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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

An experimental investigation of acoustic radiation from a source inside a large turbulent free jet

An experiment has been conducted in NASA Langley's free-jet anechoic facility to assess the effect of a free-jet shear layer on sound radiation from an acoustic source placed inside the jet. The nozzle diameter was 1.22 m and operated at an exit velocity of 35 m/s. Two different types of sources were used; one was a compact source with a nearly uniform radiation pattern, the other was a noncompact source with highly directional radiation pattern. The acoustic source was driven by pure tone and 1/3-octave band white noise. Acoustic measurements were made both inside the jet flow in the potential core region and outside the jet in the acoustic farfield. The effects of mean flow convection and mean shear refraction on sound radiation were determined. The experimental results compared favorably with analytical predictions. The effect of free-jet turbulence on sound scattering was found to be insignificant.

Ozkul, A.↗
NASA NTRS1979

Deployable antenna technology development for the Large Space Systems Technology program

The critical technologies associated with the development of deployable reflector antenna technology for the LSST program will be derived from NASA mission models and the subsequent requirements will be related to the classes of missions involved. The approach formulated for the development of reflector technology is based on the development of specific reflector concepts that have been identified as leading candidates for future applications. The development approach will be augmented by supporting technology disciplines such as controls, materials, electromagnetic analysis, as well as the capability of analytically predicting the overall performance of the large space system.

Freeland, R. E.↗
NASA NTRS1978

Effective thermal conductivity of fully and partially saturated metal wicks

The purpose of the study is threefold: (1) to perform accurate experiments covering a wide range of porosities to determine the effective thermal conductivity of sintered fiber porous metals fully saturated with air, water, and water vapor; (2) to propose correlations for these cases, and to compare these correlations with existing analytical predictions, experimental correlations and data; and (3) to determine the effective thermal conductivity of porous metals partially saturated with water and water vapor, respectively. The experimental apparatus, based on the steady-state method of comparison, is designed and used for determining the effective thermal conductivity. The wicks are made of nickel 200, stainless steel 430, and copper, covering a porosity range 0.30-0.67. Based on the experimental results, a single correlation is derived for predicting the effective thermal conductivity of all wicks fully saturated with air, water, and water vapor. For two partially saturated wick specimens with both high porosity and large matrix thermal conductivity, a liquid-vapor transition zone is observed between the phases, which increases the total combined effective thermal conductivity of the specimen.

Kar, K.↗
NASA NTRS1979

Preliminary test results with a Stirling Laboratory Research Engine

The Jet Propulsion Laboratory has designed, assembled, and initiated testing of a Stirling Laboratory Research Engine (SLRE). This preprototype engine provides a research tool to support the development of a broad range of analytical modeling and experimental efforts. The SLRE is a horizontally opposed, two-piston, single-acting Stirling engine with a split crankshaft drive mechanism. The paper discusses the preliminary results obtained during engine motoring tests and compares these results with two different analytical prediction models. Comparisons are made between experiment, the classical Schmidt analysis, and the JPL Stirling Cycle Analysis Model (SCAM). SCAM is a computerized one-dimensional, cyclic, compressible flow model of the SLRE and consists of a compilation of individual component subroutines. The formulation and current state of development of the SCAM program is briefly described.

Hoehn, F. W.↗
NASA NTRS1979

Experimental measurements of moving noise sources

The far-field pressure was measured from three different types of moving sources: a point monopole, a small model jet, and an aircraft. Results for the pressure time history produced by the point source show good agreement with those predicted analytically. Both actual and simulated forward motion of the model jet show reductions in noise levels with forward speed at all angles between the source and observer. Measurement with the aircraft over both an anechoic floor and over the ground yields a method for evaluating the transfer function for ground reflections at various angles between the moving aircraft and measurement position.

Maestrello, L.↗
NASA NTRS1979

Technique to determine location of radio sources from measurements taken on spinning spacecraft

The procedure developed to extract average source direction and average source size from spin-modulated radio astronomy data measured on the IMP-6 spacecraft is described. Because all measurements are used, rather than just finding maxima or minima in the data, the method is very sensitive, even in the presence of large amounts of noise. The technique is applicable to all experiments with directivity characteristics. It is suitable for onboard processing on satellites to reduce the data flow to Earth. The application to spin-modulated nonpolarized radio astronomy data is made and includes the effects of noise, background, and second source interference. The analysis was tested with computer simulated data and the results agree with analytic predictions. Applications of this method with IMP-6 radio data have led to: (1) determination of source positions of traveling solar radio bursts at large distances from the Sun; (2) mapping of magnetospheric radio emissions by radio triangulation; and (3) detection of low frequency radio emissions from Jupiter and Saturn.

Fainberg, J.↗
NASA NTRS1979

Design, fabrication, and test of a steel spar wind turbine blade

The design and fabrication of wind turbine blades based on 60 foot steel spars are discussed. Performance and blade load information is given and compared to analytical prediction. In addition, performance is compared to that of the original MOD-O aluminum blades. Costs for building the two blades are given, and a projection is made for the cost in mass production. Design improvements to reduce weight and improve fatigue life are suggested.

Sullivan, T. L.↗
NASA NTRS1980

Proposed method for determining the thickness of glass in solar collector panels

An analytical method was developed for determining the minimum thickness for simply supported, rectangular glass plates subjected to uniform normal pressure environmental loads such as wind, earthquake, snow, and deadweight. The method consists of comparing an analytical prediction of the stress in the glass panel to a glass breakage stress determined from fracture mechanics considerations. Based on extensive analysis using the nonlinear finite element structural analysis program ARGUS, design curves for the structural analysis of simply supported rectangular plates were developed. These curves yield the center deflection, center stress and corner stress as a function of a dimensionless parameter describing the load intensity. A method of estimating the glass breakage stress as a function of a specified failure rate, degree of glass temper, design life, load duration time, and panel size is also presented.

Moore, D. M.↗
NASA NTRS1979

Investigation of the feasibility of CARS measurements in scramjet combustion

Results are presented of analytical and experimental investigations to determine the feasibility of using coherent anti-Stokes Raman spectroscopy (CARS) to measure temperature and species concentrations in supersonic combustion experiments. Experimental CARS spectra of O2 and H2 in a laboratory flat H2 - air diffusion flame are presented. Temperatures deduced from both species generally agree with radiation corrected thermocouple measurements. Oxygen concentrations were determined from the shape of the experimental spectra. Measured H2 CARS signal magnitudes are in good agreement with analytical predictions based on H2 concentration profiles determined from spontaneous Raman scattering. Based on these results, CARS diagnostics appear to be feasible if problems associated with the supersonic flow are not too severe.

Shirley, J. A.↗
NASA NTRS1979

The effects of strain and temperature on the dynamic properties of elastomers

This paper presents the results of a program of analysis and tests to determine the dynamic properties of elastomers as a function of strain and ambient temperature. Measurements were also made to determine the temperature distribution in the elastomer samples during the tests. These measured properties were compared with analytical predictions based on a visco-elastic model designed to take into account the self-heating of the materials as a function of strain. The test method used was well-established Base Excitation Resonant Mass Technique. The specimens tested were two cylindrical button compression specimens and a shear specimen. Strain was shown to be an important parameter in determining the dynamic properties of the elastomers. In general, these properties were much more sensitive to strain than to frequency. The self-heating effect was found to account for a portion of the strain sensitivity of these properties.

Darlow, M. S.↗
NASA NTRS1979

Design of space payloads for transient environments

Current practices used to design space payload structures for transient dynamic loads are described. Included in the discussion of the design process are the estimation of preliminary loads, development of dynamic models, calculation of transient loads, verification of analytical models, establishment of development tests, definition of the qualification tests, and acquisition of flight data. An indication of the accuracy of the analytical predictions is provided by comparing them with actual test and flight data. Many illustrations and much data obtained during the Viking Project are used to clarify the current practices.

Wada, B. K.↗
NASA NTRS1980

Microprocessor realizations of range and range-rate filters in radar systems

This paper describes the implementation of digital radar range-rate filters on a microprocessor-based system. A range-rate filter processes a digitized noisy range signal to recover smoothed range data and its derivative, range rate. Two filter designs are implemented. Considerations aiding their efficient operation on an 8-bit microprocessor are discussed. The filters are subjected to a noisy range input signal of known variance, and the associated output signals are statistically analysed to determine noise-rejection characteristics. These results are compared to analytical predictions.

Fleischer, D.↗
NASA NTRS1980

Convective heating of solid propellant during ignition

A pattern search optimization procedure is used to deduce from test data on the solid rocket boosters of the Space Shuttle the convective heat transfer coefficients between the igniter and main motor combustion gases and the surface of the solid propellant by utilizing a spatial and temporal ignition transient analysis. The 'best' convective coefficients are found which will minimize the overall deviation of the analytical prediction from the ignition transient test data. Computationally, this is achieved by treating the motor in such a way that only four optimization variables must be determined. The resulting coefficients greatly improve the prediction capabilities of the ignition transient analysis for the Space Shuttle SRM.

Murph, J. E.↗
NASA NTRS1980

An analytical study of nitrogen oxides and carbon monoxide emissions in hydrocarbon combustion with added nitrogen - Preliminary results

The influence of ground-based gas turbine combustor operating conditions and fuel-bound nitrogen (FBN) found in coal-derived liquid fuels on the formation of nitrogen oxides and carbon monoxide is investigated. Analytical predictions of NOx and CO concentrations are obtained for a two-stage, adiabatic, perfectly-stirred reactor operating on a propane-air mixture, with primary equivalence ratios from 0.5 to 1.7, secondary equivalence ratios of 0.5 or 0.7, primary stage residence times from 12 to 20 msec, secondary stage residence times of 1, 2 and 3 msec and fuel nitrogen contents of 0.5, 1.0 and 2.0 wt %. Minimum nitrogen oxide but maximum carbon monoxide formation is obtained at primary zone equivalence ratios between 1.4 and 1.5, with percentage conversion of FBN to NOx decreasing with increased fuel nitrogen content. Additional secondary dilution is observed to reduce final pollutant concentrations, with NOx concentration independent of secondary residence time and CO decreasing with secondary residence time; primary zone residence time is not observed to affect final NOx and CO concentrations significantly. Finally, comparison of computed results with experimental values shows a good semiquantitative agreement.

Bittker, D. A.↗
NASA NTRS1980

A comparison of experiment and theory for sound propagation in variable area ducts

An experimental and analytical program has been carried out to evaluate sound suppression techniques in ducts that produce refraction effects due to axial velocity gradients. The analytical program employs a computer code based on the method of multiple scales to calculate the influence of axial variations due to slow changes in the cross-sectional area as well as transverse gradients due to the wall boundary layers. Detailed comparisons between the analytical predictions and the experimental measurements have been made. The circumferential variations of pressure amplitudes and phases at several axial positions have been examined in straight and variable area ducts, with hard walls and lined sections, and with and without a mean flow. Reasonable agreement between the theoretical and experimental results has been found.

Nayfeh, A. H.↗
NASA NTRS1980

Full scale wind tunnel investigation of a bearingless main helicopter rotor

A stability test program was conducted to determine the effects of airspeed, collective pitch, rotor speed and shaft angle on stability and loads at speeds beyond that attained in the BMR/BO-105 flight test program. Loads and performance data were gathered at forward speeds up to 165 knots. The effect of cyclic pitch perturbations on rotor response was investigated at simulated level flight conditions. Two configuration variations were tested for their effect on stability. One variable was the control system stiffness. An axially softer pitch link was installed in place of the standard BO-105 pitch link. The second variation was the addition of elastomeric damper strips to increase the structural damping. The BMR was stable at all conditions tested. At fixed collective pitch, shaft angle and rotor speed, damping generally increased between hover and 60 knots, remained relatively constant from 60 to 90 knots, then decreased above 90 knots. Analytical predictions are in good agreement with test data up to 90 knots, but the trend of decreasing damping above 90 knots is contrary to the theory.

Source record↗
NASA NTRS1980

Experimental investigation of graphite/polyimide sandwich panels in edgewise compression

The local and general buckling behavior of graphite/polyimide sandwich panels simply supported along all four edges and loaded in uniaxial edgewise compression was investigated. Material properties of adhesive and facings were determined from flatwise tension and sandwich beam flexure tests. Tensile and compressive material properties of the facings were determined at 116, R.T., and 589 K (-250, R.T., and 600 F) using the sandwich beam flexure test method. Results indicate that Gr/PI is a usable structural material for short term use at temperatures as high as 589 K (600 F). Buckling specimens were 30.5 X 33.0 cm (12 x 13 in.), had quasi-isotropic symmetric facings and a glass/polyimide honeycomb core. Core thicknesses varied and three panels of each thickness were tested in edgewise compression at room temperature to investigate failure modes and corresponding buckling formulas. Specimens 0.635 cm (0.25 in.) thick failed by overall buckling at loads close to the analytically predicted buckling load; all other panels failed by face wrinkling. Results of the winkling tests indicate that several buckling formulas were unconservative and therefore not suitable for design purposes; recommended wrinkling equations are presented.

Camarda, C. J.↗
NASA NTRS1980

Evaluation of space shuttle main engine fluid dynamic frequency response characteristics

In order to determine the POGO stability characteristics of the space shuttle main engine liquid oxygen (LOX) system, the fluid dynamic frequency response functions between elements in the SSME LOX system was evaluated, both analytically and experimentally. For the experimental data evaluation, a software package was written for the Hewlett-Packard 5451C Fourier analyzer. The POGO analysis software is documented and consists of five separate segments. Each segment is stored on the 5451C disc as an individual program and performs its own unique function. Two separate data reduction methods, a signal calibration, coherence or pulser signal based frequency response function blanking, and automatic plotting features are included in the program. The 5451C allows variable parameter transfer from program to program. This feature is used to advantage and requires only minimal user interface during the data reduction process. Experimental results are included and compared with the analytical predictions in order to adjust the general model and arrive at a realistic simulation of the POGO characteristics.

Gardner, T. G.↗