The aerodynamics of a cylinder submerged in the wake of another

Flow-induced fluctuating lift (CLf) and drag (CDf) forces and Strouhal numbers (St) of a cylinder submerged in the wake of another cylinder are investigated experimentally for Reynolds number (Re)=9.7×103-6.5×104. The spacing ratio L⁎ (=L/D) between the cylinders is varied from 1.1 to 4.5, where L is the spacing between the cylinders and D is the cylinder diameter. The results show that CLf, CDf and St are highly sensitive to Re due to change in the inherent nature of the flow structure. How the flow structure is dependent on Re and L⁎ is presented in a flow structure map. Zdravkovich and Pridden (1977) observed a 'kink' in time-mean drag distribution at L⁎≈2.5 for Re>3.1×104, but not for Re≤3.1×104. The physics is provided here behind the presence and absence of the 'kink' that was left unexplained since then.