This study analyzes various fluid behaviors in supersonic nozzles used in ultra-thick plate oxygen plasma cuttingapplications by implementing finite element analysis. In general, when cutting a thick plate the operation can beperformed through various methods, such as laser, plasma, and oxygen cutting. However, in the case of ultra-thickplates, the laser cutting efficiency degrades significantly; thus, plasma and oxygen cutting methods are used instead.
As the thickness of the cutting base material increases, the behavior becomes an important consideration. Previousstudies determined that the cutting quality and cutting speed at a given pressure were higher when using asupersonic nozzle than those observed when using a sonic nozzle. Therefore, the cutting efficiency is analyzeddepending on the supersonic nozzle shape when cutting ultra-thick plates of 100 mm or more. Five representativenozzle models were simulated, and the optimal conditions were confirmed by comparing each simulation result. Inconclusion, we confirmed that a divergent section length of at least 5 mm was required to ensure an effective flowchange in the supersonic nozzle; however, with a section length greater than 15 mm, the flow velocity in the pipedecreases owing to the reverse pressure gradient inside the nozzle.