TEMPORAL CHARACTERIZATION OF AIRCRAFT NOISE SOURCES.pdfVIP

42nd Aerospace Sciences Meeting and Exhibit AIAA 2004-1029 5-8 January 2004, Reno, Nevada 1 American Institute of Aeronautics and Astronautics Copyright ? 2004 by the American Institute of Aeronautics and Astronautics, Inc. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Government Purposes. All rights are reserved by the copyright owner. TEMPORAL CHARACTERIZATION OF AIRCRAFT NOISE SOURCES Ferdinand W. Grosveld ? Lockheed Martin Engineering and Sciences Hampton, VA 23681 Brenda M. Sullivan ? and Stephen A. Rizzi * NASA Langley Research Center Hampton, VA 23681 ABSTRACT Current aircraft source noise prediction tools yield time-independent frequency spectra as functions of directivity angle. Realistic evaluation and human assessment of aircraft fly-over noise require the temporal characteristics of the noise signature. The purpose of the current study is to analyze empirical data from broadband jet and tonal fan noise sources and to provide the temporal information required for prediction-based synthesis. Noise sources included a one-tenth-scale engine exhaust nozzle and a one-fifth- scale scale turbofan engine. A methodology was developed to characterize the low frequency fluctuations employing the Short Time Fourier Transform in a MATLAB? computing environment. It was shown that a trade-off is necessary between frequency and time resolution in the acoustic spectrogram. The procedure requires careful evaluation and selection of the data analysis parameters, including the data sampling frequency, Fourier Transform window size, associated time period and frequency resolution, and time period window overlap. Low frequency fluctuations were applied to the synthesis of broadband noise with the resulting records sounding virtually indistinguishable from the measured