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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Density fluctuations and radiated noise for a high-temperature supersonic jet

Experimental data on density fluctuations were obtained by the laser Schlieren method in a supersonic jet which at the nozzle exit had a Mach number of 1.43 and a stagnation temperature of about 1090 K. The jet emerged into the ambient atmosphere in an anechoic chamber, correctly expanded from a nozzle which had an exit diameter of 10.8 cm. Using the information on the density fluctuations and the mean shear obtained by probes, the autocorrelation of the radiated noise was calculated by a theory that is suitable for Mach wave emission. This theory is a modification of that developed by Ffowcs Williams and Maidanik (1965). The calculated noise field agrees well with that obtained by using microphones outside the jet.

Parthasarathy, S. P.↗
NASA NTRS1976

Static and wind tunnel near-field/far-field jet noise measurements from model scale single-flow baseline and suppressor nozzles. Volume 1: Noise source locations and extrapolation of static free-field jet noise data

A test was conducted in the Boeing Large Anechoic Chamber to determine static jet noise source locations of six baseline and suppressor nozzle models, and establish a technique for extrapolating near field data into the far field. The test covered nozzle pressure ratios from 1.44 to 2.25 and jet velocities from 412 to 594 m/s at a total temperature of 844 K.

Jaeck, C. L.↗
NASA NTRS1976

Acoustic radiation and surface pressure characteristics of an airfoil due to incident turbulence

A theoretical and experimental investigation of the noise and unsteady surface pressure characteristics of an isolated airfoil in a uniform mean velocity, homogeneous, nearly-isotropic turbulence field was conducted. Wind tunnel experiments were performed with a 23 cm chord, two dimensional NACA 0012 airfoil over a free stream Mach number range of 0.1 to 0.5. Far-field noise spectra and directivity were measured in an anechoic chamber that surrounded the tunnel open jet test section. Spanwise and chordwise distribution of unsteady airfoil surface pressure spectra and surface pressure cross-spectra were obtained. Incident turbulence intensities, length scales, spectra, and spanwise cross-spectra, required in the calculation of far-field noise and surface pressure characteristics were also measured.

Paterson, R. W.↗
NASA NTRS1976

Effects of multi-element acoustic treatment on compressor inlet noise

An analytic and experimental study was conducted with the objective of developing both a basic understanding of axially segmented inlet acoustic treatment liners, and design procedures for enhancing the suppression of compressor inlet radiated noise. Anechoic chamber measurements demonstrated that the multielement treatment produced significantly more low frequency suppression than uniform treatment. Further, in-duct spinning mode patterns generated by the rotating vehicle were successfully measured and used as input to an analytical prediction procedure, providing significant improvement in inlet suppression predictions. The study indicated that phased inlet liners can be designed to provide increased noise suppression compared to uniform treatment.

Kraft, R. E.↗
NASA NTRS1975

ATS-6 spacecraft - An EMC challenge

A series of analytical, measurement, and experimental EMI tests were performed on ATS-6. The EMC problems encountered included: (1) wiring pickup and reradiation, (2) input rectification and bias offset, (3) harmonics, (4) component degradation, (5) unbalanced shield ground, (6) inadvertent pickup, and (7) electro-explosive devices. The test program consisted of materials evaluation (with regard to shielding effectiveness, cost, weight, etc.), sun sensor RF susceptibility, cable shielding material evaluation, RF integrity of solar panels and power harnesses, anechoic chamber tests, bonding and grounding, and shielding and thermal control.

Kampinsky, A.↗
NASA NTRS1975

Fan noise reduction at subsonic and supersonic tip speeds with high Mach number inlets

Results are presented for an experimental study of two fixed geometry inlets and one translating centerbody type inlet tested in an anechoic-chamber transonic-compressor facility. The test vehicle was a 12-inch tip diameter single-stage transonic compressor with 19 rotor blades and 30 stator blades located approximately two chord lengths downstream of the rotor. It is shown that the translating centerbody type of inlet is superior to the collapsing cowl type for noise reduction at high subsonic Mach numbers, both acoustically and aerodynamically. The feasibility of using a high inlet Mach number depends largely on the maximum area ratio requirement (normally at landing). The high inlet Mach numbers are more effective in reducing high-frequency noise than low frequencies and more effective in reducing the blade passage frequency than the overall noise level.

Lumsdaine, E.↗
NASA NTRS1977

Measurements of the reflection factor of flat ground surfaces

Measurements are made of the reflection factors of asphalt, concrete, and sod at oblique angles of incidence. Initial measurements were carried out in an anechoic chamber to eliminate the effects of wind and temperature gradients. These were followed by measurements made outdoors over a wider frequency range. Data are presented for the magnitudes of the reflection factors of asphalt, concrete, and sod at angles of incidence of 38 deg and 45 deg.

Ventres, C. S.↗
NASA NTRS1977

An experimental investigation of helicopter rotor high frequency broadband noise

The paper describes experiments involving a 4.17 foot diameter model rotor operating in a 5 times 7.5 ft open jet wind tunnel enclosed in an anechoic chamber. The effects of rotor thrust, advance ratio, and the number of blades on the intensity and spectrum of high frequency broadband noise (HFBN) have been investigated. The effects of each parameter were determined by keeping the other two constant. The directivities of the two- and three-bladed rotors were measured in a direction perpendicular to the plane of the rotor disk. The effects of heading edge, pressure side, and suction side serrations on HFBN were measured under several operating conditions, and the effects of the serrations on the mean thrust generated by the rotor were studied. A scaling law is proposed to determine the location of the peak frequency and intensity of HFBN.

Lee, A.↗
NASA NTRS1977

Experimental determination of sound and high-speed flow interaction

An experimental facility for measuring the attenuation of sound at various frequencies and modes in a finite duct with high-speed flow (with or without an axial pressure gradient) is described. The facility consists of an anechoic chamber transonic compressor with inlets of different area variations (or axial gradients); sound of selected frequencies and modes is produced with eight circumferential acoustic drivers. The experimental results indicate that high Mach number inlets can increase noise propagation. In addition, an inlet with a constant axial gradient is found to have a better acoustic and aerodynamic performance than inlets of the same area ratio with steep gradients near the throat or exit.

Lumsdaine, E.↗
NASA NTRS1978

Escort - A data acquisition and display system to support research testing

A combination of a central minicomputer and test-site microcomputers has been adopted to provide on-line data acquisition and display service for a large number of different research programs. By integrating the data acquisition and recording functions in the minicomputer/microcomputer system, rapidly updated displays of selected data in terms of engineering units may be obtained. The system described here is primarily designed for steady-state test conditions, but may also provide data on slow transients associated with changing experimental conditions. Application of the system to full-scale jet engine tests, ion thruster assessments and anechoic chamber analyses are mentioned.

Miller, R. L.↗
NASA NTRS1978

Basic research in fan source noise: Inlet distortion and turbulence noise

A widely recognized problem in jet engine fan noise is the discrepancy between inflight and static tests. This discrepancy consists of blade passing frequency tones, caused by ingested turbulence that appear in the static tests but not in flight. To reduce the ingested distortions and turbulence in an anechoic chamber, a reverse cone inlet is used to guide the air into the fan. This inlet also has provisions for boundary layer suction and is used in conjunction with a turbulence control structure (TCS) to condition the air impinging on the fan. The program was very successful in reducing the ingested turbulence, to the point where reductions in the acoustic power at blade passing frequency are as high as 18 db for subsonic tip speeds. Even with this large subsonic tone suppression, the supersonic tip speed tonal content remains largely unchanged, indicating that the TCS did not appreciably attenuate the noise but effects the generation via turbulence reduction. Turbulence mapping of the inlet confirmed that the tone reductions are due to a reduction in turbulence, as the low frequency power spectra of the streamwise and transverse turbulence were reduced by up to ten times and 100 times, respectively.

Kantola, R. A.↗
NASA NTRS1978

Radar cross section measurements of a scale model of the space shuttle orbiter vehicle

A series of microwave measurements was conducted to determine the radar cross section of the Space Shuttle Orbiter vehicle at a frequency and at aspect angles applicable to re-entry radar acquisition and tracking. The measurements were performed in a microwave anechoic chamber using a 1/15th scale model and a frequency applicable to C-band tracking radars. The data were digitally recorded and processed to yield statistical descriptions useful for prediction of orbiter re-entry detection and tracking ranges.

Yates, W. T.↗
NASA NTRS1979

Analysis, design, and test of acoustic treatment in a laboratory inlet duct

A suppression prediction program based on the method of modal analysis for spinning mode propagation in a circular duct was used in the analytical design of optimized, multielement, Kevlar bulk-absorber treatment configurations for an inlet duct. The NASA-Langley ANRL anechoic chamber using the spinning mode synthesizer as a sound source was used to obtain in-duct spinning mode measurements, radial mode measurements, and far-field traverses, as well as aerodynamic measurements. The measured suppression values were compared to predicted values, using the in-duct, forward-traveling, radial-mode content as the source for the prediction. The performance of the treatment panels was evaluated from the predicted and measured data. Although experimental difficulties were encountered at the design condition, sufficient information was obtained to confirm the expectation that it is the panel impedance components which are critical to suppression at a single frequency, not the particular construction materials. The agreement obtained between measurement and prediction indicates that the analytical program can be used as an accurate, reliable, and useful design tool.

Kraft, R. E.↗
NASA NTRS1979

The effect of throttling on forward radiated fan noise

A study was undertaken to evaluate the effect of operating line throttling on inlet-arc noise from high speed fans. Experimental measurements on a 1/4-scale fan stage tested in an anechoic chamber, with and without inlet turbulence control devices, were utilized to assess the effect of constant speed throttling on the forward arc radiated noise characteristics. Different effects were observed in different speed ranges with different types of inflow turbulence control. These effects were correlated with some of the current theories on fan noise generation mechanisms, and partial success was achieved in attempting to relate the various theoretical models to the observed trends. The results of this study have an important bearing on estimating the noise characteristics of new fan designs from scaling the measured characteristics of previously tested fans.

Gliebe, P. R.↗
NASA NTRS1979

Reduction of rotor-turbulence interaction noise in static fan noise testing

Three effective inlet cleanup methods are described. A flared reverse cone inlet is used to eliminate wakes from the fan casings and/or probe supports. Boundary layer suction is employed ahead of the fan rotor and on the outer flare of the cone to reduce the boundary layer turbulence and remove any residual wakes. To reduce the midstream turbulent intensity and length scales, a turbulence control structure is used which is constructed with both a layer of honeycomb and a fine mesh screen. The effects of these cleanup methods are quantified by measuring the far-field noise in an anechoic chamber, using a high-speed 20-in.-diam fan of the current high passband type. The changes in the turbulent field impinging on this rotor are quantified by mapping the streamwise and transverse turbulent properties (spectra, intensity and length scale) with crossed hot film probes. It is convincingly shown that it is possible to clean up the inlet flow of a static fan noise test facility to a point where the static acoustic data simulate flight data.

Kantola, R. A.↗
NASA NTRS1980

Evaluation of approximate methods for the prediction of noise shielding by airframe components

An evaluation of some approximate methods for the prediction of shielding of monochromatic sound and broadband noise by aircraft components is reported. Anechoic-chamber measurements of the shielding of a point source by various simple geometric shapes were made and the measured values compared with those calculated by the superposition of asymptotic closed-form solutions for the shielding by a semi-infinite plane barrier. The shields used in the measurements consisted of rectangular plates, a circular cylinder, and a rectangular plate attached to the cylinder to simulate a wing-body combination. The normalized frequency, defined as a product of the acoustic wave number and either the plate width or cylinder diameter, ranged from 4.6 to 114. Microphone traverses in front of the rectangular plates and cylinders generally showed a series of diffraction bands that matched those predicted by the approximate methods, except for differences in the magnitudes of the attenuation minima which can be attributed to experimental inaccuracies. The shielding of wing-body combinations was predicted by modifications of the approximations used for rectangular and cylindrical shielding. Although the approximations failed to predict diffraction patterns in certain regions, they did predict the average level of wing-body shielding with an average deviation of less than 3 dB.

Ahtye, W. F.↗
NASA NTRS1980

Effect of inflow control on inlet noise of a cut-on fan

A cut-on, high tip speed fan stage was acoustically tested with three configurations of an inflow control device in the NASA Lewis anechoic chamber. Although this was a cut-on design, rotor-inflow interaction appeared to be a much stronger source of blade passing tone radiated from the inlet than rotor-stator interaction for the 1.6 mean rotor chord separation. Aft external suction applied to the area where the inflow control device joined the inlet produced a further reduction in blade passing tone suggesting that disturbances in the forward flow on the outside of the inlet were superimposed on the inlet boundary layer and were a significant source of tone noise.

Woodward, R. P.↗