Wind tunnel experiments were conducted to study the interrelation between turbulent flow field and a vibrating tube in a three-row five-column in-line square array of tubes with a pitch to diameter ratio of 2. The flow velocity and the displacement of a vibrating tube were measured with a Laser Doppler Velocimetry and two miniature accelerometers, respectively. All tubes except one at center were fixed and the center tube was flexibly mounted. The rms amplitude of the vibrating tube was measured for various flow velocities. A small peak of the amplitude was observed at reduced velocity of 9.5 or it's vicinity. It was ascertained to be a vortex induced vibration.
The autospectra of the turbulence show distinct peaks for all velocities measured at various points in the tube bank. The frequency of the peak is proportional to the wind speed; that is, the Strouhal number of dominant frequencies based on the gap speed are 0.116, 0.106 and 0.104 for natural frequencies of the vibrating tube of 14.6 Hz, 16.1 Hz and 19.5 Hz, respectively. It shows that Strouhal number get smaller as the natural frequency of the vibrating tube increases even in the same tube bank.
On arising of whirling instability, the amplitude in the streamwise direction increases more rapidly than in the lateral direction. The frequency of the vibrating tube increases as flow velocity does in the region of fluid-elastic instability.
It was found to be desirable that the flow velocity be measured at the down stream of the vibrating tube in case of vortex induced vibration, and at the up stream in case of fluid-elastic instability.
