Experimental characterization of cavitation zone and cavity oscillation mechanism transitions in planar cavitating venturis

Abstract

Cavitating venturi is a passive flow rate anchoring device used in varied industrial applications. The dynamics of the cavitation zone can be of interest to ascertain the controlled operation of cavitating venturi under varying pressure ratios. In the current work, we present the results of the complete characterization of three planar cavitating venturis with different divergent angles. Quasi-steady experiments are conducted for a pressure ratio range of 0.39–0.95 and an inlet Reynolds number range of 7.3 × 104–1.28 × 105. Shadowgraphy and high-speed imaging are used to obtain the cavitation zone length and the oscillation frequencies. Spectral proper orthogonal decomposition and discrete Fourier transform are used to assess the dynamics of the cavitation zone. The cavitation zone behavior has been delineated into three specific zones (named R1, R2, and R3 in this work) during the operation when the cavitation is fully contained within the divergent section. Two Strouhal number ranges (based on the inlet dimensions), StD,in≥ 0.1 for large-scale cloud shedding and StD,in≤ 0.05 for small-scale oscillations of the attached cavity, are ascertained as a primary indicator of the dynamic behavior. The current work confirms that the dynamics is governed by re-entrant jet at high cavitation numbers in R1 and the combined action of the re-entrant jet and the bubbly shock wave (collapse-induced) at low cavitation numbers in R3. The transition in the cavitation zone behavior in R2 primarily causes a shift in the sensitivity of the cavitation zone and the dominant frequencies over the operating pressure ratios. In the present work, we show that the span of the transition region (R2) decreases with an increase in the divergent angle.