An Experimental Stability Analysis of a Single Flexible Cylinder Positioned in an Array of Rigid Cylinders and Subject to Cross-Flow

Abstract

The fluidelastic response of a single flexible cylinder in an array of rigid cylinders, subject to cross-flow, has been investigated. Experiments were done in two wind tunnels on three different types of array: (i) a double row in-line (square) array, with pitch-to-diameter ratio P /d = 1.5; (ii) a triple row staggered (rotated-square) array, with P /d = 1.5 2; (iii) a double row version of (ii) . The modal damping logarithmic decrement was varied in the range 0.01 to 0.46. Measurements of vibration were made in both the in-flow and cross-flow directions, taking not only the vibration amplitudes, but also the power spectral density of the response over a wide frequency range and over a broad range of flow velocities. This permitted a more detailed examination of system behavior, prior to, at, and beyond the threshold of fluidelastic instabilities, as well as a better definition of the onset of instability. Fluidelastic instability was observed for downstream cylinders of both the in-line and staggered arrays, the motion in both cases being predominantly in the cross-flow direction. However, in the in-line array, further increase in flow velocity tended to shift the instability to one involving mainly in-flow motion.