Abstract
An LES was carried out to clarify the mechanism of decaying swirl in a rod-bundle. In our LES, an immersed boundary method was used to treat this complex wall boundary in the Cartesian grid system. A consistent immersed boundary method and a one-equation dynamic SGS model were introduced for an accurate simulation of no-slip wall condition. The Reynolds number based on the bulk velocity, the rod pitch and the kinematic viscosity was approximately 4100. Our computational results were compared well with experimental and computational data obtained in other studies. The results were able to represent the effect of flow geometry: the flow around the mixing-vanes caused the swirl with a large-scale fluctuation enhancing heat transfer; a vortex enhancing enthalpy mixing between channels was produced in the rod gap; this developing vortex and the decreasing wake promoted the decay of the swirl more strongly than in a pipe. The LES technique introduced in this study is useful for designing the spacer by predicting the effect of flow control.
