Three Dimensional Cross Flow-Induced Vibrations of Circular Cylinders in Tandem

Two elastically mounted cylinders with two degree of freedom (2-DOF) in tandem are numerically investigated at constant Reynolds number (Re=3900) within the subcritical range, and fixed spacing ratio (L/D) = 4. The two cylinders are identical with a moderate mass ratio m* = 7, and mass damping parameter, (m* + 1)ζ = 0.0117. Delayed Detached Eddy Simulation (DDES) model is utilized in the simulation. Three reduced velocities (Ur) of 3, 5, 14 are investigated to study the effect of vibration of the upstream cylinder (UC) with 2-DOF on the response of the downstream cylinder (DC). In addition, the associated wake patterns are investigated. It is noticed that the downstream cylinder shows a different behavior than that of a typical wake induced vibration (WIV) when the upstream cylinder which was initially in tandem with the downstream and was allowed to vibrate. It does not behave as a build-up process similar to the case when a fixed UC is used to vibrate. The mechanism of the concept “wake stiffness” is behaving differently, in the cases when the two cylinders had a synchronized motion as the wake is much complex than the case of a fixed upstream cylinder. However, the downstream cylinder response is significantly higher than that of the vortex induced vibration occurs at a single cylinder. Moreover, a completely different mechanism happens to describe the downstream oscillation when the two cylinders’ motion are not synchronized.