Study on the influence of fluid viscosity on erosion characteristics in ultrasonic coupled abrasive jet polishing (UC-AJP)

In the ultrasonic coupled abrasive jet polishing (UC-AJP) process, the pulsed effect induced by ultrasonic vibration can effectively enhance the material removal efficiency. During the polishing process, the viscosity of abrasive flow significantly affects cavitation, pulse formation and kinetic energy transfer efficiency. However, the specific impact mechanism of the viscosity on the polishing process remains unclear. To address this challenge, a dynamic model of the UC-AJP was established based on the shear-stress transport (SST) k-ω turbulence model, combined with the discrete phase model (DPM) and the Oka erosion model. The effects of the ultrasonic vibration and the fluid viscosity on the turbulence kinetic energy and the erosion characteristics were analyzed. Fixed-point erosion and polishing experiments were conducted to validate the simulation results. The results indicate that increasing the ultrasonic amplitude can effectively enhance the erosion intensity. However, as the amplitude increases, the erosion range gradually expands due to the jet diffusion caused by the enhanced turbulence. Increasing the fluid viscosity can suppress the fluid turbulent motion, thereby improving the jet collimation, but it also leads to kinetic energy dissipation in the jet pulsations and consequently reduces the erosion intensity. The polishing experiments demonstrate that for workpieces with varying initial surface roughness levels, there exists an optimal viscosity range for each case, within which the lowest achievable surface roughness can be obtained after polishing. When the initial roughness of the workpiece is 100 nm, increasing the jet viscosity from 1.0 mPa·s to 3.5 mPa·s can reduce the roughness Ra by approximately 46%; however, for workpieces with an initial roughness of 900 nm, the roughness Ra increases by approximately 12%.