Direct numerical simulation of turbulent forced and mixed convection of LBE in a bundle of heated rods with P/D=1.4

In this work, reference data obtained by means of Direct Numerical Simulations of fully-developed flow and heat transfer around a vertical rod bundle are presented. Finite-Volume computations are performed by an original discretization technique based on the representation of arbitrarily-shaped cylindrical boundaries on a non-uniform Cartesian grid. A periodic domain consisting of four subchannels of a triangular lattice of rods with a pitch-to-diameter ratio P/D=1.4 is considered as the reference geometry. A Prandtl number Pr = 0.031 is chosen to represent Liquid Lead-Bismuth Eutectic (LBE) as the working fluid. A single friction Reynolds number value is simulated, namely Reτ=550. Both forced and mixed convection regimes are investigated, buoyancy effects being introduced by imposing a Rayleigh number Ra = 5×105, corresponding to a Richardson number Ri = 0.22. Instantaneous snapshots and relevant statistics of the velocity and thermal fields are reported and discussed for the considered cases, focusing on the effect of aiding buoyancy on turbulent flow and heat transfer. Integral results are also compared against available literature data