EFFECT OF GAS CONTENT ON THE CAVITATING AND NON-CAVITATING PERFORMANCE OF AN AXIAL THREE-BLADED INDUCER

In hydraulic systems, cavitation occurs in the liquid when its pressure locally drops below its vapor pressure. This can generate vibrations, noises, and instabilities in the flow that reduce the system performance. Cavitation has been the subject of many studies but the influence of dissolved gases in these operating conditions has remained unexplored. In the present work, an experimental study is conducted on a three-bladed axial inducer at partial flow rates in cavitating and non-cavitating regimes. A closed loop with a transparent test section and constant temperature water is used. In one of the tanks, a specific device is placed in order to inject CO2 and dissolve it in water. This device makes it possible to evaluate the dissolved CO2 rate effect on the performance of the inducer. A vacuum pump decreases the pressure in the loop. A high-speed camera filming the inducer suction in various conditions enables images to transmit at a sampling rate frequency of 1 kHz allowing comparison of the flow dynamics. Based on the pressure measurements, the flow rate, and the CO2 concentration, head versus net positive suction head (NPSH) curves are set for various Reynolds numbers. The results indicate that increasing the dissolved CO2 content decreases the inducer performance: the head breakdown occurs at higher NPSH, and it increases the cavitation intensity. In fact, as the degassing takes place small gas bubbles are noticed and the single-phase flow transforms into a two-phase homogeneous mixture.