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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

High-Temperature Modal Survey of a Hot-Structure Control Surface

NASA Dryden is directing a program to test a Carbon-Silicon Carbide (C/SiC) Ruddervator Subcomponent Test Article (RSTA). The RSTA is a truncated version of the full-scale X-37 hot-structure control surface incorporating all major features including the metallic spindle and five major C/SiC quasi isotropic lay-up components secured with C/SiC fasteners. As part of NASA's Aeronautics Research Mission Directorate Hypersonics program, the RSTA will undergo thermal-structural testing to develop an extensive database for future structural design and analysis methodology validation. Ground Vibration Tests (GVTs) are routinely conducted for model validation in supporting flutter analysis for subsonic and supersonic vehicles; however, for hypersonic vehicle applications, GVT techniques are not well-established. New fabrication technologies, high-temperature materials systems, and sensors offer new opportunities to develop techniques for performing GVTs at elevated temperatures. The RSTA is comprised of materials whose stiffness both increases and decreases with increasing temperature. The impact of this type of material system interaction must be understood as it will ultimately affect hypersonic flutter analysis. The test objectives are to perform room-temperature GVTs, develop the capability to conduct high-temperature GVTs and to compare and generate an understanding of the modal characteristics which capture RSTA's material interaction when subjected to temperature varying conditions.

Spivey, Natalie D.↗
NASA NTRS2011

High-Temperature Modal Survey of a Hot-Structure Control Surface

Ground vibration tests are routinely conducted for supporting flutter analysis for subsonic and supersonic vehicles; however, for hypersonic vehicles, thermoelastic vibration testing techniques are neither well established nor routinely performed. New high-temperature material systems, fabrication technologies and high-temperature sensors expand the opportunities to develop advanced techniques for performing ground vibration tests at elevated temperatures. When high-temperature materials, which increase in stiffness when heated, are incorporated into a hot-structure that contains metallic components that decrease in stiffness when heated, the interaction between those materials can affect the hypersonic flutter analysis. A high-temperature modal survey will expand the research database for hypersonics and improve the understanding of this dual-material interaction. This report discusses the vibration testing of the carbon-silicon carbide Ruddervator Subcomponent Test Article, which is a truncated version of a full-scale hot-structure control surface. Two series of room-temperature modal test configurations were performed in order to define the modal characteristics of the test article during the elevated-temperature modal survey: one with the test article suspended from a bungee cord (free-free) and the second with it mounted on the strongback (fixed boundary). Testing was performed in the NASA Dryden Flight Research Center Flight Loads Laboratory Large Nitrogen Test Chamber.

Spivey, Natalie D.↗
NASA NTRS1975

Development and demonstration of a flutter-suppression system using active controls

The application of active control technology to suppress flutter was demonstrated successfully in the transonic dynamics tunnel with a delta-wing model. The model was a simplified version of a proposed supersonic transport wing design. An active flutter suppression method based on an aerodynamic energy criterion was verified by using three different control laws. The first two control laws utilized both leading-edge and trailing-edge active control surfaces, whereas the third control law required only a single trailing-edge active control surface. At a Mach number of 0.9 the experimental results demonstrated increases in the flutter dynamic pressure from 12.5 percent to 30 percent with active controls. Analytical methods were developed to predict both open-loop and closed-loop stability, and the results agreed reasonably well with the experimental results.

Sandford, M. C.↗
NASA NTRS1946

Flutter and oscillating air-force calculations for an airfoil in a two-dimensional supersonic flow

An account is given of the Possio theory of non stationary flow for small disturbances in a two-dimensional supersonic flow and of its application to determination of the aerodynamic forces on an oscillating airfoil. Further application is made to the problem of wing flutter in the degrees of freedom - torsion, bending, and aileron torsion. Numerical tables for flutter calculations are provided for numerous values of the Mach number greater than unity. Results for bending-torsion wing flutter are discussed. The static instabilities of divergence and aileron reversal are examined as is a one degree of freedom case of torsional oscillatory instability.

Garrick, I E↗
NASA NTRS1976

Analytical comparison of effects of solid-friction and viscous structural damping on panel flutter

A Galerkin modal analysis is presented that accounts for the effects of both solid friction and viscous structural damping on panel flutter, based on unsteady aerodynamic forces from supersonic potential flow. The eigensolutions are made by complex eigenvalue computer routines. Markedly different effects on the flutter boundary of the two types of structural damping are obtained. This result establishes that there is not, in general, an "equivalent viscous" damping for solid-friction damping. For the limiting case of the static-aerodynamic approximation, a substantially different flutter dynamic pressure is obtained for solid friction identically zero compared with solid friction approaching zero as a limit. Use of the quasi-static aerodynamic approximation eliminates that difference.

Cunningham, H. J.↗
NASA NTRS1975

Boundary-layer effect in panel flutter

The present note shows that if the supersonic Mach number is not too large, an analytical expression can be obtained for the generalized aerodynamic force relating the pressure fluctuation at the surface of a flexible plate to the plate displacement in the presence of an adjacent boundary layer. The low supersonic Mach numbers are the ones of maximum interest since it is in this Mach number region that the boundary layer has the most influence. In this respect, Dowell (1971) has already shown that the presence of a boundary layer causes about a 300% increase in flutter dynamic pressure at a Mach number of about 1.2, while it causes only about a 20% increase at a Mach number of 2.

Goldstein, M. E.↗
NASA NTRS1982

Implicit unsteady transonic airfoil calculations at supersonic freestreams

The computer code LTRAN2 has been extended to compute unsteady transonic flows about oscillating airfoils with supersonic freestreams. The LTRAN2 code uses an alternating direction implicit (ADI) algorithm to solve the two-dimensional, nonlinear, low-frequency, transonic small-disturbance (LF-TSD) equation. The modified code, LTRAN2-SS, includes a 'high-frequency' option. Steady solutions are checked against those computed by the steady TSD code, TSFOIL; unsteady computations of the linear LF-TSD equation are compared with known linear theory solutions; and new unsteady nonlinear solutions are presented. These cases include standard AGARD test cases for the NLR 7301, MBB-A3, and DO Al supercritical airfoils, as well as several NACA airfoils. The modified code enables aerodynamicists to quickly and efficiently compute transonic flows for both subsonic and supersonic freestreams, and thus resolve flutter boundaries through the full extent of the transonic dip phenomenon.

Chow, L. J.↗
NASA NTRS1975

Steady and Oscillatory, Subsonic and Supersonic, Aerodynamic Pressure and Generalized Forces for Complex Aircraft Configurations and Applications to Flutter

A general method for analyzing aerodynamic flows around complex configurations is presented. By applying the Green function method, a linear integral equation relating the unknown, small perturbation potential on the surface of the body, to the known downwash is obtained. The surfaces of the aircraft, wake and diaphragm (if necessary) are divided into small quadrilateral elements which are approximated with hyperboloidal surfaces. The potential and its normal derivative are assumed to be constant within each element. This yields a set of linear algebraic equations and the coefficients are evaluated analytically. By using Gaussian elimination method, equations are solved for the potentials at the centroids of elements. The pressure coefficient is evaluated by the finite different method; the lift and moment coefficients are evaluated by numerical integration. Numerical results are presented, and applications to flutter are also included.

Chen, L. T.↗
NASA NTRS1977

SCAR arrow-wing active flutter suppression system

The potential performance and direct operating cost benefits of an active flutter suppression system (FSS) for the NASA arrow-wing supersonic cruise configuration were determined. A FSS designed to increase the flutter speed of the baseline airplane 20 percent. A comparison was made of the performance and direct operating cost between the FSS equipped aircraft and a previously defined configuration with structural modifications to provide the same flutter speed. Control system synthesis and evaluation indicated that a FSS could provide the increase in flutter speed without degrading airplane reliability, safety, handling qualities, or ride quality, and without increasing repeated loads or hydraulic and electrical power capacity requirements.

Gordon, C. K.↗
NASA NTRS1991

Limit cycle oscillation of a fluttering cantilever plate

A response of a cantilever plate in high supersonic flow to a disturbance is considered. The Rayleigh-Ritz method is used to solve the nonlinear oscillation of a fluttering plate. It is found that the length-to-width ratio for a cantilever plate has a great effect on flutter amplitude of the limit cycle. For small length-to-width ratio, the dominant chordwise modes are translation and rotation. It is suggested that higher bending modes must be included to obtain an accurate prediction of the flutter onset and limit cycle oscillation. For large length-to-width ratio, significant chordwise bending is apparent in the flutter motion, with the trailing edge area having the largest motion.

Dowell, Earl↗
NASA NTRS1967

Nonlinear oscillations of a fluttering plate. II.

Quasi-steady aerodynamic and von Karman large deflection plate theory equations of nonlinear oscillations of fluttering plate for single mode subsonic and sonic or coupled mode supersonic oscillations

VON KARMAN EQUATION↗
NASA NTRS1976

Structural design studies of a supersonic cruise arrow wing configuration

Structural member cross sections were sized with a system of integrated computer programs to satisfy strength and flutter design requirements for several variants of the arrow wing supersonic cruise vehicle. The resulting structural weights provide a measure of the structural efficiency of the planform geometry, structural layout, type of construction, and type of material including composites. The material distribution was determined for a baseline metallic structure and the results indicate that an approximate fatigue constraint has an important effect on the structural weight required for strength but, in all cases, additional material had to be added to satisfy flutter requirements with lighter mass engines with minimum fuel onboard. The use of composite materials on the baseline configuration was explored and indicated increased structural efficiency. In the strength sizing, the all-composite construction provided a lower weight design than the hybrid construction which contained composites only in the wing cover skins. Subsequent flutter analyses indicated a corresponding lower flutter speed.

Sobieszczanski, J.↗