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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 397 records · Page 22
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NASA NTRS1975

A sounding rocket spectroheliometer for photometric studies at extreme ultraviolet wavelengths

Construction and mode of operation are described for a sounding rocket spectroheliometer used to establish the sensitivity of the EUV spectroheliometer on the Skylab Apollo Telescope Mount (ATM). The sounding rocket instrument was calibrated immediately before and after two flights and the calibration was transferred when the rocket and ATM instruments simultaneously measured the average intensity emitted by a quiet area of the solar disk. Descriptions are presented for the payload assembly and flight sequence, the optical system (telescope, spectrometer, and pointing reference camera), the vacuum pumping system, and the instrument electronics. Results obtained from the two flights in August and December 1973 are discussed, which included unambiguous determinations of the absolute intensity emitted by a region of the quiet solar disk over the wavelength range from 1350 to 300 A on two separate occasions and the establishment of photometric accuracy to that of laboratory calibration procedures.

Timothy, J. G.↗
NASA NTRS1975

Pressure Contact Sounding Data for NASA's Atmospheric Variability Experiment (AVE 3)

The basic rawinsonde data are described at each pressure contact from the surface to sounding termination for the 41 stations participating in the AVE III measurement program that began at 0000 GMT on February 6 and ended at 1200 GMT on February 7, 1975. Soundings were taken at 3-hour intervals during a large period of the experiment from most stations within the United States east of about 105 degrees west longitude. Methods of data processing, change in reduction scheme since the AVE II pilot experiment, and data accuracy are briefly discussed. An example of contact data is presented, and microfiche cards of all the contact data are included in the appendix. The AVE III project was conducted to better understand and establish the extent of applications for meteorological satellite sensor data through correlative ground truth experiments and to provide basic experimental data for use in studies of atmospheric scales of-motion interrelationships.

Fuelberg, H. E.↗
NASA NTRS1976

Real time analysis of voiced sounds

A power spectrum analysis of the harmonic content of a voiced sound signal is conducted in real time by phase-lock-loop tracking of the fundamental frequency, (f sub 0) of the signal and successive harmonics (h sub 1 through h sub n) of the fundamental frequency. The analysis also includes measuring the quadrature power and phase of each frequency tracked, differentiating the power measurements of the harmonics in adjacent pairs, and analyzing successive differentials to determine peak power points in the power spectrum for display or use in analysis of voiced sound, such as for voice recognition.

Hong, J. P.↗
NASA NTRS1976

Application of parametric and non-parametric statistics to sounding rocket dispersion including large sample and small sample theory

Analytical methods for obtaining large and small samples to be used in sounding rocket dispersion statistics are described. When the distribution of the parent population is assumed known, a method is called parametric. When no assumption is made about the parent population, the method is called nonparametric. Parametric and nonparametric methods are given for both large and small samples. The assumed distribution for the parametric case will be normal and it is shown that sample nonparametric theory is easier to apply in many cases, giving essentially the same results as parametric theory. The method is applied to the dispersion of NASA sounding rockets from 1959 to 1974.

James F. McGarvey↗
NASA NTRS1976

Stage separation study of Nike-Black Brant V Sounding Rocket System

A new Sounding Rocket System has been developed. It consists of a Nike Booster and a Black Brant V Sustainer with slanted fins which extend beyond its nozzle exit plane. A cursory look was taken at different factors which must be considered when studying a passive separation system. That is, one separation system without mechanical constraints in the axial direction and which will allow separation due to drag differential accelerations between the Booster and the Sustainer. The equations of motion were derived for rigid body motions and exact solutions were obtained. The analysis developed could be applied to any other staging problem of a Sounding Rocket System.

Ferragut, N. J.↗
NASA NTRS1976

Development of the Hawk/Nike Hawk sounding rocket vehicles

A new sounding rocket family, the Hawk and Nike-Hawk Vehicles, have been developed, flight tested and added to the NASA Sounding Rocket Vehicle Stable. The Hawk is a single-stage vehicle that will carry 35.6 cm diameter payloads weighing 45.5 kg to 91 kg to altitudes of 78 km to 56 km, respectively. The two-stage Nike-Hawk will carry payloads weighing 68 kg to 136 kg to altitudes of 118 km to 113 km, respectively. Both vehicles utilize the XM22E8 Hawk rocket motor which is available in large numbers as a surplus item from the U.S. Army. The Hawk fin and tail can hardware were designed in-house. The Nike tail can and fin hardware are surplus Nike-Ajax booster hardware. Development objectives were to provide a vehicle family with a larger diameter, larger volume payload capability than the Nike-Apache and Nike-Tomahawk vehicles at comparable cost. Both vehicles performed nominally in flight tests.

Flowers, B. J.↗
NASA NTRS1976

On sound transmission into a stiffened cylindrical shell under flight conditions

In the context of airborne-noise transmission through an aircraft fuselage, a mathematical model is presented for sound transmission into a stiffened cylindrical shell. The stiffening effect of the ring frames and stringers is approximated by a 'smeared'-stiffener theory which includes the eccentricity of the stiffeners. Numerical results are presented for a typical narrow-bodied jet in cruising flight. A comparison is made between noise transmission into a monococque shell and into a stiffened shell. The stiffeners are shown to greatly increase TL for small incidence angles, so that the effective 'window' for noise transmission is restricted to the neighborhood of normal incidence. Flow is shown to increase TL for sound waves propagating 'upstream' against the flow. Stiffeners are also shown to raise the ring frequency at which a dip in cylinder TL occurs. Limitations of the 'smeared'-stiffener theory are also discussed.

Koval, L. R.↗
NASA NTRS1976

Effect of slot width on transition and noise attenuation of a sound shield panel for supersonic wind tunnels

The effect of slot width on transition and noise attenuation of a planar rod wall sound shield has been investigated at Mach 6. Boundary layer laminarization was obtained by induced suction through adjustable slots or gaps between the rods. Transition Reynolds numbers increased significantly with increasing gap width. The local mean flow field above the suction panel rod array was uniform. Important factors for design and performance of a supersonic wind-tunnel sound shield are rod diameter, gap-to-rod diameter ratio, surface finish of the rods, and leading-edge configuration.

Harvey, W. D.↗
NASA NTRS1976

Sound generated in the vicinity of the trailing edge of an upper surface blown flap

Far-field noise data indicated that for practical upper surface blown flap configurations, the noise radiated below the flap is dominated by the noise generated in the vicinity of the trailing edge. Sound field by turbulent mixing in the trailing edge wake is investigated experimentally and theoretically. Hot-wire measurements were made downstream of the trailing edge to determine the gross turbulence mixing characteristics of the flow. This information is used as input to a theoretical analysis of the sound field. Favorable agreement is found between predicted and measured far-field noise directivities at various frequencies and noise power spectra at various directions.

Tam, C. K. W.↗
NASA NTRS1976

Preliminary evaluation of Nimbus-6 sounding data

Preliminary results on Nimbus-6 moisture and temperature soundings are discussed. The satellite takes readings of cloud-tracked winds and temperatures (with vertical resolution) in microwave and IR (15 micron and 4 micron) channels. The data are compared with ground-based radiosonde data. Isotherm patterns and thickness patterns derived from satellite data and radiosonde data are compared, as well as data on precipitable water. Satellite soundings are found to present a realistic picture of thermal and moisture fields in the vicinity of large-scale disturbances, and can be useful in initialization for large-scale numerical prediction models when properly combined with data from other sources. Limitations in vertical resolution are noted.

Tracton, M. S.↗
NASA NTRS1976

Effects of high subsonic flow on sound propagation in a variable-area duct

The propagation of sound in a converging-diverging duct containing a quasi-one-dimensional steady flow with a high subsonic throat Mach number was studied. The behavior of linearized acoustic theory at the throat of the duct was shown to be singular. This singularity implies that linearized acoustic theory is invalid. The explicit singular behavior was determined and used to sketch the development (by the method of matched asymptotic expansions) of a nonlinear theory for sound propagation in a sonic throat region.

Callegari, A. J.↗
NASA NTRS1976

Experimental determination of sound and high-speed flow interaction

A facility that was used to measure the interaction of flow with sound at high Mach numbers is described. Four inlets with different area variations (or axial gradients) were tested. Sound of selected frequencies and modes (0,0), (1,0), (2,0) was generated with eight circumferential acoustic drivers.

Lumsdaine, E.↗
NASA NTRS1976

Some factors influencing radiation of sound from flow interaction with edges of finite surfaces

Edges of surfaces which are exposed to unsteady flow cause both strictly acoustic effects and hydrodynamic effects, in the form of generation of new hydrodynamic sources in the immediate vicinity of the edge. An analytical model is presented which develops the explicit sound-generation role of the velocity and Mach number of the eddy convection past the edge, and the importance of relative scale lengths of the turbulence, as well as the relative intensity of pressure fluctuations. The Mach number (velocity) effects show that the important paramater is the convection Mach number of the eddies. The effects of turbulence scale lengths, isotropy, and spatial density (separation) are shown to be important in determining the level and spectrum of edge sound radiated for the edge dipole mechanism. Experimental data is presented which provides support for the dipole edge noise model in terms of Mach number (velocity) scaling, parametric dependence on flow field parameter, directivity, and edge diffraction effects.

Hayden, R. E.↗
NASA NTRS1977

Finite-difference theory for sound propagation in a lined duct with uniform flow using the wave envelope concept

Finite difference equations are derived for sound propagation in a two dimensional, straight, soft wall duct with a uniform flow by using the wave envelope concept. This concept reduces the required number of finite difference grid points by one to two orders of magnitude depending on the length of the duct and the frequency of the sound. The governing acoustic difference equations in complex notation are derived. An exit condition is developed that allows a duct of finite length to simulate the wave propagation in an infinitely long duct. Sample calculations presented for a plane wave incident upon the acoustic liner show the numerical theory to be in good agreement with closed form analytical theory. Complete pressure and velocity printouts are given to some sample problems and can be used to debug and check future computer programs.

Baumeister, K. J.↗
NASA NTRS1977

Sound-tube measurements of the relaxation frequency of moist nitrogen

At audible frequencies, the vibrational relaxation of nitrogen contributes significantly to the absorption of sound in still air. The accurate measurement of the humidity dependence of the relaxation frequency of nitrogen, as yet, has eluded careful measurement due to the difficulty in measuring small absorption at low frequencies. Recently, equipment has been constructed for measuring sound absorption in air as a function of humidity over the frequency range from 4 to 100 kHz. In the experiment described here, the temperature and humidity range of this equipment has been extended so that it can be used to study the relaxation absorption in nitrogen at temperatures from 311 K to 418 K. The results indicate that, over this temperature range, the frequency of maximum absorption in moist nitrogen, f, can be given by f/P = 260 x h, Hz/atm, where h is the percent mole fraction of water, and P is the pressure in atm. To the accuracy of the measurements reported here, f is independent of temperature over the range of temperatures at which the measurements were made.

Chang, D.↗
NASA NTRS1977

Nonlinear effects on sound in nearly sonic duct flows

A nonlinear theory for sound propagation in nearly sonic flows in variable area ducts is outlined. The theory is based on a quasi-one-dimensional model and the use of matched asymptotic expansions. The problem of an acoustic source located in the throat region of a duct with a converging section is treated. It is shown that the near-sonic region has a marked nonlinear effect on sound propagation in the duct.

Callegari, A. J.↗
NASA NTRS1977

The parabolic approximation for sound propagation in a stratified moving medium

Propagation of sound in a stratified moving medium is discussed through an extension of the parabolic approximation to the acoustic equations of motion for short wavelengths. The parabolic approximation is related to the theory of geometric acoustics, and it is shown that it yields an improvement in accuracy over geometric theory. Also, the approximation corrects cumulative failures of geometric theory which occur when sound propagates many wavelengths from its source. The theory is illustrated by application to simple examples of quasi-plane wave propagation.

Myers, M. K.↗