Hybrid simulations of the near field of a split-vane spacer grid in a rod bundle

Three-dimensional, unsteady simulations of isothermal turbulent flows in a rod bundle with a split-vane spacer grid have been performed using a segregated turbulence model, which is a combination of scale adaptive simulations and large eddy simulations. These simulations have been conducted within the framework of an international blind CFD benchmark exercise. A finer mesh than that submitted to the benchmark exercise was used for the present study, which improved the agreement of the turbulence predictions with the measurements. For the first time, several vortices were identified in the vicinity of the vanes. The strongest among these vortices, which was a central vortex in the core of each subchannel, was generated by the vane pair in each subchannel. Each vane also created a strong stream across the gap between two rods and towards an adjacent subchannel. Axial profiles of turbulent kinetic energy in each subchannel core exhibited two peaks, a low peak in the near-vane zone and a larger peak one hydraulic diameter downstream of the vanes.