An Experimental Study of the Flow-Induced Motions of a Flexible Cylinder in Axial Flow

Abstract

Experimental studies of the flow-induced lateral motions of a flexible tube in parallel flow are reported. The experiments were conducted in a 19.05 cm diameter test section of a blow-down type water tunnel. The flexible member, 1.59 cm in diameter and 7.92 m long, was fixed at the upstream end and free at the downstream end and was approximately neutrally buoyant. A fully-developed annular flow was realized in the test section. Photographs established the dependence of the flow-induced lateral motions on the mechanical properties, the flow velocity, and tension in the flexible member. Spectral analysis of the continuously-monitored data from an optical displacement sensor showed that the flow-induced lateral motions of the flexible member can be described as limited-band, stationary random processes. The maximum of the power spectral density shifted slightly as the flow velocity increased. The amplitude of the power spectrum attenuated rapidly with distance from the free downstream extremity of the cylinder.