Assessment of RANS models in predicting mixing flow induced by split-type vanes in rod bundle

Abstract

Turbulence model assessment is carried out based on particle image velocimetry (PIV) measurement data in a 5 × 5 rod bundle with split mixing vane for the nonlinear eddy viscosity models (NLEVMs) and the Reynolds stress transport (RST) model. The NLEVMs are applied with the two-layer wall treatment. The RST model is closed with the two-layer linear pressure strain model. The validation shows that the RST model is able to predict the mean flow vortices in the subchannel. The quadratic NLEVM predicts the similar, but smaller, vortices, while the cubic NLEVM fails to show the vortices. Comparing with the cross-flow velocities, prediction of axial velocity is relatively unsatisfactory. In general, the lateral normal Reynolds stresses are overpredicted by the models, while the axial normal Reynolds stress is underpredicted. In the near-wake region the lateral normal Reynolds stress can be reasonably predicted with the models, but the axial normal Reynolds stress cannot be predicted in a good accuracy. With the cubic term, the NLEVM predicts smaller normal Reynolds stresses, and especially small value of lateral component in the subchannel center. The NLEVMs which depend on local parameters, show relatively good prediction of the Reynolds stress in the subchannel center where the Reynolds stress is less influenced by the convection and diffusion effect. Invariant analysis of Reynolds stress anisotropy obtained with the models are carried out based on the Lumley triangle. Comparison of invariant analysis with large eddy simulation results of (Busco et al., 2019) indicates that the RST model can predict the far-wake turbulence anisotropy. The cubic NLEVM predicts non-realizable Reynolds stress close to the mixing vanes, while the quadratic model predicts inadequate turbulence anisotropy. All the models cannot predict the disk-like turbulence near the mixing vanes, which can be main reason of inaccurate prediction in the near-wake region.