Generation of discrete frequency noise due to periodic vortex shedding from a streamlined body

Abstract

The mechanism of discrete frequency noise generated from a flat plate with a sharp trailing edge immersed in a uniform oncoming flow was investigated experimentally. The results show that discrete frequency noise is caused by the periodic shedding of Karman vortices, and the necessary conditions of its generation are summarized as follows: (1) There must be a dead flow region with a definite area of a sufficiently large scale. (2) The shear layers starting from the two separation points near the trailing edge of the body must be very strong on either or both sides of the plate. A flow model was introduced to estimate the sound-pressure level theoretically and was verified experimentally as useful. The characteristics of Karman vortex shedding from a rotating blade were also examined.