Aeroacoustics over Cylinders: LES

Acoustic CFD Simulation (LES) of Airflow over Cylinders in 4 Different Positions, ANSYS Fluent Training

Description

This project simulates airflow acoustics over cylinders arranged in four different positions using Large Eddy Simulation (LES) in ANSYS Fluent. Acoustics is the branch of science concerned with mechanical waves in gases, liquids, and solids — encompassing vibration, sound, ultrasound, and infrasound — and covers the production, control, transmission, reception, and effects of these waves.

The domain was meshed in ICEM CFD using a structured mesh, with each configuration file containing approximately 2,000,000 elements and a boundary layer mesh applied around the cylinders. Given the nature of this problem, the simulation was run using a transient solver.

Methodology

This project simulates sound pressure waves generated around cylinders across four distinct positional configurations. Sound waves within a fluid arise from the vibration and reciprocating motion of fluid layers — as one layer of air moves forward, the adjacent layer is pushed forward in turn before returning to its original position. These reciprocating movements continue until the energy within the flow dissipates, and audible sound is produced once this oscillation exceeds roughly 16 cycles per second.

Air density was defined at 1.225 kg/m³, with an inlet velocity of 69.2 m/s. Flow turbulence was resolved using the LES Smagorinsky model, while acoustic behavior was captured using the Ffowcs Williams-Hawkings equations. The SST k-omega model was additionally used to solve the turbulent flow equations supporting the broader simulation setup.

Conclusion

Results include 2D pressure contours across each of the four cylinder configurations, along with Sound Pressure Level plots extracted at several defined monitoring points: a lower point at (0, -0.15 m, 0), a first point at (0.4, 0, 0), and a second point at (0.7, 0, 0), with a 100 mm spacing between cylinder centers in both the X and Y directions.

The results show a clear trend: sound pressure level increases the closer a monitoring point sits to the cylinder, confirming that the cylinder surface acts as the dominant near-field source of the generated acoustic pressure fluctuations.