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Von Glahn, U.

Publications and source records attributed to Von Glahn, U..

30 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Geometry effects on STOL engine-over-the-wing acoustics with 5:1 slot nozzles

The correspondence of far field acoustic trend with changes in the characteristics of the flow field at the wing trailing edge caused by alterations in the nozzle-wing geometry were determined at model scale with a 5:1 slot nozzle for several STOL-OTW configurations. Nozzle roof angles of 10 to 40 deg were tested with and without cutback of the nozzle sidewalls. With increasing wing size, representing several airframe/engine installations, the jet noise shielding benefits increased. With increasing nozzle roof angle, the jet velocity at the trailing edge was decreased, causing a decrease in trailing-edge and fluctuating lift noise. Cutback of the nozzle sides improved flow attachment and reduced far-field noise. The best flow attachment and least trailing-edge noise generally were obtained with a 40-deg external deflector configuration and a cutback nozzle with a 40-deg roof angle.

Von Glahn, U.↗
NASA NTRS1975

Acoustics of attached and partially attached flow for simplified OTW configurations with 5:1 slot nozzle

The acoustics of simple engine over-the-wing configurations, with complete and partially attached jet flow to the shielding surface, were studied at model scale. The nozzle consisted of a 5:1 slot nozzle operated at a nominal jet Mach number of 0.6, with the flow directed parallel to and at angles up to 10 deg toward the shielding surface. The shielding length of the surface and the nozzle height above the surface were varied. The aerodynamic results indicate that, with attached flow, the jet flow field is stretched in the flow direction resulting in locally higher velocities than those for partially attached flow or nozzle only flow. The stretching of the flow field increased the noise levels for the attached flow cases compared to those with only partially attached flow. With attached flow, the shielding benefits were substantially reduced compared with fully detached flow. Increasing the impingement angle of the jet flow from 0 to 10 deg generally caused the noise levels to increase in the mid and high frequencies.

Von Glahn, U.↗
NASA NTRS1975

Influence of multitube mixer nozzle geometry on CTOL-OTW jet noise shielding

Acoustic shielding benefits for CTOL over-the-wing (OTW) applications were obtained experimentally with various multitube nozzles using a simple board to represent a wing. Eight nozzles consisting of three to thirteen 2.36-cm diameter tubes were tested. The nozzles included single and double rings of tubes. Shielding surface lengths of 15.0 to 54.4 cm were used with each nozzle. Far-field noise data were obtained at 90 deg from the jet axis and with a nominal jet exhaust velocity of 200 m/sec. The jet noise shielding benefits for the nozzles with double rows of tubes, in terms of sound pressure level spectra, are correlated successfully as a function of an earlier developed parameter for nozzles with a single ring of tubes that includes consideration of the number of tubes and the local peak velocity in the flow field at the trailing edge of the shielding surface.

Von Glahn, U.↗
NASA NTRS1975

Forward velocity effects on under-the-wing externally blown flap noise

Noise tests were conducted with small-scale models of externally blown-flap powered-lift systems that were subjected to simulated takeoff and landing free-stream velocities by placing the nozzle-wing models in a free jet. The nozzle configurations consisted of a conical and an 8-tube mixer nozzle. The results showed that the free-stream velocity attenuated the noise from the various configurations with the amount of attenuation depending on the flap setting. More attenuation was obtained with a flap setting of 20 deg than with a flap setting of 60 deg. The dynamic effect on the total attenuation caused by aircraft motion is also discussed.

Goodykoontz, J.↗
NASA NTRS1975

Influence of mixer nozzle velocity decay characteristics on CTOL-OTW jet noise shielding

Jet noise shielding benefits for CTOL engine-over-wing configurations were obtained with model-scale multitube and lobed mixer nozzles and various shielding surface geometries. Spectral data were obtained with jet velocities from 585 to 1110 ft/sec. Correlation equations for predicting jet noise shielding benefits with single conical nozzle installations were modified to correlate the mixer nozzle data. The modification included consideration of the number of nozzle elements and the peak axial velocity decay in the flow field adjacent to the shielding surface. The effect of forward velocity on jet noise attenuation by a shielding surface is discussed.

Von Glahn, U.↗
NASA NTRS1974

Aerodynamic and acoustic performance of ejectors for engine-under-the-wing concepts

Subsonic thrust augmentation, exhaust plume velocity contours and acoustic characteristics of a small-scale, 6-tube mixer nozzle with ejector were obtained with and without a wing. Thrust augmentation up to 30 percent was achieved. Aerodynamic results showed that at a given location, greater downstream velocities are obtained with an ejector than with the baseline nozzle. Ejectors reduce high frequency noise; however, low-frequency noise amplification also occurs. Acoustic reflections off the wing increase the noise level to a ground observer. With an ejector, the acoustic benefits of forward velocity may be significantly reduced compared with the baseline nozzle.

Von Glahn, U.↗
NASA NTRS1974

Geometry considerations for jet noise shielding with CTOL engine-over-the-wing concept

Jet noise shielding benefits for CTOL engine-over-the-wing installations were obtained with various model-scale circular nozzles and wing chord geometries. Chord-to-nozzle diameter ratios were varied from 3 to 20, while ratios of nozzle height above the wing to the diameter were varied from near zero to 3. Spectral noise data were obtained with jet velocities from 640 to 1110 ft/sec. Characteristics of low frequency noise sources are discussed. Jet-noise shielding is correlated in terms of acoustic and geometric parameters. Implications of extending the model-scale data to full-scale are discussed.

Von Glahn, U.↗
NASA NTRS1973

Nozzle geometry and forward velocity effects on noise for CTOL engine-over-the-wing concept

Acoustic shielding benefits for jet noise of engine-over-the-wing for conventional aircraft (CTOL) application were studied with and without forward velocity for various small-scale nozzles. These latter included convergent, bypass and mixer, with and without forward ejector, nozzles. A 13-in. free jet was used to provide forward velocity. Far-field noise data were obtained for subsonic jet velocities from 650 to 980 ft/sec and forward velocities from zero to 260 ft/sec. The studies showed that, although shielding benefits were obtained with all nozzles, the greatest benefits were obtained with mixer nozzles. The absolute magnitude of the jet noise shielding benefits with forward velocity was similar to the variation in nozzle-only noise with forward velocity.

Von Glahn, U.↗
NASA NTRS1973

Forward velocity effects on jet noise with dominant internal noise source

Acoustic data, with and without forward velocity, were obtained with a circular nozzle using a quiet flow system and one dominated by a low-frequency internal noise source (analogous to combustion noise). Forward velocity effects were obtained by installing the test nozzle in a free jet. Far-field noise data were obtained at jet pressure ratios from 1.3 to 1.7 and forward velocities up to 260 ft/sec. With a quiet flow system, jet noise is reduced by forward velocity. With a dominant low-frequency core noise source, the portion of the noise spectra dominated by this source was not appreciably affected by forward velocity.

Von Glahn, U.↗
NASA NTRS1973

Velocity decay and acoustic characteristics of various nozzle geometries with forward velocity.

Utilizing a static test stand, 6- by 9-foot wind tunnel and 13-inch circular free jet, aerodynamic and acoustic data were obtained with a convergent circular nozzle, bypass nozzle, 6-tube mixer nozzle, and 6-tube mixer nozzle with an ejector. The aerodynamic data consist of velocity decay surveys with and without forward velocity. The acoustic data include total sound power, directivity and frequency spectra obtained statically and with forward velocity. The relation of aerodynamic and acoustic measurements statically and in forward flight for the various nozzle configurations are discussed.

Von Glahn, U.↗
NASA NTRS1972

Acoustic results obtained with upper-surface-blowing lift-augmentation systems.

The noise caused by the interaction of the jet exhaust and a wing was measured under static conditions for several versions of a small-scale STOL engine-over-the-wing configuration. Three basic nozzles were used in the tests; a circular nozzle, a 5:1 aspect ratio slot nozzle, and a 10:1 aspect ratio slot nozzle. Various flow attachment devices were included in the study. The wing included a flap that could be positioned for nominal takeoff or approach flap settings. Far field noise data are presented for the flyover mode. The data are discussed in terms of sound power and sound pressure spectra.

Von Glahn, U.↗