평판위의 난류경계층에서의 원거리 소음 및 벽 압력변동에 대한 실험적 연구

초록

The wall pressure fluctuations beneath a turbulent boundary layer over a flat plate have been investigated in an anechoic wind tunnel facility. To improve spectra characteristics in high frequency range, a 1/8" pressure-type microphone sensor, which has a pin-holed cap of various diameters, was employed in this experiment. It is shown that the pin-holed microphone sensor with a dimentionless diameter d+ of 7.1 resolves the high frequency pressure fluctuations most effectively among ones with various pin-hole diameters. The pressure events of high amplitude are found to contribute to total fluctuating pressure energies in the turbulent boundary layer significantly. The intermittent large-amplitude pressure events and their far-field sound are investigated using time-frequency localization technique of Short Time Fourier Transform(STFT). The pressure events of high amplitude are related to longitudinal quadrupole source and supposed to radiate to the far-field effectively.