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Broadband sound generation by confined turbulent jets Zhaoyan Zhang Luc Mongeau a and Steven H Frankel School of Mechanical Engineering Purdue University West Lafayette Indiana 47907 1077 Received 9 November 2001 revised 14 May 2002 accepted 17 May 2002 Sound generation by confined stationary jets is of interest to the study of voice and speech production among other applications The generation of sound by low Mach number confined stationary circular jets was investigated Experiments were performed using a quiet flow supply muffler terminated rigid uniform tubes and acrylic orifice plates A spectral decomposition method based on a linear source filter model was used to decompose radiated nondimensional sound pressure spectra measured for various gas mixtures and mean flow velocities into the product of 1 a source spectral distribution function 2 a function accounting for near field effects and radiation efficiency and 3 an acoustic frequency response function The acoustic frequency response function agreed as expected with the transfer function between the radiated acoustic pressure at one fixed location and the strength of an equivalent velocity source located at the orifice The radiation efficiency function indicated a radiation efficiency of the order kD 2 over the planar wave frequency range and kD 4 at higher frequencies where k is the wavenumber and D is the tube cross sectional dimension This is consistent with theoretical predictions for the planar wave radiation efficiency of quadrupole sources in uniform rigid anechoic tubes The effects of the Reynolds number Re on the source spectral distribution function were found to be insignificant over the range 2000 Re 20 000 The source spectral distribution function approximately obeyed a St 3 power law for Strouhal number values St 0 9 and a St 5 power law for St 2 5 The influence of a reflective open tube termination on the source function spectral distribution was found to be insignificant confirming the absence



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