Investigation of Swirling Flow in Rod Bundle Subchannels Using Computational Fluid Dynamics

Abstract

The fluid dynamics for turbulent flow through rod bundles representative of those used in pressurized water reactors is examined using computational fluid dynamics (CFD). The rod bundles of the pressurized water reactor examined in this study consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids are often used to create swirling flow in the rod bundle in an effort to improve the heat transfer characteristics for the rod bundle during both normal operating conditions and in accident condition scenarios. Computational fluid dynamics simulations for a two subchannel portion of the rod bundle were used to model the flow downstream of a split-vane pair support grid. A high quality computational mesh was used to investigate the choice of turbulence model appropriate for the complex swirling flow in the rod bundle subchannels. Results document a central swirling flow structure in each of the subchannels downstream of the split-vane pairs. Strong lateral flows along the surface of the rods, as well as impingement regions of lateral flow on the rods are documented. In addition, regions of lateral flow separation and low axial velocity are documented next to the rods. Results of the CFD are compared to experimental particle image velocimetry (PIV) measurements documenting the lateral flow structures downstream of the split-vane pairs. Good agreement is found between the computational simulation and experimental measurements for locations close to the support grid.

Correlation for cross-flow resistance coefficient using STAR-CCM+ simulation data for flow of water through rod bundle supported by spacer grid with split-type mixing vane

“…14-17, although appreciable agreement of the simulation results of the RTL-K-E model with the NLS-K-E model and the SST-K-O models is evident for the mean flow parameters; wide deviation of the turbulent fluctuation is observed. Holloway et al (2006) in their investigation attributed the success of the SST-K-O model to their near wall treatment which relies on damping of the turbulent viscosity in low Reynolds number regions rather than a two layer wall treatment as implemented in the RTL-K-E model. A better prediction by the SST-K-O model and the non-linear models are also attested to in the works of Holloway et al (2006), Ruifeng et al (2012), Gandhir andHassan (2011) andHorvath andDressel (2012).…”

Development and Implementation of CFD-Informed Models for the Advanced Subchannel Code CTF

“…Several turbulence models were utilized, and subchannel geometry varied from a 5x5 subchannel layout to a single subchannel with appropriate boundary conditions and interfaces to make use of symmetry. Holloway et al (2006) [31] examined the flow downstream of a split-vane mixing spacer grid using a CFD code and comparing predictions of lateral velocities to experimentallymeasured PIV results. Fine details in the spacer grid are analyzed by using a spacer grid with weld cutouts and a spacer grid without weld cutouts at its mixing vane split pair location.…”

Drilling of Inconel 718 with Geometry-modified Twist Drills

“…In order to obtain accurate and reliable results, the numerical computations should be performed on a high quality mesh, which is also very challenging with respect to the complex geometry of the drilling tools [28,29]. Another very important point is the choice of an appropriate turbulencemodel [23,30].…”