LAUSR

One of the major problems in oil-hydraulic poppet valve is the deteriorated performance accompanied by occurrence of cavitation. This is mainly a consequence of lack in understanding of the cavitating jet, which has inhibited the development of sufficiently general and accurate models for prediction of its performance. In the current paper, a two-phase volume of fluid (VOF) methodology combined with Schnerr-Sauer cavitation model is employed to perform quasi-direct transient fully three-dimensional calculations of the cavitating jet inside a poppet valve, with special concern on the laminar-turbulent transition. The numerical results allow separate examination of several distinctive flow characteristics, which show agreeable consistency with experimental observation. The periodic evolution of cavitation structure is related to temporal development of large-scale structure. The potential core indicated by velocity distribution, however, assumes a similar flow pattern regardless of temporal evolution of large-scale eddy. According to the different flow characteristics, the transitional process is divided into several parts, including laminar part, waving fluctuation, cross-linked vortex segments and cloud of cavitating vortexes. A comprehensive discussion on the transition is performed based on the numerical results, with primary concern on the governing mechanisms, including the formation of coherent structure organized as paired vortex, development of instability together with its effects on the coherent structure, and interaction between the vortexes. The streamwise vorticity strength accounts for less than 10% of the total vorticity in the cross-link region. It reveals that the breakdown of paired coherent structure is a result of the successive pairing process generated from combination of longitudinal and circumferential perturbation, instead of the growth of streamwise vortices as in the case of submerged circular jet.