Two-phase fluid transient induced cavitation in cryogenic pipelines

A fluid transient is a phenomenon that occurs when the flow characteristics of a fluid network change abruptly in events of rapid opening and closure of the valve, failure of pump or fluid handling component. It produces a surge in the pressure followed by an oscillation of the pressure wave. When the fluctuating pressure during the fluid transient approaches or falls below the vapor pressure, vapor cavities form at the nucleation sites, leading to cavitation. Cryogenic fluid handling systems are susceptible to such fluid transients very often in practice. The cavitation can be characterized by the growth and collapse of the bubbles due to a high-pressure gradient. Bubbles in the vicinity of solid surfaces collapse more rapidly and produce high-velocity jets and pressure waves. The resulting pressure generated as a result of either of these can impart high stresses on the material that exceeds its yield strength and may cause damage. In this study, an attempt has been made to numerically model the two-phase fluid transient induced cavitation occurring due to sudden closure of the valve using the Finite Volume Computational Fluid Dynamics (CFD) approach. Also, a one-dimensional numerical model using the Method of Characteristics (MOC) is developed, incorporating the Rayleigh-Plesset equation for modelling bubble dynamics. Results from both models are compared and it is noted that the CFD excels MOC because it incorporates the radial variation and can better visualize the two-phase fluid transients. But, the MOC method is computationally less expensive compared to CFD. (author)