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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 235 records · Page 13

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NASA NTRS1984

Pioneer 10 search for gravitational waves - No evidence for coherent radiation from Geminga

Attempts to identify a periodic gravitational wave signal from the binary Geminga in the reduced Doppler data from the Pioneer 10 spacecraft are reported. The study was performed to examine the possibility that the observed 160 min solar oscillation is driven by a gravitational wave from the binary, which has a period exactly one cycle different from the solar oscillation. Three 12 hr passes of Doppler data from Pioneer 10, now beyond the orbit of Neptune, were subjected to FFT analysis to detect a spectral gravitational wave signature. None was found. Least squares analysis of all low noise data from 1981 to characterize the amplitude and phase of a signal from Geminga also produced a null result. Finally, an upper bound was calculated for the polarization component of the potentially observable gravitational strain.

Anderson, J. D.↗

NASA NTRS1978

A computer-controlled instrumentation system for third octave analysis

An instrumentation system is described which employs a minicomputer, a one-third octave band analyzer, and a time code/tape search unit for the automatic control and analysis of third-octave data. With this system the information necessary for data adjustment is formatted in such a way as to eliminate much operator interface, thereby substantially reducing the probability for error. A description of a program for the calculation of effective perceived noise level from aircraft noise data is included as an example of how this system can be used.

Faulcon, N. D.↗

NASA NTRS1973

The effect of nozzle inlet shape, lip thickness, and exit shape and size on subsonic jet noise.

Far field noise data were taken for convergent nozzles of various shapes and sizes at subsonic velocities exceeding 400 ft/sec. For a circular nozzle, the nozzle inlet shape and lip thickness had no effect on the noise level, directivity, or spectra when compared at the same nozzle exit diameter and peak exhaust velocity. A sharp edged orifice was one exception to this statement. Coannular nozzles can produce additional high frequency noise. Blunt ended centerbodies, where there is significant base drag, also generate significant additional noise.

Olsen, W. A.↗

NASA NTRS1984

Fluid shielding of high-velocity jet noise

Experimental noise data for a nozzle exhaust system incorporating a thermal acoustic shield (TAS) are presented to show the effect of changes in geometric and flow parameters on attenuation of high-velocity jet exhaust noise in the flyover plane. The results are presented for a 10.00-cm-diameter primary conical nozzle with a TAS configuration consisting of a 2.59- or 5.07-cm-wide annular gap. Shield-stream exhaust velocity was varied from 157 to 248 m/sec to investigate the effect of velocity ratio. The results showed that increasing the annular gap width increases attenuation of high-frequency noise when comparisons are made on the same ideal thrust basis. Varying the velocity ratio had a minor effect on the noise characteristics of the nozzles investigated.

Goodykoontz, J. H.↗

NASA NTRS1973

Noise from turbomachinery

A review is made of turbomachinery noise from turbofan engines as typified by fan noise. The mechanisms and theories of fan noise are reviewed and concepts for its reduction, including acoustic suppression are discussed. Correlations of the overall noise data from several full-scale fans tested at NASA-Lewis Research Center are presented as indicative of the current state-of-the-art. Estimates are presented to show economics versus reduced noise for two quieted experimental engines, one with subsonic and one with supersonic fan tip speed. Finally, some concepts that may have the potential to reduce fan noise are indicated.

Feiler, C. E.↗

NASA NTRS1973

Noise from turbomachinery.

This paper reviews turbomachinery noise from turbofan engines as typified by fan noise. The mechanisms and theories of fan noise are reviewed and concepts for its reduction, including acoustic suppresion are discussed. Correlations of the overall noise data from several full-scale fans tested at NASA-Lewis Research Center are presented as indicative of the current state-of-the-art. Estimates are presented to show economics versus reduced noise for two quieted experimental engines, one with subsonic and one with supersonic fan tip speed. Finally, some concepts that may have the potential to reduce fan noise are indicated.

Feiler, C. E.↗

NASA NTRS1984

Satellite tracking and Earth dynamics research programs

Following an upgrading program, ranging performance capabilities of a satellite-tracking pulsed laser system were assessed in terms of range accuracy, range noise, data yield, and reliability. With a shorter laser pulse duration (2.5 to 3.0 NSEC) and a new analog pulse processing system, the systematic range errors were reduced to 3 to 5 cm and range noise was reduced to 5 to 16 cm and range noise was reduced to 5 to 15 cm on Starlette and BE-C, and 10 to 18 cm on LAGEOS. Maximum pulse repetition rate was increased to 30 pulses per minute and significant improvement was made in signal to noise ratio by installing a 3 A interference filter and by reducing the range gate window to 200 to 400 nsec. The solution to a problem involving leakage of a fraction of the laser oscillator pulse through the pulse chopper was outlined.

Pearlman, M. R.↗

NASA NTRS2002

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise

An important source mechanism of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-inch Source Diagnostic Test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust acoustic power spectra are computed and compared with the measured spectra where possible. In general, the acoustic power levels and shape of the predicted spectra are in good agreement with the measured data. The predicted spectra show the experimentally observed trends with fan tip speed, vane count, and vane sweep. The results also demonstrate the validity of using CFD-based turbulence information for fan broadband noise calculations.

Nallasamy, M.↗

NASA NTRS1973

The effect of nozzle inlet shape, lip thickness, and exit shape and size on subsonic jet noise

Far field noise data were taken for convergent nozzles of various shapes and sizes at subsonic velocities exceeding 400 feet per second. For a circular nozzle, the nozzle inlet shape and lip thickness had no effect on the noise level, directivity, or spectra when compared at the same nozzle exit diameter and peak exhaust velocity. A sharp edged orifice was one exception to this statement. Coannular nozzles can produce additional high frequency noise. Blunt ended centerbodies, where there is significant base drag, also generate significant additional noise. The total noise power generation was essentially the same for circular, slot, and plug nozzles of good aerodynamic shape. The noise radiation patterns were essentially the same for these nozzle shapes except near the nozzle exhaust axis.

Olsen, W. A.↗

NASA NTRS1961

Noise Considerations in the Design and Operation of V/STOL Aircraft

Available propulsion-system noise data have been applied to the problems of design and operation of V/STOL aircraft. In particular, considerations have been given to minimizing adverse community reaction for operations between airports and to minimizing detection due to noise for special missions. For minimizing adverse community reaction, configurations incorporating low-blade-loading rotors, low-tip-speed propellers, or turbofan-type engines are judged to be most satisfactory. For minimizing detection, consideration must be given to minimizing the noise of the generating airplane, having maximum background noise in the vicinity of the observer, and operating the aircraft at minimum altitude.

Maglieri, Domenic J.↗

NASA NTRS1985

Preliminary measurement of the noise from the 2/9 scale model of the Large-scale Advanced Propfan (LAP) propeller, SR-7A

Noise data on the Large-scale Advanced Propfan (LAP) propeller model SR-7A were taken into the NASA Lewis 8- by 6-Foot Wind Tunnel. The maximum blade passing tone decreases from the peak level when going to higher helical tip Mach numbers. This noise reduction points to the use of higher propeller speeds as a possible method to reduce airplane cabin noise while maintaining high flight speed and efficiency. Comparison of the SR-7A blade passing noise with the noise of the similarly designed SR-3 propeller shows good agreement as expected. The SR-7A propeller is slightly noisier than the SR-3 model in the plane of rotation at the cruise condition. Projections of the tunnel model data are made to the full-scale LAP propeller mounted on the test bed aircraft and compared with design predictions. The prediction method is conservative in the sense that it overpredicts the projected model data.

Dittmar, J. H.↗

NASA NTRS1988

The NASA/AHS Rotorcraft Noise Reduction Program

Research of the NASA/AHS noise reduction program is discussed, stressing work in four areas: noise prediction, testing and data base, noise reduction, and criteria development. A program called ROTONET has been developed, using a code structure divided into four main parts; main- and tail-rotor blade geometry, rotor performance, noise calculations, and noise propagation. Wind tunnel tests on individual rotors, and flight tests on a helicopter built specifically to generate a broadband main rotor noise data base have been conducted. In the field of noise reduction, researchers have performed analytical evaluations of low noise rotor concepts, and small-scale wind tunnel evaluations of noise reduction concepts. Under the supervision of the FAA, the program in conducting tests to develop criteria for helicopters and heliports.

Childress, Otis S., Jr.↗

NASA NTRS1973

Noise tests of a model engine-over-the-wing STOL configuration using a multijet nozzle with deflector

Noise data were obtained with a small scale model stationary STOL configuration that used an eight lobe mixer nozzle with deflector mounted above a 32-cm-chord wing section. The factors varied to determine their effect upon the noise were wing flap angle, nozzle shape, nozzle location, deflector configuration, and jet velocity. The noise from the mixer nozzle model was compared to the noise from a model using a circular nozzle of the same area. The mixer nozzle model was quieter at the low to middle frequencies, while the circular nozzle was quieter at high frequencies. The perceived noise level (PNL) was calculated for an aircraft 10 times larger than the model. The PNL at 500 feet for the mixer nozzle turned out to be within 1 db of the PNL for the circular nozzle. For some configurations at highly directional broadband noise, which could be eliminated by changes in nozzle and/or deflector location, occurred below the wing.

Olsen, W. A.↗

NASA NTRS1977

In-flight gyro drift rate calibration on the Viking Orbiters

The drift rates of the attitude control gyros onboard the Viking Orbiters were calibrated several times during flight. The calibration was performed by engaging the gyro control of attitude for a six-hour period, recording the Viking Orbiter coordinates of the sun and the roll reference star as a function of time, and processing these data by a computer program. The computer program calculated drift rates for each data increment, and then smoothed the calculated rate versus the time function for all the data on the basis of a Gauss-Markov gyro-drift model. The effects of data noise were minimized by using a relatively long time constant in the Gauss-Markov model and by empirically determining a set of corrections for celestial inertial scale factor error differences. In this way the rms error of the data fit was lessened.

Breckenridge, W. G.↗

NASA NTRS1993

An optimal GPS data processing technique for precise positioning

A mathematical formula to optimally combine dual-frequency GPS pseudorange and carrier phase (integrated Doppler) data streams into a single data stream is derived in closed form. The data combination reduces the data volume and computing time in the filtering process for parameter estimation by a factor of 4 while preserving the full data strength for precise positioning. The resulting single data stream is that of carrier phase measurements with both data noise and bias uncertainty strictly defined. With this mathematical formula the single stream of optimally combined GPS measurements can be efficiently formed by simple numerical calculations. Carrier phase ambiguity resolution, when feasible, is strengthened due to the preserved full data strength with the optimally combined data and the resulting longer wavelength for the ambiguity to be resolved.

Wu, Sien-Chong↗

NASA NTRS2005

Flow Measurements and Multiple Pure Tone Noise From a Forward Swept Fan

A forward-swept fan, designated the Quiet High Speed Fan (QHSF), was tested in the NASA Glenn 9- by 15-foot Low Speed Wind Tunnel to investigate its noise reduction relative to a baseline fan of the same aerodynamic performance. The objective of the Quiet High Speed Fan was a 6-dB reduction in the Effective Perceived Noise Level relative to the baseline fan at the takeoff condition. The intent of the Quiet High Speed Fan design was to provide both a multiple pure tone noise reduction from the forward sweep of the fan rotor and a rotor-stator interaction blade passing tone noise reduction from a leaned stator. The tunnel noise data indicted that the Quiet High Speed Fan was quieter than the baseline fan for a significant portion of the operating line and was 6 dB quieter near the takeoff condition. Although reductions in the multiple pure tones were observed, the vast majority of the EPNdB reduction was a result of the reduction in the blade passing tone and its harmonics. Laser Doppler Velocimetry (LDV) and shroud unsteady pressure measurement data were obtained upstream of the QHSF and baseline rotors to improve the understanding of the shocks which propagate upstream of the two fans when they are operated at high speeds. The flow phenomena that produce multiple pure tone noise is discussed and compared to measurements of the fan acoustic inlet modes and the far field noise signature of the fan.

Weir, Donald S.↗

NASA NTRS2016

Characterization of AlMn TES Impedance, Noise, and Optical Efficiency in the First 150 mm Multichroic Array for Advanced ACTPol

The Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope features large arrays of multichroic pixels consisting of two orthogonal-polarization pairs of superconducting bolometers at two observing frequency bands. We present measurements of the detector properties and noise data in a subset of a fielded multichroic array of AlMn transition-edge sensor (TES) detectors. In this array, the distribution of critical temperature T(sub c) across detectors appears uniform at the percent level. The measured noise-equivalent power (NEP) distributions over approximately 1200 detectors are consistent with expectations. We find median NEPs of 4.0×10(exp −17) W/ √ Hz for low-band detectors and 6.2×10(exp −17) W/ √ Hz for high-band detectors under covered-window telescope test conditions with optical loading comparable to observing with precipitable water vapor approximately 0.5 mm. Lastly, we show the estimated detector optical efficiency, and demonstrate the ability to perform optical characterization over hundreds of detectors at once using a cryogenic blackbody source.

Crowley, Kevin T.↗

NASA NTRS1976

Flight effects on JT8D engine jet noise as measured in the NASA Ames 40-by 80-foot wind tunnel

A JT8D-17 turbofan engine was tested in a 40 x 80 ft wind tunnel to determine flight effects on jet noise. The engine was configured as a baseline with conical nozzle, a quiet nacelle 20-lobe ejector/suppressor, and an internal mixer with conical nozzle. Tunnel-off and tunnel-on noise tests were conducted over a range of nozzle pressure ratios (1.2 to 2.1), primary jet velocities (275 to 550 m/s), and tunnel velocities up to 100 m/s. Aft quadrant noise data were measured by a pair of traversing microphones located on a 3-m sideline relative to the engine centerline. Unique correlations and analysis procedures were developed in order to define far-field flight effects from the relatively near-field noise measurements. The ejector/suppressor experienced a significant loss of suppression relative to static measurements during flight while the internal mixer indicated a slight gain in suppression. It is concluded that the wind tunnel is a viable method for studying flight effects on engine jet noise.

Strout, F. G.↗