CFD Analysis of Supercritical Converging Flow Structure

Rapid advances in state-of-the-art computational fluid dynamics (CFD) analyses are being made in simulating multi-phase flow fields, particularly where fluid-structural member interactions, air-water interfaces (free surfaces), and bubbly mixtures are involved. Coupled equations link the Navier-Stokes equations of fluid motion with structural deformation equations to simulate both fluid and structural response to either steady-state or transient boundary conditions. Consequently, defensible calculations that are based on the best formulas used in engineering practice can be utilized for comprehensive hydraulic structural design. Problems associated with frothy free surfaces, bubble formation, and air migration can now benefit from CFD implementation of research results regarding two-phase, air-water flow. A case study which illustrates the benefits of CFD analyses to guide difficult hydraulic structure designs is presented. The case study consists of supercritical flow in a steep pipeline with sharp curves and converging flows. The pipeline normally flows under open-channel flow regime, but air bulking and run-up could potentially cause undesirable hydraulic performance. The CFD analysis was used to evaluate these turbulent flow conditions which could reduce the pipeline flow capacity and cause other undesirable flow characteristics. Information determined from the CFD analysis provided valuable guidelines in developing the final design.