Numerical investigation of arc and droplet dynamics in local dry underwater welding under varying ambient pressures

Abstract

A comprehensive numerical model was developed to investigate the effects of varying ambient pressures on arc and molten metal behaviors in local dry underwater welding (LDUW). The model accounted for the influence of ambient pressure on the thermophysical properties of plasma (mass density, specific enthalpy, specific heat, electrical conductivity, thermal conductivity, and viscosity), ensuring high accuracy of simulation results. The results revealed that increasing ambient pressure significantly concentrated the arc shape and altered the spatial distribution of metal vapor. This constriction fundamentally modified the arc plasma properties by reducing the effective heat transfer area and intensifying the interactions between plasma and molten metal. Key parameters such as arc temperature, plasma velocity, current density, and electromagnetic force all decreased with increasing ambient pressure, leading to reduced energy input to the weld pool. Furthermore, the increased ambient pressure altered the droplet transfer behavior. Higher ambient pressures reduced the droplet detachment frequency, while increasing droplet size due to the enhanced constriction of the arc and the altered surface tension forces at the plasma-droplet interface. To validate the numerical model, experiments were conducted using high-speed imaging to capture the real-time droplet processes, and the arc temperature distribution wad measured using spectroscopic methods. The experiments results showed excellent agreement with the simulation data, confirming the reliability of the model. This study provides valuable insights into the impact of ambient pressure on LDUW, offering a solid foundation for optimizing welding parameters to improve process efficiency and weld quality under varying high ambient pressure conditions.