Showing papers on "Leading edge published in 1989"

Stability of three-dimensional boundary layers

Abstract: The computational modeling of the transition process characteristic of flows over swept wings is discussed. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full three-dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that regular stability theory is insufficient to explain the discrepancies between experiments and between theory and experiment. The leading edge region of a swept wing will be considered in a three-dimensional spatial simulation with random disturbances as the initial conditions.

Structure of Tip Clearance Flow in an Isolated Axial Compressor Rotor

Abstract: Ensemble-averaged and phase-locked flow patterns in various tip clearances of two axial compressor rotors were obtained by aperiodic multisampling technique with a hot wire in the clearance and with a high-response pressure sensor on the casing wall. A leakage flow region distinct from a throughflow region exists at every clearance. In the case of a small tip clearance, the leakage jet flow interacts violently with the throughflow near the leading edge, and a rolling-up leakage vortex decays downstream. As the clearance increases, a stronger leakage vortex comes into existence at a more downstream location, and a reverse flow due to the vortex grows noticeably. A scraping vortex is recognized at the pressure side near the trailing edge only for the small clearance. A horseshoe vortex appears in the upstream half of the through flow region for every tip clearance. The solidity does not affect the flow pattern substantially except for the interaction of the leakage vortex with the adjacent blade and wake.

Direct numerical study of leading-edge contamination

Abstract: Instability, turbulence, and relaminarization in the attachment-line region of swept and unswept cylindrical bodies are studied by numerical solution of the full Navier-Stokes equations. The flow is simulated over a strip containing the attachment-line and treated as homogeneous in the spanwise direction; the disturbances decay exponentially upstream. Transpiration through the wall may be prescribed. The new method, which admits completely general disturbance, agrees with published linear-stability results, which were limited to an apparently restrictive form of disturbance. Fully developed turbulent solutions with sweep are generated and compare well with the experiment. The turbulence is subcritical (except for blowing), resulting in large hysteresis loops. By lowering the sweep Reynolds number, or increasing the suction, the turbulent flow is made to relaminarize. The relaminarization Reynolds number is much less sensitive to suction than the linear-stability Reynolds number. Extensive attempts to detect the postulated nonlinear instability of the unswept flow failed, suggesting that this flow is linearly and nonlinearly stable.

Rotor-stator interaction in a diffuser pump

Abstract: The interaction between impeller blades and diffuser vanes in a diffuser pump was investigated. Steady and unsteady pressure measurements were taken on the diffuser vanes, and the shroud wall of a vaned and a vane less diffuser. Steady, unsteady, and ensemble averaged unsteady data, as well as frequency spectra are presented. The measurements were made for different flow coefficients, shaft speeds, and radial gaps between impeller blade trailing and diffuser vane leading edge (1.5% and 4.5% based on impeller discharge radius). The resulting lift on the vane, both steady and unsteady, was computed from the pressure measurements at mid vane height. The magnitude of the fluctuating lift was found to be greater than the steady lift. The pressure fluctuations were larger on the suction side than on the pressure side attaining their maximum value, of the same order of magnitude as the total pressure rise across the pump, near the leading edge. Pressure fluctuations were also measured across the span of the vane. and those near the shroud were significantly smaller than those near the hub. The pressure fluctuations on the shroud wall itself were larger for the vaned diffuser than a vaneless diffuser. Lift, vane pressure, and shroud wall pressure fluctuations decreased strongly with increasing radial gap.

Flow-thermal-structural study of aerodynamically heated leading edges

Abstract: A finite element approach for integrated fluid-thermal-structural analysis of aerodynamically heated leading edges is presented. The Navier-Stokes equations for high speed compressible flow, the energy equation, and the quasi-static equilibrium equations for the leading edge are solved using a single finite element approach in one integrated, vectorized computer program called LIFTS. The fluid-thermal-structural coupling is studied for Mach 6.47 flow over a 3-in diam cylinder for which the flow behavior and the aerothermal loads are calibrated by experimental data. Issues of the thermal-structural response are studied for hydrogen-cooled, super thermal conducting leading edges subjected to intense aerodynamic heating.

Programmable air bearing slider including magnetic read/write element

Abstract: An air bearing slider according to the present invention provides a programmable slider wherein the fly height of the read/write head may be conveniently controlled using electrical signals. In an air bearing slider according to the present invention, the rear of the slider is made to fly lower by altering the angle of attack of a rear air bearing region. In one embodiment of the present invention, a slider configuration includes a first air bearing region at the leading edge of the slider and a second air bearing region at the slider's trailing edge. The first air bearing region includes a tapered region. A deformable central region, including a non air bearing surface, joins the first and second air bearing regions and controls the relative angle between the air bearing surfaces. The relative angle is adjusted by deforming the central region using a layer of piezoelectric material which overlays the central region. A conventional read/write head is placed on the rear portion of the second air bearing region.

Experimental Shock-Wave Interference Heating on a Cylinder at Mach 6 and 8

Abstract: This paper presents the details of an experimental study of shock-wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet. The study, which was conducted at Mach numbers of 6.3, 6.5, and 8.0, has provided 1) detailed pressure and heat-transfer-rate distributions for a two-dimensional shock-wave interference on a cylinder and 2) insight into the effects of temperature-d ependent specific heats on the phenomena. The peak pressure and heat-transfer rates were 2-25 times the undisturbed flow stagnation-point levels. The peak levels and their gradients increased with Mach number. Variation in specific heats and, hence, in the ratio of specific heats with temperature is manifested in slightly lower loads and amplification factors than for corresponding perfect-gas conditions.

Mixed Convection Along a Wavy Surface

Abstract: The results of a study of mixed-convection flow along a wavy surface are presented. The forced-convection component of the heat transfer contains two harmonics. The amplitude of the first harmonic is proportional to the amplitude of the wavy surface; the second harmonic is proportional to the square of this amplitude. Thus, for a slightly wavy surface, only the influence of the first harmonic can be detected. The natural-convection component is a second harmonic, with a frequency twice that of the wavy surface. Since natural convection has a cumulative effect, the second harmonic eventually becomes the dominant component far downstream from the leading edge where forced convection is the dominant heat transfer mode. The results also demonstrate that the total mixed-convection heat flux along a wavy surface is smaller than that of a flat surface.

Cooling of turbine blades

Abstract: In order to facilitate efficient use of high pressure cooling air in a turbine rotor blade its aerofoil has a triple-pass convoluted cooling air duct in its leading edge region, and a triple-pass convoluted cooling air duct in its mid-chord region, both of them being fed from a common high pressure inlet in the root of the blade. The trailing edge region has a single-pass duct fed by low pressure cooling air from an inlet located just under the blade platform. The shroud of the blade also has cooling air passages and these are fed from the ends of respective ones of the ducts. Air from the ducts also exits through rows of film cooling holes to film cool the concave flank of the aerofoil and through a row of holes in its trailing edge to remove heat from the thinner metal section in that area.

In-Flight Flow Visualization Characteristics of the NASA F-18 High Alpha Research Vehicle at High Angles of Attack

Abstract: Surface and off-surface flow visualization techniques were used to visualize the 3-D separated flows on the NASA F-18 high alpha research vehicle at high angles of attack. Results near the alpha = 25 to 26 deg and alpha = 45 to 49 deg are presented. Both the forebody and leading edge extension (LEX) vortex cores and breakdown locations were visualized using smoke. Forebody and LEX vortex separation lines on the surface were defined using an emitted fluid technique. A laminar separation bubble was also detected on the nose cone using the emitted fluid technique and was similar to that observed in the wind tunnel test, but not as extensive. Regions of attached, separated, and vortical flow were noted on the wing and the leading edge flap using tufts and flow cones, and compared well with limited wind tunnel results.

Separation control on an airfoil by periodic forcing

Abstract: The introduction of transverse velocity fluctuations into a separated shear layer on an airfoil at high angles of attack is presently demonstrated to be an effective separation-control technique. Airfoil aerodynamic characteristics, including poststall lift and drag as well as maximum lift coefficient and stall angle, all exhibited improvements controlled forcing at 20 deg angle of attack led to an increased spreading of the mean velocity profile, together with increased turbulence activity; separation moved from the leading edge to about 80 percent of chord.

High taper wing tip extension

Abstract: A highly tapered wing tip extension added to the tip of an existing swept, trapezoidal airplane wing for reducing high speed drag significantly. A smaller, highly swept, extension does not require a leading edge device to protect against low speed stall. A larger, less swept, extension requires a tapered slat for which two mechanisms are presented. The principles of the present invention are also applicable to the design of new aircraft.

Turbulence Measurements in a Multistage Low-Pressure Turbine

Abstract: The flow in the rotor blades of a five-stage low-pressure turbine was investigated experimentally using hot-film probes. Time averaging, Fourier transforms, and ensemble averaging are applied for data reduction. The techniques prove to be a very helpful instrument for the assessment of the flow characteristics in the relative frame. A strong interaction is identified between two successive rows of rotor blades. A physical model, developed from velocity and turbulence results, gives a comprehensive understanding of the phenomenon. The main parameter is the nonuniformity of the flow entering the downstream blade row. Separation occurs when the wake of the upstream rotor blades enters the blade passage near the leading edge, preferably on the pressure side. The interaction is quasi-steady in the relative frame and rotates with the rotor speed. It was observed only in one of three investigated blade rows. Further studies are necessary to identify the mechanism correlating the nonuniformity to the separation. (orig.).

An experimental study of turbine vane heat transfer with leading edge and downstream film cooling

Abstract: This paper presents the effects of downstream film cooling, with and without leading edge showerhead film cooling, on turbine-vane external heat transfer. Steady-state experimental measurements were made in a three-vane linear two-dimensional cascade. The principal independent parameters were maintained over ranges consistent with actual engine conditions. The test matrix was structured to provide an assessment of the independent influence of parameters of interest, namely, exit Mach number, exit Reynolds number, coolant-to-gas temperature ratio, and coolant-to-gas pressure ratio. The data obtained indicate that considerable cooling benefits can be achieved by utilizing downstream film cooling. The downstream film cooling process was shown to be a complex interaction of two competing mechanisms. The thermal dilution effect, associated with the injection of relatively cold fluid, results in a decrease in the heat transfer to the airfoil. Conversely, the turbulence augmentation, produced by the injection process, results in increased heat transfer to the airfoil.

Experimental investigation of the F/A-18 vortex flows at subsonic through transonic speeds

Abstract: A subsonic-to-transonic speed wind tunnel study has been conducted to deepen understanding of the nature and possibilities for control of vortical flows associated with wing leading edge extensions (LEXs) on the F/A-18 aircraft; these vortical phenomena encompass vortex breakdown and vortex interactions with vertical stabilizers. Wind tunnel results were correlated with in-flight flow visualizations as well as handling-qualities trend data from a USN F-18 with LEX fences to improve the vertical tail buffet environment. Attention is given to the sensitivity of the vortex flows to Re and Mach numbers, reduced vertical tail excitation due to the presence of a LEX fence, and the interpretation of off-body flow visualizations.

Control apparatus for automobile air-conditioners

Abstract: An apparatus for controlling an automobile air-conditioner wherein the direction of solar radiation is determined based on a signal which is obtained by retarding the leading edge of a solar radiation signal and the position of an air-distributing door is controlled according to the thus obtained signal. A signal whose leading and trailing edges are progressively increasing and decreasing, respectively, is used for the calculation of a signal corresponding to the thermal load in the vehicle passenger compartment. The operation of various components of the air-conditioner including a blower is controlled by the result of calculation of the thermal load signal.

Vortex Dynamics of Delta Wings

Abstract: The typical angle of attack for maximum lift of a delta wing is about 35°, which is much higher than for a two-dimensional airfoil. The delta wing is, therefore, suitable for highly maneuverable aircraft. In this paper, experimental results for delta wings is reviewed. The review is made from the perspective of fundamental fluid dynamic mechanisms. In particular, the balance between vorticity generation on the surface and freestream convection of it is used to understand how different parameters affect the leading edge vortices which dominate the aerodynamics of a delta wing at high angles of attack.

Blade of composite materials and its manufacturing process

Abstract: The blade of composite materials and its manufacturing process according to the invention are such that the spar includes at least one bundle (10a, 10b) extending longitudinally in the shell (4), between the fillings of the leading edge (12a) and the trailing edge (12c) and which adheres directly to the laminated pressure face and suction face coverings, (4a, 4b) of the rigid shell (4). Beyond the blade footing (3), the spar is shaped to form a root loop flexible in torsion (8) and passing round an attaching socket (9) on the hub. Application to variable pitch multi-blade propellers for the streamlined tail rotors of helicopters.

Experimental Investigation of Rotor-Stator Interaction in a Centrifugal Pump With Several Vaned Diffusers

Abstract: This paper describes an experimental investigation of rotor-stator interaction in a centrifugal pump with several vaned diffusers. Steady and unsteady diffuser vane pressure measurements were made for a two-dimensional test impeller. Unsteady impeller blade pressure measurements were made for a second two-dimensional impeller with blade number and blade geometry identical to the two-dimensional impeller used for the diffuser vane pressure measurements. The experiments were conducted for different flow coefficients and differeent radial gaps between the impeller blade trailing edge and the diffuser vane leading edge (5 and 8 percent of the impeller discharge radius). The largest pressure fluctuations on the diffuser vanes and the impeller blades were found to be of the same order of magnitude as the total pressure rise across the pump. The largest pressure fluctuations on the diffuser vanes were observed to occur on the suction side of the vane near the vane leading edge, whereas on the impeller blades the largest fluctuations were observed to occur at the blade trailing edge. However, the dependence of the fluctuations on the flow coefficient was found to be different for te diffuser vanes and the impeller blades; on the vane suction side, the fluctuations were largest for the maximum flow coefficient and decreased with decreasing flow coefficient, whereas at the blade trailing edge, the fluctuations were smallest for the maximum flow coefficient and increased with decreasing flow coefficient. Increasing the number of the diffuser vanes resulted in a significant decrease of the impeller blade pressure fluctuations. The resulting lift on the diffuser vanes was computed from the vane pressure measurements; the magnitude of the fluctuating lift was found to be larger than the steady lift.

Navier-Stokes computations of lee-side flows over delta wings

Abstract: Solutions to the Navier-Stokes equations for the flow over delta wings are computed with emphasis on the separated vortical flows developing on the lee side at high angles of attack. A recently developed implicit algorithm is used which employs upwind differencing for the pressure and convection terms and central differencing for the shear stress and heat transfer terms. Solutions to both the three-dimensional equations and the approximate conical flow equations are compared parametrically with an extensive experimental data base at supersonic speeds. The computations indicate that the conical flow approximation provides results in close agreement with the three-dimensional equations, even to angles of attack as high as 20 degrees. Good agreement with experimentally measured pressures and vapor screen photographs is obtained for the conditions investigated. The method predicts the classical pattern of vortical flow over a delta wing and transition to other flow patterns as the leading edge sweep angle and leading edge normal Mach number are varied.

Functional wing morphology and aerodynamics of panorpa germanica (insecta: mecoptera)

Abstract: The functional wing morphology of the wings of the scorpion fly Panorpa germanica L. was investigated using a combination of light microscopy, high-speed cinematography, wing manipulation and mechanical testing In rising forward flight the wings are flapped 40° out of phase along a shallow stroke plane, the forewings leading. Aerodynamic analysis suggests that unsteady effects are important in flight During the downstroke, both wings are straight and cambered, the chord being parallel to the body axis, which is angled 45° upwards from horizontal. Both wings are supinated at lower stroke reversal, the hindwing to a much greater extent, and flex ventrally halfway along their length for the first half of the upstroke. Flexion is parallel to the chord in the hindwing, but is oblique in the forewing, so distal forewing areas are supinated relative to proximal areas The behaviour of the wings is related to their structure. Spars at the leading and trailing edges of both wings support the wing during the downstroke, and flexion during the upstroke is facilitated by buckling of the weak ventral thyridium region. The oblique flexion seen in the forewing is due to its relatively longer leading edge spar The differences between the wings are, in turn, related to their pitch control mechanisms. The forewing has a well-developed clavus, like that of the forewing of a locust, and pitch is altered by relative movement of this and the leading edge, but only within a narrow range. Oblique flexion is necessary to invert the aerofoil. The weaker and less well-developed clavus of the hindwing, more similar to that of the Diptera, allows a greater degree of supination, effected largely by wing inertia. No oblique flexion is necessary

The effect of asymmetric vortex wake characteristics on a slender delta wing undergoing wing rock motion

Abstract: An experimental investigation into the fluid mechanisms responsible for wing rock on a slender delta wing with 80 deg leading edge sweep has been conducted. Time history and flow visualization data are presented for a wide angle-of-attack range. The use of an air bearing spindle has allowed the motion of the wing to be free from bearing friction or mechanical hysteresis. A bistable static condition has been found in vortex breakdown at an angle of attack of 40 deg which causes an overshoot of the steady state rocking amplitude. Flow visualization experiments also reveal a difference in static and dynamic breakdown locations on the wing. A hysteresis loop in dynamic breakdown location similar to that seen on pitching delta wings was observed as the wing was undergoing the limit cycle oscillation.

Low speed wind tunnel investigation of the flow about delta wing, oscillating in pitch to very high angle of attack

Abstract: Six-component airload histories were obtained for models of aspect ratio 1, 1.5, and 2. Examples are given from data obtained over a range of 'reduced frequency' parameters from 0.01 to 0.08. They include the unsteady response of the leading-edge vortices, as evidenced both by the time-dependent airloads and motion pictures of smoke released from the leading edge and illuminated by a thin sheet of laser light.

Surface Injection Effect on Mass Transfer From a Cylinder in Crossflow: A Simulation of Film Cooling in the Leading Edge Region of a Turbine Blade

Abstract: A naphthalene sublimation technique is used to study the effect of surface injection on the mass (heat) transfer from a circular cylinder in crossflow. Using a heat/mass transfer analogy the results can be used to predict film cooling effects in the leading edge region of a turbine blade. Air injection through one row of circular holes is employed in the stagnation region of the cylinder. Streamwise and spanwise injection inclinations are studied separately, and the effects of blowing rate and injection location relative to the cylinder front stagnation line are investigated. Streamwise injection produces significant mass transfer increases downstream of the injection holes, but a relatively small increase is observed between holes, normal to the injection direction. The mass transfer distribution, measured with spanwise injection through holes located near the cylinder front stagnation line, is extremely sensitive to small changes in the injection hole location relative to stagnation. When the centers of the spanwise injection holes are located 5° or more from the stagnation line, the holes lay entirely on one side of the stagnation line and the injection affects the mass transfer only on that side of the cylinder, approaching the pattern observed with streamwise injection.Copyright © 1989 by ASME

Geometrical and structural properties of an Aeroelastic Research Wing (ARW-2)

Abstract: Transonic steady and unsteady pressure tests were conducted on a large elastic wing known as the DAST ARW-2 wing. The wing has a supercritical airfoil, an aspect ratio of 10.3, a leading edge sweepback angle of 28.8 deg and is equipped with two inboard and one outboard trailing edge control surfaces. The geometrical and structural characteristics are presented of this elastic wing, using a combination of measured and calculated data, to permit future analyst to compare the experimental surface pressure data with theoretical predictions.

Venturi enhanced airfoil

Abstract: A basic airfoil has its operating performance improved by incorporating one or more apertures in the airfoil adjacent its trailing edge. These apertures extend from the upper surface of the airfoil down through to the lower surface of the airfoil. The entry port and the exit port of these apertures has a greater circumference than that of the throat circumference which is intermediate thereto. This structure forms a venturi having a vertical axis. Spaced below the throat of the aperture are a plurality of air nozzles that communicate with an air plenum chamber within the airfoil. A source of pressurized air is connected to the plenum chamber. The leading edge of the airfoil causes air to flow across both the upper surface and lower surface of the airfoil. The venturi creates a strong suction on the upper surface of the airfoil to enhance the airfoil's pressure differential. When the axis of the venturi is inclined forwardly with respect to the horizontal axis of the airfoil, a vector thrust in the forward direction is created in the same direction as that of the low pressure side of the airfoil. The venturi enhanced airfoil can be utilized both in a horizontal fixed airfoil or its structure can also be incorporated into the tail rudder of an aircraft or helicopter. The venturi enhanced airfoil can be oriented in any position between the horizontal and vertical axes.