Direct Numerical Simulation of turbulent flows with an impedance boundary condition

Abstract

Direct numerical simulations (DNS) of turbulent pipe flows are carried out to investigate the suppression of previously-identified internal noise sources with an acoustic liner using a time-domain acoustic liner model developed by Tam and Auriault (AIAA Journal, 34(5), 917-923, 1996). The liner model is implemented and tested in an in-house DNS code. Validation tests are conducted to show its correct implementation in the DNS solver. In order to study the liner model capability a number of tests are carried out with different liner parameters and flow Mach Numbers. To understand the effect of the liner on the acoustic and turbulent components of the unsteady wall pressure, an azimuthal/axial Fourier transform is applied and the acoustic and turbulent wavenumber regimes are clearly identified. It is found that the spectral component occupying the turbulent wavenumber range is unaffected by the liner, whereas the acoustic wavenumber components are strongly attenuated, with individual radial modes evident as each cuts on with increasing Strouhal number. The acoustic wavenumber analysis shows that the acoustic component of the wall pressure prevails over the hydrodynamic wall pressure. This allows the acoustic liner model to dissipate the acoustic field only, leaving the hydrodynamic component statistically unchanged. Furthermore, a DNS of a pipe/jet configuration is computed to study the effects of the acoustic liner model on the far-field noise. Noise prediction is performed using the Ffowcs Williams-Hawkings (FWH) method. The FWH method has also been tested to identify the best configuration of the FWH surface. A conical-shaped surface proved to be a better surface. Furthermore, results show far-field noise reduction when the liner model is present.

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ORCID for Richard Sandberg: orcid.org/0000-0001-5199-3944

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