Showing papers on "Aircraft noise published in 1992"

Active control of interior noise in model aircraft fuselages using piezoceramic actuators

Abstract: Active control of interior noise in model aircraft fuselages using piezoceramic actuators is experimentally studied. The actuators are bonded directly to the structure and error information is taken from up to two microphones located in the interior acoustic field. The results demonstrate that global attenuation of the order of 10 to 15 dB of interior noise can be achieved with piezoceramic actuators, irrespective of whether the shell system is vibrating at an acoustic or structural resonant frequency. The work also proves that active control using vibration (moment) inputs works well when a floor simulating that of an aircraft is installed in the model. This result suggests that the technique will be successful in controlling interior noise in realistic aircraft structures.

Effect of Personal and Situational Variables on Noise Annoyance: with Special Reference to Implications for En Route Noise

Abstract: Over 680 publications from 282 social surveys of residents' reactions to environmental noise have been examined to locate 495 published findings on 26 topics concerning non-noise explanations for residents' reactions to environmental noise This report (1) tabulates the evidence on the 26 response topics, (2) identifies the 495 findings, and (3) discusses the implications for en route noise assessment After controlling for noise level, over half of the social survey evidence indicates that noise annoyance is not strongly affected by any of the nine demographic variables examined (age, sex, social status, income, education, homeownership, type of dwelling, length of residence, or receipt of benefits from the noise source), but is positively associated with each of the five attitudinal variables examined (a fear of danger from the noise source, a sensitivity towards noise generally, the belief that the authorities can control the noise, the awareness of non-noise impacts of the source, and the belief that the noise source is not important)

Progress Towards Quieter Civil Helicopters

Abstract: A review of recent developments in helicopter noise reduction is presented. The paper includes a discussion of the present state of understanding of helicopter noise radiation mechanisms, and a review of actual noise reductions achieved by the manufacturers over the past decade. An analysis of progress achieved in meeting certification targets is given, together with an evaluation of the impact on design. Future trends in helicopter noise reduction based on current noise research programmes are discussed, and suggestions advanced for possible additional areas of study.

Single sensor active noise cancellation based on the EM algorithm

Abstract: The authors develop an approach to active noise cancellation using a single microphone. The noise field is modelled as a stochastic process, and a time-adaptive algorithm based on a modification of the block-estimate-maximize (EM) algorithm is used to adaptively estimate the parameters of this process. Based on these parameter estimates a canceling signal is generated. The algorithm developed is evaluated with recordings of aircraft noise, and has been implemented in real time with a single AT&T DSP32C chip. >

Aircraft noise annoyance and average versus maximum noise levels.

Abstract: A questionnaire study was performed in seven areas located around the airports of Landvetter and Save, Gothenburg, in an attempt to elucidate the extent of annoyance in populations exposed to aircraft noise. Noise exposure was estimated as the energy equivalent level (Aircraft Noise Level—FBN) or as the number of aircraft with levels that exceeded 70 dBA, combined with the maximum noise level. The results were compared with data obtained from the earlier Scandinavian Aircraft Noise Investigation. The results supported the conclusion that the annoyance reaction is better related to the number of aircraft and the maximum noise level than to energy equivalent levels for noise exposure.

Advanced Study for Active Noise Control in Aircraft (ASANCA)

Abstract: Aircraft interior noise and vibration measurements are included in this paper from ground and flight tests. In addition, related initial noise calculations with and without active noise control are conducted. The results obtained to date indicate that active noise control may be an effective means for reducing the critical low frequency aircraft noise.

Air Force Procedure for Predicting Noise around Airbases: Noise Exposure Model (Noisemap) Technical Report

Abstract: : NOISEMAP was the name given to the original Fortran program, developed for the USAF in the mid 1970's to calculate total noise exposure around military airbases. NOISEMAP now refers to a suite of programs that automate the noise exposure calculation process from operations data collection to final contour plotting. The noise calculation part of this suite of programs is now called NMAP 6.1 (the 6.1 being the current version number). New algorithms for calculating lateral attenuation and an expanded database are included in this version 6.1. NOISEMAP has also been rehosted from operation on a CDC mainframe computer to run on a desktop microcomputer (IBM compatible). This report is a technical overview of the algorithms used in NMAP 6.1. Most of these algorithms were originally outlined by Dr William Galloway in the report 'Community Noise Exposure Resulting from Aircraft Operations: Technical Review' published in November 1974. This report covers all the current algorithms used in NMAP 6.1 and includes an example computation for a single aircraft takeoff and ground runup operation. Acoustics, Engine Noise, Noise Modeling, Sound, Community Noise Exposure, Aircraft Noise, Environmental Impact.

An evaluation of some alternative approaches for reducing fan tone noise

Abstract: The potential of two alternative approaches for reducing fan ton noise was investigated in this study. One of these approaches increases the number of rotor blades to shift the tone noise to higher frequencies that are not rated as strongly by the perceived noise scale. This alternative fan also would have a small number of long chord stator vanes which would reduce the stator response and lower rotor-stator interaction noise. Comparison of the conventional and alternative fan concepts showed that this alternative approach has as large or larger a perceived tone noise reduction potential as the conventional approach. The other alternative, a high Mach number inlet, is evaluated both for its noise attenuation and for its change in noise directivity.

Advanced takeoff procedures for high-speed civil transport community noise reduction

Abstract: Advanced takeoff procedures were developed for a Mach 2.62 high-speed civil transport configuration (HSCT) equipped with turbine bypass engines, with the goal of reducing the takeoff noise levels for certification to FAR 36, Stage 3 noise levels. The detailed takeoff and landing module for the Flight Optimizations System (FLOPS) computer program was used to generate takeoff profiles. All takeoff procedures were constrained to meet a FAR takeoff field length of 11,000 feet, as well as the minimum required engine-out climb gradients for each airbome segment. Aircraft noise levels at the FAR 36 certification points were calculated using the Aircraft Noise Prediction Program (ANOPP). The study showed that using advanced takeoff procedures in noise certification could result in a 2.25 dB reduction in the amount of noise suppression required to certify this configuration for Stage 3 noise limits. Advanced procedures also resulted in an 8 percent reduction in the 100 EPNdB noise footprint area compared to basic FAR 36 takeoff procedures. In addition, improvements in the lift-to-drag ratio using high-lift devices were shown to produce 1.81 dB more noise reduction when used in combination with advanced takeoff procedures.

On the scaling of small-scale jet noise to large scale

Abstract: An examination was made of several published jet noise studies for the purpose of evaluating scale effects important to the simulation of jet aeroacoustics Several studies confirmed that small conical jets, one as small as 59 mm diameter, could be used to correctly simulate the overall or perceived noise level (PNL) noise of large jets dominated by mixing noise However, the detailed acoustic spectra of large jets are more difficult to simulate because of the lack of broad-band turbulence spectra in small jets One study indicated that a jet Reynolds number of 5 x 10(exp 6) based on exhaust diameter enabled the generation of broad-band noise representative of large jet mixing noise Jet suppressor aeroacoustics is even more difficult to simulate at small scale because of the small mixer nozzles with flows sensitive to Reynolds number Likewise, one study showed incorrect ejector mixing and entrainment using a small-scale, short ejector that led to poor acoustic scaling Conversely, fairly good results were found with a longer ejector and, in a different study, with a 32-chute suppressor nozzle Finally, it was found that small-scale aeroacoustic resonance produced by jets impacting ground boards does not reproduce at large scale

Annoyance Caused by Aircraft En Route Noise

Abstract: A laboratory experiment was conducted to quantify the annoyance response of people on the ground to en route noise generated by aircraft at cruise conditions. The en route noises were ground-level recordings of eight advanced turboprop aircraft flyovers and six conventional turbofan flyovers. The eight advanced turboprop en route noises represented the NASA Propfan Test Assessment aircraft operating at different combinations of altitude, aircraft Mach number, and propeller tip speed. The conventional turbofan en route noises represented six different commercial airliners. The overall durations of the en route noises varied from approximatelybreak 40 to 160 sec. In the experiment, 32 subjects judged the annoyance of the en route noises as well as recordings of both the takeoff and landing noises of each of 5 conventional turboprop and 5 conventional turbofan aircraft. Each of the noises was presented at three sound pressure levels to the subjects in an anechoic listening room. Analyses of the judgments found small differences in annoyance between three combinations of aircraft type and operation. Current tone and duration corrections did not significantly improve en route noise annoyance prediction. The optimum duration-correction magnitude for en route noise was approximately 1 dB per doubling of effective duration.

Update of Aircraft Profile Data for the Integrated Noise Model Computer Program. Volume 1. Final Report

Abstract: : This report provides aircraft takeoff and landing profiles, aircraft aerodynamic performance coefficients and engine performance coefficients for the aircraft data base (Database 9) in the Integrated Noise Model (INM) computer program. Flight profiles and coefficients are provided for 92 aircraft, covering a wide range of civil transport aircraft types, and selected general aviation and military aircraft. Appendix A list the aircraft flight profiles; Appendix B lists the aerodynamic and engine coefficients. The aerodynamic and engine coefficients, upon which the profiles are based, are in the format specified in Society of Automotive Engineers (SAE) Aerospace Information Report (AIR) 1845. To the extent possible, the coefficients and flight profiles are based upon the reference conditions specified in SAE AIR 1845

Update of Aircraft Profile Data for the Integrated Noise Model Computer Program

Abstract: This report provides aircraft takeoff and landing profiles, aircraft aerodynamic performance coefficients and engine performance coefficients for the aircraft data base (Database 9) in the Integrated Noise Model (INM) computer program. Flight profiles and coefficients are provided for 92 aircraft, covering a wide range of civil transport aircraft types, and selected general aviation and military aircraft. Appendix A lists the aircraft flight profiles; Appendix B lists the aerodynamic and engine coefficients. The aerodynamic and engine coefficients, upon which the profiles are based, are in the format specified in Society of Automotive Engineers (SAE) Aerospace Information Report (AIR) 1845. To the extent possible, the coefficients and flight profiles are based upon the reference conditions specified in SAE AIR 1845.

MD-80 aft cabin noise control: A case history

Abstract: The interior noise technology program to improve the noise environment in the aft cabin of the MD-80 twin jet aircraft is discussed. Two potential noise control treatments were identified: vibration absorber devices for the airframe and for the engine. A series of ground and flight tests using in-service aircraft was then conducted. These tests showed that the vibration absorbers for the airframe and engine decreased aircraft noise significantly.

Aircraft overflight study: Effect of aircraft altitude upon sound levels at the ground

Abstract: The report summarizes that literature review, discussing sound divergence, atmospheric absorption, attenuation due to intervening hills and heavily wooded areas, soft-ground attenuation, and the acoustical descriptors that are of potential concern to the Park Service as the aircraft flies by. Finally, the report concludes with a summary of the effect of aircraft altitude upon sound levels on the ground, taking all these factors into account. Included in the summary is a discussion of the potential acoustical effectiveness of using altitude as a mitigation measure for any adverse effects of aircraft sound within the National Park System.

Acoustics of Transonic Flow Around an Oscillating Flap

Abstract: Investigation of noise mechanisms due to unsteady transonic flow is important for aircraft noise reduction. In this work, the near-field impulsive noise due to an oscillating flap is simulated numerically. The problem is modeled by the two-dimensional high frequency transonic small disturbance equation (VTRAN2 code). The three types of unsteady shock wave motion have been identified. Two different important disturbances exist in the pressure signal. The disturbances are related to the unsteady motion of the supersonic pocket and fluctuating lift, and drag forces. Pressure wave signatures, noise frequency spectra, and noise directivity are shown.

The Dornier 328 Acoustic Test Cell (ATC) for interior noise tests and selected test results

Abstract: To perform acoustic studies for achieving low noise levels for the Dornier 328, an acoustic test cell (ATC) of the Dornier 328 has been built. The ATC consists of a fuselage section, a realistic fuselage suspension system, and three exterior noise simulation rings. A complex digital 60 channel computer/amplifier noise generation system as well as multichannel digital data acquisition and evaluation system have been used. The noise control tests started with vibration measurements for supporting acoustic data interpretation. In addition, experiments have been carried out on dynamic vibration absorbers, the most important passive noise reduction measure for low frequency propeller noise. The design and arrangement of the current ATC are presented. Furthermore, exterior noise simulation as well as data acquisition are explained. The most promising results show noise reduction due to synchrophasing and dynamic vibration absorbers.

Advanced subsonic transport approach noise: The relative contribution of airframe noise

Abstract: With current engine technology, airframe noise is a contributing source for large commercial aircraft on approach, but not the major contributor. With the promise of much quieter jet engines with the planned new generation of high-by-pass turbofan engines, airframe noise has become a topic of interest in the advanced subsonic transport research program. The objective of this paper is to assess the contribution of airframe noise relative to the other aircraft noise sources on approach. The assessment will be made for a current technology large commercial transport aircraft and for an envisioned advanced technology aircraft. NASA's Aircraft Noise Prediction Program (ANOPP) will be used to make total aircraft noise predictions for these two aircraft types. Predicted noise levels and areas of noise contours will be used to determine the relative importance of the contributing approach noise sources. The actual set-up decks used to make the ANOPP runs for the two aircraft types are included in appendixes.

A NASA Lewis comparative propulsion system assessment for the High-Speed Civil Transport

Abstract: The topics covered include the following: High Speed Research (HSR) Propulsion System Studies; HRS System Study flowpath; design point aircraft sizing - no noise constraint; impact of noise constraint; noise impact on aircraft size; takeoff gross weight assessment; impact of High Speed Civil Transport (HSCT) high-altitude flyover noise; HSR NO(x) reduction status; current assessment of HSCT ozone depletion; influence of non-optimum cruise altitude on range; and influence of subsonic leg on range.

Helicopter noise prediction - The current status and future direction

Abstract: The paper takes stock of the progress, assesses the current prediction capabilities, and forecasts the direction of future helicopter noise prediction research. The acoustic analogy approach, specifically, theories based on the Ffowcs Williams-Hawkings equations, are the most widely used for deterministic noise sources. Thickness and loading noise can be routinely predicted given good plane motion and blade loading inputs. Blade-vortex interaction noise can also be predicted well with measured input data, but prediction of airloads with the high spatial and temporal resolution required for BVI is still difficult. Current semiempirical broadband noise predictions are useful and reasonably accurate. New prediction methods based on a Kirchhoff formula and direct computation appear to be very promising, but are currently very demanding computationally.

Advances in tilt rotor noise prediction

Abstract: The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, are studied. The results of flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. The wing under the rotor is found to obstruct the inflow, causing a deficit in the inflow velocities over the inboard region of the rotor. Discrete frequency harmonic thickness and loading noise mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various noise prediction methods using the WOPWOP code. The analysis indicates that the partial ground plane created by the wing below the rotor results in a primary sound source for hover.