This research investigates the acoustic performance of axial fans using a broadband noise source model, comparing a standard base fan with a modified version featuring perforated blades. The study aims to find out how perforation in the blades affects noise levels while keeping the efficiency of the aerodynamic system by testing and analyzing noise levels from both configurations. The comparison results will tell us a lot about how well blade piercing reduces noise in axial fans. This could lead to the creation of coolers that are quieter and work better in a wide range of situations, from HVAC systems to computer hardware.A reference paper called “Reducing the aerodynamic noise of the axial flow fan with perforated surface” guided this study.

Reference [1]: Yadegari, Mehdi, et al. “Reducing the aerodynamic noise of the axial flow fan with perforated surface.” Applied Acoustics 215 (2023): 109720.

Simulation Process

There are two separate domains in the simulation: a smaller circular region containing a fan rotor and a bigger domain around it representing the surroundings and the shroud. Next, the model is discretized into 4889858 and 10132179  polyhedral + Hexagonal cells as shown in Fig. 2. The multiple reference frames (MRF) method is used to model the rotating rotor of the fan. The fan is rotating with 2818rpm angular velocity. More importantly, the Broadband Noise Source acoustic model is our option for the current simulation. According to the reference paper, the SST k-ω model is utilized to account for the turbulent nature of the flow.

Figure 1: Polyhedra grid over 3D Axial Fan CFD Simulation

Post-processing

The acoustic power level plot shows how the base axial fan (Case 1) and the fan with perforated blades (Case 2) compare over a distance of about 5 meters. The overall sound profiles of both fan designs are similar, with the loudest noise levels happening within the first meter of the source. In general, the base fan (red line) has a little more acoustic power than the perforated blade fan (blue line), especially at the highest frequencies. The base fan hits almost 48 dB at the first peak, while the perforated blade fan hits about 43 dB. This is the most noticeable change. This proves that the design of the perforated blades works to lower the maximum noise output. As the distance from the fan rises, the acoustic power levels for both designs drop rapidly, converging to similar values beyond the 2-meter mark. The difference between the two cases, shown by the green line, shows how the open blade design cuts down on noise. The difference curve always indicates positive values, which means that the perforated blade fan has a lower noise profile across the whole range tested. However, the benefits decrease as the distance increases. After looking at this acoustic analysis and the velocity contour data, we can say that the perforated blade design makes a big difference in reducing noise, especially in the close-range area where fan noise is usually the worst. The perforated blades probably stop intense swirls from forming and lower turbulence, which makes the noise level lower overall.

Figure 2: Acoustic Power Level of  Fan Noise Acoustics CFD Simulation Using Broadband Noise Source Model

Figure 3: Velocity Distribution of  Fan Noise Acoustics CFD Simulation Using Broadband Noise Source Model