Local cavitation due to water hammer

Abstract

The phenomenon of vapour cavitation due to water hammer is investigated ex-perimentally using high frequency pressure transducers (piezoelectric and strain gauges). The water hammer is caused by a sudden closure of a ball valve mounted at the end of the steel pipe. A short-duration pressure pulse, as well as high frequency cavitation pressure oscillations is observed. The high frequency pressure oscillations appear just after the vapour cavity collapse, whereas the pressure pulse does not occur immediately after collapse but is delayed from 0 to the water hammer period $2L/c$, s. The experiments have shown that the maxi-mum high frequency pressure oscillation, directly proportional to the pressure wave velocity, can be many times higher than the maximum water hammer pres-sure amplitude as well as short-duration pressure pulse. The influence of liquid evaporation duration and the steady state losses on the maximum high frequency cavitation pressure oscillation are shown. Growing pressure reduction is accom-panied by gas desorption from the liquid. The liberated air reduces the amplitude of the pressure increase and prolongs the period of oscillations. The experiments have shown that there are three phases of the maximum amplitude of high fre-quency pressure oscillations for each fixed steady state loss. The frequency of va-pour cavitation pressure oscillations depends on the duration of the oscillations. For the test cases, the frequency increases during the cavitation from ca. 400 to 900 Hz for steel pipes