Ducted Fan: Noise and Thrust

Ducted Fan: Noise and Thrust CFD Study, ANSYS Fluent

Description

This project simulates a ducted fan installed within a room, investigating both its acoustic behavior and thrust performance. Airflow enters the room through a doorway at 0.5 m/s, while an outlet is positioned on the wall where the ducted fan is mounted, with the fan itself rotating at 1000 rpm.

The 3D geometry was designed in Design Modeler, representing a 2×3 m rectangular room with a 2.5 m ceiling height and a 30 cm diameter fan. The domain was meshed in ANSYS Meshing, initially generating a tetrahedral mesh that was then converted to polyhedral elements to reduce element count and computational cost, totaling 699,432 elements.

Methodology

Gravitational acceleration was included in the negative Y-direction at 9.81 m/s², with the k-epsilon Realizable model employed to capture the expected wake structures and turbulence around the fan. A dedicated rotating zone was defined around the fan using the Moving Reference Frame (MRF) approach, while the Ffowcs Williams-Hawkings (FW-H) acoustic model was used to predict the resulting acoustic effects.

Conclusion

Two sound receivers were placed within the room to evaluate the fan's noise impact — one positioned directly in front of the fan (Receiver 1), and another near the room's entrance by the door (Receiver 2). Flow contours show air entering the domain at 0.5 m/s, forming a wake around the fan zone before exiting the domain, with the duct itself acting as a natural silencer that limits how far the fan's sound propagates.

As a result, while the sound pressure level remains high at Receiver 1 (closest to the fan), it drops to an acceptable range by Receiver 2, posing no concern for occupants near the entrance. This is confirmed by the A-weighted sound pressure level, which peaks at 80 dB — comfortably below the 120 dB threshold typically associated with harmful noise exposure. The simulation also reports a fan thrust force of 54.113455 N.