Wave Equation: Aeroacoustics Model

Description

This CFD project investigates the aeroacoustic behavior of air flowing past a cylinder, using the Wave Equation acoustic model in ANSYS Fluent to characterize the resulting sound field. As air flows around the cylinder, unsteady vortex shedding in the wake generates pressure fluctuations that radiate outward as sound, a classic aeroacoustic phenomenon relevant to noise prediction around bluff bodies such as struts, cables, or landing gear components in aerospace applications. The two-dimensional geometry was constructed in ANSYS Design Modeler, and a structured mesh consisting of 23,264 elements was generated in ANSYS Meshing to accurately resolve both the near-wall flow behavior and the acoustic field around the cylinder.

Methodology

The simulation was performed in transient (unsteady) mode, since capturing the time-varying flow structures responsible for sound generation requires resolving flow behavior at each time step rather than a steady-state average. A pressure-based solver was employed, consistent with the low-speed, incompressible flow regime of the working fluid. The Wave Equation acoustic model was then applied on top of the resolved flow field to compute how the pressure fluctuations generated by vortex shedding propagate as acoustic waves through the domain. This is a widely used two-step, hybrid aeroacoustic approach, where the flow field is solved first and the acoustic field is derived from it separately, rather than solving both simultaneously.

Analysis

At the conclusion of the simulation, sound pressure levels were extracted at defined receiver points placed in the domain, allowing the acoustic response to be evaluated at specific locations of interest. The acoustic source data was exported in ASD, or Acoustic Source Data, format, enabling further post-processing or use in downstream acoustic analysis tools. The frequency spectrum captured extended up to 100,000 Hz, with the results showing that the maximum sound pressure levels occurred at frequencies below 10,000 Hz, a pattern consistent with the dominant tonal noise typically produced by periodic vortex shedding off a cylinder, often referred to as an Aeolian tone, rather than broadband high-frequency turbulent noise.