Article
On the effect of the turbulent shear stresses on the acoustic boundary condition of acoustic liners with grazing mean flow (en)
* Presenting author
Abstract:
Acoustic wall liners are used in many applications for sound attenuation in flow ducts. In most practical applications, the front of the liner consists of a rigid wall made acoustically permeable by perforations, which are exposed to a turbulent flow. It is known that a turbulent flow can greatly change the acoustic behavior of the liner compared to the no-flow case. This change must be adressed correctly in the effective acoustic boundary condition of the liner if precise predictions of sound attenuation should be achieved. The process to be described is the diffusion of acoustic shear stress through the turbulent flow boundary layer. An important, nearly unexplored issue in this process is the relaxation of turbulence, i.e. the temporal reaction of the turbulent stresses with respect to the acoustic displacement at the liner wall. In our work, we investigate the general case of a relaxing flow by means of two simplified models, which are supported by DNS data. As a result, the two limiting cases - non-relaxing or fully relaxed flow - yield considerable differences in the effective boundary condition. Surprisingly, there are also indications that the limiting case of fully relaxed flow may never be reached in reality.