Influence of cavitation on the acoustic boundary conditions in water hammer experiments

Sebastian Klein,Michael Oschwald,Tobias Traudt

doi:10.1088/1742-6596/1909/1/012015

Abstract

A water hammer event is created by stopping a flow in a pipeline using a fast closing valve. The pressure is measured at three different positions upstream the valve. Cavitation occurs close to the valve and is detected by vapour pressure in the pipeline. Frequencies in the liquid part of the pipe were measured and statistically evaluated in order to analyse whether cavitation acts as a boundary condition of acoustics.Without cavitation one side of the pipe is an open end, while the other side is a closed end. In presence of cavitation the cavity should act like an open end due to the high change of acoustic impedance from liquid to gaseous phase. Therefore it is expected that the oscillating behavior is changing from an open/close to an open/open system. The measured frequencies indeed show a change towards an open/open configuration. It is shown that cavitation acts as a boundary condition in this system.

Highlights

Stopping a flow by closing a valve rapidly in a fluid system generates a high amplitude pressure wave which leads to acoustic oscillations inside the fluid system
In water hammer experiments cavitation occurs close to the valve, since pressure amplitudes are largest here. Such tests with an optical access have been performed at the Fast Transient Test Facility (FTTF) at DLR Lampoldshausen by Traudt et al [3] and Bombardierri et al [4]
Summary A hypothesis was made that cavitation in water hammer experiment acts as a boundary condition for pressure oscillations in the liquid part

Summary

Introduction

Stopping a flow by closing a valve rapidly in a fluid system generates a high amplitude pressure wave which leads to acoustic oscillations inside the fluid system. In water hammer experiments cavitation occurs close to the valve, since pressure amplitudes are largest here. Such tests with an optical access have been performed at the Fast Transient Test Facility (FTTF) at DLR Lampoldshausen by Traudt et al [3] and Bombardierri et al [4]. The influence of static pressure and the occurrence of cavitation on the damping of water hammer waves in the same experiment were investigated by Klein et al [5, 6]

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