study. The propeller fan has a very complicated vortical flow field near the rotor tip compared with axial fan and compressor rotors. It is found that three vortex structures are formed near the rotor tip: the tip vortex, the leading edge separation vortex, and the tip leakage vortex. The tip vortex is so strong that it dominates the flow field near the tip. Its formation starts from the blade tip suction side near the midchord. Even at the design condition the tip vortex convects nearly in the tangential direction, thus impinging on the pressure surface of the adjacent blade. The leading edge separation vortex develops close along the tip suction surface and disappears in the rear region of the rotor passage. The tip leakage vortex is so weak that it does not affect the flow field in the rotor.

Twisted stator vane

Abstract: A compressor stator includes an outer casing supporting a row of stator vanes extending radially inwardly therefrom. Each vane includes pressure and suction sides extending axially between leading and trailing edges and radially between a root and a tip. The root and tip are twisted relative to a pitch section disposed therebetween. Each vane tip is radially convex adjacent a leading edge for defining an axially concave outer flowpath in the casing for reducing peak velocity of airflow for enhanced efficiency.

Investigation of advanced turbulence models for the flow in a generic wing-body junction

Abstract: The predictive performance of several turbulence models, among them formulations based on non-linear stress-strain relationships and on stress-transport equations, is examined in a collaborative university-industry study directed towards a generic wing-body junction. The geometry consists of a variation of the symmetric NACA 0020 aerofoil mounted on a flat plate, with the oncoming stream aligned with the aerofoil's symmetry plane. The dominant feature of this flow is a pronounced horseshoe vortex evolving in the junction region following separation ahead of the aerofoil's leading edge. This case is one of 6 forming a broad programme of turbulence-model validation by UMIST, Loughborough University, BAE Systems, Aircraft Research Association, Rolls-Royce plc and DERA. Key aspects of this collaboration were a high level of interaction between the partners, the use of common grids and boundary conditions, and numerical verifications aimed at maximizing confidence in the validity of the computational solutions. In total, 12 turbulence models were studied by four partners. Model performance is judged by comparing solutions with experimental data for pressure fields on the plane wall and around the aerofoil; for velocity, turbulence energy, shear stress and streamwise normal stress in the upstream symmetry plane; and for velocity, turbulence energy and shear stress in cross-flow planes downstream of the aerofoil leading edge. The emphasis of the study is on the structure of the horseshoe vortex and its effects on the forward flow. The main finding of the study is that, for this particular 3D flow, second-moment closure offers predictive advantages over the other models examined, especially in terms of the far-field structure of the horse-shoe vortex, although no model achieves close agreement with the experimental data in respect of both mean flow and turbulence quantities.

Airfoils with improved strength and manufacture and repair thereof

Abstract: Methods for repairing and manufacturing a gas turbine airfoil, and the airfoil repaired and manufactured with such methods are presented with, for example, the repair method comprising providing an airfoil having specified nominal dimensions, the airfoil comprising a first material, the first material having a creep life and a fatigue life, the airfoil further comprising a leading edge section and a trailing edge section; removing at least one portion of at least one section of the airfoil to create at least one deficit of material for the airfoil relative to the specified nominal dimensions, the at least one section selected from the group consisting of the leading edge section and the trailing edge section; providing at least one insert comprising a second material, the second material having a creep life that is at least substantially equal to the creep life of the first material, and a fatigue life that is at least substantially equal to the fatigue life of the first material; and disposing the at least one insert onto the airfoil such that the at least one deficit of material is substantially eliminated.

Disc separator plate with air dam

Abstract: A stationary disc separator plate for use in a disc drive to suppress turbulence near a disc drive read/write head used to read data from and write data to a rotatable disc. The stationary plate is supported adjacent the disc and has substantially circular inner and outer circumferences. A leading edge and a trailing edge of the plate define an open portion to accommodate radial movement of the head adjacent the disc. A trailing edge air dam disposed at the trailing edge of the plate diverts a substantial portion of an airflow generated by rotation of the disc away from the open portion to reduce an airflow velocity at the head. In disc drives having multiple discs, a plate is preferably disposed between each pair of adjacent discs. Air vents preferably extend through the thickness of the plate to reduce aerodynamic drag and hence power consumption by the drive.

Semiconductor memory having double data rate transfer technique

Abstract: The semiconductor memory includes a memory cell which handles a clock signal, an address fetch and a command circuit. The memory cell is designated by an address signal and stores data. The clock signal is supplied thereto so as to provide timing for an access to the memory cell, and the clock signal has a leading edge and a trailing edge. The address fetch circuit fetches the address signal for designating the memory cell in synchronism with both of the leading edge and trailing edge of the clock signal. The command circuit fetches a command signal for instructing the access to the memory cell in synchronism with both of the leading edge and the trailing edge of the clock signal.

Theory for broadband Noise of Rotor and Stator Cascades with Inhomogeneous Inflow Turbulence Including Effects of Lean and Sweep

Abstract: The problem of broadband noise generated by turbulence impinging on a downstream blade row is examined from a theoretical viewpoint. Equations are derived for sound power spectra in terms of 3 dimensional wavenumber spectra of the turbulence. Particular attention is given to issues of turbulence inhomogeneity associated with the near field of the rotor and variations through boundary layers. Lean and sweep of the rotor or stator cascade are also handled rigorously with a full derivation of the relevant geometry and definitions of lean and sweep angles. Use of the general theory is illustrated by 2 simple theoretical spectra for homogeneous turbulence. Limited comparisons are made with data from model fans designed by Pratt & Whitney, Allison, and Boeing. Parametric studies for stator noise are presented showing trends with Mach number, vane count, turbulence scale and intensity, lean, and sweep. Two conventions are presented to define lean and sweep. In the "cascade system" lean is a rotation out of its plane and sweep is a rotation of the airfoil in its plane. In the "duct system" lean is the leading edge angle viewing the fan from the front (along the fan axis) and sweep is the angle viewing the fan from the side (,perpendicular to the axis). It is shown that the governing parameter is sweep in the plane of the airfoil (which reduces the chordwise component of Mach number). Lean (out of the plane of the airfoil) has little effect. Rotor noise predictions are compared with duct turbulence/rotor interaction noise data from Boeing and variations, including blade tip sweep and turbulence axial and transverse scales are explored.

Method of forming a slider/suspension assembly

Abstract: A slider/suspension design and assembly method include securing a slider to a suspension assembly for use in a magnetic disk drive data recording device. To this end, a solder fillet bond is applied at the leading edge surface of the slider to provide a structural connection of the slider to the flexure, while also enabling the slider-suspension assembly to be separated without damage during the process. The slider/suspension assembly is initiated by forming a plurality of sliders on a wafer, in such a manner that the trailing edge surfaces of the sliders form the front side of the wafer, and the leading edge surfaces of the sliders form the backside of the wafer. A plurality of thin film data transducing elements and a plurality of electrical contact pads are then formed on the wafer front side.

Gas turbine engine compressor blade restoration method

Abstract: A method of repairing a gas turbine engine compressor blade airfoils includes machining away airfoil material along leading and trailing edges and a radially outer tip of the airfoil to form leading edge, trailing edge, and tip cut-backs. Then beads of welding material are welded onto the leading edge, trailing edge, and tip cut-backs. Then some of the weld material is machined away from the weld bead to obtain desired finished dimensions of the leading and trailing edges and radially outer tip. Blade material along only radially outermost portions of the leading and trailing edges extending from the tip towards a base of the airfoil is machined away. A rounded corner is formed between the leading edge and trailing edge cut-backs and unmachined portions of the airfoil between the outermost portions of the leading and trailing edges and the base of the airfoil.

Cfd-based analysis of nonlinear aeroelastic behavior of high-aspect ratio wings

Abstract: A nonlinear aerodynamic methodology has been loosely coupled to a geometrically exact beam structural analysis to study the static aeroelastic behavior of a high-aspect-ratio wing. The aim of the present effort was to investigate the effects of adding aerodynamic nonlinearity on the elastic behavior, in particular identifying the areas of nonlinearities and their importance. Care was taken to evaluate the Euler solver and the transfer of data between the aerodynamic and structural modules to identify sources of numerical error that may contribute to incorrect modeling of large deflections. It was found that sensitivities near the wing tip and leading edge required additional attention when clustering the computational aerodynamic grid near the surface. Further, the transfer of loads from the Euler code to the structural code requires that the nonlinear drop of forces and moments be modeled as exactly as possible. Otherwise errors in the predicted geometric deformations of up to 10% can occur. These are exacerbated for cases with large deflections and twist. For loosely coupled static aeroelastic simulations, the nonlinear aerodynamic predictions provided by the solution of the Euler equations are lower than the predictions of the vortex panel code. This results in lower predicted bending and twist by the higher-order aerodynamic code, indicating that the divergence and possibly flutter speeds predicted by lower-order aerodynamics may be overly conservative.

Casing treatment for compressors

Abstract: A cast assembly for a gas turbine engine compressor, the compressor including a plurality of axial flow stators and a rotor having a plurality of axial flow blades, each of the blades having a tip section and a leading edge. The assembly comprises a stator outer platform, a boss, a passage, a blade outer shroud and a circumferential slot. A boss is formed in the platform and includes a passage. The passage includes an inlet and an outlet. The inlet is disposed in the circumferential slot. The outlet being disposed upstream of the leading edge of the blades. The passage circumferentially converges inward from the inlet to the outlet. The outer shroud joins with said outer platform during the assembly of the compressor such that the circumferential slot is formed downstream and proximate to the leading edge of the blades. The circumferential slot is in flow communication with the inlet and converges axially.

Slider with high pitch-stiffness air bearing design

Abstract: A slider utilizes a triple-etch, high pitch-stiffness side rail ABS design. The slider is characterized by a relatively deep shallow recession at its leading edge, which maximizes the cavity area while at the same time increases the pitch angle to achieve DLC pad clearance as required by smooth media ABS designs. The slider ABS has a shallower recession at the trailing edge, which provides low gram-load sensitivity and low flying standard deviation. The slider ABS further presents a decreased sensitivity in response to altitude variations.