Simulation of Flow-Induced Acoustic Resonance of Bluff Bodies in Duct Flow

It is well known that the periodic vortex shedding from bluff bodies in a duct can excite the transverse acoustic mode if the frequencies are comparable. There is a considerable body of experimental work investigating this phenomenon for multiple cylinders. Numerical studies are somewhat less common, partially because it is difficult to couple the acoustics and the hydrodynamic field. This paper implements a hydrodynamic analogy proposed by Tan et al. in which the acoustic field is represented by a velocity excitation of the incompressible hydrodynamics at the domain extents. Two alternatives to this boundary condition are considered: rigid body vibration and surface potential flow. In all three cases, the flow field for two tandem cylinders with a spacing ratio of 2.5D has been simulated with uRANS and an RSM turbulence model. It has been found that a rigid body vibration is not a good model of acoustic excitation. However, imposing a potential flow at the surface of the cylinders yields promising results. The success of the new boundary condition implies that the coupling between the acoustic field and the hydrodynamics is not reorganizing the wake directly, but rather simply modifying the generation of vorticity at the surface. Furthermore, it is envisaged that the new modeling approach will be easier to implement for complex geometries, such as tube arrays.