Showing papers on "Aircraft noise published in 1991"

Aeroacoustics of Flight Vehicles: Theory and Practice. Volume 1: Noise Sources

Abstract: Methodology recommended to evaluate aeroacoustic related problems is provided, and approaches to their solutions are suggested without extensive tables, nomographs, and derivations. Orientation is toward flight vehicles and emphasis is on underlying physical concepts. Theoretical, experimental, and applied aspects are covered, including the main formulations and comparisons of theory and experiment. The topics covered include: propeller and propfan noise, rotor noise, turbomachinery noise, jet noise classical theory and experiments, noise from turbulent shear flows, jet noise generated by large-scale coherent motion, airframe noise, propulsive lift noise, combustion and core noise, and sonic booms.

Human response to aircraft noise

Abstract: The human auditory system and the perception of sound are discussed. The major concentration is on the annnoyance response and methods for relating the physical characteristics of sound to those psychosociological attributes associated with human response. Results selected from the extensive laboratory and field research conducted on human response to aircraft noise over the past several decades are presented along with discussions of the methodology commonly used in conducting that research. Finally, some of the more common criteria, regulations, and recommended practices for the control or limitation of aircraft noise are examined in light of the research findings on human response.

Development of an annoyance model based upon elementary auditory sensations for steady-state aircraft interior noise containing tonal components

Abstract: The purpose of this investigation was to develop a noise annoyance model, superior to those already in use, for evaluating passenger response to sounds containing tonal components which may be heard within current and future commercial aircraft. The sound spectra investigated ranged from those being experienced by passengers on board turbofan powered aircraft now in service to those cabin noise spectra passengers may experience within advanced propeller-driven aircraft of the future. A total of 240 sounds were tested in this experiment. Sixty-six of these 240 sounds were steady state, while the other 174 varied temporally due to tonal beating. Here, the entire experiment is described, but the analysis is limited to those responses elicited by the 66 steady-state sounds.

Propulsive lift noise

Abstract: Propulsive life noise is the increase in noise that occurs when airframe surfaces are placed in the propulsive system's exhaust to increase their lift force. Increased local flow velocities and turbulence levels, due to the propulsive system exhaust gases passing along the airframe lifting surfaces, cause an increase in maximum lift coefficient. The airplane's flight speed required for takeoff and landing can then be significantly reduced, allowing operation from shorter runways than those of conventional commercial airports. Unfortunately, interaction of high velocity turbulent exhaust flow with the airframe's solid surfaces generates additional noise radiation. Aeroacoustic processes that cause propulsive lift noise also are present in airframe noise and propulsive system installation noise. Research studies of propulsive lift noise led to development of improved methods of predicting noise radiation from surfaces in turbulent flows. Noise reduction and prediction methods of aircraft noise are discussed.

An updated catalog of 318 social surveys of residents' reactions to environmental noise (1943-1989)

Abstract: All social surveys of residents' reactions to environmental noise in residential areas which were described in English language publications from 1943 to 1989 are identified. A total of 318 surveys are described. The surveys are indexed by country, noise source, and data of survey. The publications and reports from each survey are listed in a bibliography. Twenty-four surveys are listed which are available for secondary analysis from a data archive.

Active sound attenuation across a double wall structure

Abstract: The possibility of achieving significant local and global sound attenuation across a flat double wall is demonstrated. It is also shown that sound can be prevented from entering the interior of a cabinlike environment. The approach used is unlike established active noise control techniques.

The NASA Aircraft Noise Prediction Program Improved Propeller Analysis System

Abstract: The improvements and the modifications of the NASA Aircraft Noise Prediction Program (ANOPP) and the Propeller Analysis System (PAS) are described Comparisons of the predictions and the test data are included in the case studies for the flat plate model in the Boundary Layer Module, for the effects of applying compressibility corrections to the lift and pressure coefficients, for the use of different weight factors in the Propeller Performance Module, for the use of the improved retarded time equation solution, and for the effect of the number grids in the Transonic Propeller Noise Module The DNW tunnel test data of a propeller at different angles of attack and the Dowty Rotol data are compared with ANOPP predictions The effect of the number of grids on the Transonic Propeller Noise Module predictions and the comparison of ANOPP TPN and DFP-ATP codes are studied In addition to the above impact studies, the transonic propeller noise predictions for the SR-7, the UDF front rotor, and the support of the enroute noise test program are included

Quiet aircraft design and operational characteristics

Abstract: The application of aircraft noise technology to the design and operation of aircraft is discussed. Areas of discussion include the setting of target airplane noise levels, operational considerations and their effect on noise, and the sequencing and timing of the design and development process. Primary emphasis is placed on commercial transport aircraft of the type operated by major airlines. Additionally, noise control engineering of other types of aircraft is briefly discussed.

Flyover-noise measurement and prediction

Abstract: Details are presented for the measurement and prediction of aircraft flyover noise to be used for certification, research and development, community noise surveys, airport monitors, and pass fail criteria. Test details presented are applicable to all types of aircraft, both large and small, and the use of Federal Aviation Regulations (FAR) Part 36 (ref. 1) is emphasized. Accuracy of noise measurements is important. Thus, a pass-fail criterion should be used for all noise measurements. Finally, factors which influence the sound propagation and noise prediction procedures, such as atmospheric and ground effects, are also presented.

Annoyance caused by advanced turboprop aircraft flyover noise: Comparison of different propeller configurations

Abstract: A laboratory experiment was conducted to compare the annoyance of flyover noise from advanced turboprop aircraft having different propeller configurations with the annoyance of conventional turboprop and turbofan aircraft flyover noise. A computer synthesis system was used to generate 40 realistic, time varying simulations of advanced turboprop takeoff noise. Of the 40 noises, single-rotating propeller configurations (8) and counter-rotating propeller configurations with an equal (12) and unequal (20) number of blades on each rotor were represented. Analyses found that advanced turboprops with single-rotating propellers were, on average, slightly less annoying than the other aircraft. Fundamental frequency and tone-to-broadband noise ratio affected annoyance response to advanced turboprops, but the effects varied with propeller configuration and noise metric. The addition of duration corrections and corrections for tones above 500 Hz to the noise measurement procedures improved annoyance prediction ability.

Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 2: Development of theory for wing shielding

Abstract: A unified theory for aerodynamics and noise of advanced turboprops is presented. The theory and a computer code developed for evaluation at the shielding benefits that might be expected by an aircraft wing in a wing-mounted propeller installation are presented. Several computed directivity patterns are presented to demonstrate the theory. Recently with the advent of the concept of using the wing of an aircraft for noise shielding, the case of diffraction by a surface in a flow has been given attention. The present analysis is based on the case of diffraction of no flow. By combining a Galilean and a Lorentz transform, the wave equation with a mean flow can be reduced to the ordinary equation. Allowance is also made in the analysis for the case of a swept wing. The same combination of Galilean and Lorentz transforms lead to a problem with no flow but a different sweep. The solution procedures for the cases of leading and trailing edges are basically the same. Two normalizations of the solution are given by the computer program. FORTRAN computer programs are presented with detailed documentation. The output from these programs compares favorably with the results of other investigators.

Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 3: Application of theory for blade loading, wakes, noise, and wing shielding

Abstract: Results of the program for the generation of a computer prediction code for noise of advanced single rotation, turboprops (prop-fans) such as the SR3 model are presented. The code is based on a linearized theory developed at Hamilton Standard in which aerodynamics and acoustics are treated as a unified process. Both steady and unsteady blade loading are treated. Capabilities include prediction of steady airload distributions and associated aerodynamic performance, unsteady blade pressure response to gust interaction or blade vibration, noise fields associated with thickness and steady and unsteady loading, and wake velocity fields associated with steady loading. The code was developed on the Hamilton Standard IBM computer and has now been installed on the Cray XMP at NASA-Lewis. The work had its genesis in the frequency domain acoustic theory developed at Hamilton Standard in the late 1970s. It was found that the method used for near field noise predictions could be adapted as a lifting surface theory for aerodynamic work via the pressure potential technique that was used for both wings and ducted turbomachinery. In the first realization of the theory for propellers, the blade loading was represented in a quasi-vortex lattice form. This was upgraded to true lifting surface loading. Originally, it was believed that a purely linear approach for both aerodynamics and noise would be adequate. However, two sources of nonlinearity in the steady aerodynamics became apparent and were found to be a significant factor at takeoff conditions. The first is related to the fact that the steady axial induced velocity may be of the same order of magnitude as the flight speed and the second is the formation of leading edge vortices which increases lift and redistribute loading. Discovery and properties of prop-fan leading edge vortices were reported in two papers. The Unified AeroAcoustic Program (UAAP) capabilites are demonstrated and the theory verified by comparison with the predictions with data from tests at NASA-Lewis. Steady aerodyanmic performance, unsteady blade loading, wakes, noise, and wing and boundary layer shielding are examined.

Modeling Lateral Attenuation of Aircraft Flight Noise

Abstract: : Airbase and/or airport noise prediction models such as the Air Force NOISEMAP computer program are used to forecast the long term noise exposure from aircraft flight and ground activity at a facility. Noise contour maps from these calculations are used to assess the potential adverse effects such noise may have on the environment and to assist nearby communities in performing compatible land use planning. To calculate the noise exposure at any specified ground position located to the side of a flight path, a variety of noise attenuation mechanisms must be accounted for if the model is to predict levels that are in reasonable agreement with field noise measurements. For such locations, the attenuation effects are usually grouped as being due to: (1) wave divergence (spherical spreading), (2) atmospheric absorption, and (3) lateral attenuation, (the combined attenuation due to ground, meterological, forward flight, and engine/airplane installation effects).

The effect of onset rate on aircraft noise annoyance

Abstract: Noise from military aircraft operating at high speeds and low altitude can exhibit high onset rates, which are thought to increase the annoyance of these sounds. A set of listening experiments was undertaken to examine this effect and to evaluate the validity of an onset rate adjustment currently used in the environmental assessment of this type of noise. A basic set of 12 stereo sound recordings was prepared, consisting of four types of military aircraft with various onset rates plus one civil aircraft. These aircraft flyby sounds were presented at four sound levels to subjects in an indoor listening facility (nominal SEL of 95, 85, 75, and 65 dB) and at an outdoor facility (nominal SEL of 115, 105, 95, and 85 dB). Indoor sounds were filtered according to a typical residential noise reduction curve. Sounds were presented in random order, at random time intervals, and random approach from either in front of or behind the subjects. Subjects rated each sound on a seven‐point annoyance scale. Two companion experiments were also performed at the outdoor facility. These experiments used modified military aircraft sounds with particular onset rates from 5 to 100 dB/s and decay rates from 2 to 30 dB/s. Analysis of the results of these experiments examined the effects of onset and decay rates, level, SEL, and duration. [Work sponsored by USAF AAMRL/BBE.]

Analysis of interior noise ground and flight test data for advanced turboprop aircraft applications

Abstract: Interior noise ground tests conducted on a DC-9 aircraft test section are described. The objectives were to study ground test and analysis techniques for evaluating the effectiveness of interior noise control treatments for advanced turboprop aircraft, and to study the sensitivity of the ground test results to changes in various test conditions. Noise and vibration measurements were conducted under simulated advanced turboprop excitation, for two interior noise control treatment configurations. These ground measurement results were compared with results of earlier UHB (Ultra High Bypass) Demonstrator flight tests with comparable interior treatment configurations. The Demonstrator is an MD-80 test aircraft with the left JT8D engine replaced with a prototype UHB advanced turboprop engine.

Aircraft flying position detecting device

Abstract: PURPOSE:To surely obtain aircraft flying position detection information to follow aircraft with high precision in response to the change of atmospheric temperature by calculating sound velocity based on aircraft noise detection information, and calculating an elevation angle based on the calculated result. CONSTITUTION:A first arriving time difference detecting means 20U calculates a cross-correlation function with a first elevation angle detecting microphone MICU arranged in a first direction based on a reference microphone MICL, and detects first arriving time difference required for an aircraft noise to arrive. A second arriving time difference detecting means 20A calculates the cross-correlation function with the noise detection signal of a second elevation angle detecting microphone MICA intersecting the first direction at right angles based on the reference microphone MICL, and detects second arriving time difference required for the aircraft noise to arrive. A passing detecting means 20H calculates the cross-correlation function with the noise detection signal of a passing detecting microphone MICH arranged in the proceeding direction of the aircraft, and detects the point of time when the aircraft passed a prescribed measuring plane. An elevation angle arithmetic means 51 calculates the sound velocity based on the passing time difference detected by the means 20H, and obtains the elevation angle.

Active control of helicopter transmission noise

Abstract: An account is given of an effort to reduce helicopter transmission noise by 10 dB, using active methods, as part of the NASA-Lewis/US Army Propulsion Directorate Advanced Rotorcraft Transmission technology integration and demonstration program The transmission used as a test stand is that of the CH-47C forward rotor Attention is presently given to the active control system's actuators, sensors, and control algorithms

The effects of ambient noise level from road traffic on peoples responses to aircraft noise

Abstract: There have been many studies carried out in different countries on peoples' response to either aircraft or road traffic noise. A few studies have included the effect of background noise level from road traffic on annoyance reaction to aircraft noise; however, these studies have provided inconclusive results as to whether or not there is any significant difference in peoples' responses to aircraft noise with different levels of background noise from road traffic. It seems that some of the earlier studies did not appear to differentiate sufficiently between 'low' and 'high' background noise levels; therefore, in the present study it was decided to select survey sites which exhibit extreme categories of road traffic noise exposure. The site category was confirmed by field noise measurement of both sources, and the peoples' reactions were derived from factual data of a social survey.

Study on Evaluation about Aircraft Noise Around Airport

Abstract: The measurements of aircraft noise around several airports and survey on reactions of people to aircraft noise were taken in 1984 and 1985. Some results about duration of aircraft noise and relations between PNL and Sound level A and D of aircraft noise are found by statistacal analysis of data obtained in the survey and measurements. These results indicate that WECPNL is an effective measure of aircraft noise not only in physical but also in psychological evaluation.

Acoustic Background Noise Variation in Air Force Platforms and Its Effect on Noise Removal Algorithms

Abstract: : In this study of short-term noise variation in Air Force platforms, we followed two avenues of investigation. First, we applied quantitative measures of variation to individual noise recordings, and compared the results across various aircraft. Some measures used were simple descriptive statistics, but we also measured attenuation obtained by spectral restoration (spectral subtraction), applied to the noise signal alone. The noise attenuation obtained for real aircraft environments was in most cases about the same as predicted theoretically for white Gaussian noise, but in some instances was considerably higher, especially in the presence of propeller noise. Second, we applied the nonparametric Mann-Whitney statistic to test the stationarity of power spectrum estimates on time scales of 200 to 800 ms. There was little or no evidence of nonstationarity in large jet or turboprop aircraft. In fighter aircraft and helicopters, there was some evidence of nonstationarity confined to more or less narrow frequency ranges. The nonstationarity found did not appear to limit the performance of special restoration algorithms. The noise recordings used were taken from the RADC/EEV database of field recordings made in the E-3A, E-4B, EC- 135, E-130, P-3C, F-15, F-16, F-4, A-10, HH-53 and Tornado aircraft.

Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 5: Propagation of propeller tone noise through a fuselage boundary layer

Abstract: An analysis of tone noise propagation through a boundary layer and fuselage scattering effects was derived. This analysis is a three dimensional and the complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The outer wave field is constructed analytically from an incident wave appropriate to the source and a scattered wave in the standard Hankel function form. For the incident wave, an existing function - domain propeller noise radiation theory is used. In the boundary layer region, the wave equation is solved by numerical methods. The theoretical analysis is embodied in a computer program which allows the calculation of correction factors for the fuselage scattering and boundary layer refraction effects. The effects are dependent on boundary layer profile, flight speed, and frequency. Corrections can be derived for any point on the fuselage, including those on the opposite side from the source. The theory was verified using limited cases and by comparing calculations with available measurements from JetStar tests of model prop-fans. For the JetStar model scale, the boundary layer refraction effects produce moderate fuselage pressure reinforcements aft of and near the plane of rotation and significant attenuation forward of the plane of rotation at high flight speeds. At lower flight speeds, the calculated boundary layer effects result in moderate amplification over the fuselage area of interest. Apparent amplification forward of the plane of rotation is a result of effective changes in the source directivity due to boundary layer refraction effects. Full scale effects are calculated to be moderate, providing fuselage pressure amplification of about 5 dB at the peak noise location. Evaluation using available noise measurements was made under high-speed, high-altitude flight conditions. Comparisons of calculations made of free field noise, using a current frequency-domain propeller noise prediction method, and fuselage effects using this new procedure show good agreement with fuselage measurements over a wide range of flight speeds and frequencies. Correction factors for the JetStar measurements made on the fuselage are provided in an Appendix.

Human Response to Helicopter Noise: A Test of A-Weighting

Abstract: : Department of Defense and U.S. Army police has long been to adjust measured helicopter noise levels upwards to account for the special character of helicopter noise in terms of human and community annoyance. In the United States, the A-weighted Day/Night Average Sound Level (DNL) descriptor is used most often for this purpose, but research has shown that it is not completely adequate. Also, many questions remain about human perception of, and response to, helicopter noise. This study is an extension of earlier research that tested human response to the noise of an Army UH-1H (Huey) helicopter flown over various indoor environments. This report documents a follow-up test using six different helicopters to replicate and expand on the earlier study. The data generally indicate that the A-weighted DNL is inadequate for assessing helicopter noise. The C-weighted scale was also tried and found inadequate. Helicopter noise measurement by either scale must be corrected to accurately correspond to human perceptions. Measuring indoors, the use of A-weighting to assess helicopter noise requires an offset that varies with helicopter A- weighted sound exposure level (ASEL), and this offset varies for different helicopters.