Semi-active method to control tonal noise from fans

摘要

Tonal noise originates from non-uniform flow that causes circumferentially varying bladernforces and gives rise to a considerably larger radiated dipolar sound at the blade passagernfrequency and its harmonics. This paper presents an overview of a semi-active method torncontrol tonal fan noise from axial and centrifugal fans using obstruction in the flow torndestructively interfere with the primary non-uniform inlet flow. The flow controlrnobstruction is located such that the secondary radiated noise is of equal magnitude butrnopposite in phase compared to the primary noise. Several analytical, numerical andrnexperimental methods to design and to locate the obstruction are summarized.