PIV Experiment Research Of Lateral Flow Field In Rod Bundles Of Support Grids With Vanes

The thermal hydraulic performance in the fuel assemblies mostly depends the lateral flow characteristics generated by the mixing vanes of support grids. This paper has studied the lateral flow field in rod bundles of support grids with vanes both in particle image velocimetry(PIV) and CFD.This paper consists of three parts. The first part, the experimental facility was designed and constructed to measure the lateral flow field of rod bundles by PIV. The main work of this part was to study the flow field in cross-sections of 2x2 rod bundles scaled to be 2.5 times larger than the actual bundle size. Measurements were acquired at four Reynolds numbers ranging from 33000 to 45000 and for ten streamwise locations ranging from-2 to 9 hydraulic diameters downstream of the grid. The flow evolution downstream of the grid spacer was demonstrated through the comparison of the lateral velocity and axial vorticity for six vane angles of the mixing vanes ranging from 20° to 45° relative to the axial flow direction. The experiment results implied that the effects of the Reynolds number and vane angle in the lateral flow field are apparent. The second part, based on the experimental results, CFD modles have been built. Numerical simulation was performed at various operating conditions matching to the experiment using ANSYS CFX. The magnitudes and distributions of lateral velocity and vorticity were compared with the experimental data. The main objective of this part was to study the effect of turbulence models on the lateral flow field. The proper turbulence models to simulate flow in rod bundles were suggested based on the comparison to the experimental results. The results of numerical simulation validated the vorticity decreases downstream of the grid spacer and is affected by the Reynolds number and vane angle. The third part, based on the analysis and discussions of experimental and numerical results, the experimental facility was developed and a 5×5 experimental set-up was built. The rod bundles were placed vertically and the working fluid flowed from the bottom of the test section in an upward direction. The pressure drop in rod bundles were acquired by pressure transducer. The preliminary experiment of 5×5 rod bundles was conducted by PFV. This paper conducted the study of the lateral flow field in rod bundles of support grids with vanes both in particle image velocimetry(PIV) and CFD. The paper study reveals that the effects of the Reynolds number and vane angle in the lateral flow field.Some hydraulic data were obtained to benchmark numerical mesh and computational fluid dynamics(CFD) models. The contribution of this work is to provide the foundation for the experiments of the thermal hydraulic performance in the fuel assemblies.