On the computation of low-subsonic turbulent pipe flow noise with a hybrid LES/LPCE method

Abstract

Aeroacoustic computation of a fully-developed turbulent pipe flow at Rer. 175 and M = 0.1 is conducted by LES/LPCE hybrid method. The generation and propagation of acoustic waves are computed by solving the linearized perturbed compressible equations (LPCE), with acoustic source DP(x,t)/Dt attained by the incompressible large eddy simulation (LES). The computed acoustic power spectral density is closely compared with the wall shear-stress dipole source of a turbulent channel flow at Re,= 175. A constant decaying rate of the acoustic power spectrum, f(-8/5) is found to be related to the turbulent bursts of the correlated longitudinal structures such as hairpin vortex and their merged structures (or hairpin packets). The power spectra of the streamwise velocity fluctuations across the turbulent boundary layer indicate that the most intensive noise at omega(+) < 0.1 is produced in the buffer layer with fluctuations of the longitudinal structures (k(z)R < 1.5).