Showing papers on "Leading edge published in 1998"

Post-stall flow control on an airfoil by local unsteady forcing

Abstract: By using a Reynolds-averaged two-dimensional computation of a turbulent flow over an airfoil at post-stall angles of attack, we show that the massively separated and disordered unsteady flow can be effectively controlled by periodic blowing–suction near the leading edge with low-level power input. This unsteady forcing can modulate the evolution of the separated shear layer to promote the formation of concentrated lifting vortices, which in turn interact with trailing-edge vortices in a favourable manner and thereby alter the global deep-stall flow field. In a certain range of post-stall angles of attack and forcing frequencies, the unforced random separated flow can become periodic or quasi-periodic, associated with a significant lift enhancement. This opens a promising possibility for flight beyond the static stall to a much higher angle of attack. The same local control also leads, in some situations, to a reduction of drag. On a part of the airfoil the pressure fluctuation is suppressed as well, which would be beneficial for high-α buffet control. The computations are in qualitative agreement with several recent post-stall flow control experiments. The physical mechanisms responsible for post-stall flow control, as observed from the numerical data, are explored in terms of nonlinear mode competition and resonance, as well as vortex dynamics. The leading-edge shear layer and vortex shedding from the trailing edge are two basic constituents of unsteady post-stall flow and its control. Since the former has a rich spectrum of response to various disturbances, in a quite wide range the natural frequency of both constituents can shift and lock-in to the forcing frequency or its harmonics. Thus, most of the separated flow becomes resonant, associated with much more organized flow patterns. During this nonlinear process the coalescence of small vortices from the disturbed leading-edge shear layer is enhanced, causing a stronger entrainment and hence a stronger lifting vortex. Meanwhile, the unfavourable trailing-edge vortex is pushed downstream. The wake pattern also has a corresponding change: the shed vortices of alternate signs tend to be aligned, forming a train of close vortex couples with stronger downwash, rather than a Karman street.

Modification of lifting body aerodynamics using synthetic jet actuators

Abstract: The control of separated flow on an unconventional airfoil using synthetic jet actuators was investigated experimentally. A symmetric airfoil based on the aft portion of a NACA four-digit series airfoil with a cylindrical leading edge was used in the experiment. The tests were conducted at Rec=3(10)5. For a>5°, the flow separated from the airfoil surface. Applying synthetic jet control near the leading edge, upstream of the separation point, reattached the separated flow fixangle of attack up to 18°. The effect of control location and amplitude was investigated for different angles of attack. Hot wire measurements in the nearwake of the airfoil revealed a transient passing of vortices associated with the transition from separated to reattached flow on the airfoil.

Free convection boundary-layer flow of a micropolar fluid from a vertical flat plate

Abstract: We examine theoretically the steady free convection from a vertical isothermal flat plate immersed in a micropolar fluid. The governing non-similar boundary-layer equations are derived and are found to involve two material parameters, K and n. These equations are solved numerically using the Keller-box method for a range of values of both parameters. A novel feature of the numerical solution is that the boundary layer develops a two-layer structure far from the leading edge. This structure is analysed using asymptotic methods and it is shown that there are two different cases to be considered, namely when n ¬= 1/2 and when n = 1/2. The agreement between the numerical results and the asymptotic analysis is found to be excellent in both cases. The present paper enables a complete description of the flow to be made for all values of K and n, and for all distances from the leading edge for which the boundary-layer approximation is valid.

Active flow control applied to an airfoil

Abstract: Results of numerical simulations of active flow control applied to an airfoil using the Reynoldsaveraged Navier-Stokes equations are presented. The simulations are first compared with the poststall separation control experiments of Seifert et al.1'12 on a NACA0015 at 1.2 x 106 chord Reynolds number. The jet is introduced tangential to the surface at the leading edge of the airfoil. The calculated lift increments are in good agreement with the experimental data. Two flow-control techniques for a NACA0012 airfoil at a chord Reynolds number of 8.5 x 10 6 are investigated. The first technique utilizes a small, 0.5% chord, steady jet, and the second method employs a synthetic jet of a similar scale. Performance benefits are obtained by placing the actuators very near the airfoil leading edge on the suction surface. A significant increase in lift (29%) is obtained using the synthetic jet actuator in the post-stall regime. At lower lift, the steady jet actuator significantly reduces drag by rotating the lift vector upstream.

Front propagation: Precursors, cutoffs, and structural stability

Abstract: We discuss the problem of fronts propagating into metastable and unstable states. We examine the time development of the leading edge, discovering a precursor which in the metastable case propagates out ahead of the front at a velocity more than double that of the front and establishes the characteristic exponential behavior of the steady-state leading edge. We also study the dependence of the velocity on the imposition of a cutoff in the reaction term. These studies shed light on the problem of velocity selection in the case of propagation into an unstable state. We also examine how discreteness in a particle simulation acts as an effective cutoff in this case.

Role of Blade Passage Flow Structures in Axial Compressor Rotating Stall Inception

Abstract: The influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception. The computations displayed a short length-scale (or spike) type of stall inception similar to that seen in experiments; to the authors’ knowledge this is the first time such a feature has been simulated. A central feature observed during the rotating stall inception was the tip clearance vortex moving forward of the blade row leading edge. Vortex kinematic arguments are used to provide a physical explanation of this motion as well as to motivate the conditions for its occurrence. The resulting criterion for this type of stall inception (which appears generic for axial compressors with tip-critical flow fields) depends upon local flow phenomena related to the tip clearance and it is thus concluded that the flow structure within the blade passages must be addressed to explain the stability of an axial compression system which exhibits such short length-scale disturbances.© 1998 ASME

Dynamics of spontaneous spreading with evaporation on a deep fluid layer

Abstract: The spontaneous spreading of a thin volatile film along the surface of a deep fluid layer of higher surface tension provides a rapid and efficient transport mechanism for many technological applications. This spreading process is used, for example, as the carrier mechanism in the casting of biological and organic Langmuir–Blodgett films. We have investigated the dynamics of spontaneously spreading volatile films of different vapor pressures and spreading coefficients advancing over the surface of a deep water support. Laser shadowgraphy was used to visualize the entire surface of the film from the droplet source to the leading edge. This noninvasive technique, which is highly sensitive to the film surface curvature, clearly displays the location of several moving fronts. In this work we focus mainly on the details of the leading edge. Previous studies of the spreading dynamics of nonvolatile, immiscible thin films on a deep liquid layer have shown that the leading edge advances in time as t3/4 as predicted by laminar boundary layer theory. We have found that the leading edge of volatile, immiscible spreading films also advances as a power law in time, talpha, where alpha ~ 1/2. Differences in the liquid vapor pressure or the spreading coefficient seem only to affect the speed of advance but not the value of the spreading exponent, which suggests the presence of a universal scaling law. Sideview laser shadowgraphs depicting the subsurface motion in the water reveal the presence of a single stretched convective roll right beneath the leading edge of the spreading film. This fluid circulation, likely caused by evaporation and subsequent surface cooling of the rapidly spreading film, resembles a propagating Rayleigh–Benard convective roll. We propose that this sublayer rotational flow provides the additional dissipation responsible for the reduced spreading exponent.

Active control of flow-induced cavity resonance

Abstract: Grazing flows over open cavities may result in the excitation of self-sustaine d flow oscillations at the acoustic resonance frequency of the cavity system. The associated pressure oscillations and radiated sound are objectionable in situations where they may cause excessive structural vibrations, resulting in acoustic fatigue, or excessive sound radiation in the vicinity of the cavity. Many solutions have been proposed to solve this problem, including for example leading edge spoilers, trailing edge deflectors, and leading edge airmass injection. Most of these control methods are "passive" i.e. they do not require dynamic control systems. Active control methods, which do require dynamic controls, have also been implemented with success for different cases of flow instabilities. Previous investigations of the control of flow-excited cavity resonance have used mainly one or more loudspeakers located within the cavity wall. In the present study, an oscillated spoiler hinged near the leading edge of the cavity orifice is proposed as the actuation device. Experiments were performed using a side-branch cavity installed within the wall of a closed test section wind tunnel. The spoiler was driven using a moving coil loudspeaker. A microphone located within the cavity was used as the feedback sensor. A loop shaping feedback control design methodology was followed in order to ensure robust controller performance over different, varying flow conditions. Cavity pressure level attenuation of up to 20 dB was achieved around the critical velocity, relative to the level in presence of the spoiler held stationary. Actuation effort was low. The spoiler peak displacement was typically smaller than 4% of the mean spoiler angle (i.e. smaller than 1 degree). The control scheme was found to provide robust performance for transient operating conditions (for example when the controller was abruptly turned on, or the flow velocity varied). The potential advantages of oscillated leading edge spoilers relative to loudspeakers for cavity resonance problems are reduced encumbrance (especially for low-frequency applications), and reduced actuation effort.

Study of the Unsteady Flow Features on a Stalled Wing

Abstract: The occurrence of large scale structures in the post stall flow over a rectangular wing at high angles of attack was investigated in a small-scale subsonic wind tunnel. Mean and time dependent measurements within the separated flow field suggest the existence of two distinct angle of attack regimes beyond wing stall. The shallow stall regime occurs over a narrow range of incidence angles (2-3 deg.) immediately following the inception of leading edge separation. In this regime, the principal mean flow structures, termed stall cells, are manifested as a distinct spanwise periodicity in the chordwise extent of the separated region on the model surface with possible lateral mobility not previously reported. Within the stall cells and on the wing surface, large amplitude pressure fluctuations occur with a frequency much lower than anticipated for bluff body shedding, and with minimum effect in the far wake. In the deep stall regime, stall cells are not observed and the separated region near the model is relatively free of large amplitude pressure disturbances.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

Abstract: The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Re ex = 6 x 10 5 and 1.2 x 10 6 ). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

Nonlinear convective/absolute instabilities in parallel two-dimensional wakes

Abstract: The linear versus nonlinear convective/absolute instability of a family of plane wake profiles at low Reynolds number is investigated by numerically comparing the linearized and the fully nonlinear impulse responses. Through an analysis of the linear flow response obtained by direct numerical simulation (DNS), the linear temporal and spatiotemporal instability properties are retrieved, in excellent agreement with the properties obtained by Monkewitz [Phys. Fluids 31, 3000 (1994)] from the study of the associated viscous dispersion relation. Nonlinear terms are then shown to limit the amplitude to a saturation level within the response wave packet, while leaving the trailing and leading edges unaffected. For this family of open shear flows, the velocities of the fronts, formed between the trailing or leading edge and the central saturated region, are thus selected according to the linear Dee and Langer criterion [Phys. Rev. Lett. 50, 383 (1983)], whereas the front solutions are fully nonlinear. This proper...

Unsteady Stall Control Using Dynamically Deforming Airfoils

Abstract: Introduction An experiment documenting the compressible flow over a dynamically deforming airfoil is presented. This airfoil, which has a leading edge radius that can be dynamically changed, was tested at various defor- mation rates for fixed airfoils angle of attack. Selected leading-edge shapes were also tested during airfoil os- cillation. These tests show that for a range of Mach numbers observed on the retreating blades of heli- copter rotors the dynamic stall vortex can be avoided by the judicious variation of leading-edge curvature

Centrifugal Pump Performance Drop Due to Leading Edge Cavitation: Numerical Predictions Compared With Model Tests

Abstract: Note: Using Smart Source Parsing 22-26 3 Reference LMH-CONF-1997-004View record in Web of Science Record created on 2005-11-04, modified on 2017-05-10

Inflatable structures to control aircraft

Abstract: An inflatable structure to control aircraft and a method of modifying the shape of an aircraft airfoil before and during flight, which includes inflating or deflating at least one inflatable bladder positioned on an aircraft wing. The inflatable structures to control aircraft include an aircraft wing structure, at least one inflatable section positioned on an aircraft wing structure in at least one location selected from the group of an upper surface, a lower surface, a leading edge and a trailing edge of the aircraft wing structure. The inflatable section is provided for modifying the shape of the aircraft wing before or during flight for causing desired flight characteristics. An elastic wing skin is provided to cover the wing structure and the inflatable structures.

Slider and electro-magnetic coil assembly

Abstract: A slider supports or stores a device such as an electro-magnetic coil assembly, an electronic component, or an optical component, and includes an underside formed of a taper, a flat or patterned air bearing surface, and a recessed region. The recessed region receives the device without significantly affecting the aerodynamic performance of the air bearing surface, and is located at the slider trailing edge. The weight of the device can be compensated by the suspension gram load. In certain applications the device underside is recessed relative to the air bearing surface, while in other application the device underside is flush with the air bearing surface. The device includes an electrical conductor that extends along the recessed region. According to another embodiment, the slider includes a vertical channel located in a front side of the slider that extends along the entire slider depth. The vertical channel accommodates the electrical conductor of the device. One or more horizontal channels may optionally be formed in the slider front side, at an angle relative to the vertical channel, such that at least one of these horizontal channels is connected to the vertical channel. According to yet another embodiment, the slider is modularly formed, and has an upper section, a lower section secured to the upper section, wherein the upper slider section includes a taper at a leading edge, and a flat or patterned air bearing surface. A recessed region is defined by a trailing edge of the upper slider section, and the lower slider section.

Turbine blade with trailing edge root section cooling

Abstract: A convectively cooled turbine blade 10 has two distinct cooling air passage systems. The first system 30 cools the blade leading edge and emits cooling air through outlet passageways 36 in the leading edge arranged in showerhead array. The second system 38 includes a five-pass series flow passage comprising five cooling passage sections 41-45 that extend in series through the remainder of the blade. One of the passage sections includes a plurality of recesses 92,94 near the trailing edge 20 of the turbine blade to retain cooling air flow to the trailing edge adjacent the root portion of the blade.

Ribbed turbine blade tip

Abstract: A gas turbine engine turbine blade (10) squealer tip (28) includes an airfoil tip cap (29) having an airfoil shape (30) and pressure and suction sides (32, 34) joined together at chordally spaced apart leading and trailing edges (20, 22) of the tip cap (29). The squealer tip (28) further includes a plurality of squealer ribs (36) extend outward from the tip cap (29) between the leading and trailing edges (20, 22) and substantially parallel channels (38) between the squealer ribs (36). The squealer ribs (36) and channels may have rectangular cross-sections and may also include a trailing edge rib (42) along a portion of the suction side including the trailing edge and/or a leading edge rib (48) curved around an axially extending portion of the leading edge (20). The squealer ribs (36) are preferably angled in an axially aft direction (46) from the leading edge (20) on the suction side towards the trailing edge (22) on the pressure side. Channel ribs may be disposed between the squealer ribs (36) and across the channels and may be arranged such that only one of the channel ribs is disposed across each of the channels. The squealer tip (28) may be constructed with no apertures through the tip cap (29) in the channels between squealer ribs (36).

Blunt-leading-edge raked wingtips

Abstract: An airplane having a fuselage (11), opposed main wings (12), and blunt-leading-edge raked wingtips (8) is provided Each main wing includes an outboard end (9) and a leading edge (14) having an outboard end leading-edge nose and nose radius One blunt raked wingtip (8) is located at each main wing outboard end (9) and includes a leading edge (20) swept back from the main wing leading edge (14) Each blunt raked wingtip (8) further includes a plurality of local airfoils each having a leading-edge nose radius and a chord The nose radius is greater than about 2% of the local chord for the majority of the airfoils The relative bluntness of the raked wingtips minimizes boundary-layer separation, drag associated with boundary-layer separation, and premature buffeting of the aircraft during low speed flight

Investigation of confluent boundary layers in high-lift flows

Abstract: The confluent boundary layers over a three-element high-lift airfoil are studied using both numerical and experimental approaches. The results suggest that wake prediction is crucial to the convergence and accuracy of the overall solution. At maximum lift, unsteadiness is observed in the experiment, which is not captured by computations. However, solutions at maximum lift indicate that, although the flow is attached over the flap, the separation bubble at the leading edge of the slat upper surface is coupled with inviscid flow reaching the compressibility limit. The thickened slat wake results in a displacement of near-surface flow over the main element and limits the main element from gaining more lift. The trends in the confluent boundary layers development require all aspects of the physics be modeled appropriately, including transition, turbulence, and inviscid-viscous interaction

High efficiency ceiling fan

Abstract: Ceiling fan blades for low speed fan operation. The blades have a positive twist at the root motor portion of the blade and a slightly twisted rounded tip. The chord of the blades taper down from the root to the rounded tip, and have a tapered airfoil from the aft forward aft edge to the trailing edge. The airfoil has a combination of a rounded leading edge with sharp trailing edge, and a square leading edge and rounded trailing edge. The blades can be twenty inches in length and twenty-six inches in length, and be used in ceiling fans having two, three, four or more blades in a ceiling mount. The ceiling fan blades are optimized to operate in ceiling fans running at low speed ranges of approximately 50 to approximately 200 revolutions per minute(rpm) with an enhanced axial airflow which provide substantial energy savings and increased air flow over conventional flat planar ceiling fan blades.

Rotary seal with enhanced lubrication and contaminant flushing

Abstract: A resilient, ring shaped interference-type hydrodynamic rotary seal having waves on the lubricant side which provide increased film thickness and flushing action by creating contact pressure induced angulated restrictions formed by abrupt restrictive diverters. The angulated restrictions are defined by projecting ridges, corners at the trailing edge of the waves, or simply by use of a converging shape at the trailing edge of the waves which is more abrupt than the gently converging hydrodynamic inlet shape at the leading edge of the waves. The abrupt restrictive diverter performs two functions; a restricting function and a diverting function. The angulated restrictions cause a local film thickness restriction which produces a damming effect preventing a portion of the lubricant from leaking out of the dynamic sealing interface at the trailing edge of the wave, and results in a much thicker lubricant film thickness under the waves. This contributes to more film thickness in the remainder of the dynamic sealing interface toward the environment because film thickness tends to decay gradually rather than abruptly due to the relative stiffness of the seal material. Because of the angle of the abrupt restrictive diverter relative to the relative rotation direction, in conjunction with the restriction or damming effect, a strong diverting action is produced which pumps lubricant across the dynamic sealing interface toward the environment. The lubricant diversion is caused by the component of the rotational velocity tangent to the abrupt restrictive diverter. The component of rotational velocity normal to the abrupt restrictive diverter causes a portion of the lubricant film to be pumped past the abrupt restrictive diverter, thereby assuring adequate lubrication thereof.

Air dams positioned between spinning disks for reducing the vibration in a data storage device

Abstract: A vibration-reduction device for a disk drive includes providing air dams that regulate air intake and air expulsion relative to gaps between adjacent data disks of a disk stack. In the preferred embodiment, the dams are formed by a number of arrays of fingers, with each gap between adjacent data disks receiving a finger from each of the arrays. The fingers within a gap are spaced apart to partition the gap into air flow cells. The fingers cleave circulating air from the gap before the air has sufficient rotational velocity to expel itself as a result of centrifugal force. Thus, the air is expelled in a controlled manner that retards aerodynamic forces having sufficient energy to induce vibration of the disks. In another embodiment, each finger of an array has a configuration that defines nonuniform clearances between the finger and each data disk on the opposite sides of the finger. For example, each finger may have a cross section in which the dimension of the leading edge is greater than the dimension of the trailing edge, with the leading edge being forward of the trailing edge with respect to the direction of disk rotation. This geometry reduces the likelihood that local turbulence will induce aerodynamic forces having a sufficient magnitude to induce disk vibration. Other geometries that provide nonuniform finger-to-disk clearance may be substituted, particularly if disk rotation is bidirectional.

Heat Transfer in a Rotating Radial Channel With Swirling Internal Flow

Abstract: This paper presents experimental results for heat transfer in swirling internal flow, obtained in two ways. A test rig simulated a rotating blade’s leading edge internal passage with heated walls and screw-shaped cooling swirl generated by flow introduced through discrete tangential slots. Spatially resolved variations of the surface heat transfer coefficients were measured in the rotating rig using an IR radiometer.A blade tested in the actual engine environment had similar geometry of the leading edge cooling passage. The blade surface temperatures were mapped in the engine with thermal paints and compared with a traditional convective cooling configuration. The data from the rotating rig and engine measurements are also compared with non-rotating heat transfer results obtained in the hot cascade using a traversing pyrometer at a realistic wall-to-coolant temperature ratio.The results are presented for realistic rotational numbers, ranging from 0 to 0.023, and for representative Reynolds number of 20,000 based on the channel diameter. The effect of Coriolis forces is evident with the change of direction of the rotation. A slight negative influence of the crossflow, which increased toward the outer radius of the channel, was recorded in the rig test results.The results presented will assist in better understanding of the screw-shaped swirl cooling technique, providing the next step toward the application of this highly-effective internal cooling method for the leading edges of turbine blades.© 1998 ASME

Apparatus and method for applying heat bondable lamina to a substrate

Abstract: Apparatus and method for making a plurality of substrates laminated on two sides by applying a plurality of laminate sheets to corresponding plurality of substrates. The apparatus includes a lamina supply member capable of holding a supply of lamina from which successive sheets of lamina can be cut. One or more cutters are disposed in the apparatus such that the cutters are capable of cutting through the lamina to provide successive sheets of laminate. One or more heaters are provided for bonding sheets of laminate to corresponding sides of a substrate whereby the corresponding top and bottom laminated substrate is formed. The supply of lamina is characterized by a current leading edge. The supply of lamina is cut through along a cutting line at a predetermined distance from the current leading edge of the lamina. This provides a first sheet of laminate having a trailing edge at the cutting line. Cutting also provides the lamina supply with a successive leading edge at the cutting line. There is substantially no wasted lamina material between the trailing edge of the laminate sheet and the successive leading edge of the lamina. The laminate sheets are then bonded to the top and bottom sides of a corresponding substrate. The steps of cutting the lamina along a cutting line and bonding the resultant laminate sheets to the top and bottom sides of a corresponding substrate are repeated a plurality of times to yield the plurality of laminated substrates.

Electroformed sheath and airfoiled component construction

Abstract: A sheath for covering and protecting a component leading edge of an airfoiled component is disclosed. The sheath includes a sheath leading edge, and a first protective side and a second protective side, wherein the first and second protective sides are merged at the sheath leading edge. A cavity is formed between the first and second protective sides, wherein the cavity is adapted to have the airfoiled component positioned therein and engage an inside surface of each of the first and second protective sides. The sheath is formed from a material including cobalt, and preferably a nickel-cobalt composition. Preferred embodiments include cobalt in the nickel-cobalt composition present between 8-32 wt. % and 30-54 wt. %, based on the weight of the sheath. An airfoiled component construction is also disclosed. This construction includes a main structural component formed in the shape of an airfoil, wherein the main structural component has a leading edge, and a sheath covering and protecting the leading edge, wherein the sheath is formed from a material including cobalt such as a nickel-cobalt composition. Preferred embodiments include cobalt in the nickel-cobalt composition present between 8-32 wt. % and 30-54 wt. %, based on the weight of the sheath.

Stabilizing the Advancing Front of Thermally Driven Climbing Films

Abstract: higher surface tension. Experimental investigations have shown films have been shown to be important in the operation of gas that the application of a large temperature gradient produces a thin climbing film whose leading edge develops a pronounced cap- diffusion electrodes in which the oxidation reaction occurs illary rim which breaks up into vertical rivulets. In contrast, almost exclusively in the region above the normal meniscus smaller temperature gradients produce thicker films whose profiles position (1). Enhanced spreading behavior has also been decrease monotonically toward the substrate with no evidence of observed in boundary lubrication problems in which the a rim or subsequent film breakup. We have previously shown evaporation of volatile impurities in the spreading films eswithin linear stability analysis that a climbing film can undergo a tablishes a spontaneous concentration gradient (2). Flows fingering instability at the leading edge when the film is sufficiently created by gradients in surface tension, whether induced by thin or the shear stress sufficiently large for gravitational effects temperature or concentration variations, are commonly to be negligible. In this work we show that thicker films which called thermocapillary or Marangoni-driven flows. These experience significant drainage cannot form a capillary rim and types of flows, which become dominant in situations where spread in stable fashion. Gravitational drainage helps promote a straight advancing front and complete surface coverage. Our the surface-to-volume ratio of the liquid film is large, are numerical predictions for the entire shape and stability of the receiving increased attention as technological advances enclimbing film are in good agreement with extensive experiments courage the production of smaller and lighter componentry. published years ago by Ludviksson and Lightfoot (AIChE J. 17, Although temperature or concentration gradients can 1166 (1971)). We propose that the presence of a counterflow therefore be used very effectively to guide a spreading film which eliminates the capillary rim can provide a simple and gen- to coat a substrate, the coating process will be unsuccessful eral technique for stabilizing thermally driven films in other geom- if the liquid spreads nonuniformly and suffers any instability etries. q 1998 Academic Press at the leading edge. Several groups have shown that ther

Flow control device to eliminate cavity resonance

Abstract: A flow control device and method for eliminating flow-induced cavity resonance within a closed or nearly closed end flow passage (20) having an inlet opening (30) defined between an upstream inlet edge (32) and a downstream inlet edge (34). The passage accepts exterior fluid flow (38) therein via the opening (30). The flow control device includes a stationary inlet guide vane (44) having a leading edge (46), a trailing edge (48), and a number of support members (50) to connect the vane to the inlet. The vane (44) is positioned such that the vane leading edge intercepts the exterior fluid flow shear layer, and the vane trailing edge extends into the passage at the inlet. In a preferred embodiment, the inlet guide vane is located approximately midway between the upstream and downstream inlet edges. The inlet guide vane is cross-sectionally shaped as a cambered airfoil. Flow-induced cavity resonance is reduced or eliminated in the closed or nearly closed end passage through the interception of the free shear layer passing over the inlet opening with an inlet guide vane flow control device.

AFT flowing serpentine airfoil cooling circuit with side wall impingement cooling chambers

Abstract: A gas turbine engine hollow airfoil includes an airfoil outer wall having width wise spaced aparted pressure and suction side walls joined together at chordally spaced apart leading and trailing edges of the airfoil and extending longitudinally from a root to a tip. At least one internal aft flowing serpentine cooling circuit inside the airfoil has an exit that is positioned aft of the entrance so as to have a chordal flow direction afterwards from the leading edge to the trailing edge within the serpentine circuit. At least one longitudinally extending first side wall impingement chamber is in downstream fluid communication with the serpentine cooling circuit within the airfoil and positioned between one of the side walls, preferably the pressure side wall, and a first inner wall bounding the serpentine cooling circuit. Impingement cooling apertures are disposed in the first inner wall between one of the serpentine channels and the side wall impingement chamber. A first plurality of side wall film cooling holes may extend out from the first side wall impingement chamber through the pressure side wall. At least one tip cooling hole extending out of at least one of the impingement chambers may be disposed through a longitudinally outer tip wall of the tip of the airfoil.

Impeller assembly with asymmetric concave blades

Abstract: An impeller assembly (10) for agitating a fluid (31) contained in a vessel (30) and dispersing a gas introduced therein. The impeller assembly (10) includes an impeller having a plurality of generally radially extending blades (16). Each of the blades (16) includes diverging upper and lower sheet-like portions having generally radially extending leading edges. The upper and lower portions are joined to form a generally V-shaped cross-section with a trailing vertex. The width of the upper portion of each blade (16) is greater than the width of the lower portion of the blade such that the upper portion leading edge extends forwardly of the lower portion leading edge, thus producing an upper portion overhang to capture and disperse rising gas bubbles (34). The impeller assembly (10) further comprises a drive assembly (17) for rotating the impeller assembly (10).