X-ray measurements within unsteady cavitation

The purpose of this work is to describe the two-phase flow structure of cloud cavitation. The experimental study is performed in a cavitation tunnel equipped with a Venturi-type test section. The geometry studied is characterized by a convergent angle of 18° and a divergent angle of 8°. It leads to regular large vapour cloud shedding. The flow is investigated by means of an X-ray attenuation device. Twenty-four collimated detectors enable the instantaneous volume fraction of the vapour phase to be measured at different locations of the two-phase flow. The X-ray intensity measurement mode enables fast data acquisition (1,000 Hz). The results are compared with double optical probe measurements. The influences of the velocity and the size of the cavitation area on the time–space distribution of the vapour fraction are studied. The convection velocity of the vapour structures is estimated. The mean distribution of the volume fraction of the vapour phase during the shedding cycle is computed using the phase- averaging method.