Flow-induced acoustic resonances of piping system containing closed side-branches are sometimes encountered in power plants. In U.S. NPP, the steam dryer had been damaged by high cycle fatigue due to acoustic-induced vibration under a power uprating condition. The steam piping systems of actual power plants often have nearly saturated wet steam condition. Resonance frequency at branch section is one of important factors for evaluation and prediction of acoustic resonance. However, the resonance frequency in steam condition could not be estimated by using theoretical equation since the end correction under steam condition is not clarified. In addition, sound speed in wet steam, which is evaluated by theoretical isentropic equation, may be different from practical sound speed in wet steam. Although there are several previous studies about acoustic resonance, most of them are not steam flow but air flow. In the present study, the end correction in each dry and wet steam and sound speed of wet steam was evaluated from experimental results of dominant frequency of fluctuating pressure. As a result, method for predicting resonance frequency by using theoretical equation in each dry and wet steam condition was proposed.

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