Acoustical evaluation of the NASA Lewis 9- by 15-foot low speed wind tunnel
Milo D. Dahl, Richard P. Woodward, United States. National Aeronautics and Space Administration. Scientific and Technical Information Program
National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1992 - Technology & Engineering - 64 pages
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1/3-octave band 103 Distance 250 Distance 500 Hz intervals 6-dB decay line 60 axis absorption coefficient acoustic free field acoustic source acoustic treatment Acoustical Evaluation airflow atmospheric absorption axis 60 bulk absorber Center frequency decay with distance decay/doubling r 30 deg 6-dB decay/doubling Distance at 345 distance measurements domain plot effects of early effects of late Figure 44.—Continued Frequency domain measurement frequency range frequency response frequency spectra Hz/sec incident signal interference pattern interference ripple intervals of late Kevlar late reflections m/sec maximum deviations measured in setup measurement setups measurements in selected Microphone traverse angle off-axis measurements path length pure tone reflected path reflected signal reflection effects measured reflection interference reflections from upstream reflections using setup section using setup selected 500 Hz shown in figure Sideline 75 sideline location Signals from paths tracking filter bandwidth tunnel test section turboprop view of measurement wall wind tunnel