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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 1,675 records · Page 93
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NASA NTRS1984

Propagation of propeller tone noise through a fuselage boundary layer

In earlier experimental and analytical studies, it was found that the boundary layer on an aircraft could provide significant shielding from propeller noise at typical transport airplane cruise Mach numbers. In this paper a new three-dimensional theory is described that treats the combined effects of refraction and scattering by the fuselage and boundary layer. The complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The model for the incident waves is a near-field frequency-domain propeller source theory developed previously for free field studies. Calculations for an advanced turboprop (Prop-Fan) model flight test at 0.8 Mach number show a much smaller than expected pressure amplification at the noise directivity peak, strong boundary layer shielding in the forward quadrant, and shadowing around the fuselage. Results are presented showing the difference between fuselage surface and free-space noise predictions as a function of frequency and Mach number. Comparison of calculated and measured effects obtained in a Prop-Fan model flight test show good agreement, particularly near and aft of the plane of rotation at high cruise Mach number.

Hanson, D. B.↗
NASA NTRS1983

Turbulence measurements in two shock-wave/shear-layer interactions

Measurements of the longitudinal component of the mass-flow fluctuations have been made in an 8-deg compression corner flow and a reattaching shear layer at a Mach number of approximately 2.9 and unit Reynolds number of about 7 x 10 to the 7th per m. The data include turbulence intensities and probability density distributions. Significant turbulence amplification occurs in both interactions. A qualitative explanation in terms of direct shock effects, extra strain rates, and their relative contribution, is suggested.

Hayakawa, K.↗
NASA NTRS1984

Relativistic dispersion and the generation of auroral kilometric radiation

Under the conditions at which auroral kilometric radiation (AKR) is known to be produced by a plasma sheet electron region, relativistic effects of the dispersion of extraordinary-mode waves near the electron cyclotron frequency are found to be very significant. The application of linear theory and computer simulation to a model distribution indicates that an extraordinary mode of a particular Reynolds number dominated the radiation emission due to the cyclotron maser instability, suggesting that hot electrons determine the propagation characteristics of AKR and that larger growth rates are possible for direct amplification of extraordinary waves in the auroral region than had been predicted by calculations employing cold plasma dispersion.

Pritchett, P. L.↗
NASA NTRS1984

Modification of the strato-mesospheric temperature and wind structure resulting from the 26 February 1979 solar eclipse

Temperature and wind behavior observed during the February 1979 solar eclipse shows significant change immediately following and up to one hour after totality. Stratospheric and mesospheric data obtained from Fort Churchill, Manitoba, indicate quite clearly a cooling trend between 50-60 kilometers with the maximum temperature decrease of approximately 10 C evident above 52 kilometers. This temperature perturbation was accompanied by an amplification of the meridional wind speed of 20-30 mps near 60 kilometers. These results are essentially in agreement with those obtained at Wallops Island during the March 1970 solar eclipse. Although the stratosphere was under the large-scale influence of a stratospheric warming, the short-term perturbations caused by radiative changes as a result of the solar eclipse did not appear to be masked.

Schmidlin, F. J.↗
NASA NTRS1984

Effect of curvature on three-dimensional boundary layer stability

The problem of the stability of a three-dimensional laminar boundary layer formed on a curved surface is considered. A calculation scheme, which takes account of the curvature of the flow streamlines and of the surface is proposed for the prediction of the development of small amplitude temporal disturbances. Computations have been performed for the flow over the windward face of an infinitely long yawed cylinder and comparisons have been made with experimental data. These indicate that the theory correctly predicts many of the features of the unstable laminar flow. The theory also suggests that transition, in this particular situation, is dominated by traveling disturbance waves and that, at the experimentally observed transition location, the wave which has undergone greatest total amplification has an amplitude ratio of approximately e to the 11th. When the effects of curvature are omitted the maximum amplitude ratio at transition is about e to the 17th.

Malik, M. R.↗
NASA NTRS1984

Wave interactions in swept-wing flows

Crossflow instabilities dominate disturbance growth in the leading-edge region of swept wings. It is well known that streamwise vortices in a boundary layer strongly influence the behavior of other disturbances. Amplification of crossflow vortices near the leading edge produces a residual spanwise nonuniformity in the mid-chord regions where Tollmien-Schlichting (T-S) waves are strongly amplified. Should the T-S wave undergo double-exponential growth because of this effect, the usual transition prediction methods would fail. Thus, it is important to study interactions of this sort and to develop more realistic criteria for transition prediction.

Reed, H. L.↗
NASA NTRS1984

Effects of nozzle design parameters on the extent of quiet test flow at Mach 3.5

Tests results at the NASA Langley Research Center, involving a Mach 3.5 pilot quiet tunnel, have shown that laminar-layered nozzle walls improve boundary layer stability and reduce stream disturbance levels caused by eddy Mach wave radiation. This type of wall design is required to obtain transition Reynolds numbers on tests models as high as those previously observed in supersonic flight vehicles. The Mach 3.5 pilot nozzle wall boundary layers were tested for Tollmein-Schlichting and Goertler linear amplification, and, in an analysis of Goertler vortices in two axisymmetric Mach 5 nozzles, transition values were found to vary. These values were applied to several nozzles with similar throat heights but different expansion rates. Among the nozzles included in the study, a flat-wall radial flow nozzle and a proposed rod-wall nozzle were tested. For the highest test unit Reynolds number, it was determined that the nozzle wall surface finish should not exceed 0.3 micron. Oil flow studies have indicated that Goertler vortex disturbances were the dominant mechanism causing transition on the walls of the pilot nozzle.

Beckwith, I. E.↗
NASA NTRS1984

Progress in optical parametric oscillators

It is pointed out that tunable coherent sources are very useful for many applications, including spectroscopy, chemistry, combustion diagnostics, and remote sensing. Compared with other tunable sources, optical parametric oscillators (OPO) offer the potential advantage of a wide wavelength operating range, which extends from 0.2 micron to 25 microns. The current status of OPO is examined, taking into account mainly advances made during the last decade. Attention is given to early LiNbO3 parametric oscillators, problems which have prevented wide use of parametric oscillators, the demonstration of OPO's using urea and AgGaS2, progress related to picosecond OPO's, a breakthrough in nanosecond parametric oscillators, the first demonstration of a waveguide and fiber parametric amplification and generation, the importance of chalcopyrite crystals, and theoretical work performed with the aim to understand the factors affecting the parametric oscillator performance.

Fan, Y. X.↗
NASA NTRS1984

Potential for coherent Doppler wind velocity lidar using neodymium lasers

Existing techniques for the frequency stabilization of Nd:YAG lasers operating at 1.06 micron, and the high-gain amplification of radiation at that wavelength, make possible the construction of a coherent Doppler wind velocity lidar using Nd:YAG. Velocity accuracy and range resolution are better at 1.06 micron than at 10.6 microns at the same level of the SNR. Backscatter from the atmosphere at 1.06 micron is greater than that at 10.6 microns by about 2 orders of magnitude, but the quantum-limited noise is higher by 100 also. Near-field attenuation and turbulent effects are more severe at 1.06 micron. In some configurations and environments, the 1.06-micron wavelength may be the better choice, and there may be technological advantages favoring the use of solid-state lasers in satellite systems.

Kane, T. J.↗
NASA NTRS1982

Rapid diagnostic methods for influenza virus in clinical specimens - A comparative study

A comparison of five rapid viral diagnostic techniques for identifying influenza virus in nasopharyngeal aspirates has been made on patients with influenza-like illnesses. Initial results with immune electron microscopy were positive in only one of 11 specimens from which virus was isolated and further work abandoned. Four other rapid tests were carried out on 39 specimens from which influenza virus had been isolated in tissue culture in 28. Of these 28 specimens yielding virus, 24 (85.7 percent) were positive by an indirect fluorescent antibody test (IFAT) on nasopharyngeal cells, 18 (64.3 percent) by enzyme-linked immunosorbent assay (ELISA), 19 (67.8 percent) by enzyme-linked fluorescent assay (ELFA), and 26 (92.8 percent) by a rapid tissue culture amplification method (TCA) in a continuous Rhesus monkey kidney line (LLC-MK2) with identification of virus by fluorescent antibody. In terms of sensitivity, simplicity, and rapidity, a combination of the IFAT and TCA methods seems to be very useful.

Evans, A. S.↗
NASA NTRS1984

Effect of parallel refraction on magnetospheric upper hybrid waves

Large amplitude (not less than 10 mV/m) electrostatic plasma waves near the upper hybrid (UH) frequency have been observed from 0 to 50 deg magnetic latitude (MLAT) during satellite plasma-pause crossings. A three-dimensional numerical ray-tracing calculation, based on an electron distribution measured during a GEOS 1 dayside intense upper-hybrid wave event, suggests how UH waves might achieve such large amplitudes away from the geomagnetic equator. Refractive effects largely control the wave amplification and, in particular, the unavoidable refraction due to parallel geomagnetic field gradients restricts growth to levels below those observed. However, a cold electron density gradient parallel to the field can lead to upper hybrid wave growth that can account for the observed emission levels.

Engel, J.↗
NASA NTRS1984

Energy Diagnostics and Impact Studies of FGGE Global Data Sets and GLAS GCM Simulations

An analysis of a case study of the favorable impact of satellite data assimilation on model cyclone prediction is discussed. Also discussed is the isolation of systematic biases in the vertical structure of satellite derived temperatures which in all probability negatively impact the prediction of ocean cyclones during periods of rapid baroclinic amplification. Access to CYBER 205 and transfer of software for Eulerian and quasi-Lagrangian diagnostic studies of atmospheric circulation are discussed.

Johnson, D. R.↗
NASA NTRS1984

Full scale experiments into the use of large eddy breakup devices for drag reduction on aircraft

An experimental investigation in flight was performed to explore the feasibility of using LEBU (Large-Eddy-Breakup) devices to reduce the drag of aircraft. Two geometrical shapes of ribbons were used, and the development of local skin friction was monitored downstream. The aircraft was a swept-wing attack aircraft, and the flights covered the entire subsonic regime from M=0.92 down to stall conditions; flight altitudes were 1, 4.5, 7 and 10 km to explore various combinations of angle of attack, Mach - and Reynolds numbers. Some information was obtained concerning the turbulence characteristics downstream, and a discussion of the downstream amplification due to the drag at the device is also presented.

Bertelrud, A.↗
NASA NTRS1985

A survey of major east coast snowstorms, 1960-1983. Part 2. Summary of surface and upperlevel characteristics

Surface and upper-level characteristics of selected meteorological fields are summarized. Two major types of sea level development are described and applied to the cases at hand, with a few storm systems showing characteristics of both types. Aspects such as rapid sea level deepening, coastal frontogenesis, cold air damming, low level jet formation, the development of an S-shaped isotherm pattern, diffluence downwind of a negatively tilted upper level trough axis, upper level confluence and an increase of geopotential heights at the base of the upper level trough characterized the pre-cyclogenetic and cyclogenetic periods of many of the storm systems. Large variability was also observed, especially with regard to the spatial dimensions of the surface and upper level systems, as well as variations in trough/ridge amplification and the evolution of upper level jet streak systems. The influence of transverse circulations associated with a confluent jet streak entrance region and the diffluent exit region of a jet streak/trough system on the production of snowfall is also discussed.

Kocin, P. J.↗
NASA NTRS1985

Turbulence and wave particle interactions in solar-terrestrial plasmas

Activities in the following study areas are reported: (1) particle and wave processes in solar flares; (2) solar convection zone turbulence; and (3) solar radiation emission. To investigate the amplification of cyclotron maser radiation in solar flares, a radio frequency. (RF) heating model was developed for the corona surrounding the energy release site. Then nonlinear simulations of compressible convection display prominent penetration by plumes into regions of stable stratification at the base of the solar convection zone, leading to the excitation of internal gravity waves there. Lastly, linear saturation of electron-beam-driven Langmuir waves by ambient density fluctuations, nonlinear saturation by strong turbulence processes, and radiation emission mechanisms are examined. An additional section discusses solar magnetic fields and hydromagnetic waves in inhomogeneous media, and the effect of magnetic fields on stellar oscillation.

Dulk, G. A.↗
NASA NTRS1985

A cosmic ray driven instability

The interaction between energetic charged particles and thermal plasma which forms the basis of diffusive shock acceleration leads also to interesting dynamical phenomena. For a compressional mode propagating in a system with homogeneous energetic particle pressure it is well known that friction with the energetic particles leads to damping. The linear theory of this effect has been analyzed in detail by Ptuskin. Not so obvious is that a non-uniform energetic particle pressure can addition amplify compressional disturbances. If the pressure gradient is sufficiently steep this growth can dominate the frictional damping and lead to an instability. It is important to not that this effect results from the collective nature of the interaction between the energetic particles and the gas and is not connected with the Parker instability, nor with the resonant amplification of Alfven waves.

Dorfi, E. A.↗
NASA NTRS1983

Gravitational lens effects of a cosmological density of compact objects

Amplification of quasar light by a cosmological density of compact objects causes significant effects on many quasars in magnitude-limited samples. For lens masses solar mass less than 100,000 solar mass the continuum would be amplified by a magnitude or more but the line emission would not. Examination of the UV selected sample of Marshall et al. (1983) gives limits to more than 90 percent statistical confidence of Omega(c) less than 0.1 for a mass between 200 and 100,000 solar mass, where Omega(c) is the mean density of objects of mass M relative to the closure density. Preliminary results from an X-ray selected sample may probe to more than 0.1 solar mass and give a value for Omega(c) of less than one. These limits indicate that the remnants of an early population of massive stars cannot make a cosmologically significant contribution to the mass density of the universe. On a separate topic, recent work on the enhanced surface density of quasars near galaxies due to lensing by stars in the galaxy halos is reviewed.

Canizares, C. R.↗
NASA NTRS1985

Experimental study of forward-located jet-interaction nozzles

The effects of forward-mounted sonic jet-interaction nozzles with one, three equal, or one large and two small orifices on the transitional or turbulent boundary-layer flow over a biconic (9-deg-25-arcmin/6-deg) model at angle of attack -10 to the 15 deg and Reynolds number 8.10 x 10 to the 6th/ft are investigated experimentally using pressure taps, force measurements, oil-flow visualization, and schlieren photography in the 20-in. Mach-6 wind tunel at NASA Langley. The injection flow rates are 0.055 and 0.026 lbm/s, with stagnation pressure 500 psia, stagnation temperature 1000 R, and dynamic pressure 8.7 psia. The results are presented in diagrams, graphs, and photographs and characterized. Moment amplification factors of 1.0 or better (maximum 1.8 at angle of attack 15 deg and flow rate 0.055 lbm/s) are observed for all nozzle types, but the configuration with three unequal orifices is found to give improvements of 10 percent over the single-orifice nozzle at a given flow rate.

Cavalleri, R. J.↗