CHARACTERISTICS OF LOW-FREQUENCY VARIATIONS EMBEDDED IN VORTEX-SHEDDING PROCESS

Experiments were made to study the flow characteristics in the near-wake region 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 rear end of the vortex formation region show the presence of low-frequency variations at Reynolds numbers of 10⁴. The low-frequency variations noted in the velocity signals and the base pressure measured at the bluff body appear to be well correlated. These experimental observations suggest a physical picture that the variations of vortex formation length and base pressure are closely related in a real-time manner.