C. Norberg, AN EXPERIMENTAL INVESTIGATION OF THE FLOW AROUND A CIRCULAR-CYLINDER - INFLUENCE OF ASPECT RATIO, Journal of Fluid Mechanics, 258, 1994, pp. 287-316
The investigation is concentrated on two important quantities - the St
rouhal number and the mean base suction coefficient, both measured at
the mid-span position. Reynolds numbers from about 50 to 4 x 10(4) wer
e investigated. Different aspect ratios, at low blockage ratios, were
achieved by varying the distance between circular end plates (end plat
e diameter ratios between 10 and 30). It was not possible, by using th
ese end plates in uniform flow and at very large aspect ratios, to pro
duce parallel shedding all over the laminar shedding regime. However,
parallel shedding at around mid-span was observed throughout this regi
me in cases when there was a slight but symmetrical increase in the fr
ee-stream velocity towards both ends of the cylinder. At higher Re, th
e results at different aspect ratios were compared with those of a 'qu
asi-infinite cylinder' and the required aspect ratio to reach conditio
ns independent of this parameter, within the experimental uncertaintie
s, are given. For instance, aspect ratios as large as L/D = 60-70 were
needed in the range Re approximate to 4 x 10(3)-10(4). With the small
est relative end plate diameter and for aspect ratios smaller than 7,
a bi-stable flow switching between regular vortex shedding and 'irregu
lar flow' was found at intermediate Reynolds number ranges in the subc
ritical regime (Re approximate to 2 x 10(3)).