Numerical analysis on the flow field structure and deflection characteristics of water jets under nozzle moving conditions

Abstract

High-pressure water jets under nozzle moving conditions are widely utilized for rock breakage in geotechnical engineering. The nozzle motion state significantly influences the jet flow field and flow characteristics, thus changing its rock-breaking performance. In this paper, a single-jet nozzle model with different traverse speeds was established to investigate the jet flow field features and deflection characteristics and analyze the effects of nozzle traverse speed and jet pressure through numerical simulations. The jet flow fields under nozzle fixed and moving conditions were compared in terms of the distributions of vorticity, velocity, pressure and turbulence kinetic energy, and deflection characterization. Jet flow patterns photographed by an ultra-high-speed camera indicated the deflection of the jet flow field under the nozzle moving condition. The simulation results show that the flow field structure of the moving jet contains the non-deflection zone and deflection zone. The jet time-averaged velocity and vorticity are distributed symmetrically in the non-deflection zone, which is similar to the flow patterns under the nozzle fixed condition. As the jet prolongs further, the vorticity value increases and the vorticity distribution is more concentrated and closer to the nozzle outlet in the moving direction owing to more intense turbulence, resulting in the non-self-similarity of jet velocity dimensionless distribution on cross-sections and jet flow deflection to the opposite direction. The faster the traverse speed and the lower the jet pressure, the greater the jet flow deflection degree. The jet centerline velocities decay exponentially with the standoff distance, and the attenuation degree increases as the traverse speed increases. As the standoff distance increases, the jet deflection distance increases in a quadratic parabola and the deflection angle and impact angle both increase linearly, and decrease exponentially with increasing jet pressure. There is a positive relationship between the jet deflection characterization and the traverse speed.