Different kinds of orifice are widely used as a resistance element to reduce pressure in various piping systems. However, due to strong shear and turbulence mechanisms around the orifice, it is susceptible to instabilities that generate pressure fluctuations and pipe vibrations. Especially when cavitation occurs, this effect can be very strong. The present work tries to characterize orifice-induced instability by means of numerical simulations and assess pipe vibration levels. Firstly, by taking an elongated orifice as an example, the fluctuating pressure around the orifice is obtained by a Large Eddy Simulation with a 2D unsteady model of cavitation. Secondly, the pipe vibration response is studied with experiment. The variation trends of pressure fluctuation and pipe vibration are analysed under different operation conditions. The results of the simulations can provide a good explanation for pipe vibration. A relationship between orifice cavitation-induced instability and vibration is established based on numerical simulations and experimental results.

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