Flow induced vibration measurement for a 4 x 4 rod bundle with spacer grids by the Laser Doppler Vibrometer

In order to develop a feasible method for measuring FIV of both spacer grid and rod, two experiments are conducted in this study. First, the simultaneous verification tests between the LDV and piezoelectric accelerometer have been performed. For the case of vibration occurring in a channel with water, the measured signal by the LDV need to be modified while not affecting the measured vibration value. The results show that the LDV is a good candidate for measuring vibration under flow conditions. Then, the LDV is employed to measure the FIV of a specified 4 x 4 rod bundle with spacer grids. Both turbulence and vortex excite the rod bundle, and a strong vortex induced resonance is found when the flow velocity is 7.35 m/s. The vibration intensity is amplifying with increasing the flow velocity. Moreover, 'lock-in' phenomenon and two types of vortex shedding with St numbers of 0.15 and 0.26 are found. (c) 2021 Published by Elsevier Ltd.

Automated summary

Two experiments were conducted in this study to develop a feasible method for measuring FIV of both spacer grid and rod. The first experiment involved verification tests between LDV and piezoelectric accelerometer, while the second experiment utilized LDV to measure the FIV of a specified 4 x 4 rod bundle with spacer grids. Results showed strong vortex-induced resonance and increasing vibration intensity with flow velocity, along with the discovery of 'lock-in' phenomenon and two types of vortex shedding.