Galloping response of a cylinder with upstream wake interference

A compliantly-mounted rigid cylinder was towed at Re = 3 x 10(4), 4.75 diam eters behind a stationary leading cylinder of the same size. An in-line con figuration and a 12-degree staggered arrangement each produced large-amplit ude galloping responses, and an upward extension of the frequency lock-in r ange to a reduced velocity of at least 17. The frequency lock-in begins at nearly the same free-stream reduced velocity as a single cylinder, while a large phase change in the lift force occurs at higher reduced velocities, w hich can be extrapolated from the single-cylinder lock-in point. Force spec tra indicate that shedding from the upstream cylinder is completely unaffec ted by motions of the trailing cylinder. Furthermore, the motion-coupled pe aks suggest that only one lift force cycle and one or two drag force cycles occur per oscillation, the latter depending on the offset. (C) 2001 Academ ic Press.