Numerical investigation on the orifice cavitating water jet considering the fluid viscosity’s effects on bubbles’ growth and collapse

Abstract

The initial radius of bubble t Time ρ m The density of mixture u m The velocity of mixture μ m The viscosity of mixture α The volume fraction of vapor phase ρ v The density of vapor phase u v The velocity of vapor phase R e Mass transfer source term connected to the growth of the vapor bubbles R c Mass transfer source term connected to the collapse of the vapor bubbles n Bubble number density F vap Evaporation coefficient F cond Condensation coefficient ℜ B Bubble radius 1 Introduction Cavitation is a common hydraulic phenomenon in nature, and the collapse of the bubbles will generate a significant force of impact. So, cavitating water jets are widely used in many engineering fields such as cleaning, cutting, mining and improving the fatigue strength of materials [1-5]. Many experiments and simulations have been conducted to investigate cavitating water jets [6-11]. Since the computational fluid dynamics (CFD) was put forward in 1950s, Abstract This paper attempts to investigate the effects of fluid viscosity on cavitation generation. Different from the traditional cavitation models in which the Rayleigh-Plesset equation is simplified neglecting the second-order term and the surface tension force term, the primitive R-P equations with different dynamic viscosity values are solved by mathematical software and numerical solutions are obtained. Then, the method of curve fitting is selected to get the approximate expressions of bubble radius about time. Based on the expressions, the rate of change of bubble radius about time under different viscous conditions can be approximately obtained which will be written as in-house code to enhance the traditional cavitation models by UDFs. Numerical simulations of high-speed water jets issuing from a nozzle are carried out. The simulated cavitation characteristics match the supercavity experiments very well. The result shows a more homogenous distribution of vapor volume fraction while the viscosity of fluid increases. The pressure and velocity also change more slowly and smoothly along the nozzle under more viscous conditions. Simulations of external flow fields are also made based on the modified model to show the cavitation characteristics under submerged condition.