Wind tunnel tests for mean drag and lift coefficients on multiple circular cylinders arranged in-line

Mean drag and lift coefficients were studied for groups of two, three, and four circular cylinders arranged in-line, in both smooth and turbulent flow conditions. Effects of varying surface roughness and cylinder size were also investigated. Reynolds numbers for the tests ranged from 2.7×104 to 8.6×104. The majority of the tests were conducted with cylinder arrays sequentially arranged, with their tops aligned on a plane parallel to the incoming free stream. The tested arrays also included combinations with unequal-diameter cylinders. Drag and lift force were measured separately on each cylinder. In many cases, results from smooth and turbulent flow experiments differed significantly. The critical spacing of three to four diameters reported in the literature for two cylinders in tandem in smooth flow was observed to occur in this study for the two-cylinder case as well as in three- and four-cylinder cases. This feature weakened or disappeared in turbulent flow. The force ratio F* was introduced as a measure of the net effects of shielding and interference on the mean drag of the entire cylinder group, which was found to be closely related to the number of cylinders in the group, turbulence and spacing.