Characteristics of low-frequency variations embedded in vortex-shedding process

Experiments were made to study the flow characteristics in the near-wake re gion of a two-dimensional bluff body, namely a trapezoidal cylinder (prism) or a circular cylinder. The instantaneous velocity signals obtained at the inner edge of the separated shear layer and in the neighbourhood of the re ar end of the vortex formation region show the presence of low-frequency va riations at Reynolds numbers of 10(4). The Pow-frequency variations noted i n the velocity signals and the base pressure measured at the bluff body app ear to be well correlated. These experimental observations suggest a physic al picture that the variations of vortex formation length and base pressure are closely related in a real-time manner. (C) 1999 Academic Press.