Flow-induced Vibration Generation Mechanism Of Two Tandem Circular Cylinders

The vibrations of many structures due to fluid flows reduce the life of the respective installations and must be taken into account in the design of the structures.The arrangement of the commercial installations is so complex that we should use the simplest laboratory model construction to study the vibration mechanism. Two identical cylinders in tandem arrangement could be chosen as the simplest case. We use hotwire to investigate the vortex structure in the wake behind the downstream cylinder and between the two cylinders. In the power spectra figure, we know that both cylinders vibrate at the natural frequency, and the vibration frequency didn’t change with the reduced velocity increased. O n the contrary, the vortex frequency increased as the reduced velocity increased. Using the laser vibrometer, we can calculate the vibration amplitude. For L/D = 1.2, 1.5, 2.0, 2.5, 3.0, after the vortex resonance, the vibration amplitude of the downstream cylinder is increased violently as the reduced velocity increasing.We used the PIV to investigate the wake structure behind the downstream cylinder and between the two cylinders. When we moved the hotwire behind the downstream cylinder horizontally, the frequency peak is weaker.Finally, we used the Pressure Scanner to get the pressure distribution on the cylinders, then calculate the lift coefficient and drag coefficient. With the amplitude data, wake structure and the pressure data, we can analyze the vibration generation mechanism.