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  • 1
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    Verification of a one-dimensional analysis of sound propagation in a variable area duct without flow (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-12891)
    Schlagwort(e): ACOUSTICS
    Format: text
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  • 2
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    Pressure transfer function of a JT15D nozzle due to acoustic and convected entropy fluctuations (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-22951)
    Schlagwort(e): ACOUSTICS
    Materialart: Acoustical Society of America; vol. 72
    Format: text
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  • 3
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    Verification of elastic-wave static displacement in solids (1980)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: The solution of the nonlinear differential equation which describes an initially sinusoidal finite-amplitude elastic wave propagating in a solid contains a static-displacement term in addition to the harmonic terms. The static-displacement amplitude is theoretically predicted to be proportional to the product of the squares of the driving-wave amplitude and the driving-wave frequency. The first experimental verification of the elastic-wave static displacement in a solid (the 111 direction of single-crystal germanium) is reported, and agreement is found with the theoretical predictions.
    Schlagwort(e): ACOUSTICS
    Materialart: Applied Physics Letters; 37; Nov. 1
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Propeller tip vortex - A possible contributor to aircraft cabin noise (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: Wind tunnel model tests support the hypothesis that a propeller tip vortex may subject a downstream wing surface to greater excitation than would be experienced by the aircraft fuselage side wall exposed to propeller-generated noise, ultimately transmitting this structural response to incident dynamic pressure to the cabin interior. Even if structure-borne excitations are less efficient than airborne excitations in the creation of cabin noise, the higher level of the former could still govern cabin noise levels.
    Schlagwort(e): ACOUSTICS
    Materialart: Journal of Aircraft; 19; Jan. 198
    Format: text
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  • 5
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    Why credible propeller noise measurements are possible in the acoustically untreated NASA Lewis 8 ft by 6 ft wind tunnel (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: An explanation is presented for the lack of acoustic reflections in noise studies of propfan models in the NASA-Lewis 8 x 6 ft wind tunnel, where trials were run at Mach numbers 0.5-0.85. The highly directional propeller noise, i.e., mainly in the plane of rotation, experiences a convective effect due to the high subsonic axial Mach number. Reflected sounds are carried downstream, out of range of the acoustic sensors in the tunnel. Furthermore, reflected noise is less audible, and therefore does not affect measurements near peak values. It is suggested that some data contamination may occur below Mach 0.6, and that measurements be performed on higher harmonics generated by low level reflected noise.
    Schlagwort(e): ACOUSTICS
    Materialart: Acoustical Society of America, Journal (ISSN 0001-4966); 75; 1913
    Format: text
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  • 6
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    A possible explanation for the present difference between linear noise theory and experimental data for supersonic helical tip speed propellers (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: High speed turboprops are attractive candidates for future aircraft because of their high propulsive efficiency. However, the noise of their propellers may create a cabin environment problem for the aircraft powered by these propellers. The noise of some propeller models was measured, and predictions of the noise using a method based on the Ffowcs Williams-Hawkins equation were made. The predictions and data agree well at lower helical tip Mach numbers but deviate above Mach 1.0. Some possible reasons why the theory does not predict the data and focuses on improvement of the aerodynamic inputs as the most likely remedy are investigated. In particular, it is proposed that an increase in the drag and a decrease in the lift near the tip of the blade where the majority of the noise is generated, is warranted in the input to the theory.
    Schlagwort(e): ACOUSTICS
    Materialart: NASA-TM-83467 , E-1781 , NAS 1.15:83467
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
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    Cross spectra between temperature and pressure in a constant area duct downstream of a combustor (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The feasibility of measuring pressure temperature cross spectra and coherence and temperature-temperature cross spectra and coherence at spatially separated points along with pressure and temperature auto-spectra in a combustion rig was investigated. The measurements were made near the inlet and exit of a 6.44 m long duct attached to a J-47 combustor. The fuel used was Jet A. The cross spectra and coherence measurements show the pressure and temperature fluctuations correlate best at low frequencies. At the inlet the phenomena controlling the phase relationship between pressure and temperature could not be identified. However, at the duct exit the phase angle of the pressure is related to the phase angle of the temperature by the convected flow time delay. Previously announced in STAR as N83-23116
    Schlagwort(e): ACOUSTICS
    Materialart: AIAA PAPER 83-0762
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
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    Low frequency noise in a quiet, clean, general aviation turbofan engine (1984)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A quiet, clean, general aviation, turbofan engine was instrumented to measure the fluctuating pressures in the combustor, turbine exit duct, engine nozzle and the far field. Both a separate flow nozzle and an internal mixer nozzle were tested. The fluctuating pressure data are presented in overall pressure and power levels and in spectral plots. The combustor data are compared to recent theory and found to be in excellent agreement. The results indicate that microphone correction procedures for elevated mean pressures are questionable. Ordinary coherence function analysis suggests the presence of an additional low frequency noise source downstream of the turbine that is due to the turbine itself. Low frequency narrowband data and coherence function analysis are presented.
    Schlagwort(e): ACOUSTICS
    Materialart: NASA-TM-83520 , E-1879 , NAS 1.15:83520
    Format: application/pdf
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  • 9
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    Fluid shielding of high-velocity jet noise (1984)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: 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.
    Schlagwort(e): ACOUSTICS
    Materialart: NASA-TP-2259 , E-1705 , NAS 1.60:2259
    Format: application/pdf
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  • 10
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    Inverted velocity profile semi-annular nozzle jet exhaust noise experiments (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Experimental noise data are shown for a conical nozzle with a semi-annular secondary flow passage having secondary to primary velocity ratios ranging from 1.0 to 1.4. Spectral data are presented at different directivity angles in the flyover plane with the semi-annular flow passage located either on the same side or opposite side relative to an observer. A 10.0 cm diameter primary conical nozzle was used with a 2.59 cm and 5.07 cm wide annular gap secondary nozzle. Similar trends were observed for both nozzle configurations. In general, near the peak noise location and at velocity ratios greater than 1.0, noise levels were larger on the side where the secondary passage was closest to an observer. At velocity ratios near 1.0 the opposite was true. When compared to predicted noise levels for a conical nozzle alone operating at the same ideal thrust, the semi-annular configuration showed no benefit in terms of noise attenuation.
    Schlagwort(e): ACOUSTICS
    Materialart: NASA-TM-83525 , E-1890 , NAS 1.15:83525
    Format: application/pdf
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