CFD aided design and experimental validation of an innovative Air Assisted Pure Water Jet cutting system

Water jet cutting has always been a promising technology because of its extreme simplicity and flexibility, even if it often suffers a lack of control on its process parameters, especially if compared to technologies such as laser cutting or electro-discharge machining. Recent studies have showed how the presence of water inside the orifice causes disturbances and instabilities which systematically affect the jet structure, both during the jet formation and the cutting process. These disturbances can be neglected in industrial applications, but they can play a relevant role in case of high-precision water jet machining. The aim of the research presented in this paper is to develop an innovative system able to modify the orifice flow field by means of a simple modification of the standard cutting head geometry; the system allows the controlled injection of air inside the primary orifice to prevent the jet instabilities and to adapt the level of jet coherence to the specific machining operation. The fluid dynamics aspects of the outflow process are investigated by means of a 3D numerical simulation with the Ansys Fluent CFD solver, while considerable experimental efforts are provided in order to validate the numerical model and finally evaluate the system performances on real case studies.