RIASSUNTO
ABSTRACT
Rust removal is a necessary step of surface coating treatment in shipbuilding and ship repairing industry. As one of the efficient and environment protecting application methods, the derusting technique using ultra-high pressure water jet is favorable in many developed shipyards. The straight cone nozzle, as a key part of ultra-high pressure water equipment which commonly used to clean the outer hull of ship vessels, is regarded as the main research object in this paper. The numerically simulates taking the internal and external flow fields of the nozzle into account was carried out via the volume of fluid (VOF) mode by CFD package. The cavitation effect which is frequently encountered in the case of high velocity flow condition was also included in this simulation. Two parameters that have a great influence on the hydrodynamics inside the nozzle are considered,including the convergence angle and aspect ratio. Some analysis results of axial velocity, turbulent kinetic energy, nozzle cavitation distribution are provided, and the influence of cavitation on water jet performance under different nozzle parameters is also briefly analyzed. Through comparing the cases in relation with different nozzle convergence angle and aspect ratio, it is found that when the convergence angle becomes larger the effect of cavitation on hydrodynamic performance becomes greater, the nozzle characterized by convergence angle of 30° and the aspect ratio of 2 has best hydrodynamic performance.
INTRODUCTION
The shipbuilding and ship repairing industry as one of the supporting industries in China, develops rapidly and makes great contribution to the economic growth in China. In the field of ship repairing industry, rust removal is a necessary process. However, the traditional gritblasting process are still wildly used for ship hull rust removal by far, although there are a lot of disadvantages related to it, such as inefficiency, environmental pollution and danger to operators (Qu, 2016).
The ultra-high pressure water jet technique (U-HPWJT) is a unique method that uses ultra-high pressure water pump to generate highly ultra-high velocity water jet through a nozzle. The U-HPWJT has the advantages of good cleaning quality, high cleaning velocity, environmental friendly and high safety performance. The U-HPWJT is used to perform various operating processes in industry, such as surface cleaning, material cutting, and crushing (Shi et al., 2014). With the development of industrial technology, the U-HPWJT has been greatly developed and has a good application prospect in industrial cleaning, hydraulic cutting, drilling and derusting (Han and Ma, 2016).