Wind tunnel experiments were conducted to study the resonant interaction between turbulent flow field and an in-line square array of tubes with a pitch to diameter ratio of 2. The velocity of flow and the amplitude of a vibrating cylinder were measured with a Laser Doppler Velocimeter.
All tubes except one at the center were fixed and the center tube was flexibly mounted whose natural frequency was 13.3 Hz. The turbulent flow field was measured with both stable and unstable vibration of the center tube. The center tube was found to abruptly begin to vibrate with large amplitude at a certain fixed wind speed.
The auto spectra of the turbulence show distinct peaks for all velocities measured at various points in the tude bank. The frequency of the peak is proportional to the wind speed ; that is, the Strouhal number of dominant frequency is 0.16 based on the gap speed and the diameter of the tube. The auto spectrum of turbulence with a stably vibrating tube does not show any resonance between them. But the auto spectrum after the occurrence of instability show resonance in the vicinity of the flexibly mounted tube.
In the spectrum of turbulence just after the whirling instability, there are sharp peaks whose frequencies are multiple numbers of the tube natural frequency and the dominant frequency is about four times of the natural frequency. For slightly higher velocity than the critical velocity, four peaks (13.3, 26.6, 43, 56.3 Hz) are found and the last one is its dominant frequency.
