Axial-flow-induced vibration of an elastic cylinder placed between two cylinders

This work aims to investigate experimentally the flow-induced vibration of an elastic cylinder placed between two rigid cylinders subjected to an axial flow. The center-to-center distances P 1 ∗ and P 2 ∗ between the elastic cylinder and rigid cylinders may or may not be the same, varying from ∞ (an isolated cylinder) to 1.21 where asterisk denotes normalization by the cylinder diameter D and/or the maximum axial flow velocity U m a x . The lateral vibration of the elastic cylinder is measured simultaneously with flow along the y and z directions, normal to and in the plane through the three-cylinder axes, respectively. Given a reasonably large dimensionless velocity U ¯ = 6 . 98 , the root-mean-square vibration amplitude A y r m s ∗ grows by only 7.3%, while A z r m s ∗ contracts by 19.5% as P 1 ∗ ( = P 2 ∗ ) diminishes from ∞ to 1.57, where the first letter of the subscript in A y r m s ∗ or A z r m s ∗ denotes the lateral vibration direction. However, a further decrease in P 1 ∗ ( = P 2 ∗ ) to 1.21 leads to an increase in both A y r m s ∗ and A z r m s ∗ . The two distinct behaviors are linked to the eddy motions in the gaps between the cylinders. In the latter case, the eddies are observed to move away from the rigid-cylinder wall and may actively interact with those near the elastic-cylinder wall, exciting shear-layer instabilities and subsequently causing an appreciably rise in u r m s ∗ around the elastic cylinder. Thus, A y r m s ∗ and A z r m s ∗ grow. On the other hand, such eddy and shear layer interactions are absent in the former case. Given a fixed P 1 ∗ and P 1 ∗ ≠ P 2 ∗ , A y r m s ∗ and A z r m s ∗ exhibit strong dependence on P 2 ∗ if P 1 ∗ ≥ 1.57 but not so much if P 1 ∗ 1.57. This dependence is linked to the distinct eddy motions between the two gaps of the cylinders.