Abstract
Ventilating fans usually have silencers connecting to the suction side and to the delivery side of the fan. A fan with a silencer box designed to save space in duct systems has been developed and produced. A study to develop a quieter multi-blade centrifugal fan with a silencer box has been examined for exchanging the ordinal fan with a silencer box for a newly designed fan with the box. It was uncertain in the initial stage that air-rubbing noise from surface flow over the absorptive liner inside the silence box was the main noise source induced by higher flow velocity in the passage of the silencer. However, the result of analysis of the computational fluid dynamics with respect to this ordinal fan system indicated that the separated flow of the silencer splitter induced a biased flow at the inlet of the fan impeller. It was also estimated that this biased flow at the inlet acted as the dominant aerodynamic noise source. The situation of the biased flow at the inlet of the impeller was recognized by flow visualization using the tuft method. Various shapes of the silencer splitter designed by trial and error were studied with numerical flow analysis and experiments taking into account flow visualization and noise measurements to determine which shape improved the separated flow and the biased flow at the inlet of the fan impeller. In the final stage, we identified an optimal design for the silencer splitter which does not induce the biased flow at the inlet
