Cavitating Flows in Hydraulic Multidimensional CFD Analysis

The effect of cavitation plays a fundamental role in the hydraulic components design and the capability of predicting its causes and characteristics is fundamental for the optimization of fluid systems. In this paper, a multidimensional CFD approach is used to analyze the cavitating phenomena typical of hydraulic components using water as operating fluid. An open source fluid-dynamics code is used and the original cavitation model (based on a barotropic equation of state and homogeneous equilibrium assumption) is extended in order to account also for gases dissolved in the liquid medium. The effect of air dissolution into liquid water is modeled by introducing the Henry law for the equilibrium condition, and the time dependence of solubility is calculated on a Bunsen Coefficient basis. Furthermore, a simplified approach to turbulence modeling for compressible flows is coupled to the cavitation model and implemented into the CFD code. The turbulence effects on cavitating regions are addressed for different operating conditions. In the analysis, both basic geometries and water hydraulic poppet valves are addressed, and the numerical results are compared to experimental measurements available in literature. In particular, the reference test case with abrupt section change geometries, such as the forward facing step, is investigated. The recirculating regions, the vena contracta position, the reattachment point and the pressure and velocity fields are calculated under conditions where cavitation is expected. Furthermore, the diverging and converging flows in hydraulic valves are simulated and the influence of the seat shape on cavitation onset, pressure distribution and discharge coefficient is discussed.