EXPERIMENTAL-STUDY OF CELLULAR SHEDDING VORTICES BEHIND A TAPERED CIRCULAR-CYLINDER

The dynamic behavior of shedding vortices in turbulent wake behind a t apered circular cylinder is experimentally studied by hotwire measurem ents in a low-speed wind tunnel. Four tapered cylinders with the same fineness ratio but different tapered ratio are used in the investigati ons. The Reynolds number based on the cylinder's mean diameter ranges from 4.0 x 10(3) to 1.4 x 10(4). Data show that two to three constant- frequency vortex cells of the shedding vortices along the spanwise dir ection are observed in the operating Reynolds number range. The corres ponding Strouhal number based on the vortex shedding frequency and the cylinder's local diameter varies with respect to the taper ratio of t he cylinder. It is also found that most of the spanwise shedding vorti ces are well aligned across the intersection region of the vortex cell s except the vortex dislocation occurs to cause vortex lines discontin uous, in which the phase difference between the adjacent vortex cells jumps from pi to -pi. By applying the pseudo-visualization technique i n conjunction with the peak-valley counting method, a simplified model is proposed to explain the relationship between the velocity modulati on and the vortex dislocation. (C) 1998 Elsevier Science Inc. All righ ts reserved.