On the use of (U)RANS and LES approaches for turbulent incompressible single phase flows in nuclear engineering applications

Abstract

The present paper gives some ideas and guidelines one should keep in mind while running (U)RANS or LES computations. The paper starts with (U)RANS approaches, advocating the use of Reynolds Stress Models for complex flows and recommending further work on modeling of turbulent heat fluxes, which remains today too basic in industry. The superiority of wallresolved models vs. wall-modeled in RANS is recalled and the use of adaptive wall treatment is suggested. The concept of Unsteady RANS is finally questioned. Then, important issues around LES are raised. The mesh refinement criteria are recalled for wall-resolved LES and the use of wall models addressed. The production of DNS and wallresolved LES calculations for flow understanding and RANS validation is encouraged.

Direct numerical simulation of fluid flow in a 5x5 square rod bundle

“…Pseudo-2D calculations [6] have been performed with the commercial finite volume code STAR-CCM+ [1] to estimate the Taylor microscale (𝜆 = √ ). The results have been used to design the LES and DNS numerical experiments performed with Nek5000 [7]. The DNS mesh has been designed such that the distance between Gauss-Lobatto-Legendre (GLL) points is smaller than min( 𝜆 2 ,η).…”

Advanced benchmark of the flow through a mixing vane grid – Large eddy simulation validation

“…In order to perform industrial and affordable computations, wall-modeled LES is used, especially by EDF and CEA (see below for the particular case of Framatome). This approach might give correct mean values (see Benhamadouche [13]). However, its use is still subject to discussion and objections (see Piomelli [14]) and this approach using wall functions concepts can also be seen as a very first step of hybrid RANS/LES technique (using a logarithmic profile for example).…”

Mitigating Hydrogen Risks in Light-Water Nuclear Reactors: A CFD Simulation of the Distribution and Concentration

“…The study demonstrated that CFD could provide accurate and reliable predictions of fluid flow and heat transfer in complex geometries and for non-Newtonian fluids. In addition, CFD has been used to study single-phase flows in nuclear engineering applications using both Unsteady Reynolds Average Navier-Stokes (URANS) and Large Eddy Simulation (LES) approaches [4]. The authors reviewed the use of URANS and LES approaches for turbulent incompressible single-phase flows in nuclear engineering applications.…”