Experimental Study on Wall Pressure Fluctuations and Their Far-field Sound in the Turbulent Boundary Layer

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 transducer with a dimentionless diameter d+ of 7.9 resolves the high frequency pressure fluctuations most effectively among ones with 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 the turbulent structure in the near-wall region were correlated using the Variable-Interval Time Average(VITA) technique. The large-amplitude pressure events and their far-field sound are investigated using the time-frequency localization technique of Short Time Fourier Transform(STFT). The pressure events of large-amplitude are related to longitudinal quadrupole sources and supposed to radiate to the far-field effectively.