High-Pressure Flow in Converging/Diverging Annulus with Cavitation under Near-Closing Conditions

Abstract

Summary Presented is a steady-state computational-fluid-dynamics (CFD) analysis of flow through a thick sharp-edge annulus (i.e., an orifice integrated with a rigid concentric cylinder, creating annulus flow conditions). With the upstream Reynolds numbers up to 435,000, the fluid studied is water and the percentage of closure of the annulus system is bounded between 50 and 97%. The various annulus geometries necessary to quantify annulus flow are identified and investigated using CFD tools. For the flow entering the converging/diverging annulus, two parametric models are developed from CFD simulation results. The first model estimates the downstream/upstream-pressure ratio when choked flow is started. The second model estimates a discharge coefficient for the annulus system. Using these models, the annulus volumetric flow rate can be estimated for both choked- and unchoked-flow conditions. The utility of these models is later demonstrated on a pseudosteady-state annulus flow problem where the annular blowout preventer (BOP) is closing.