Quiet rim driven ventilation fan design

Auxiliary ventilation fans are commonly used as a form of temperature and humidity control of working environments. However, they often generate high noise levels that cause permanent hearing impairment from prolonged exposure. Dominant noise sources from ventilation fans such as noise due to the aerodynamic interaction of the fan with the struts to support the hub motor and the blade-duct tip gap can be eliminated using a rim driven fan. However, tones from blade steady loading and thickness and the broadband airfoil self-noise of the fan are not eliminated. This noise is proportional to the 4-6th power of the tip speed. Hence, the approach here is to design a ring driven ventilation fan that reduces the fan tip speed while optimizing the blade profile to retain aerodynamic performance. The fan design has been 3D printed and implemented using a motor mounting system to validate the predicted performance. The motor mounting system integrates the fan design, a bell mouth shaped duct and a brushless DC motor. The experiments show good agreement with the predicted mechanical power, axial flow, and radiated noise over a range of speeds. Results suggest that a ring driven fan reduces noise while maintaining aerodynamic performance.