A Flow around Cylinder acoustic analysis is a computer simulation that helps engineers understand the noise created when air or water flows past a round object. This “whistling” sound is caused by a process called vortex shedding. This report uses a powerful technique called the Acoustic Wave Model CFD in ANSYS Fluent. Unlike other methods, the wave model acoustic Fluent approach calculates the sound waves directly within the simulation domain at the same time as the fluid flow. This type of Acoustic CFD analysis provides a complete picture of aeroacoustics—from the creation of unsteady pressure pulses on the cylinder to the way the sound travels away from it. This is very important for designing quieter products, such as car antennas, overhead power lines, and aircraft landing gear. For comprehensive acoustic simulations and noise analysis techniques, explore our specialized collection at CFDLAND Acoustic CFD Simulations.

Figure 1: A conceptual illustration of turbulent flow and vortex shedding behind a cylinder, which is the primary source of flow-induced noise.

Simulation Process: LES and Wave Equation Modeling for Aeroacoustics

To perform this acoustic Fluent simulation, a 2D model of a circular cylinder inside a rectangular fluid domain was created. The simulation was set up as transient, meaning it calculated the results over time. This is essential because sound and vortex shedding are time-dependent events. To accurately model the turbulence that causes noise, the Large Eddy Simulation (LES) model was chosen. After the fluid flow simulation reached a stable, repeating pattern of vortex shedding, the Wave Equation Model was activated directly within ANSYS Fluent. This model uses the unsteady pressure fluctuations on the cylinder’s surface as the source of the sound. It then solves the acoustic wave equations to calculate how these sound waves travel throughout the entire computational domain.

Post-processing: CFD Analysis, Linking Vortex Shedding Dynamics to Acoustic Wave Propagation

The sound pressure contour in Figure 2 shows the direct effect of this fluid motion. The alternating red and blue patterns are the sound waves propagating away from the cylinder. These are very small pressure changes, ranging from -5.56e-05 Pa to 5.26e-05 Pa, but they represent the audible noise. The most important finding here is the shape of these sound waves. They form a clear dipole pattern, which looks like a figure-eight, with the loudest sound traveling perpendicular (up and down) to the direction of the flow. This dipole signature is the classic, unmistakable fingerprint of noise generated by vortex shedding.

The most important achievement of this simulation is the successful use of the Wave Acoustic Model to capture the entire aeroacoustic process in a single, unified simulation. The model correctly linked the creation of the von Karman vortex street in the fluid (the cause) to the generation of a propagating acoustic wave with a perfect dipole pattern (the effect). This proves the model is a powerful and accurate tool for engineers to directly predict and analyze flow-induced noise.

Figure 2: Contours of sound pressure from the Acoustic Wave Model, showing sound waves propagating away from the cylinder in a distinct pattern.

The analysis begins with the cause of the noise: the fluid dynamics. The velocity streamlines in Figure 4 clearly show the formation of a von Karman vortex street, which is the classic pattern of alternating vortices shedding from the cylinder. The flow accelerates around the cylinder, reaching a maximum velocity of 128 m/s in the wake. This high-speed, unstable flow is the engine driving the noise. The static pressure contour in Figure 3 shows the details of this process. There is a high-pressure point at the very front of the cylinder (3169.85 Pa), where the flow stops. In the wake, behind the cylinder, the formation of vortices creates a large region of very low pressure, dropping to -7708.03 Pa. It is the constant, alternating creation of these low-pressure vortices that acts like a drumbeat, pushing on the surrounding fluid and creating sound waves.

Figure 3: Contours of static pressure around the cylinder, highlighting the high-pressure stagnation point at the front and the low-pressure wake region behind it.

Figure 4: Velocity streamlines from the Fluent simulation, visualizing the von Karman vortex street and high-velocity zones that generate noise.