A Flow around Cylinder acoustic analysis using the FW-H model CFD is a computer simulation that helps engineers understand how noise is created when a fluid (like air or water) flows past a simple object like a cylinder. This is a very common problem in engineering, seen in heat exchangers, tall buildings, and even car antennas. The unsteady, swirling flow behind the cylinder, known as vortex shedding, creates pressure pulses that we hear as sound.

Using the FW-H model in Fluent, we can perform an Acoustic CFD study to predict this noise. The simulation first calculates the fluid flow and then uses the Ffowcs Williams-Hawkings (FW-H) model to convert the fluid pressure data into sound data. This Cylinder acoustic Fluent analysis allows us to predict the loudness (Sound Pressure Level), the pitch (frequency), and the direction of the noise. This is essential for designing quieter and safer products. For additional Acoustic CFD simulations, explore our comprehensive collection here.

Simulation process: Fluent Setup, Transient Flow and FW-H Acoustic Model Activation

To accurately capture the noise-generating physics, the simulation was configured as a transient analysis in ANSYS Fluent. This is very important because noise from vortex shedding is an unsteady, time-dependent event that a steady-state simulation cannot see. After the fluid flow simulation reached a stable, repeating pattern, the FW-H acoustic model was activated. This powerful tool in Fluent acts as a post-processor, using the saved transient flow data to calculate sound propagation. To measure the predicted sound, two virtual microphones, called acoustic receivers, were placed in the simulation. These receivers were positioned at different distances from the cylinder (0.665m and 2.4m) to capture how the sound changes as it travels away from the source.

Post-processing: Correlating Vortex Shedding with Acoustic Signatures

The simulation results provide a complete engineering story, successfully linking the fluid dynamics of vortex shedding to the acoustic noise it produces. The spectral analysis contours in Figures 1 and 2 show the frequency content of the noise at both receivers. At Receiver-1 (0.665m from the cylinder), the maximum sound pressure level (SPL) reaches a significant 92 dB. At Receiver-2 (2.4m away), the maximum SPL drops to 78 dB. This 14 dB reduction in loudness is a critical finding that validates the model’s ability to capture acoustic decay, the natural process of sound getting quieter as it moves away from its source. The analysis also shows the noise is strongest at low frequencies (below 1000 Hz), which is a classic signature of noise from bluff body vortex shedding.

Figure 1: Spectral Analysis of Sound Pressure Level at Receiver-1 (0.665m from cylinder), showing a peak noise of 92 dB.

Figure 2: Spectral Analysis of Sound Pressure Level at Receiver-2 (2.4m from cylinder), showing noise decay to a peak of 78 dB

The time history of acoustic pressure at Receiver-1, shown in Figure 3, reveals the direct cause of this noise. The pressure oscillates in a very regular, repeating pattern between -8 Pascals and +8 Pascals. This perfectly stable, wave-like signal is the “sound” of the vortices shedding, one after another, from the top and bottom of the cylinder. This alternating pressure field, also visible in the pressure contour in Figure 4, creates what is known as a dipole sound source, which is the main noise mechanism here.

The most important achievement of this simulation is the precise calculation of the vortex shedding frequency directly from the acoustic data. The time between pressure peaks in Figure 3 is approximately 0.0005 seconds. This corresponds to a dominant frequency of (1 / 0.0005s) = 2000 Hz. This value represents the “pitch” of the sound generated by the cylinder. By successfully modeling the flow, predicting the sound levels, and extracting the exact frequency of the primary noise source, this FW-H model CFD analysis provides a highly reliable tool for any engineering application where flow-induced noise is a concern.

Figure 3: Time History of Acoustic Pressure at Receiver-1, illustrating the stable, periodic pressure waves from vortex shedding.

Figure 4: Contours of the pressure field around the cylinder, showing the alternating high and low-pressure zones that create the dipole sound source.