Numerical Investigation of Flow Structure in Pipe Elbow With Large Eddy Simulation Approach

At the JAEA (Japan Atomic Energy Agency), the simulation code “MUGTHES (MUlti Geometry simulation code for THErmal-hydraulic and Structure heat conduction analysis in boundary fitted coordinate)” has been developed. MUGTHES employs LES (Large Eddy Simulation) approach to calculate unsteady thermal-hydraulic phenomena and the BFC (Boundary Fitted Coordinate) system to simulate complex geometry in the system. In this study, numerical simulations for pipe elbow flows in various curvature radius ratio (Rc/D) conditions at several Reynolds number conditions. By the numerical simulation in pipe elbow at a laminar flow condition of Re = 700, the numerical schemes and the evaluation method of metrics in BFC system are verified and an appropriate mesh arrangement for elbow pipe is considered. By the numerical simulations in pipe elbow with the ratio of Rc/D = 2 under turbulent flow condition of Re = 60,000, the LES approach using standard Smagorinsky model with wall function law is examined in comparison with the experimental results. Moreover, numerical simulation for the 1/3-scaled water experiment at Re = 3.7×10⁶ which simulates the primary cooling system of the JSFR (Japan Sodium-cooled Fast Reactor) is conducted. From comparisons of axial velocity profiles, applicability of MUGTHES to the elbow pipe flow is confirmed and the characteristic of three-dimensional flow structure relating to the structural integrity of the elbow pipe is discussed.