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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 973 records · Page 54

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NASA NTRS1982

A study of resonant-cavity and fiberglass-filled parallel baffles as duct silencers

Acoustical performance and pressure drop were measured for two types of splitters designed to attenuate sound propagating in ducts - resonant-cavity baffles and fiberglass-filled baffles. Arrays of four baffles were evaluated in the 7- by 10-foot wind tunnel number 1 at Ames Research Center at flow speeds from 0 to 41 m/sec. The baffles were 2.1 m high, 305 to 406 mm thick, and 3.1 to 4.4 m long. Emphasis was on measurements of silencer insertion loss as affected by variations of such parameters as baffle length, baffle thickness, perforated skin geometry, cavity size and shape, cavity damping, wind speed, and acoustic field directivity. An analytical method for predicting silencer performance is described and compared with measurements. With the addition of cavity damping in the form of 25-mm foam linings, the insertion loss above 250 Hz of the resonant-cavity baffles was improved 2 to 7 db compared with the undamped baffles; the loss became equal to or greater than the insertion loss of comparable size fiberglass baffles at frequencies above 250 Hz. Variations of cavity size and shape showed that a series of cavities with triangular cross-sections (i.e., variable depth) were superior to cavities with rectangular cross sections (i.e., constant depth). In wind, the undamped, resonant-cavity baffles generated loud cavity-resonance tones; the tones could be eliminated by cavity damping.

Soderman, P. T.↗

NASA NTRS1984

Adaptation of two-dimensional transonic analysis code, TSFOIL, for use in modeling adaptive wall test sections

The effects of the elastic deformation of the wind tunnel wall held to a streamline-like shape were simulated numerically. The wall itself is simulated by a finite element model and is allowed to deform under the pressure loading developing in the wind tunnel with an airfoil model present. A modified version of the transonic analysis program, TSFOIL, is then used to determine the resulting flow field with the effects of the deformed wall included, the shape of the wall and the flow field. Once a result from a particular operating condition was obtained, the pressure distribution on the airfoil in the wind tunnel model is compared with solutions generated by TSFOIL in the free air mode.

Webb, J.↗

NASA NTRS1984

Observing system simulation experiments related to space-borne Lidar wind profiling. Part 2: Sensitivity to atmospheric and instrumental influences

Three major potential sources of errors that influence the performance of the proposed LIDAR wind profiling systems are accounted for in the following simulation studies. First, the coherent CO2 laser system proposed by NOAA/ERL for the WINDSAT requires distributions of 10 microns size aerosol concentrations throughout the atmosphere to determine the Doppler shifted backscatter signal. Second, atmospheric influences such as clouds and precipitation affect the LIDAR system's ability to obtain complete vertical wind profiles. In this study, experiments are reported on in which the complete wind profiles are only available in model generated cloud-free regions down to model cloud tops. Third, constraints on the available power required for the expected operational lifetime duration of a LIDAR system govern the number of pulses which can be used to sample a 300 km square area.

Dlouhy, R.↗

NASA NTRS1986

Generating Independent Preionizing Pulses for Lasers

Simple pulse-coupling winding on saturable reactor core lets core act as pulse transformer, passing preionizing pulse from winding to tapered transmission line, then to laser. Laser prepared for independent firing pulse, which follows preionizing pulse. Winding is simple, light in weight, low in bulk and power consumption, and inexpensive.

Pacala, T. J.↗

NASA NTRS1985

Continuous laminar smoke generator

A smoke generator capable of emitting a very thin, laminar stream of smoke for use in high detail flow visualization was invented. The generator is capable of emitting a larger but less stable rope of smoke. The invention consists of a pressure supply and fluid supply which supply smoke generating fluid to feed. The feed tube is directly heated by electrical resistance from current supplied by power supply and regulated by a constant temperature controller. A smoke exit hole is drilled in the wall of feed tube. Because feed tube is heated both before and past exit hole, no condensation of smoke generating occurs at the smoke exit hole, enabling the production of a very stable smoke filament. The generator is small in size which avoids wind turbulence in front of the test model.

Weinstein, L. M.↗

NASA NTRS1984

Qualification of the T2 wind tunnel in cryogenic operation. A: Thermal field, preliminary study of a schematic model

The T2 wind tunnel is described. The process of generating a cyrogenic gust using the example of a test made at very low temperature is presented. Detailed results of tests on temperatures for flow in the settling chamber, the interior walls of the system, and the metal casing are given. The transverse temperature distribution in the settling chamber and working section, and of the thermal gradients in the walls, are given as a function of the temperature level of the test.

Dor, J. B.↗

NASA NTRS1985

Description and test results of a variable speed, constant frequency generating system

The variable-speed, constant frequency generating system developed for the Mod-0 wind turbine is presented. This report describes the system as it existed at the conclusion of the project. The cycloconverter control circuit is described including the addition of field-oriented control. The laboratory test and actual wind turbine test results are included.

Brady, F. J.↗

NASA NTRS1985

Performance Test of Laser Velocimeter System for the Langley 16-foot Transonic Tunnel

An investigation in the Langley 16-Foot Transonic Tunnel has been conducted in which a laser velocimeter was used to measure free-stream velocities from Mach 0.1 to 1.0 and the flow velocities along the stagnating streamline of a hemisphere-cylinder model at Mach 0.8 and 1.0. The flow velocity was also measured at Mach 1.0 along the line 0.533 model diameters below the model. These tests determined the performance characteristics of the dedicated two-component laser velocimeter at flow velocities up to Mach 1.0 and the effects of the wind tunnel environment on the particle-generating system and on the resulting size of the generated particles. To determine these characteristics, the measured particle velocities along the stagnating streamline at the two Mach numbers were compared with the theoretically predicted gas and particle velocities calculated using a transonic potential flow method. Through this comparison the mean detectable particle size (2.1 micron) along with the standard deviation of the detectable particles (0.76 micron) was determined; thus the performance characteristics of the laser velocimeter were established.

Meyers, J. F.↗

NASA NTRS1986

In-flight photogrammetric measurement of wing ice accretions

A photographic instrumentation system was developed for the Lewis icing research aircraft to measure wind ice accretions during flight. The system generates stereo photographs of the accretions which are then photogrammetrically measured by the Air Force Arnold Engineering and Development Center. The measurements yield a survey of spatial coordinates of an accretion's surface to an accuracy of at least + or - 0.08 cm. The accretions can then be matched to corresponding icing cloud and aerodynamic measurements. The system is being used to measure rime, mixed, and clear natural ice accretions.

Mcknight, R. C.↗

NASA NTRS1986

In-flight photogrammetric measurement of wing ice accretions

Mcknight, R. C.↗

NASA NTRS1987

The laminar separation sensor - An advanced transition measurement method for use in wind tunnels and flight

Wind tunnel and flight tests have recently been conducted by the NASA Langley Research Center to explore the ability of laminar separation hot-film sensors to identify the presence of laminar separation as the principal mode of instability amplification leading to transition. This paper describes the different sensor configurations evaluated during the course of testing and presents results from the flight and wind tunnel evaluations. Plans for the next generation of sensors are briefly discussed.

Manuel, G. S.↗

NASA NTRS1987

Observation by Pioneer 7 of He(+) in the distant coma of Halley's comet

Plasma analyzer data obtained by Pioneer 7 during its approach to about 12.1 million km from the nucleus of Comet P/Halley are presently interpreted as He(+) generated by charge exchange of the solar wind He(2+) with neutral cometary material. The maximum He(+) flux was detected several hours after the closest March 20, 1986 approach of the spacecraft, and is noted to be not only larger than expected, but also to exhibit large, discontinuous flux changes.

Mihalov, J. D.↗

NASA NTRS1989

Effect of velocity ratio on plane mixing layer development

An experimental study has been conducted to investigate the effect of velocity ratio on the development of a plane mixing layer to self-similarity. Plane mixing layers with five different velocity ratios (0.5, 0.6, 0.7, 0.8 and 0.9) were generated in a newly designed mixing layer wind tunnel with both initial boundary layers tripped. For each velocity ratio, mean flow and turbulence measurements were obtained at eight streamwise locations with a single cross-wire probe. The results indicate that the splittter plate wake plays a very dominant and, in some cases, a lasting role in the development of the mixing layer. For velocity ratios between 0.5 and 0.7, self-similarity of the mixing layer was observed with the asymptotic states comparable. Mixing layers with the higher velocity ratios failed to achieve a self-similar state within the measurement domain. The development distance decreased with increasing velocity ratio up to 0.7, after which it appeared to increase. Almost all of the observed effects may be attributed to the presence and subsequent behavior of the splitter plate wake.

Mehta, R. D.↗

NASA NTRS1991

3-D CFD in a day - The laser digitizer project

The computation of airflow over complex configurations requires a complete description of the geometry. This can be obtained from CAD data, from blueprints, or from actual models. In any case, the time required is currently estimated at 4 to 6 months. It is proposed to shorten this time by a factor of 10 to 100 through the use of automated software, a fast, highly parallel computer and a three-dimensional laser digitizer. This device can provide (x,y,z) coordinates of surface points at rates exceeding 14,500/sec. Thus, it is possible to digitize an entire model in a few minutes. The accuracy of measurement on a flat white surface is better than 0.005 inches. Higher accuracy is available at higher cost. This work discusses the challenges which remain to be addressed. In particular, the surface point data need to be converted into a surface description, the surface description needs to be made into a surface grid, and the surface grid used to make a volume grid for the flow solver. Algorithms are kept in place or in mind for all of these problems. Integration of the more mature flow solution and visualization algorithms then allows generation of solution graphics directly from a wind tunnel model.

Merriam, Marshal↗

NASA NTRS1991

Comparison of laser transit anemometry data analysis techniques

Two techniques for the extraction of two-dimensional flow information from laser transit anemometry (LTA) data sets are presented and compared via a simulation study and experimental investigation. The methods are a probability density function (PDF) estimation technique and a marginal distribution analysis technique. The simulation study builds on the results of previous work and provides a quantification of the accuracy of both techniques for various LTA data acquisition scenarios. The experimental comparison consists of using an LTA system to survey the flow downstream of a turbulence generator in a small low-speed wind tunnel. The collected data sets are analyzed and compared.

Humphreys, William M., Jr.↗

NASA NTRS1992

Open airscrew VTOL concepts

The following concepts, based on using open airscrew(s) for VTOL maneuvers, are re-examined in light of current technology: (1) tip-driven helicopters, (2) compound helicopters; and (3) high-speed VTOL aircraft, represented by tiltrotors, tiltwings, retractoplanes and stoppable rotors. Criteria, permitting one to compare performance of aircraft using diverse lifting and propelling methods are established. Determination of currently possible performance, indication of near-future potentials, and comparison of those items with the baseline levels (as represented by contemporary shaft-driven helicopters, first generation tiltrotors, and commercial turboprop fixed-wind aircraft) constitutes bulk of this report.

Stepniewski, W. Z.↗

NASA NTRS1994

On the physics of waves in the solar atmosphere: Wave heating and wind acceleration

New calculations of the acoustic wave energy fluxes generated in the solar convective zone have been performed. The treatment of convective turbulence in the sun and solar-like stars, in particular, the precise nature of the turbulent power spectrum has been recognized as one of the most important issues in the wave generation problem. Several different functional forms for spatial and temporal spectra have been considered in the literature and differences between the energy fluxes obtained for different forms often exceed two orders of magnitude. The basic criterion for choosing the appropriate spectrum was the maximal efficiency of the wave generation. We have used a different approach based on physical and empirical arguments as well as on some results from numerical simulation of turbulent convection.

Musielak, Z. E.↗

NASA NTRS1995

Properties of ultra low frequency upstream waves at Venus and Saturn: A comparison

The upstream regions of all planets, except Pluto, have been investigated, using in situ spacecraft measurements and a variety of analysis techniques. The detailed studies at Earth indicate that these waves are generated locally in the magnetically connected solar wind by the interaction with ions backstreaming from the shock. However, since the properties of the solar wind vary with heliocentric distance and since properties of planetary shocks depend on plasma beta, interplanetary magnetic field (IMF) spiral angle and Mach number, the amount of heating, acceleration efficiencies, etc. significantly change with heliocentric distance. In turn the waves seen at each planet propagate not in the same but different (physical) propagation modes. In this paper we compare the ULF wave observations at an outer and an inner planet. We use the results of the ratio, quantites easily derivable with sufficient accuracy at each planet. We use the full electromagnetic dispersion relation for comparison with theoretical predictions.

Orlowski, D. S.↗