Geometrical transition properties of vortex cavitation and associated flow-choking characteristics in poppet valves

Poppet valves have become increasingly significant in ensuring precise digital flow rate and pressure control in hydraulic systems, necessitating a more profound understanding of the geometrical properties of cavitation in them, as well as associated flow-choking conditions. Through a comparative analysis with experimentally observed cavity images, we found that large eddy simulation (LES) turbulence modeling effectively replicates the geometrical properties of cavitation in these valves. The analysis demonstrated that cavitation is generated from vortices that result from the interaction between the notch contracta flow and the surrounding fluid structure. Variations in the internal or external vena contracta conditions result in fixed or discrete cavities, and the length-to-diameter ratio serves as a measure of the transition between internal and external vena contracta flow properties. This study establishes a threshold length-to-diameter ratio of approximately 2 for the tested poppet valves. More specifically, in notch structures with a smaller valve opening, longer sealing length, and smaller throttling angle (corresponding to a larger length-to-diameter ratio), the liquid-to-vapor transfer process is more evident than that in the reverse direction. A long-standing vapor cavity becomes fixed inside the notch, leading to a more pronounced flow-choking phenomenon. In contrast, for structures with a smaller length-to-diameter ratio, the cavitation process for discrete vapor cavities is more complete, ensuring fluid flow continuity and significantly reducing the occurrence of the flow-choking phenomenon.