Instability of the cavitating flow in a venturi reactor

The instability characteristics of cavitating flow were experimentally investigated in a venturi tube in a recirculating flow loop. The fluctuation process of cavitation flow in the venturi was observed using high-speed photography. The sequential images were analyzed using the light intensity comparison technique and the cavitation length for each image was evaluated. The temporal cavitation length fluctuation vectors were determined at the specified operating condition (the cavitation number and operating pressure). The frequency components of oscillation were obtained using the fast Fourier transform (FFT) method. The effects of cavitation number and operating pressure on the Strouhal numbers and amplitudes of fluctuations were obtained. It was found that cavitation number has a major effect on the fluctuation characteristics of the cavitating flow in comparison with the effect of operating pressure. It was observed that at lower cavitation numbers, periodic separation, shedding and collapsing of the cloud-like cavities are observed together with the re-entrant jet motion. At higher cavitation numbers, the simple fluctuation mode with a sinusoidal pattern is observed.