Experimental Investigations on Flow Visualization and Numerical Simulation Analysis in Bundle Channels of 19-rod Helical Fuels

Based on the advanced measurement method of stereoscopic particle image velocity (SPIV), the visualization experiments on the 3D flow field distribution in bundle channels of 19-rod helical fuels with four blades were primarily performed, and the overall velocity field distributions in different cross sections were obtained. The axial and transverse velocity distribution characteristics for different-height cross sections under different flow velocities in spiral-fuel bundles were mainly analyzed. Moreover, in accordance with the visual experimental bundle test section in this paper, the numerical study models including structured grid partition and turbulence flow on the basis of the same structure as the experimental test section were established, and the numerical calculation and comparative analysis of the flow field distributions in 19-rod bundle assembly with four-blade spiral fuels under the same working conditions were carried out. The experimental and analytical results show that, the axial and transverse flow fields in the four-blade spiral fuel bundle channels are periodically distributed at different-hight cross sections along the increasing heights of the helical fuel assembly. For the axial velocity, the flow field under conditions of different velocities and different cross sections have a similar zonal distribution characteristic, and the internal channels shows higher axial velocity while the side channels as well as the corner channels have a relatively low velocity distribution. As for the cross-flow velocity, it flows along the rotation direction of the spiral fuel on the whole, and the flow field under different flow velocities also has a similar star-like distribution characteristic with significant transverse velocity typically distributed in the vicinity of grooves of helical fuel rods. The cross-flow velocity increases linearly with the axial flow velocity, and it is higher near the sunken zone of the four-blade spiral fuel. The numerical analysis results show that the calculated results of the axial velocity and transverse velocity based on SST k-ω turbulence model are in good agreement with the experimental data in terms of flow field distribution, and the SST k-ω turbulence model has good applicability to the analysis of flow field in 19-rod bundle channels of spiral fuels. The calculated results of flow field distributions also show an obvious characteristic of periodic distribution, which supports consensually the experimental data under different test conditions. In general, the average transverse flow velocity approximately holds a share of 1.6% in the axial flow velocity while the maximum cross-flow velocity accounts for the proportion of about 4% under different flow velocities and different cross sections.