Experimental Study of Thermal Cavitation in an Orifice

Some experimental tests were performed studying the flow of water thought an orifice, in order to investigate the onset of the various cavitation structures and the effects of cavitation at different cavitation numbers and temperature. Different flow rates have been tested for different values of temperature. The results show that the cavitation originates at the inlet of the flow constriction area. It grows intensively and transforms into a cavitating cloud. As flow rate was increased, it was observed that the cavitating cloud travels downstream of the hole oscillating around the exit position and it is connected to the hole inlet through a sheet having a complex turbulent structures. The decrease in the cavitation number causes a corresponding increase of the width of the cavitating area especially in proximity of the critical cavitation number. In particular, it was observed that the critical cavitation number increases as the temperature increase. The behavior of the cavitation phenomenon can be related to the pressure fluctuations measured downstream of the orifice; a Fourier Transform of the downstream pressure signal was performed. The development of the cavitation phenomenon for lower cavitation numbers affects the pressure frequency components, related to the impacts due to vapor bubbles implosions. Finally, soma numerical simulations have been performed; the simulation results were compared with the experimental ones.