The Spectrum and Directivity Extrapolation Method of an Acoustic Wind Tunnel Test for a Scaled Airframe Noise

The wind tunnel test for a scaled airframe model normally can not obtain the high frequency components when transform the scaled model to full scale. Meanwhile, due to the limitation of the acoustic wind tunnel facilities, the measurement can not perform a full acoustic directivity covering from 0 to 180 degrees. In order to extend the frequency and polar angle information acquired by wind tunnel test results, a method for extrapolation of frequency and directivity of a 1:7.6 scaled full airframe wind tunnel test data is developed. The entire sound pressure spectrum is decomposed into two segments: low frequency segment and mid-high frequency segment. Each segment is fitted by a spectrum envelope with different slopes generated from flight test spectrums. An auto regressive model (AR model) is also developed and applied to extrapolate the acoustic directivity in this paper.