Response characteristics of wake galloping of two square prisms to their relative position and flow velocity

Abstract

In this experimental study, fluid dynamic response characteristics of wake galloping between two square prisms of same size in tandem and staggered arrangement to their relative position and free stream velocity were investigated. An immovable square prism of size d was fixed at upstream side and another vibratile square prism was placed at downstream side. The relative position of the vibratile downstream prism to the upstream prism was varied in the range from 1.6 d to 3.1 d in stream-wise direction, and in the range from 0.0 d to 2.1 d in cross flow direction. The vibratile prism at downstream side is elastically supported at it's both end and is ristricted to vibrate in only cross-flow direction. Instantaneous displacement of vibratile prism was measured by means of Laser Displacement Anemometer, and degree of vibration was evaluated by rms value of the fluctuating displacement. At first, response characteristics of wake galloping to relative position and flow velocity were investigated by free-vibration experiments in tandem and staggered arrangements using a wind tunnel. From the experiments, it was found that the response characteristics can be classified into three patterns in relation to relative positions and free stream velocities. Then the wake galloping phenomena occurred in the free-vibration experiments were reproduced by forced-vibration experiments in a water channel to conduct flow visualization. The visualization results well explained the phenomena observed in the wind tunnel experiment.

Keywords

• wake galloping
• two square prisms
• tandem and staggered arrangement
• flow-induced vibration