Experimental investigation of cavitating flow around chamfered cylinders vertically inserted in a circular pipe

Abstract

An experimental investigation was conducted to study the cavitating flow around cylinders with different chamfer angles vertically inserted in a circular pipe. The experiments were performed in a variable-pressure closed-loop cavitation rig at a constant Reynolds number of Re=1.2×105 with cavitation numbers corresponding from inception to supercavitation. In practical hydraulic systems, numerous structures can be modeled as vertically inserted chamfered cylinders and the cavitation phenomenon can occur around such structures with serious side effects. This work is an attempt to understand the cavity dynamics and the influence of the chamfer angle θ on the characteristics of cavitating flows, with the aim of providing guidelines for designing relevant structures. The low- and high-speed images of the cavitating flow in different cavitation regimes were analyzed to investigate the dynamics of the cavitating flow around the cylinder with chamfer angle θ=60°. From the space–time diagram obtained from the high-speed series, it is found that for cavitation number σ>0.80, the shedding of the small vapor filaments is induced by interfacial instabilities; for cavitation number σ<0.75, the re-entrant jet accounts for the periodic shedding of the vapor clouds. In the transition region (0.75<σ<0.80), the shedding is caused by a complex combination of both mechanisms. The dominant shedding frequency, expressed as Strouhal number St, drops with the decrease of the cavitation number σ in the regime dominated by interfacial instabilities; while in re-entrant jet regime, it is almost insensitive to the change of the cavitation number σ. In addition, the influences of the chamfer angle θ on the inception condition, cavity length, pressure drop, and pressure fluctuation are also discussed in the present work. With the increase of θ, the cavitation resistance becomes better and the pressure drop through the test section decreases.