NUMERICAL STUDY ON THE TURBULENCE STRUCTURES IN CLOSELY SPACED ROD BUNDLE SUBCHANNELS

Fully developed turbulent flow through simulated rod bundle subchannels formed by a rod-trapezoidal duct was numerically studied. With a simple coordinate system transformation from an orthogonal cylindrical system to a nonorthogonal curvilinear system, the highly irregular flow passage of a rod-trapezoidal duct was converted to that of a regular rectangle. An empirical anisotropic eddy viscosity distribution based on existing experimental data was used in conjunction with the algebraic stress model to address the influence of coherent large-scale cross-gap eddy motion, whose existence in closely spaced rod bundle subchannels has been substantiated by extensive hot-wire measurements. Results of the calculation are compared with experimental data, with emphasis on secondary flow and turbulence kinetic energy. The credibility of this numerical scheme was established through a series of numerical tests on simple geometry flows.