Contribution
On the acoustic boundary layer of a wall lining with turbulent grazing flow
* Presenting author
Abstract:
It is well known that passive acoustic wall linings, which are widely used, for example, to reduce noise in aircraft engines, can change their acoustic properties significantly when a turbulent flow is present. The mean grazing flow interacts with the acoustic flow in the small openings of the face-sheet of the lining. This induces a high acoustic shear stress at the wall (compared to the no-flow case). The effect of the shear stress must be adressed correctly in the acoustic boundary condition if precise predictions of the sound attenuation of the lining should be achieved. Unfortunately, in most models the shear stress effect and the effect of the turbulence are ignored. However, their consideration leads to complicated research questions: How is the particle velocity and the shear stress linked in the acoustic boundary layer, and how the two fields are interacting with each other? How the temporal reaction of the turbulent stresses with respect to the acoustic displacement at the liner wall can be described? How does the information propagates from the wall through the turbulent boundary layer? This report will present our current state of insight on this subject, supported by DNS data.