Investigation on internal flow characteristics and cavitation mechanism of a counter-rotating cavitation algae removal device

Abstract

To address the ambiguous cavitation mechanism and limited algae inactivation efficiency of conventional hydrodynamic cavitation devices, this work systematically investigates a counter-rotating hydrodynamic cavitation device. Combining high-speed flow visualization and numerical simulations, it comprehensively analyzes complex flow structures and cavitation evolution within the rotor interaction gap. Through detailed analysis of velocity, pressure, and vortex structures, the multi-physical coupling mechanism of cavitation is thoroughly revealed. The superposition of radial and tangential velocities between counter-rotating rotors generates strong shear and induces periodic pressure pulsations. These pulsations act as the dominant driving force for cavitation inception. High-vorticity regions align well with low-pressure zones in spatial distribution. Low-pressure vortex cores provide essential hydrodynamic conditions for cavitation bubble nucleation and growth. In turn, cavitation phase change intensifies flow shear and turbulent fluctuations. It promotes the stretching and fragmentation of vortex structures. A bidirectional dynamic coupling pattern of vortices inducing cavitation and cavitation strengthening vortices is, thus, formed, along with a multi-scale cavitation-vortex-turbulence synergistic mechanism. In addition, Chlorella inactivation experiments are conducted at a rotor speed of 3200 rpm to quantitatively evaluate the biological treatment performance. Results show that after 20 min of treatment, the maximum absorbance of Chlorella decreases by 88.2%. These findings confirm that micro-jets and strong oxidative radicals from cavitation bubble collapse can effectively damage algal cell structures and photosynthetic systems.