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05.05 Improving Tools for Subsonic Aircraft Noise Prediction

Improving single flyover noise prediction for subsonic aircraft
Time: 5:00 pm

Author: Oleksandr Zaporozhets

Abstract ID: 2352

Current ICAO Doc 9911 provides the algorithm to calculate aircraft noise levels for any kind of airport flight scenario. The essential difference exists between the measured and calculated sound levels, especially for single flight noise events. Doc 9911 recommends using this method for equivalent sound levels L and noise indices L first of all. A number of national noise regulations still require for single noise event assessment. An article analyzes a number of reasons to explain the inaccuracy of noise event calculations. For example, the differences between calculated balanced flight parameters (thrust and velocity first of all) and supervised in real flights may influence the accuracy first of all. Statistical data was gathered to make more general view on these differences and some proposal to use them in calculations has being proved. Also, the assumptions of the ICAO Doc 9911 method may contribute to the inaccuracy of calculations. Among them are the homogeneous atmosphere for sound propagation, generalized for overall fleet noise directivity pattern, etc. Ground effect model defines the values for aircraft absent in operation currently. The first assumption provides a conflict with flight path calculations for varied atmosphere parameters with height over the surface.

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Design, development, testing and application of digital MEMS pressure sensor array for full-scale vibroacoustic measurements
Time: 11:00 am

Author: Pankaj Joshi

Abstract ID: 2671

This manuscript addresses design, development, and application of micro-electro-mechanical systems (MEMS) based digital pressure sensor array for vibroacoustic measurements. These vibroacoustic measurements were conducted on a A320 type single aisle aircraft demonstrator subjected to broadband as well as tonal excitations. Cabin noise levels were measured with both condenser microphones as well as digital MEMS pressure sensor array. The measured cabin noise shows strong qualitative as well as quantitative agreement between both type of measurement devises for full scale cabin noise measurements inside an aircraft demonstrator. The observed strong agreement is valid for both single wall (fuselage with thermal insulation) and double wall (fuselage with thermal insulation and trim panel) cabin noise measurements. Such strong agreement within 1.0 dB tolerance is significantly motivating for further development of reliable but low-cost MEMS based measurement devises and corresponding efficient data post-processing algorithms for full scale vibroacoustic measurements in general. Additionally, it is also demonstrated that the large number of MEMS based digital pressure sensors can be used in areas where the physical space constraints are high. This demonstration shows strong potential to derive additional vibroacoustic indicator for the development and the testing of future noise control solutions in a non-traditional way.

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Empirical prediction of flight effect on subsonic coaxial-jet noise by introducing an adjusted flight velocity term
Time: 2:40 pm

Author: Incheol Lee

Abstract ID: 2719

The effect of forward flight on jet noise is difficult to quantify through flyover tests since only the total noise is measured in a full-scale flyover test, and the contribution of the jet noise is difficult and sometimes nearly impossible to identify. Thus, most studies on the flight effect have been carried out through model-scale experiments with a single-stream jet simulator in a free jet facility. In this paper, the effect of forward flight was captured by using an adjusted flight velocity term (?V) to describe jet velocity in a new prediction of coaxial-jet noise. The new jet noise prediction method assumes that there are three components: primary, secondary, and mixed components with no filter functions. The coefficient ? is determined by a thorough investigation of the model-scale data gained from an experiment in the anechoic wind tunnel of ONERA. The value of ? is 1 for the primary component, 0.5 for the secondary component, and a linear function of the angle for the mixed component. The simple adjustment of the flight velocity successfully embodied the effect of forward flight at all angles, with no separate velocity exponent or an additional term.

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Empirical estimation of engine-integration noise for high bypass ratio turbofan engines
Time: 4:40 pm

Author: Incheol Lee

Abstract ID: 2723

To investigate the impact of installation on jet noise from modern high-bypass-ratio turbofan engines, a model-scale noise experiment with a jet propulsion system and a fuselage model in scale was conducted in the anechoic wind tunnel of ONERA, CEPRA 19. Two area ratios (an area of the secondary nozzle over an area of the primary nozzle), 5 and 7, and various airframe configurations such as wing positions relative to the tip of the engine nacelle and flap angles, were considered. Based on the analysis of experimental data, an empirical model for the prediction of engine installation noise was proposed. The model comprises two components: one is the interaction be-tween the jet and the pressure side of the wing, and the other is the interaction between the jet and the flap tip. The interaction between the jet and the pressure side of the wing contributes to the noise at the low frequencies (? 1.5 kHz), and the interaction between the jet and the flap tip con-tributes to the noise at the high frequencies. The proposed model showed a good agreement with the experimental data.

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Advanced procedure noise model validation using airport noise monitor networks
Time: 5:40 pm

Author: Jacqueline Thomas

Abstract ID: 2842

Advanced operational flight procedures that utilize modifications to thrust, airspeed, altitude, and configuration can be implemented to mitigate noise impacts for communities surrounding airports. Evaluating and designing such procedures requires accurate modeling of the aircraft performance, source noise, and atmospheric propagation of the source noise to the ground. Modeling frameworks to assess advanced procedures have been developed but must be validated to ensure their results are reasonable. This paper presents validation of such noise models using a network of ground noise monitoring data at Seattle-Tacoma International airport and ADS-B operational radar flight profiles from the OpenSky database. Modeled noise from operational flights of several aircraft types are shown to be consistent with noise monitor data when reasonable flap settings and atmospheric corrections for the actual weather at the time of flight are used. Discrepancies that exist between the modeled and measured noise results are identified to determine where current noise modeling methods must be improved to accurately represent all relevant noise sources.

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Validation of the aviation environmental design tool’s noise model using high fidelity weather
Time: 6:00 pm

Author: Ana Gabrielian

Abstract ID: 2846

To enable sustainable aviation growth, mitigation of environmental effects must be developed in parallel. To further this effort, these effects are modeled using capabilities such as the Aviation Environmental Design Tool (AEDT), a program that is able to model aircraft performance, fuel burn, emissions, and noise. Past and current projects are performed with the intent of improving the accuracy of the models within AEDT to capture various real-world effects. This paper targets the sensitivity of the noise prediction and propagation by varying multiple assumptions within AEDT. To validate the noise capabilities, multiple streams of real-world data will be used to accurately model actual flights to and from SFO airport. This data includes High-Fidelity weather data,?detailed flight performance characteristics from airline flight data records and noise monitoring data obtained from stations around the airport. The results from this study are expected to offer recommendations and help users prioritize and more accurately quantify community noise exposure using AEDT.

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Subtraction Analysis for Predicting the Propagation Effects of Aircraft Noise
Time: 5:20 pm


Abstract ID: 2855

In 2013, the Federal Aviation Administration and Volpe National Transportation System Center conducted a series of acoustic measurements with a propeller driven aircraft operating in the regions near Houston, Texas. The recorded data on octave band sound levels, aircraft locations, temperature and wind speed profiles were used in the current study to quantify the uncertainties for predicting the propagation effects of aircraft noise. Use of the Aviation Environmental Design Tool (AEDT) was explored for its accuracy and validity in real world scenarios offered by the dataset. The sound exposure level (SEL) data for each section of a flight path was used instead of the time history data for reducing the directivity effect of the sound source due to the change in its relative positions with the receivers. A subtraction-based method was introduced to analyze the propagation effect in which the SELs between two receiver locations were compared. The use of the subtraction method reduces the possible influences of the sound power variations along the flight paths. The measured data for a spiral and a level flight event were presented and the AEDT predictions on the propagation effects were examined in this paper.

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Development of Fly Neighborly helicopter model specific operational noise abatement guidance from acoustic flight test data
Time: 12:20 pm

Author: Juliet Page

Abstract ID: 3210

Improved helicopter noise abatement guidance has been developed based on acoustic test data acquired by NASA, FAA and Volpe in support of the Helicopter Association International (HAI)’s Fly Neighborly Program.  This higher fidelity material was developed to supplement previous training programs based on pilot and operator feedback. The manner of presentation allows pilots to readily interpret the directional noise emission of their vehicle at different operating conditions.  Flight path, airspeed, approach descent rate, and deceleration rate can be assessed to optimize flight patterns both during the pre-flight planning stage and in real time during flight operations in response to local conditions and events. The resultant sound directivity would be displayed as colored noise exposure contours overlaid onto a map of the area in the vicinity of the helicopter. New Fly Neighborly training modules have been developed utilizing directional operational noise plots based on Volpe’s Advanced Acoustic Model (AAM) modeling with empirical sound sphere data from dedicated US Government helicopter flight tests.  This paper will describe the acoustic analyses and will present the updated noise guidance for the AS350, AS365, AW139, Bell 205, Bell 206, Bell 407, R-44, R-66 and S-76D helicopters.

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