Wake and Vortex-Sheddings from Different Diameter Cylinders in Tandem

The paper associated with two tandem cylinders presents the upstream cylinder size (diameter d) effect on global parameters of the downstream cylinder (diameter D) including time-mean and fluctuating drag (C-D, C-D'), fluctuating lift (C-L'), Strouhal number (St), and flow structures at spacing ratio L/d = 1.0-8.0, and diameter ratio d/D = 0.2-1.0, where L is the distance between the center of the upstream cylinder and the forward stagnation point of the downstream cylinder. The Reynolds number is kept constant at 4.27 x 10(4) based on D. C-D, C-D' and C-L' are measured using a sectional load cell, flow structures are obtained using a PIV technique. The critical L/d dividing the reattachment and coshedding flows is larger at smaller d/D. In the coshedding regime, the shedding frequency of the downstream cylinder locks-in with that of the upstream cylinder for d/D = 1.0, 0.8 and 0.6, in addition to a subharmonic lock-in for d/D = 0.6. The lock-in however does not occur at d/D = 0.4 and 0.2. C-D in general increases with d/D. C-D' and C-L' both generally wane and grow as d/D decreases from 1.0 to 0.6 and 0.4 to 0.2, respectively.