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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Advanced turboprop aircraft flyover noise: Annoyance to counter-rotating-propeller configurations with a different number of blades on each rotor: Preliminary results

A laboratory experiment was conducted to quantify the annoyance of people to the flyover noise of advanced turboprop aircraft with counter-rotating propellers (CRP) having a different number of blades on each rotor (nxm, e.g., 10 x 8, 12 x 11). The objectives were: (1) compare annoyance to nxm CRP advanced turboprop aircraft with annoyance to conventional turboprop and jet aircraft; (2) determine the effects of tonal content on annoyance; and (3) determine the ability of aircraft noise measurement procedures and corrections to predict annoyance for this new class of aircraft. A computer synthesis system was used to generate 35 realistic, time-varying simulations of advanced turboprop takeoff noise in which the tonal content was systematically varied to represent combinations of 15 fundamental frequency (blade passage frequency) combinations and three tone-to-broadband noise ratios. The fundamental frequencies, which represented blade number combinations from 6 x 5 to 13 x 12 and 7 x 5 to 13 x 11, ranged from 112.5 to 292.5 Hz. The three tone-to-broadband noise ratios were 0, 15, and 30 dB. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs were presented at D-weighted sound pressure levels of 70, 80, and 90 dB to 64 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three categories of aircraft and examine the effects of the differences in tonal content among the advanced turboprop noises. The annoyance prediction ability of various noise measurement procedures and corrections is also examined.

Mccurdy, David A.↗
NASA NTRS1988

Advanced turboprop aircraft flyover noise: Annoyance to counter-rotating-propeller configurations with an equal number of blades on each rotor, preliminary results

A laboratory experiment was conducted to quantify the annoyance of people to the flyover noise of advanced turboprop aircraft with counter-rotating propellers (CRP) having an equal number of blades on each rotor. The objectives were: to determine the effects of total content on annoyance; and compare annoyance to n x n CRP advanced turboprop aircraft with annoyance to conventional turboprop and jet aircraft. A computer synthesis system was used to generate 27 realistic, time-varying simulations of advanced turboprop takeoff noise in which the tonal content was systematically varied to represent the factorial combinations of nine fundamental frequencies and three tone-to-broadband noise ratios. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs were presented at three D-weighted sound pressure levels to 64 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three aircraft types and examined the effects of the differences in tonal content among the advanced turboprop noises. The annoyance prediction ability of various noise metrics is also examined.

Mccurdy, David A.↗
NASA NTRS1976

A computer program for the determination of the acoustic pressure signature of helicopter rotors due to blade thickness

A computer program is presented for the determination of the thickness noise of helicopter rotors. The results were obtained in the form of an acoutic pressure time history. The parameters of the program are the rotor geometry and the helicopter motion descriptors, and the formulation employed is valid in the near and far fields. The blade planform must be rectangular, but the helicopter motion is arbitrary; the observer position is fixed with respect to the ground with a maximum elevation of 45 deg above or below the rotor plane. With these restrictions, the program can also be used for the calculation of thickness noise of propellers.

Mall, G. H.↗
NASA NTRS1980

Aeropropulsion in year 2000

A sampling of probable future engine types, such as convertible engines for helicopters, turboprops for fuel-conservative airliners, and variable-cycle engines for supersonic transports are presented. Related technology improvements in propellers, materials, noise suppression, etc. are reviewed.

Weber, R. J.↗
NASA NTRS1980

Aeropropulsion in year 2000

The paper demonstrates that many advances can be anticipated in propulsion systems for aircraft in the next 20 years. A survey is presented of probable future engine types, including convertible engines for helicopters, turboprops for fuel efficient airliners, and variable cycle engines for supersonic transports. Also examined is the use of rotary engines in general aviation aircraft. Finally, a review is given of related technology improvements in propellers, materials, noise suppression, and digital electronic controls.

Weber, R. J.↗
NASA NTRS1980

Advanced transport aircraft technology

Various elements of the NASA aircraft energy efficiency program are described. Regarding composite structures, the development of three secondary and three medium-primary components to validate structural and fabrication technology is discussed. In laminar flow control, the design of advanced airfoils having large regions of supercritical flow with features which simplify laminarization are considered. Emphasis is placed on engine performance improvement, directed at developing advanced components to reduce fuel consumption in current production engines, and engine diagnostics aimed at identifying the sources and causes of performance deterioration in high-bypass turbofan engines. In addition, the results of propeller aerodynamic and acoustic tests have substantiated the feasibility of achieving the propeller efficiency goal of 80% and confirmed that the effect of blade sweep on reducing propeller source noise was 5-6 dB.

Winblade, R. L.↗
NASA NTRS1984

Solution of the wave equation for open surfaces involving a line integral over the edge

A simple mathematical model of a stationary source distribution for the supersonic-propeller noise-prediction formula of Farassat (1983) is developed to test the validity of the formula solutions. The conventional thickness source term is used in place of the Isom thickness formula; the relative importance of the line and surface integrals in the solutions is evaluated; and the numerical results are compared with those obtained with a conventional retarded-time solution in tables. Good agreement is obtained over elevation angles from 10 to 90 deg, and the line-integral contribution is found to be significant at all elevation angles and of the same order of magnitude as the surface-integral contribution at angles less than 30 deg. The amplitude-normalized directivity patterns for the four cases computed (x = 1.5 or 10; k = 5.0 or 50) are presented graphically.

Farassat, F.↗
NASA NTRS1986

Interaction of airborne and structureborne noise radiated by plates. Volume 1: Analytical study

The interaction of airborne and structureborne noise radiated by aircraft materials was examined. The theory and results of several computer simulations of the noise radiated by thin, isotropic, rectangular aluminum plates due to fully coherent combined acoustic and vibrational inputs is presented. The most significant finding was the extremely large influence that the relative phase between inputs has on the combined noise radiation of the plates. Phase dependent effects manifest themselves as cross terms in both the dynamic and acoustic portions of the analysis. Computer simulations show that these cross terms can radically alter the combined sound power radiated by plates constructed of aircraft-type materials. The results suggest that airborne-structureborne interactive effects could be responsible for a significant portion of the overall noise radiated by aircraft-type structures in the low frequency regime. This implies that previous analytical and experimental studies may have neglected an important physical phenomenon in the analayses of the interior noise of propeller dirven aircraft.

Mcgary, M. C.↗
NASA NTRS1989

Propeller modelling effects on interior noise in cylindrical cavities with application to active control

The coupling of a vibrating finite elastic cylinder and its interior cavity, closed with rigid end caps, is examined. Results are presented for several types of excitation including a point force, a single external acoustic monopole, and an array of external monopoles. Modal spectra are examined for a frequency range typical of the harmonic noise produced by advanced turbo-props. The effect of frequency and source distribution on modal content is presented. Significant interface modal filtering, which would have a beneficial impact on an active system for reducing interior noise, was found to occur for all cases. Some preliminary experimental data for a stiffened, composite cylinder are presented and discussed.

Silcox, R. J.↗
NASA NTRS1993

Takeoff/approach noise for a model counterrotation propeller with a forward-swept upstream rotor

A scale model of a counterrotating propeller with forward-swept blades in the forward rotor and aft-swept blades in the aft rotor (designated F39/A31) has been tested in the NASA Lewis 9- by 15-Foot Anechoic Wind Tunnel. This paper presents aeroacoustic results at a takeoff/approach condition of Mach 0.20. Laser Doppler Velocimeter results taken in a plane between the two rotors are also included to quantify the interaction flow field. The intention of the forward-swept design is to reduce the magnitude of the forward rotor tip vortex and/or wakes which impinge on the aft rotor, thus lowering the interaction tone levels.

Woodward, Richard P.↗
NASA NTRS1992

Comparison of radiated noise from shrouded and unshrouded propellers

The ducted propeller in a free field is modeled using the finite element method. The generation, propagation, and radiation of sound from a ducted fan is described by the convened wave equation with volumetric body forces. Body forces are used to introduce the blade loading for rotating blades and stationary exit guide vanes. For an axisymmetric nacelle or shroud, the problem is formulated in cylindrical coordinates. For a specified angular harmonic, the angular coordinate is eliminated, resulting in a two-dimensional representation. A finite element discretization based on nine-node quadratic isoparametric elements is used.

Eversman, Walter↗
NASA NTRSDate not supplied

Preliminary Aeroacoustic Measurements from the AART in the NFAC 40-by 80-Foot Wind Tunnel

The primary objective: determine the aerodynamics and acoustics related to an auxiliary propulsor mounted behind an isolated wing in the National Full Scale Aerodynamic Complex 40-by 80-Foot Wind Tunnel. The primary data points match test conditions for in-flow stereo PIV measurements completed in the Ames 7x10 in 2018. The propeller consists of a Sensenich L26H commercial off the shelf blade set and hub, with a 26 inch diameter; propeller performance is measured with an internal balance integrated in the test stand. The wing is a NACA 0015 with a 12 inch chord; 58.5 inches in height for full wing configuration; 40.5 inches in height for the half wing configuration.

Aeroacoustics↗
NASA NTRS1980

Prediction of the interior noise levels of high-speed propeller-driven aircraft

The theoretical basis for an analytical model developed to predict the interior noise levels of high-speed propeller-driven airplanes is presented. Particular emphasis is given to modeling the transmission of discrete tones through a fuselage element into a cavity, estimates for the mean and standard deviation of the acoustic power flow, the coupling between a non-homogeneous excitation and the fuselage vibration response, and the prediction of maximum interior noise levels. The model allows for convenient examination of the various roles of the excitation and fuselage structural characteristics on the fuselage vibration response and the interior noise levels, as is required for the design of model or prototype noise control validation tests.

Rennison, D. C.↗
NASA NTRS1988

A new diagnostic method for separating airborne and structureborne noise radiated by plates with applications for propeller driven aircraft

The anticipated application of advanced turboprop propulsion systems is expected to increase the interior noise of future aircraft to unacceptably high levels. The absence of technically and economically feasible noise source-path diagnostic tools has been a prime obstacle in the development of efficient noise control treatments for propeller-driven aircraft. A new diagnostic method that permits the separation and prediction of the fully coherent airborne and structureborne components of the sound radiated by plates or thin shells has been developed. Analytical and experimental studies of the proposed method were performed on an aluminum plate. The results of the study indicate that the proposed method could be used in flight, and has fewer encumbrances than the other diagnostic tools currently available.

Mcgary, Michael C.↗
NASA NTRS1982

Propeller flow visualization techniques

Propeller flow visualization techniques were tested. The actual operating blade shape as it determines the actual propeller performance and noise was established. The ability to photographically determine the advanced propeller blade tip deflections, local flow field conditions, and gain insight into aeroelastic instability is demonstrated. The analytical prediction methods which are being developed can be compared with experimental data. These comparisons contribute to the verification of these improved methods and give improved capability for designing future advanced propellers with enhanced performance and noise characteristics.

Stefko, G. L.↗