Turbulent boundary layer noise in pipe flow

A turbulent pipe flow noise at ReD = 5000 (or Re&_tau; = 175) and M = 0.1 is invesitgated by a LES/ LPCE hybrid method. The near-wall turbulences are computed by incompressible large eddy simulation, while the generation and propagation of the acoustic waves are solved by the linearized perturbed compressible equations, with acoustic sources represented by a material derivative of the hydrodynamic pressure, DP/Dt. The power spectral density of acoustic pressure computed by the present method is closely compared to the dipole source spectrum of the wall shear stress fluctuations of Hu, Morfey and Sandham [JFM,2003], who investigated the noise sources in a turbulent channel flow at low Mach numbers.A constant decaying rate of - 8/5 shown in the power spectrum turns out to be closely related to the length scales of longitudinal turbulent coherent structures such as hairpin-type vortices and their merged structures. It is found that the most intense noise (&_omega;+ &_leq; 0.1) is produced in the buffer layer with streamwise fluctuations of those streak-like structures in the wavenumber range of k_xR < 1.5. Some high frequency components of TBL noise seem to be attributed by small-scale structures in the log-law regime.