Using eigenmode forcing to investigate flow instability mechanisms causing whistling sound

In flow acoustical problem sets, there is typically a large disparity of scales between hydrodynamical and acoustical phenomena both in amplitude and spatial extent. This results in major difficulties for low Mach number and high Reynolds number applications, resolving both acoustic and flow fields in a compressible flow simulation and applying correct boundary conditions.
Consequently, during the design process of flow guiding structures, flow and acoustic fields are only investigated separately, or a forward coupled simulation workflow (standard hybrid aeroacoustic approach) is used. This methodology, however, fails to accurately predict any flow instability mechanism caused by backcoupling of the acoustic field to the flow field, as it is the case for whistling sound.
This work presents a novel approach to excite flow instabilities such as the whistling mechanism by applying acoustical mode forcing on an otherwise incompressible flow simulation.
This allows for optimal domain size and boundary conditions of the incompressible flow domain. Furthermore, in contrast to strong direct coupling of the flow and acoustic domains, all interpolation tasks can be performed a priori. The relatively low computational cost makes this method especially well applicable to the task of designing complex flow guiding structures such that whistling is mitigated in an early development stage.