Showing papers on "Airfoil published in 1991"

Low-speed aerodynamics : from wing theory to panel methods

Abstract: Introduction and Background. Fundamentals of Inviscid, Incompressible Flow. General Solution of the Incompressible, Potential Flow Equations. Small Disturbance Flow Over Three Dimensional Airfoils. Exact Solutions with Complex Variables. Perturbation Methods. Three-Dimensional Small Disturbance Solutions. Numerical (Panel) Methods. Singularity Elements and Influence Coefficients. Two-Dimensional Numerical Solutions. Three-Dimensional Numerical solutions. Unsteady Aerodynamics. Advanced Topics. Airfoil Integrals. Singularity Distribution Integrals. Principle Value of the Lifting Surface Integral. Sample Computer Programs.

Aeroelastic Analysis of Wings Using the Euler Equations with a Deforming Mesh

Abstract: Modifications to the CFL3D three-dimensional unsteady Euler/Navier-Stokes code for the aeroelastic analysis of wings are described. The modifications involve including a deforming mesh capability that can move the mesh to continuously conform to the instantaneous shape of the aeroelastically deforming wing and also including the structural equations of motion for their simultaneous time integration with the governing flow equations. Calculations were performed using the Euler equations to verify the modifications to the code and as a first step toward aeroelastic analysis using the Navier-Stokes equations. Results are presented for the NACA 0012 airfoil and a 45-deg sweptback wing to demonstrate applications of CFL3D for generalized force computations and aeroelastic analysis. Comparisons are made with published Euler results for the NACA 0012 airfoil and with experimental flutter data for the 45-deg sweptback wing to access the accuracy of the present capability. These comparisons show good agreement and, thus, the CFL3D code may be used with confidence for aeroelastic analysis of wings. The paper describes the modifications that were made to the code and presents results and comparisons that assess the capability.

Wide chord fan blade

Abstract: A laminated airfoil for use in a high bypass engine. The airfoil preferably has a large tip chord and is comprised of alternating layers of thin metallic foil and elastomeric layers. The exterior surfaces of the airfoil are comprised of a thin, metallic foil. The airfoil also has a metal sheath secured to the leading edge. High strength metal members extend through the dovetail root sections.

Further experiments on vortex formation around an oscillating and translating airfoil at large incidences

Abstract: The starting flows past a two-dimensional NACA 0012 airfoil translating and oscillating at large incidences are investigated by visualization experiments and numerical calculations. The airfoil model is set in motion impulsively and subjected simultaneously to a constant translation and harmonic oscillation in pitch. The evolution of the vortex wake is followed in a sequence of streamline visualizations and the wake pattern generated is analysed. The parameters varied in the visualization experiment are the Reynolds number ranging from 1500 to 10000, the reduced frequency from 0.1 to 1.0, the mean incidence 30° or 15° and the angular amplitude 15° or 7°. There are also two additional parameters of special interest: the airfoil cross-section and the pitching axis. The effects of these parameters are discussed in relation to the resultant wake patterns. Some comparison is made with the results of earlier experiments.

Air-cooled turbine blade

Abstract: An air-cooled gas turbine blade providing improved cooling characteristics is disclosed. The turbine blade includes several internal passages for conveying cooling air therethrough during turbine operation to provide the desired cooling effect. Two distinct passages are provided to cool the airfoil leading and trailing edges, respectively. Two serpentine cooling passages are disposed so as to efficiently cool each side of the airfoil. Disposed in the middle of the airfoil is an additional, distinct passage. The platform is cooled by three serpentine cooling passages. Two of these passages are in outlet fluid communication with the inlet to the middle airfoil passage. As cooling air traverses these two passages, heat is transferred, from the base simultaneously cooling it and warming the air. This warmed air is next directed through the middle airfoil passage, providing a slight warming effect to the center portion of the airfoil. This counteracts the tendency of the side cooling passages to over cool the center of the airfoil. In this way, a more uniform temperature gradient can be achieved throughout the airfoil, as well as the platform, minimizing internal stresses and enhancing blade operating characteristics.

Unsteady flow past an airfoil pitching at a constant rate

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

Method of making replacement airfoil components

Abstract: A method for replacing airfoil components includes the steps of identifying a portion of the airfoil to be replaced, removing the portion by a nonconventional machining process, such as continuous wire electrical discharge machining, and forming a replacement member utilizing a similar cutting process. A cutting path utilized to remove the portion to be replaced and to form the replacement member includes interlocking projections and sockets and may include one or more tapers along the cutting path so that the portion may be removed only by lifting in one direction. In cases where an entire airfoil is replaced, a first projection may be tapered in one direction while a second projection is tapered in an opposite direction so that the airfoil may not be removed as long as its adjacent flowpath walls are fixed relative to one another. Gas bending load dampers and zero gap standoffs may also be included for precision alignment of the replacement member and further securement of the replacement member in the airfoil.

Static Aeroelastic Control Using Strain Actuated Adaptive Structures

Abstract: In this study, the feasibility of using representative box wing adaptive structures for static aeroelastic control is examined. A deformable typical section is uti lized to derive the optimal and suboptimal relations for induced strain actuated adaptive wings, and the relations developed are used to design representative adaptive lifting sur faces which are assessed in trade studies. The optimal relations developed showed that op timal adaptive airfoil designs are possible for some realistic configurations, and effective sub-optimal designs can be achieved for others. In addition, the important parameters associated with inducing curvature and twist, thereby altering the lifting forces on the air foil, are determined. The most important of which were found to be the airfoil thickness ratio, the actuation strain produced by the induced strain actuators, and the relative stiff ness ratio of the actuator to the wing skin for both camber and twist control. The stiffness coupling parameter and the wing aspect ...

Effects of freestream turbulence on the performance characteristics of an airfoil

Abstract: The lift and drag characteristics and associated flowfields over the suction surface of an NACA 0015 airfoil with an aspect ratio of 2.9 were obtained at a Reynolds number of 250,000 for conditions both with and without freestream turbulence (FST).

Apparatus for preloading an airfoil blade in a gas turbine engine

Abstract: Apparatus for preloading an airfoil blade attached to a rotor disk in a gas turbine engine. The dovetail root of a composite fan blade is preloaded to prevent rubbing and wear against the dovetail slot of a metal rotor disk during fan windmilling, with the aircraft engine off, due to wind and breezes at the airport. A resilient material is inserted into the lower portion of the slot below the engaged blade root. The disk has a radius which intersects the slot. The material is acted upon by a device which adjustably compresses the inserted material perpendicular to the radius of the disk. This causes the compressed material to exert a radially outward force against the bottom of the engaged root of the blade.

Internally cooled airfoil

Abstract: A hollowed, internally cooled airfoil per gas turbine engines with an improved internal configuration for pronounced impingement cooling. Internal ribs extend across the hollowed interior and cooling passages through these ribs cause impingement cooling of the next-adjacent rib as well as the internal surfaces of both the pressure side and suction side of the airfoil.

Method for depositing material on the tip of a gas turbine engine airfoil using linear translational welding

Abstract: A method for depositing material on a tip of a gas turbine engine airfoil includes the steps of: selecting a linear principal weld path across the airfoil tip relative to an airfoil contour at the tip; selecting a weld bead stitch pattern to substantially completely cover the airfoil tip with the stitch pattern crisscrossing the linear principal weld path between opposite edges of the airfoil and advancing across the airfoil in the direction of the linear principal weld path; and depositing at least a first layer of tip material corresponding to the weld bead stitch pattern and the linear principal weld path by welding.

Flexible tailored elastic airfoil section

Abstract: A flexible airfoil section for a wing or a blade comprising a streamlined shape and an elastic structure whose stiffness distribution along its chord and span is tailored to provide a desirable cambered shape with proportional increases in camber with increases in lift, mounted to a supporting structure such that the airfoil sections are free to pivot about axes near their leading and trailing edges. In operation, the foil derives much of its lift from elastic bending deformation of its flexible shape, thereby achieving a higher lift than a symmetric foil at the same angle of attack while postponing the onset of flow separation and stall and, for operation in water, of ventilation and cavitation. A wing or blade of general planform comprising flexible elastic airfoil sections which can be used to stabilize, or to control the direction of travel of, as well as provide side force for, a watercraft such as a sailboat or a sailboard, or for application to a variety of aircraft components and configurations to provide lift and side force and as well can serve as the aerodynamic surfaces of various types of fluid machinery including fans, helicopter rotors and wind turbines operating in subsonic flow.

Helicopter rotor blades

Abstract: Flow separation behind the notch region of a swept tip of a helicopter rotor blade is reduced by features of the geometry and aerodynamic characteristics of the notch region itself. In particular it has been found beneficial for a forwardly swept leading edge portion to extend at an angle between 30 degrees and 55 degrees from a reference line parallel to a blade pitch change axis and the leading edge of the aerofoil in the notch region incorporates blade droop.

Multi-element airfoil optimization for maximum lift at high Reynolds numbers

Abstract: An experimental study has been performed to assess the maximum lift capability of a supercritical multielement airfoil representative of an advanced transport aircraft wing. The airfoil model was designed with a leading-edge slat and single or two-segment trailing-edge flaps. Optimization work was performed at various slat/flap deflections as well as gap/overhang positions. Landing configurations and the attainment of maximum lift coefficients of 4.5 with single-element flaps and 5.0 with two-segment flaps was emphasized. Test results showed a relatively linear variation of the optimum gap/overhang positioning of the slat versus slat deflection, considerable differences in optimum rigging between single and double segment flaps, and large Reynolds number effects on multielement airfoil optimization.

Three-position variable camber krueger leading edge flap

Abstract: A variable camber flap assembly having first and second operative positions. A rotatable drive arm powers first and second linkage subassemblies. The first linkage subassembly extends the flap panel in a downward and forward direction to its operative positions, and also rotates a hinged bullnose outwardly so as to foreshorten the distance between the leading and trailing edges of the flexible flap panel, increasing the camber of the flap. The second linkage subassembly cooperates with the first to angularly orientate the flap panel in its operative positions, and also positions the trailing edge of the panel relative to the leading edge of the airfoil. In the first operative position the trailing edge of the panel is spaced forwardly from the leading edge of the airfoil so as to form an aerodynamic slot; in the second operative position the flap panel is drawn rearwardly so that its trailing edge forms an aerodynamic seal with the airfoil.

Airfoil design method using the Navier-Stokes equations

Abstract: An airfoil design procedure is described that was incorporated into an existing 2-D Navier-Stokes airfoil analysis method. The resulting design method, an iterative procedure based on a residual-correction algorithm, permits the automated design of airfoil sections with prescribed surface pressure distributions. The inverse design method and the technique used to specify target pressure distributions are described. It presents several example problems to demonstrate application of the design procedure. It shows that this inverse design method develops useful airfoil configurations with a reasonable expenditure of computer resources.

Variable camber control of airfoil

Abstract: An airfoil camber control apparatus utilizes a cable of shape memory alloy affixed at its ends to a front interior portion of the airfoil. A tensioning system is connected to a rear interior portion of the airfoil and to the cable. When electrical current is applied to the cable to heat it, it returns to its remembered, shorter length, thereby applying tension to the tensioning system to alter the position of the rear portion of the airfoil relative to the front portion.

Drag and lift in nonadiabatic transonic flow

Abstract: Transonic flows with heat addition over airfoils have been calculated for different angles of attack. The fluid is a mixture of an inert carrier gas and a small amount of a condensible vapor. For the phase change process coupled to the flow, two limiting cases are investigated: nonequilibrium condensation after significant supersaturation and homogeneous nucleation and equilibrium condensation. Numerical calculations based on the Euler equations are linked with either the classical nucleation theory coupled with microscopic or macroscopic droplet growth laws or an equilibrium process

Moving surface boundary-layer control as applied to two-dimensional airfoils

Abstract: The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through an experimental program complemented by a flow visualisation study. The moving surface was provided by rotating cylinders located at the leading edge and upper surface of the airfoil. The results suggest that the leading-edge rotating cylinder effectively extends the lift curve without substantially affecting its slope, thus increasing the maximum lift and delaying stall. When used in conjunction with a second cylinder on the upper surface, further improvements in the maximum lift and stall angle are possible. The maximum coefficient of lift realised was around 2.73, approximately three times that of the base airfoil. The maximum delay in stall was around 48 deg. In general, the performance improves with an increase in the ratio of cylinder surface speed Uc to the freestream speed U.

Transonic Low-Reynolds Number Airfoils

Abstract: Airfoils operating in the unexplored high-Mach—low-Reynolds number regime are computationally investigated. The motivations are 1) quantificatio n of achievable airfoil performance levels; 2) quantificatio n of parameter sensitivities which impact vehicle sizing; 3) identification of possible shortcomings in the computational methods employed; and 4) identification of test data required for adequate validation of the airfoil designs and performance prediction methods. The investigation centers on candidate airfoils developed for proposed ultrahigh altitude aircraft (UHAA) having both a high-ceiling and a long-range requirement. Computational studies indicate that 35-km ceiling performance at M — 0.60, Re — 200,000 hinges on the effective use of transonic flow to enhance transition and reduce separation-bubble losses. The separation bubbles become associated with large lambda shock structures at the highest tolerable Mach numbers. Airfoil performance predictions are parameterized by quantities dependent only on altitude and vehicle characteristics, and independent of flight trim conditions. For the airfoils designed, no flaps are necessary to achieve nearly optimal performance at both 35-km ceiling conditions as well as lower 15-25-km altitudes where long-range cruise would occur. Variation in airfoil thickness between 11-15% has surprisingly little impact on aerodynamic performance.

Spiroid-tipped wing

Abstract: The spiroid-tipped wing, in its basic form, comprises a wing-like lifting surface and a spiroidal tip device (i.e., spiroid) integrated so as to minimize the induced drag of the wing-spiroid combination and/or to alleviate noise effects associated with concentrated vorticity wakes that trail from lifting surfaces. The ends of the spiroid are attached to the wing tip at approproate sweep and included angles to form a continuous and closed extension of the wing surface. For a fixed wing aircraft the spiroid configuration on the right side is of opposite hand to that on the left side. The spiroid geometry incorporates airfoil cross sections with specified thickness, camber and twist. The airfoil thickness varies in relation to the local sweep angle being a minimum at an intermediate position where the sweep angle is zero. The camber and twist vary approximately linearly and change sign at some intermediate position between the spiroid ends so as to produce the optimum spiroid loading. Increasing the size of the spiroid in relation to the overall span of the lifting surface is used to further reduce drag and noise. The concept of the spiroid-tipped wing may include the use of more than one spiroid on each wing tip in any number of forms which may be selected to be adaptable to other design requirements and operational limitations. More generally the spiroid wing tip system is a generic geometric concept which can be adapted to achieve drag reduction and noise for most applications which incorporate wings or wing-like devices (i.e., lifting surfaces) such as helicopters, propellers, etc. including non-aeronautical applications.

Ultra-soft, ultra-elastic gel airfoils

Abstract: A novel rotating aerodynamic toy made of a ultra-elastic gel airfoil which is suitable for launch in light or heavy wind conditions and capable of performing various aerodynamic effects including climb, stall, return, straight-line flight and other aerobatics. The ultra-elastic properties of the airfoil allow the airfoil to transform by at least 50% extension of its aerodynamic profile at launch and; while in flight; one or more preselected sized cavities and holes, slots and holes, cavities, slots and holes and cavities, slots, or holes provide handling, elastic control of airfoil profile stretching for flight, and flight stability.

Prediction of ice shapes and their effect on airfoil performance

Abstract: Calculations of ice shapes and the resulting drag increases are presented for experimental data on a NACA 0012 airfoil. They were made with a combination of LEWICE and interactive boundary-layer codes for a wide range of conditions which include air speed and temperature, the droplet size and liquid water content of the cloud, and the angle of attack of the airfoil. In all cases, the calculated results account for the drag increase due to ice accretion and, in general, show good agreement.

Moving surface boundary-layer control: Studies with bluff bodies and application

Abstract: The concept of moving surface boundary-layer control has proved quite successful in increasing lift and delaying stall of slender bodies like airfoil sections. We assess effectiveness of the concept in reducing drag of bluff bodies, such as a two-dimensional flat plate at large angles of attack, rectangular prisms, and three-dimensional models of trucks, through an extensive wind-tunnel test program.

Vertical windmill with omnidirectional diffusion

Abstract: A vertical windmill employing aerodynamic lift includes stators that form an omnidirectional diffuser and can rotate out of the wind to reduce the destructive tendencies in high winds. A braking mechanism included in the windmill uses rotation of the airfoils to reduce the lift caused by the wind and disengagement of the airfoils to reduce nearly all lift on the airfoils. Centrifugal force is used to activate the brake in high winds, both to slow the rotor speed and, in extreme winds, to stop the rotor. A motor is provided to drive the windmill to simplify controls and increase energy production.

Analysis of the onset of dynamic stall

Abstract: The dynamic stall characteristics of several airfoils have been investigated to assess the effects of compressibility, unsteadiness, and airfoil geometry on the onset of dynamic stall. For the purpose of understanding the physical phenomena in the range of low reduced frequency of practical importance, it is found that the flow before the onset of stall can be considered quasisteady and hence predicted using inviscid theory. For moderate Reynolds number, our analysis predicts the presence of a separation bubble at the airfoil leading edge and suggests that bubble bursting, or failure to reattach after the initial separation, is the onset mechanism. It is found in numerical simulation that at angles of attack close to static stall minor movements in transition point location can cause bursting of the separation bubble and that bursting is more susceptible to transition location in a locally supersonic flow than in subsonic flow. Finally, it is found that the delay between passage through the static stall angle and the onset of dynamic stall decreases with increasing unsteadiness. This result suggests that separation is being promoted rather than delayed and that the lift benefits from dynamic stall only for the duration of the separation process.

Fully coupled implicit method for thermochemical nonequilibrium air at suborbital flight speeds

Abstract: A CFD technique is described in which the finite-rate chemistry in thermal and chemical nonequilibrium air is fully and implicitly coupled with the fluid motion. Developed for use in the suborbital hypersonic flight speed range, the method accounts for nonequilibrium vibrational and electronic excitation and dissociation, but not ionization. The steady-state solution to the resulting system of equations is obtained by using a lower-upper factorization and symmetric Gauss-Seidel sweeping technique through Newton iteration. Inversion of the left-hand-side matrices is replaced by scalar multiplications through the use of the diagonal dominance algorithm. The code, named CENS2H (Compressible-Euler-Navier-Stokes Two-Dimensional Hypersonic), is fully vectorized and requires about 8.8 x 10 to the -5th sec per node point per iteration using a Cray X-MP computer. Converged solutions are obtained after about 2400 iterations. Sample calculations are made for a circular cylinder and a 10 percent airfoil at 5 deg angle of attack. The calculated cylinder flow field agrees with that obtained experimentally. The code predicts a 10 percent change in lift, drag, and pitching moment for the airfoil due to the thermochemical phenomena.

Euler flow predictions for an oscillating cascade using a high resolution wave-split scheme

Abstract: A compressible flow code that can predict the nonlinear unsteady aerodynamics associated with transonic flows over oscillating cascades is developed and validated. The code solves the two-dimensional, unsteady Euler equations using a time-marching, flux-difference splitting scheme. The unsteady pressures and forces can be determined for arbitrary input motions, although this paper will only address harmonic pitching and plunging motions. The code solves the flow equations on a H-grid which is allowed to deform with the airfoil motion. Predictions are presented for both flat plate cascades and loaded airfoil cascades. Results are compared to flat plate theory and experimental data. Predictions are also presented for several oscillating cascades with strong normal shocks where the pitching amplitudes, cascade geometry and interblade phase angles are varied to investigate nonlinear behavior.Copyright © 1991 by ASME