Numerical Simulations of Developing Flow and Vortex Street in a Rectangular Channel with a Cylindrical Core

Abstract

Three-dimensional, unsteady simulations of developing turbulent flows in a rectangular channel containing a cylindrical rod have been performed to investigate their sensitivity to the choices of inlet boundary conditions and turbulence models. These effects have been examined by comparing the present predictions with experimental results and with previous predictions using the streamwise- periodic boundary condition. Among all methods, large eddy simulations (LES), employed in a downstream sub-domain of the channel as part of the segregated hybrid model, reproduced most accurately the experimental results. However, the unsteady Reynolds-averaged Navier-Stoke (URANS) simulations are still an acceptable choice for rod bundle analysis, making fairly accurate predictions with a much lower computational cost. Unsteady inviscid (Euler) simulations with a developed inlet velocity distribution predicted the onset of gap instability, which proves that this is an inviscid flow mechanism, associated with the azimuthally inflected velocity distribution. Previous URANS simulations with the streamwise-periodic boundary condition overpredicted the vortex street Strouhal number in rod-bundle flows, whereas the present URANS predictions for a developing flow with uniform inlet velocity were fairly close to the measurements.