Improvement and validation of three-dimensional thermal-hydraulic analysis code (II); Task 1: Incorporation of k- two-equation turbulence model with COMMIX-1A

Muramatsu, Toshiharu; Maekawa, I.*; Ninokata, Hisashi; Aoki, Tadao

COMMIX-1A is a single-phase three-dimensional thermal-hydraulic analysis code with finite difference method developed at U.S.Argonne National Laboratory. The code is provided with one-equation turbulence model in terms of turbulent kinetic energy, k. However the major shortcoming of the model is that the transport of turbulent length scale is not accounted for. Therefore the supplementary equation related to the turbulent length scale has been added to the original model. The dissipation rate of turbulent kinetic energy has been selected as the unknown variable of the additional equation. The model governed by the set of two equations is thus called "k- model". The incorporated k- model in the COMMIX-1A has been validated in the analyses of the following three turbulence experiments: (1)Pipe flow, (2)Expansion flow and (3)Buoyancy flow. In turbulent pipe flow of Re=3.910, calculated velocity distribution agrees well within the error of 1 %, but distribution of k is underestimated by maximum 73% in the axial region. In the turbulent channel expansion flow case with backward facing step, calculated reattachment length is overestimated by 18 %. In the enclosed buoyancy driven recirculating flow case, calculated temperature, k and distributions have shown good agreement with those of the experiment with accuracy of second order in space.