Direct Numerical Simulation of Fluid Flow in a 5x5 Square Rod Bundle Using Nek5000

TL;DR

This paper presents a detailed direct numerical simulation of flow in a 5x5 square rod bundle at Reynolds 19000 using Nek5000, providing insights into turbulence and flow physics relevant to nuclear reactor design.

Contribution

It offers one of the first publicly available DNS studies of multi-pin rod bundles, serving as a reference for flow physics and reduced-resolution modeling techniques.

Findings

Detailed velocity and Reynolds stress profiles

Analysis of turbulence anisotropy

Turbulent kinetic energy budget insights

Abstract

Rod bundle flows are commonplace in nuclear engineering, and are present in light water reactors (LWRs) as well as other more advanced concepts. Inhomogeneities in the bundle cross section can lead to complex flow phenomena, including varying local conditions of turbulence. Despite the decades of numerical and experimental investigations regarding this topic, and the importance of elucidating the physics of the flow field, to date there are few publicly available direct numerical simulations (DNS) of the flow in multiple-pin rod bundles. Thus a multiple-pin DNS study can provide significant value toward reaching a deeper understanding of the flow physics, as well as a reference simulation for development of various reduced-resolution analysis techniques. To this end, DNS of the flow in a square 5x5 rod bundle at Reynolds number of 19,000 has been performed using the highly-parallel spectral element code Nek5000. The geometrical dimensions were representative of typical LWR fuel designs. The DNS was designed using microscales estimated from an advanced Reynolds-Averaged Navier-Stokes (RANS) model. Characteristics of the velocity field, Reynolds stresses, and anisotropy are presented in detail for various regions of the bundle. The turbulent kinetic energy budget is also presented and discussed