Showing papers on "Leading edge published in 2003"

Summary of the Delft University Wind Turbine Dedicated Airfoils

Abstract: This paper gives an overview of the design and wind tunnel test results of the wind turbine dedicated airfoils developed by Delft University of Technology (DUT). The DU-airfoils range in maximum relative thickness from 15% to 40% chord. The first designs were made with XFOIL. Since 1995 RFOIL was used, a modified version of XFOIL, featuring an improved prediction around the maximum lift coefficient and capabilities of predicting the effect of rotation on airfoil characteristics. The measured effect of Gurney flaps, trailing edge wedges, vortex generators and trip wires on the airfoil characteristics of various DU-airfoils is presented. Furthermore, a relation between the thickness of the airfoil leading edge and the angle-of-attack for leading edge separation is given.Copyright © 2003 by Delft University of Technology

Flexural stiffness in insect wings II. Spatial distribution and dynamic wing bending

Abstract: The dynamic, three-dimensional shape of flapping insect wings may influence many aspects of flight performance. Insect wing deformations during flight are largely passive, and are controlled primarily by the architecture and material properties of the wing. Although many details of wing structure are well understood, the distribution of flexural stiffness in insect wings and its effects on wing bending are unknown. In this study, we developed a method of estimating spatial variation in flexural stiffness in both the spanwise and chordwise direction of insect wings. We measured displacement along the wing in response to a point force, and modeled flexural stiffness variation as a simple mathematical function capable of approximating this measured displacement. We used this method to estimate flexural stiffness variation in the hawkmoth Manduca sexta, and the dragonfly Aeshna multicolor. In both species, flexural stiffness declines sharply from the wing base to the tip, and from the leading edge to the trailing edge; this variation can be approximated by an exponential decline. The wings of M. sexta also display dorsal/ventral asymmetry in flexural stiffness and significant differences between males and females. Finite element models based on M. sexta forewings demonstrate that the measured spatial variation in flexural stiffness preserves rigidity in proximal regions of the wing, while transferring bending to the edges, where aerodynamic force production is most sensitive to subtle changes in shape.

Magnetic heads for perpendicular recording with trapezoidal pole tips

Abstract: Electromagnetic transducers are disclosed having write poles with a leading edge that is smaller than a trailing edge, which can reduce erroneous writing for perpendicular recording systems. The write poles may have a trapezoidal shape when viewed from a direction of an associated medium. The write poles may be incorporated in heads or sliders that also contain read elements such as magnetoresistive sensors, and may be employed with information storage systems such as disk drives.

Rod and cone contributions to the a‐wave of the electroretinogram of the macaque

Abstract: The electroretinogram (ERG) of anaesthetised dark-adapted macaque monkeys was recorded in response to ganzfeld stimulation and rod- and cone-driven receptoral and postreceptoral components were separated and modelled. The test stimuli were brief (< 4.1 ms) flashes. The cone-driven component was isolated by delivering the stimulus shortly after a rod-saturating background had been extinguished. The rod-driven component was derived by subtracting the cone-driven component from the mixed rod–cone ERG. The initial part of the leading edge of the rod-driven a-wave scaled linearly with stimulus energy when energy was sufficiently low and, for times less than about 12 ms after the stimulus, it was well described by a linear model incorporating a distributed delay and three cascaded low-pass filter elements. Addition of a simple static saturating non-linearity with a characteristic intermediate between a hyperbolic and an exponential function was sufficient to extend application of the model to most of the leading edge of the saturated responses to high energy stimuli. It was not necessary to assume involvement of any other non-linearity or that any significant low-pass filter followed the non-linear stage of the model. A negative inner-retinal component contributed to the later part of the rod-driven a-wave. After suppressing this component by blocking ionotropic glutamate receptors, the entire a-wave up to the time of the first zero-crossing scaled with stimulus energy and was well described by summing the response of the rod model with that of a model describing the leading edge of the rod-bipolar cell response. The negative inner-retinal component essentially cancelled the early part of the rod-bipolar cell component and, for stimuli of moderate energy, made it appear that the photoreceptor current was the only significant component of the leading edge of the a-wave. The leading edge of the cone-driven a-wave included a slow phase that continued up to the peak, and was reduced in amplitude either by a rod-suppressing background or by the glutamate analogue, cis-piperidine-2,3-dicarboxylic acid (PDA). Thus the slow phase represents a postreceptoral component present in addition to a fast component of the a-wave generated by the cones themselves. At high stimulus energies, it appeared less than 5 ms after the stimulus. The leading edge of the cone-driven a-wave was adequately modelled as the sum of the output of a cone photoreceptor model similar to that for rods and a postreceptoral signal obtained by a single integration of the cone output. In addition, the output of the static non-linear stage in the cone model was subject to a low-pass filter with a time constant of no more than 1 ms. In conclusion, postreceptoral components must be taken into account when interpreting the leading edge of the rod- and cone-driven a-waves of the dark-adapted ERG.

Neural edge enhancer for supervised edge enhancement from noisy images

Abstract: We propose a new edge enhancer based on a modified multilayer neural network, which is called a neural edge enhancer (NEE), for enhancing the desired edges clearly from noisy images. The NEE is a supervised edge enhancer: Through training with a set of input noisy images and teaching edges, the NEE acquires the function of a desired edge enhancer. The input images are synthesized from noiseless images by addition of noise. The teaching edges are made from the noiseless images by performing the desired edge enhancer. To investigate the performance, we carried out experiments to enhance edges from noisy artificial and natural images. By comparison with conventional edge enhancers, the following was demonstrated: The NEE was robust against noise, was able to enhance continuous edges from noisy images, and was superior to the conventional edge enhancers in similarity to the desired edges. To gain insight into the nonlinear kernel of the NEE, we performed analyses on the trained NEE. The results suggested that the trained NEE acquired directional gradient operators with smoothing. Furthermore, we propose a method for edge localization for the NEE. We compared the NEE, together with the proposed edge localization method, with a leading edge detector. The NEE was proven to be useful for enhancing edges from noisy images.

Variable geometry turbocharger

Abstract: A variable geometry turbocharger includes vanes disposed therein having an inner airfoil surface oriented adjacent a turbine wheel, and an outer airfoil surface oriented opposite and parallel to the inner airfoil surface. The vane includes first and second axial surfaces that are each positioned perpendicular to and interposed between the inner and outer airfoil surfaces. A vane leading edge is positioned along a first inner and outer airfoil surface junction, and a trailing edge is positioned along a second inner and outer airfoil surface junction. One or more of the first and second axial surfaces have a composite construction comprising a solid section that extends a distance from the leading edge towards the trailing edge, and a cored-out section that extends a distance from the trailing edge towards the leading edge.

Leading-Edge Vortex Structure of Nonslender Delta Wings at Low Reynolds Number

Abstract: The velocity field near the apex region of moderately swept delta wings was measured in a water tunnel, using a version of stereoscopic digital particle imaging velocimetry. Flow visualization was also used to verify these results. In contrast to most recent studies, low angles of attack were emphasized, with most data in the range of 5–20 deg. Delta wings of 50- and 65-deg leading-edge sweep and 30-deg windward-side bevels were tested at Reynolds numbers of 6x10^3 –1.5x10^4. At these low Reynolds numbers, secondary leading-edge vortices were weak, giving way to essentially stagnant flow outboard of the primary leading-edge vortices at the higher angles of attack. Otherwise, velocity data for the 65-deg wing were consistent with well-known observations for slender delta wings. The 50-deg wing exhibited unexpectedly strong primary leading-edge vortices at low angles of attack, with a generally conical velocity field. Upstream progression of vortex breakdown with increasing angle of attack exhibited extensive regions of streamwise undulation. Leading-edge shear-layer rollup was observed in crossflow planes well downstream of the breakdown region, but with an increased occurrence of paired vortical structures of opposite sign inside the shear layer itself.

Analysis of actin dynamics at the leading edge of crawling cells: implications for the shape of keratocyte lamellipodia

Abstract: Leading edge protrusion is one of the critical events in the cell motility cycle and it is believed to be driven by the assembly of the actin network. The concept of dendritic nucleation of actin filaments provides a basis for understanding the organization and dynamics of the actin network at the molecular level. At a larger scale, the dynamic geometry of the cell edge has been described in terms of the graded radial extension model, but this level of description has not yet been linked to the molecular dynamics. Here, we measure the graded distribution of actin filament density along the leading edge of fish epidermal keratocytes. We develop a mathematical model relating dendritic nucleation to the long-range actin distribution and the shape of the leading edge. In this model, a steady-state graded actin distribution evolves as a result of branching, growth and capping of actin filaments in a finite area of the leading edge. We model the shape of the leading edge as a product of the extension of the actin network, which depends on actin filament density. The feedback between the actin density and edge shape in the model results in a cell shape and an actin distribution similar to those experimentally observed. Thus, we explain the stability of the keratocyte shape in terms of the self-organization of the branching actin network.

Flexible shear-stress sensor skin and its application to unmanned aerial vehicles

Abstract: Shear-stress information is of great interest for many fluidic dynamic monitoring/diagnostics application. To obtain such information on non-planar surfaces has long been a significant challenge. This paper describes the development of flexible shear-stress sensor skin and its application on the detection of leading edge flow separation for delta planform unmanned aerial vehicles (UAVs). The sensor skin contains a 1-D array of 36 shear-stress sensors, which can cover the 180° surface of the 1.27 cm diameter semicylindrical UAV leading edge with 5° resolution. The implementation process of the sensor skin is significantly simplified by a packaging scheme based on solder bonding and flexible printed circuit board (PCB). The flexible shear-stress sensor skin in both wind tunnel and real flight tests detected the flow separation along the leading edge successfully.

An Investigation of Vortex Flows over Low Sweep Delta Wings

Abstract: This paper presents the results of a recent investigation into the vortex structure over a nonslender delta wing with leading edge sweep, Λ = 50°. A flow visualisation study in water tunnel experiments has shown profound sensitivity of the vortex structure to Reynolds number. As Reynolds number was reduced, the trajectory of the vortex core moved inboard toward the wing centre-line, and the onset of breakdown was noticeably delayed. The results provide the first experimental evidence of the dual vortex structure that has been observed in previous computational studies. The formation of these dual vortices was also sensitive to Reynolds number, and its formation was not observed at the very low end of values considered. Digital Particle Image Velocimetry (DPIV) measurements of the cross-flow have yielded axial vorticity data at a number of streamwise stations and incidences. At low incidences only a very weak vortex structure was observed with a strong shear layer forming very close to the wing surface. As incidence was increased the shear layer lifted from the surface but reattachment was still observed. Increasing incidence also resulted in a movement of the reattachment line towards the model centre-line, until ultimately reattachment failed.

Turbine blade having angled squealer tip

Abstract: A turbine blade (18) for a gas turbine engine, including an airfoil (24) and integral dovetail (22) for mounting the airfoil (24) along a radial axis (17) to a rotor disk (16) inboard of a turbine shroud (20). The airfoil (24) further includes: first and second sidewalls (28, 30) joined together at a leading edge (32) and a trailing edge (34), where the first and second sidewalls (28,30) extend from a root (36) disposed adjacent the dovetail (22) to a tip plate (48) for channeling combustion gases (12) thereover; and, at least one tip rib (50/52) extending outwardly from the tip plate (48) between the leading and trailing edges (32, 34). The tip rib (50/52) is oriented so that an axis (58/82) extending longitudinally therethrough is at an angle (6/Phi) respect to the radial axis (17) for at least a designated portion (60) of an axial length of the turbine blade (18). Such angle (6/Phi) varies across the designated portion (60).

Leading edge noise from thick foils in turbulent flows

Abstract: The prediction of dipole sound from the diffraction of turbulence by the leading edge of a rigid foil is made using acoustic analogies for homogeneous flows with and without mean shear. The Green’s function accounts for the foil thickness and leading edge shape. A comparison between the theory and published measurements suggests that the foil thickness exponentially attenuates the dipole sound pressure power spectrum by the product of the convection wavenumber and half the maximum section thickness. The ratio of the predicted dipole sound from the mean shear source to the source without mean shear is determined to be proportional to the ratio of the mean shear to the frequency of the sources.

Wind Tunnel Aeroacoustic Tests of Six Airfoils for Use on Small Wind Turbines: Preprint

Abstract: Aeroacoustic tests of seven airfoils were performed in an open jet anechoic wind tunnel. Six of the airfoils are candidates for use on small wind turbines operating at low Reynolds number. One airfoil was tested for comparison to benchmark data. Tests were conducted with and without boundary layer tripping. In some cases a turbulence grid was placed upstream in the test section to investigate inflow turbulence noise. An array of 48 microphones was used to locate noise sources and separate airfoil noise from extraneous tunnel noise. Trailing edge noise was dominant for all airfoils in clean tunnel flow. With the boundary layer untripped, several airfoils exhibited pure tones that disappeared after proper tripping was applied. In the presence of inflow turbulence, leading edge noise was dominant for all airfoils.

Organized modes and the three-dimensional transition to turbulence in the incompressible flow around a NACA0012 wing

Abstract: The transition to turbulence in the incompressible flow around a NACA0012 wing at high incidence is studied by DNS in the Reynolds number range 800–10000. Two main routes are identified for the two-dimensional transition mechanisms: that to aperiodicity beyond the von Karman mode via a period-doubling scenario and the development of a shear-layer instability, forced by the fundamental oscillation of the separation point downstream of the leading edge. The evolution of the global parameters as well as the variation law of the shear-layer instability wavelength are quantified. The history of the three-dimensional transition mechanisms from a nominally two-dimensional flow structure is identified beyond the first bifurcation, as well as the preferred spanwise wavelengths.

Active Control of Separation From the Flap of a Supercritical Airfoil

Abstract: Active flow control in the form of periodic zero-mass-flux excitation was applied at several regions on the leading edge and trailing edge flaps of a simplified high-lift system t o delay flow separation. The NASA Energy Efficient Transport (EET) supercritical airfoil was equipped with a 15% chord simply hinged leading edge flap and a 25% chord simply hinged trailing edge flap. Detailed flow features were measured in an attempt to identify optimal actuator placement. The measurements included steady and unsteady model and tunnel wall pressures, wake surveys, arrays of surface hot-films, flow visualization, and particle image velocimetry (PIV). The current paper describes the application of active separation control at several locations on the deflected trailing edge flap. High frequency (F(+) approx.= 10) and low frequency amplitude modulation (F(+)AM approx.= 1) of the high frequency excitation were used for control. Preliminary efforts to combine leading and trailing edge flap excitations are also reported.

Turbine blade platform cooling system

Abstract: Aspects of the invention relate to a cooling system for a blade platform that can provide cooling to and reduce stress on the platform. Aspects of the invention relate to including one or more channels in the blade platform such that the channels extend from the trailing edge face of the platform toward, but terminate prior to, the leading edge face of the platform. The channels can be generally oval or oblong in conformation. Extending between the hollow shank and the channels can be a plurality of cooling holes. During engine operation, coolant is supplied to the shank of the blade assembly. Because the pressure at the shank is greater than the pressure at the trailing edge of the platform, coolant flow is induced through the cooling holes and into the channels. After flowing through the channels, the coolant can be dumped at the trailing edge.

Particle image velocimetry and visualization of natural and forced flow around rectangular cylinders

Abstract: Particle image velocimetry (PIV) measurements and flow visualization in a water tunnel show that vortex shedding at the leading and trailing edges of rectangular cylinders can be simultaneously phase-locked to transverse velocity perturbations when the applied perturbation Stp is close to an impinging leading-edge vortex/trailing-edge vortex shedding (ILEV/TEVS) frequency. The transverse perturbations, analogous to β-mode duct acoustic resonances, are generated through harmonic oscillations of the sidewalls. When this occurs, the leading-edge vortices are found always to pass the trailing edge at the same phase in the perturbation cycle regardless of the chord-to-thickness (c/t) ratio. Applying perturbations at an Stp not equal to the natural global frequency also results in phase-locked vortex shedding from the leading edge, and a near wake with a frequency equal to the perturbation frequency. This is consistent with previous experimental findings. However, vortex shedding at the trailing edge is either weaker or non-existent. PIV results and flow visualization showed trailing-edge vortex growth was weaker because leading-edge vortices arrive at the trailing edge at a phase in the perturbation cycle where they interfere with trailing-edge shedding. The frequencies at which trailing-edge vortices form for different c/t ratios correspond to the natural ILEV/TEVS frequencies. As in the case of natural shedding, peaks in base suction occur when the leading-edge vortices pass the trailing edge at the phase in the perturbation cycle (and thus in the leading-edge shedding cycle) that allows strong trailing-edge shedding. This is the reason for the similarity in the St vs. c/t relationship for three seemingly different sets of experiments.

Effect of Leading-Edge Curvature on Airfoil Separation Control

Abstract: Separation control on NACA 0012 and NACA 0015 airfoils was compared under incompressible conditions, using leading-edgeperiodicexcitation, in orderto assess the effect of leading-edgecurvature. Both lift and moment coefe cients were considered to compare and analyse control effectiveness. In contrast to the relatively mild NACA 0015 trailing-edge stall, NACA 0012 stall was dominated by a leading-edge bubble-bursting mechanism that gave rise to alternating intervals of partial attachment and separation, but with no regular frequency. Low-amplitude excitation downstream of the bubble enhanced poststall lift and signie cantly attenuated the associated unsteadiness. In general, larger momentum coefe cients were required for NACA 0012 separation control due to the large centrifugal acceleration of the e ow around the leading edge. Because of the different stalling characteristics, relatively high- and low-excitation frequencies were effectivefor the NACA 0012 and NACA 0015 airfoils, respectively. However, the combination of high-excitation amplitudes with relatively low frequencieswas effective on the NACA 0012, and this was believed to be associated with the large harmonic content of the evolving perturbations.

Surface plasma discharge for controlling leading edge contamination and crossflow instabilities for laminar flow

Abstract: The present invention provides a system and method for controlling leading edge contamination and crossflow instabilities for laminar flow on aircraft airfoils that is lightweight, low power, economical and reliable. Plasma surface discharges supply volumetric heating of the supersonic boundary layers to control the Poll Reynolds number and the cross flow Reynolds number and delay transition to turbulent flow associated with the leading edge contamination and crossflow instabilities. A closed-loop feedback control system that incorporates these principles includes three primary components: heat-flow sensors, a PID controller, and plasma discharge elements. Heat-flow sensors distributed around the airfoil surface provide root-mean-square (rms) pulsations of the heat flow to the airfoil skin. These data are fed to the PID controller to determine the flow state (laminar or turbulent) and to drive voltage inputs to the plasma discharge elements, which provide the volumetric heating of the boundary layer on a time scale necessary to adapt to changing flight conditions and delay transition to turbulent flow.

Experimental and Numerical Investigation of Impingement on a Rib-Roughened Leading-Edge Wall

Abstract: Effective cooling of the airfoil leading-edge is imperative in gas turbine designs. Amongst several methods of cooling the leading edge, impingement cooling has been utilized in many modern designs. In this method, the cooling air enters the leading edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. The crossover jets impinge on a smooth leading-edge wall and exit through the film holes, and, in some cases, form a crossflow in the leading-edge cavity and move toward the end of the cavity. It was the main objective of this investigation to measure the heat transfer coefficient on a smooth as well as rib-roughened leading-edge wall. Experimental data for impingement on a leading edge surface roughened with different conical bumps and radial ribs are reported by the same authors, previously. This investigation, however, deals with impingement on different horseshoe ribs and makes a comparison between the experimental and numerical results. Three geometries representing the leading-edge cooling cavity of a modern gas turbine airfoil with crossover jets impinging on 1) a smooth wall, 2) a wall roughened with horseshoe ribs, and 3) a wall roughened with notched-horseshoe ribs were investigated. The tests were run for a range of flow arrangements and jet Reynolds numbers. The major conclusions of this study were: a) Impingement on the smooth target surface produced the highest overall heat transfer coefficients followed by the notched-horseshoe and horseshoe geometries. b) There is, however, a heat transfer enhancement benefit in roughening the target surface. Amongst the three target surface geometries, the notched-horseshoe ribs produced the highest heat removal from the target surface which was attributed entirely to the area increase of the target surface. c) CFD could be considered as a viable tool for the prediction of impingement heat transfer coefficients on an airfoil leading-edge wall.Copyright © 2003 by ASME

Cooled turbine blade

Abstract: The air-cooled turbine blade (120,130) for gas turbine engine has several air inlets (22,25,28) in the root (400) of the blade Some of the inlets may be partially (31) or totally (91) blocked off Jets of air (52) may enter a leading edge (13) passage (37) and may impact on ribs (55) on the inside of the leading edge There are ribs and air outlets (40,61) at the blade tip Air from the main inlet flows through sinusoidal passages (46) inside the blade leading to many small outlets at the trailing edge

Method and apparatus for cooling an airfoil

Abstract: An improved cooling design and method for cooling airfoils within a gas turbine engine is provided which includes a plenum longitudinally located within the leading edge of the airfoils. Within the plenum are positioned a plurality of turbulence promoters to provide enhanced heat transfer within the leading edge. Also, the cooling design includes a plurality of inlets to receive cooling air from an internal cavity of the airfoil as well as a plurality of outlets located within a trench on the exterior surface of the leading edge through which the cooling air exits to film cool the leading edge.

Cooling structure of stationary blade, and gas turbine

Abstract: A collision plate having plural small holes is provided at an interval from a bottom surface of an inner shroud to form a chamber and guides cooling air from the small holes into the chamber. A leading edge flow path is provided at a leading edge side along a width direction and introduces the cooling air. A side flow path is provided along both sides of the inner shroud and guides the cooling air to a trailing edge side. A header is formed along the width direction near the trailing edge and guides the cooling air from the side flow path. Plural trailing edge flow paths are formed at the trailing edge side at intervals along a width direction, in which one end of each flow path is connected to the header and the other end is open at the trailing edge, and the cooling air in the header is ejected from the trailing edge.

Influence of airfoil shape on performance in insect flight

Abstract: Recent developments in Micro-Aerial Vehicles have stimulated research into insect aerodynamics. DNS studies of insect flight showed the important role of vortex shedding on the performance characteristics of insects. Most airfoils considered where thick and had an unnatural, blunt (elliptic) trailing and/ or leading edge. Experimental results of fixed airfoils also performing at sub-critical Reynolds numbers suggest a significant performance loss due to thickness and blunt leading and trailing edges, since they promote unfavorable separation of the boundary layer. In this study a flapping insect wing is modeled with a sinusoidal plunging airfoil. The corresponding two-dimensional unsteady, incompressible Navier-Stokes equations are solved with respect to a body-fixed coordinate system. This non-inertial coordinate system introduces a body force. The equations are solved with a validated and verified Navier-Stokes solver for Reynolds number 150, Strouhal number 0.25 and dimensionless amplitude (A/c) 1.5. The aerodynamic performance characteristics of a blunt 10% ellipse and N0010 airfoil are compared, statically and dynamically, with the thinner and sharper 2% ellipse, N0002 and N4702 airfoil.

Analysis of digital timing methods with BaF2 scintillators

Abstract: Various digital methods were examined for determining the relative arrival times of pulses from to 5.08×2.54 cm BaF 2 scintillators. In this study, pulses from the photomultiplier tubes were digitized by a 1 Gs/s analog-to-digital converter and post processed with multiple techniques. These techniques include: (1) leading edge discrimination, (2) moment-analysis, (3) constant-fraction discrimination, (4) digital constant-fraction discrimination, (5) triangular pulse shaping with a leading edge linear regression, and (6) pulse-shape fitting. Average timing resolutions of 456±8 ps were obtained with constant-fraction discrimination, which is slightly higher than the analog average resolution of 419±7 ps. This study explores the application of these digital techniques for pulse-timing applications and their potential advantages and limitations.

Turbine stage one shroud configuration and method for service enhancement

Abstract: A stator shroud segment is provided that includes an outer shroud having a leading edge groove and a trailing edge groove, both grooves of the outer shroud opening in a first, axial direction; and a plurality of inner shrouds each having a leading edge hook and a trailing edge hook The hooks of the inner shrouds project in a second, axial direction, diametrically opposite the first axial direction and the leading and trailing hooks of each of the inner shrouds are respectively engaged with the leading and trailing edge grooves of the outer shroud so as to axially and radially lock the inner shrouds to the outer shroud The assembly simplifies access to and removal of the inner shroud(s) without added complexity