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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

A parametric study of blade vortex interaction noise for two, three, and four-bladed model rotors at moderate tip speeds Theory and experiment

An investigation of blade slap due to blade vortex interaction (BVI) has been conducted. This investigation consisted of an examination of BVI blade slap for two, three, and four-bladed model rotors at tip Mach numbers ranging from 0.20 to 0.50. Blade slap contours have been obtained for each configuration tested. Differences in blade slap contours, peak sound pressure level, and directivity for each configuration tested are noted. Additional fundamental differences, such as multiple interaction BVI, are observed and occur for only specific rotor blade configurations. The effect of increasing the Mach number on the BVI blade slap for various rotor blade combinations has been quantified. A peak blade slap Mach number scaling law is proposed. Comparison of measured BVI blade slap with theory is made.

Leighton, K. P.↗
NASA NTRS2003

A Time Domain Analysis of Gust-Cascade Interaction Noise

The gust response of a 2 D cascade is studied by solving the full nonlinear Euler equations employing higher order accurate spatial differencing and time stepping techniques. The solutions exhibit the exponential decay of the two circumferential mode orders of the cutoff blade passing frequency (BPF) tone and propagation of one circumferential mode order at 2BPF, as would be expected for the flow configuration considered. Two frequency excitations indicate that the interaction between the frequencies and the self interaction contribute to the amplitude of the propagating mode.

Nallasamy, M.↗
NASA NTRS1982

METEOSAT studies of clouds and radiation budget

Radiation budget studies of the atmosphere/surface system from Meteosat, cloud parameter determination from space, and sea surface temperature measurements from TIROS N data are all described. This work was carried out on the interactive planetary image processing system (IPIPS), which allows interactive manipulationion of the image data in addition to the conventional computational tasks. The current hardware configuration of IPIPS is shown. The I(2)S is the principal interactive display allowing interaction via a trackball, four buttons under program control, or a touch tablet. Simple image processing operations such as contrast enhancing, pseudocoloring, histogram equalization, and multispectral combinations, can all be executed at the push of a button.

Saunders, R. W.↗
NASA NTRS1989

Adaptive numerical solutions of the Euler equations in 3D using finite elements

The development of an adaptive mesh solution for a flow involving shock interaction on a swept cylinder and an initial solution for a flow past a complex fighter configuration is reported. The finite element solution algorithm, the mesh generation, and the adaptivity of the solution are described. Sample results for the flow past an F-18 configuration at Mach 0.9 and alpha of 3 deg and for shock interaction on a swept cylinder at Mach 8.04 are summarized.

Peraire, J.↗
NASA NTRS1988

Interactive grid generation for fighter aircraft geometries

An interactive procedure to construct grids about fighter aircraft configurations using a 'state-of-the-art' workstation is described. A multiple-block grid topology is used to minimize grid skewness. Grid points on the surface of a configuration are precomputed and stored on the faces of appropriate blocks. Grid points at intermediate and far field boundary surfaces are computed with analytical functions and stored on appropriate faces. Grid points in the interior of blocks are computed using transfinite interpolation with Lagrangian and exponential blending functions. Interactive software has been written for the IRIS 3030 graphics workstation to control the shape and spacing of grid points on intermediate and far field boundaries, and to control the interior interpolation.

Smith, Robert E.↗
NASA NTRS1986

Low-speed stability and control characteristics of a transport model with aft-fuselage-mounted advanced turboprops

A limited experimental investigation was conducted in the Langley 4- by 7-Meter Tunnel to explore the effects of aft-fuselage-mounted advanced turboprop installations on the low-speed stability and control characteristics of a representative transport aircraft in a landing configuration. In general, the experimental results indicate that the longitudinal and lateral-directional stability characteristics for the aft-fuselage-mounted single-rotation tractor and counter-rotation pusher propeller configurations tested during this investigation are acceptable aerodynamically. For the single-rotation tractor configuration, the propeller-induced aerodynamics are significantly influenced by the interaction of the propeller slipstream with the pylon and nacelle. The stability characteristics for the counter-rotation pusher configuration are strongly influenced by propeller normal forces. The longitudinal and directional control effectiveness, engine-out characteristics, and ground effects are also presented. In addition, a tabulated presentation of all aerodynamic data presented in this report is included as an appendix.

Applin, Z. T.↗
NASA NTRS1975

Improvements to the SADSAM computer program for aeroelasticity analysis

A computer program for calculating the elastic element forces and strain energy distribution for normal mode shapes is presented. The subjects discussed are: (1) revised aerodynamic force representation, (2) flap aerodynamics, (3) chordwise motions and aerodynamic forces, (4) wing-tail interaction, and (5) gust analysis. An aircraft configuration used in sample gust analysis is included.

Schwendler, R. G.↗
NASA NTRS1975

Centaur Standard Shroud (CSS) static ultimate load structural tests

A series of tests were conducted on the jettisonable metallic shroud used on the Titan/Centaur launch vehicle to verify its structural capabilities and to evaluate its structural interaction with the Centaur stage. A flight configured shroud and the interfacing Titan/Centaur structural assemblies were subjected to tests consisting of combinations of applied axial and shear loads to design ultimate values, including a set of tests on thermal conditions and two dynamic response tests to verify the analytical stiffness model. The strength capabilities were demonstrated at ultimate (125 percent of design limit) loads. It was also verified that the spring rate of the flight configured shroud-to-Centaur forward structural deflections of the specimen became nonlinear, as expected, above limit load values. This test series qualification program verified that the Titan/Centaur shroud and the Centaur and Titan interface components are qualified structurally at design ultimate loads.

Source record↗
NASA NTRS1986

SIRTF fine guidance sensor analysis - Focal plane configuration issues

The interrelationship of the issues of sensitivity, image centroiding precision, and field-of-view, and how they interact with the SIRTF pointing requirement to determine a fine guidance sensor focal plane configuration, are examined. While the examples are specifically oriented toward SIRTF, this approach is general and can be applied to other CCD-based star sensor systems.

Stier, Mark T.↗
NASA NTRS1987

An adaptive finite element scheme for the Euler and Navier-Stokes equations

The implementation of two explicit finite element schemes for the solution of the compressible Euler and Navier-Stokes equations is presented. The schemes can be employed with general unstructured triangular meshes in two dimensions. Either scheme can therefore be used as the basic solver in a solution adaptive mesh procedure in a direct manner. The particular adaptive approach which is advocated here is intended for the solution of steady state problems only and involves an adaptive regeneration of the grid at prescribed stages during the false transient. The grid regeneration is accomplished by a mesh generator which has the capability of generating triangular grids over computational domains of arbitrary shape. The procedure is illustrated by solving transonic flows over multi-airfoil configurations and high speed flows, involving shock interactions, past circular cylinders.

Morgan, K.↗
NASA NTRS1989

AdaNET prototype library administration manual

The functions of the AdaNET Prototype Library of Reusable Software Parts is described. Adopted from the Navy Research Laboratory's Reusability Guidebook (V.5.0), this is a working document, customized for use the the AdaNET Project. Within this document, the term part is used to denote the smallest unit controlled by a library and retrievable from it. A part may have several constituents, which may not be individually tracked. Presented are the types of parts which may be stored in the library and the relationships among those parts; a concept of trust indicators which provide measures of confidence that a user of a previously developed part may reasonably apply to a part for a new application; search and retrieval, configuration management, and communications among those who interact with the AdaNET Prototype Library; and the AdaNET Prototype, described from the perspective of its three major users: the part reuser and retriever, the part submitter, and the librarian and/or administrator.

Hanley, Lionel↗
NASA NTRS1992

Postbuckling failure of composite plates with holes

This paper summarizes a study focused on understanding the failure mechanisms present in a plate with a centrally located circular hole loaded inplane into the postbuckling range of deflections. The study was numerical and experimental in nature and had as a goal the a priori prediction of failure using existing failure data from several sources, together with a stress analysis. The maximum stress failure criterion was used to predict failure and both intra- and interlaminar stresses were considered. Four laminates were considered. The phenomenon of modal interaction, or the jumping from one deformed configuration to another, is discussed. With this jumping, the plate configuration may change from one half-wave in the loading direction to two half-waves in the loading direction. The study concludes that the failure in (+/-45/0/90)2s and (+/-45/2(2))2s laminates is due to fiber compression failure and is predictable. The failure load is, for the most part, independent of response configuration. The (+/-45/0/(6))s laminate fails due to interlaminar shear along the simple support, while the response and failure of the (+/-45)4s laminate is governed to a large degree by material nonlinearities and progressive failure.

Lee, H. H.↗
NASA NTRS2002

Contrail Formation in Aircraft Wakes Using Large-Eddy Simulations

In this work we analyze the issue of the formation of condensation trails ("contrails") in the near-field of an aircraft wake. The basic configuration consists in an exhaust engine jet interacting with a wing-tip training vortex. The procedure adopted relies on a mixed Eulerian/Lagrangian two-phase flow approach; a simple micro-physics model for ice growth has been used to couple ice and vapor phases. Large eddy simulations have carried out at a realistic flight Reynolds number to evaluate the effects of turbulent mixing and wake vortex dynamics on ice-growth characteristics and vapor thermodynamic properties.

Paoli, R.↗
NASA NTRS2004

Minimum-Time and Vibration Avoidance Attitude Maneuver for Spacecraft with Torque and Momentum Limit Constraints in Redundant Reaction Wheel Configuration

In this paper, we present an optimal open-loop slew trajectory algorithm developed at GSFC for the so-called "Yardstick design" of the James Webb Space Telescope (JWST). JWST is an orbiting infrared observatory featuring a lightweight, segmented primary mirror approximately 6 meters in diameter and a sunshield approximately the size of a tennis court. This large, flexible structure will have significant number of lightly damped, dominant flexible modes. With very stringent requirements on pointing accuracy and image quality, it is important that slewing be done within the required time constraint and with minimal induced vibration in order to maximize observing efficiency. With reaction wheels as control actuators, initial wheel speeds as well as individual wheel torque and momentum limits become dominant constraints in slew performance. These constraints must be taken into account when performing slews to ensure that unexpected reaction wheel saturation does not occur, since such saturation leads to control failure in accurately tracking commanded motion and produces high frequency torque components capable of exciting structural modes. A minimum-time constraint is also included and coupled with reaction wheel limit constraints in the optimization to minimize both the effect of the control torque on the flexible body motion and the maneuver time. The optimization is on slew command parameters, such as maximum slew velocity and acceleration, for a given redundant reaction wheel configuration and is based on the dynamic interaction between the spacecraft and reaction wheel motion. Analytical development of the slew algorithm to generate desired slew position, rate, and acceleration profiles to command a feedback/feed forward control system is described. High-fidelity simulation and experimental results are presented to show that the developed slew law achieves the objectives.

Ha, Kong Q.↗
NASA NTRS2006

Causes of Extremely Fast CMEs

We study CMEs observed by LASCO to have plane of the sky velocities exceeding 1500 km/sec. We find that these extremely fast CMEs are typically associated with flares accompanied by erupting prominences. Our results are consistent with a single CME initiation process that consists of three stages. The initial stage is brought about by the emergence of new magnetic flux, which interacts with the pre-existing magnetic configuration and results in a slow rise of the magnetic structure. The second stage is a fast reconnection phase with flaring, filament eruption and a sudden increase of the rise velocity of the magnetic structure (CME). The third stage consists of propagation in the corona. We discuss the sources of these CMEs and the need for improved understanding of the first and third stages.

solar flares↗
NASA NTRS1988

The effects of canard-wing flow-field interactions on longitudinal stability, effective dihedral and potential deep-stall trim

The literature available on high aspect ratio canard configurations shows them to have some unique stability characteristics. Using a generic canard-wing model, the effects of canard-wing flow-field interactions on stability were investigated in the NASA Langley Twelve-Foot Low-Speed Wind Tunnel. Results for the attached flow regime indicate linear interactions shift the neutral point of a canard configuration forward, but the effect of a canard on a wing can change significantly when the flow over the surface begins to separate, even several degrees below stall. The asymmetry of the canard downwash in a sideslip condition can result in an increment in effective dihedral roughly proportional to canard lift coefficient. At very high angles of attack the presence of a wing can cause an incremental normal force on a canard, contributing to the possibility of a deep-stall trim point. This effect is greater for a high canard and less for a low one.

Muchmore, C. B., Jr.↗
NASA NTRS1988

An interactive grid generation technique for fighter aircraft geometries

This paper describes an interactive procedure to construct grids about fighter aircraft using a state-of-the-art workstation. The aircraft are characterized by a fuselage with an integrated canopy over the cockpit, an engine inlet, an area ruled midsection, canards, and highly-swept cranked delta wings or strakes integrated into the wings and tail surfaces. The grid topology, configuration surface grid, exterior grid computation, and computational interactive process are addressed.

Smith, Robert E.↗