Instabilities of blow-down type Venturi cavitation considering thermodynamic effect

It is known that thermodynamic effect of cavitation could not be ignored in liquids such as cryogenic liquids, refrigerants, and high temperature water. This effect could delay and suppress the further development of cavitation, thus improve the suction performance in cases of hydraulic machinery. However, the influence of thermodynamic effect on cavitation instabilities has not been adequately discussed. For this purpose, a series of systematically designed experiments of Venturi cavitation in a blow-down type cavitation tunnel have been carried out, using water as the working liquid at different temperatures. For the first time, the cavitation instabilities were analyzed and identified with controlled degrees of thermodynamic effect Sigma*. The mean cavitation length L*(c)(av) and three types of cavitation instabilities were recognized through an image post-processing method. A decrease of L*(c)(av) is observed with an increasing Sigma*. For all Sigma* conditions, cavitation surge (system instability), cloud shedding, and oscillations of the attached cavitation length occur at small, middle, and large pressure recovery number (kappa) conditions, respectively. The thermodynamic effect mainly influences the range of kappa for different cavitation instabilities. Cavitation surge and transition from cloud shedding to oscillations of attached cavitation length shift to a lower kappa with an increasing Sigma*.