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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.

An interim procedure for predicting externally blown flap (EBF) noise spectra anywhere below a powered lift aircraft is presented. Both engine-under-the-wing and engine-over-the-wing EBF systems are included. The method uses data correlations for the overall sound pressure level based on nozzle exit area and exhaust velocity along with OASPL directivity curves and normalized one-third-octave spectra. Aircraft motion effects are included by taking into account the relative motion of the source with respect to the observer and the relative velocity effects on source strength.

A literature survey on low-frequency core engine noise is presented. Possible sources of low frequency internally generated noise in core engines are discussed with emphasis on combustion and component scrubbing noise. An interim method is recommended for predicting low frequency core engine noise that is dominant when jet velocities are low. Suggestions are made for future research on low frequency core engine noise that will aid in improving the prediction method and help define possible additional internal noise sources.

An experimental investigation of the jet noise radiated to the far field from a 15.2-cm-diam potential flow convergent nozzle has been conducted. Tests were made with unheated airflow over a range of subsonic nozzle exhaust velocities from 62 to 310m/sec. Mean and turbulent velocity measurements in the flow field of the nozzle exhaust indicated no apparent flow anomalies. Acoustic measurements yielded data uncontaminated by internal and/or background noise to velocities as low as 152m/sec. Finally, no significantly different acoustic characteristics between the potential flow nozzle and simple convergent nozzles were found.

The Lewis Research Center cold-flow model externally blown flap (EBF) noise research test program is summarized. Both engine under-the-wing and over-the-wing EBF wing section configurations were studied. Ten large scale and nineteen small scale EBF models were tested. A limited number of forward airspeed effect and flap noise suppression tests were also run. The key results and conclusions drawn from the flap noise tests are summarized and discussed.

The sensitivity of flap interaction noise to variations in engine-under-the-wing externally blown flap geometry was investigated with a large cold-flow model. Both 2- and 3-flap wing sections (7-ft chord) with trailing flap angles up to 60 deg were employed. Exhaust nozzles included coaxial, plug, and 8- and 13-inch diameter conical configurations. These nozzles were tested at two positions below the wing. The effects of these geometry variations on noise level, directivity, and spectral shape are summarized in terms of exhaust flow parameters evaluated at the nozzle exit and at the flap impingement station. The results are also compared with limited flap noise data available from tests using real engines.

Noise tests were conducted on a large scale, cold flow model of an engine-under-the-wing externally blown flap lift augmentation system employing a mixer nozzle. The mixer nozzle was used to reduce the flap impingement velocity and, consequently, try to attenuate the additional noise caused by the interaction between the jet exhaust and the wing flap. Results from the mixer nozzle tests are summarized and compared with the results for a conical nozzle. The comparison showed that with the mixer nozzle, less noise was generated when the trailing flap was in a typical landing setting (e.g., 60 deg). However, for a takeoff flap setting (20 deg), there was little or no difference in the acoustic characteristics when either the mixer or conical nozzle was used.

Noise tests were conducted on a small-scale model of an externally blown flap lift augmentation system. The nozzle/wing model was subjected to external flow that simulated takeoff and landing flight velocities by placing it in a 33-centimeter-diameter free jet. The results showed that external flow attenuated the noise associated with the various configurations tested. The amount of attenuation depended on flap setting. More attenuation occurred with a trailing-flap setting of 20 deg than with one of 60 deg. Noise varied with relative velocity as a function of the trailing-flap setting and the angle from the nozzle inlet.

The results of preliminary acoustic tests of the engine over the wing concept are summarized. The tests were conducted with a small wing section model (32 cm chord) having two flaps set at the landing position, which is 30 and 60 deg respectively. The engine exhaust was simulated by an air jet from a convergent nozzle having a nominal diameter of 5.1 centimeters. Factors investigated for their effect on noise include nozzle location, wing shielding, flap leakage, nozzle shape, exhaust deflectors, and internally generated exhaust noise.

A summary is given of the noise suppression tests conducted for the STOL aircraft. The tests were made using a large scale mixer nozzle and externally blown flap model. Data were obtained over a range of nozzle exhaust velocities (172 to 284 m/sec) and flap angles. Comparisons were made between the results of the mixer nozzle and those obtained with a standard single convergent nozzle. The resulting conclusions show that a reduction in noise level did occur using the mixer nozzle system.

Noise data were obtained with a large externally blown flap model. A fan-jet engine exhaust was simulated by a 1/2-scale bypass nozzle supplied by pressurized air. The nozzle was pylon mounted on a wing section having a double-slotted flap for lift augmentation. Noise radiation patterns and spectra were obtained for nozzle exhaust velocities between 400 and 1150 ft/sec. The blown flap noise data are in good agreement with previous small model results extrapolated to test conditions by Strouhal scaling. The results indicate that blown flap noise must be suppressed to meet STOL aircraft noise goals.

Noise tests of externally blown flaps with the engine under the wing and engine over the wing configurations were conducted. Flap noise data obtained on a TF-34 aircraft are discussed. Noise data obtained during a free-jet forward-speed-effect analysis are presented. Noise sources associated with upper surface flap blowing are described. Results of a small scale configuration screening study and some large scale model test data are analyzed. The noise data for the engine over wing configurations are compared with the engine under the wing configurations.

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. Implications of extending the small-scale model acoustic data to full-scale aircraft are discussed briefly and indicate a sizeable flyover noise attenuation may be achieved due to shielding by the wing.

Screening tests of upper surface blowing on externally blown flaps configurations were conducted. Noise and turning effectiveness data were obtained with small-scale, engine-over-the-wing models. One large model was tested to determine scale effects. Nozzle types included circular, slot, D-shaped, and multilobed. Tests were made with and without flow attachment devices. For STOL applications the particular multilobed mixer and the D-shaped nozzles tested were found to offer little or no noise advantage over the round convergent nozzle. High aspect ratio slot nozzles provided the quietest configurations. In general, upper surface blowing was quieter than lower surface blowing for equivalent EBF models.

Externally-blown-flap noise research can be summarized by the following remarks: With lower-surface blowing, the sources of the flap noise are begining to be understood and the noise scaling laws have been established. Further, progress has been made on suppressing the flap interaction noise at the large flap deflections used during landing. Recent small-scale noise tests of configurations using external upper-surface blowing indicate that engine-over-the-wing configurations may be promising.

Noise measurement data on various types of blown flap configurations for STOL aircraft, discussing integration effects between jet and flap assembly

Spherical shell potential extension to shells of differing diameters for intermolecular forces in globular molecules, considering binary gaseous mixtures

Noise reduction effectiveness of mixer nozzle for increasing lift capability in STOL aircraft

Space Rankine cycle power systems technology applied to ground-based power systems

Boiler inlet impedance frequency response in single tube heat exchanger when pump-fed with oscillating flow

Local heat transfer and static pressure data for steam condensation in vertical downflow tube

Heat transfer coefficients of steam condensation in vertical downflow with liquid-vapor interface inside small tube-type condenser

Ion bundles produced in a pulse-excited corona discharge are used as tracers with a radar-like pulse transit-time measuring instrument in order to provide a measurement of airspeed that is independent of all variables except time and distance. The resulting instrumentation need not project into the air stream and, therefore, will not cause any interference in supersonic flow. The instrument was tested at Mach numbers ranging from 0.3 to 3.8. Use of the proper instrumentation and technique results in accuracy of the order of 1 percent.

A photomicrographic technique for investigating eupercooled. water droplets has been devised and. used. to determine the spontaneous freezing temperatures of eupercooled. water droplets of the size ordinarily found. in the atmosphere. The freezing temperatures of 4527 droplets ranging from 8.75 to 1000 microns in diameter supported on a platinum surface and 571 droplets supported on copper were obtained. The average spontaneous freezing temperature decreased with decrease in the size of the droplets. The effect of size on the spontaneous freezing temperature was particularly marked below 60 microns. Frequency-distribution curves of the spontaneous freezing temperatures observed for droplets of a given size were obtained. Although no droplet froze at a temperature above 20 0 F, all droplets melted at 32 F. Results obtained with a copper support did not differ essentially from those obtained with a platinum surface.

A method is presented for estimating the noise generated by deflection of the engine exhaust for under-the-wing and over-the-wing versions of an externally blown flap configuration for powered lift. Correlation equations and curves are given for the OASPL and directivity and for spectra scaled to a high bypass 25,000-pound thrust size engine. Data are taken from TF34 engine tests and from large cold flow model tests. The correlations are empirical, and thus application of this prediction procedure is limited to geometrically similar configurations. Application of the method is illustrated by calculated sample footprints.

Acoustic measurements for large model engine-over-the-wing (EOW) research configurations having both conventional and powered lift applications were taken for flap positions typical of takeoff and approach and at locations simulating flyover and sideline. The results indicate that the noise is shielded by the wing and redirected above it, making the EOW concept a prime contender for quiet aircraft. The large-scale noise data are in agreement with earlier small-model results. Below the wing, the EOW configuration is about 10 PNdB quieter than the engine-under-the-wing externally-blown-flap for powered lift, and up to 10 dB quieter than the nozzle alone at high frequencies for conventional lift applications.

Noise tests were conducted on a large scale model of an externally blown flap lift augmentation system, employing a mixer nozzle. The mixer nozzle consisted of seven flow passages with a total equivalent diameter of 40 centimeters. With the flaps in the 30 - 60 deg setting, the noise level below the wing was less with the mixer nozzle than when a standard circular nozzle was used. At the 10 - 20 deg flap setting, the noise levels were about the same when either nozzle was used. With retracted flaps, the noise level was higher when the mixer nozzle was used.

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.

Data were obtained on the noise generated by an air jet impinging on a large flat board. The board was large enough so that the flow leaving the edges of the board generated no significant noise. The impingement angle, nozzle shape and size, jet velocity, and the distance from the nozzle to the board were varied in the experiment. Far-field noise data are presented. The nozzle-alone noise contribution to the total noise was generally small and was subtracted from the total, leaving the impingement-only noise. The impingement-only noise was adequately correlated by eighth power of the peak impingement velocity and first power of the impingement area. The spectral data were correlated by a Strouhal number based on the peak impingement velocity and a characteristic impingement diameter.

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.

Noise tests were conducted using simulated mixer-type nozzles and a small scale model of an externally blown flap, lift augmentation system. The mixer nozzles were simulated with orifice plates.

NASA research and development work on the noise of aircraft engines suitable for use on conventional take-off and landing subsonic cruise airplanes is reviewed. The work discussed was part of the NASA Quiet Engine program. Salient results in the areas of fan, jet and complete propulsion system noise are presented and briefly discussed.

Preliminary acoustic tests of the engine-over-the-wing concept as a method for reducing the aerodynamic noise created by conventional and short takeoff aircraft are discussed. Tests were conducted with a small wing section model having two flaps which can be set for either the landing or takeoff positions. Data was acquired with the flaps set at 10 degrees and 20 degrees for takeoff and 30 and 60 degrees for landing. The engine exhaust was simulated by an air jet from a convergent nozzle. Far field noise data are presented for nominal pressure ratios of 1.25, 1.4 and 1.7 for both the flyover and sideline modes.

Noise data were obtained with a model of an externally blown flap of the type that is currently being considered for STOL aircraft. The noise caused by impingement of the jet on the flap is much louder than the nozzle jet noise. It is especially so directly below the wing. The noise level increases as the jet velocity and flap angle are increased. The sound power level increased with the sixth power of velocity. Several physical variations to the STOL model configuration were also tested. Two such variations, a large board and a slotless curved plate wing, had the same power spectra density (Strouhal number curve) as the model.