TITLE:
Investigating the Effects of Interface Topology on Flow Development in Rod Bundle Supported by Spacer Grid with Split Mixing Vane Using STAR-CCM+
AUTHORS:
Vincent Yao Agbodemegbe, Edward Shitsi, Felix Ameyaw, Henry Cecil Odoi, Isaac Kwasi Baidoo
KEYWORDS:
CFD, Spacer Grid, Split Vane, Interface Topology, Turbulence, STAR-CCM+
JOURNAL NAME:
Journal of Power and Energy Engineering,
Vol.10 No.11,
November
30,
2022
ABSTRACT: Flow development downstream of a spacer grid is dependent on the upstream conditions and the imposed interface topology,especially at inlet and outlet boundaries. In STAR-CCM+,all interfaces fall into two groups, direct and indirect. A direct interface directly joins together two boundaries composingthe interface either permanently or temporarily, for the case of rigid body motion. An explicit connection is created between cells on each side of the interface,so that mass and energy or either of them will occur across the interface. Three options of interface topology namely, in-place, periodic andrepeating are available to be imposed at the inlet-outlet boundaries for a flowproblem. In the present work, computational fluid dynamic simulation usingSTAR-CCM+ was performed for the flow of water at a bundle’s Reynoldsnumber of Re1= 3.4×104through a 5 ×5 rod bundle geometry supported by spacer grid with and without split mixing vanes for which the rod-to-rodpitch to diameter ratio was 1.33 and the rod to wall pitch to diameter ratio was 0.74. The two-layer k-epsilon turbulence model with an all y+ automatic wall treatment function in STAR-CCM+ wasadopted for an isothermal singlephase (water) flow through the geometry with and without imposed cyclic periodic interface boundary condition of fully developed flow type at inletand outlet boundaries. The objectives were to primarily investigate the extent of predictability of the experimental data by the Computational Fluid Dynamic (CFD)simulation as a measure of reliability on the CFD code employed,and also study the effects of the imposed interface topology on flow redistribution in the presence and absence of split mixing vane. Validation of simulationresults with experimental data showed a good correlation of mean flow parameters with experimental data. Generally, the agreement of simulation results with data obtained from the experimental investigation confirmed the suitability of the CFD code, STAR-CCM+ to analyze the physical problem considered.Trends of flow redistribution downstream of the spacer grid indicate that, the split mixing vanes acted to quickly bring the flow to an equitable redistributiondownstream of the spacer grid irrespective of the imposed inlet-outlet interface topology. For the case of the spacer grid without mixing vanes, some extentsof deviation wererealized between the model with no imposed interface topology and that with imposed periodic interface topology. The variation in trends shows that, a much longer inlet segment of the domain is required to completely nullify the effect of the inlet-outlet interface topology on flow distribution in the absence of mixing vanes which may lead to a relatively higher demand forcomputational resourcesthan required in the presence of mixing vanes.