Examples of unsteady CFD validation system response quantities in a cylinder array

A validation study for several CFD models of the time-varying flow through a confined bank of cylinders is presented. The geometry is cylinders arranged on equilateral triangles with pitch to diameter ratio of 1.7 to represent a scaled subsection of the lower plenum of a high temperature reactor. Time-resolved Particle Image Velocimetry (PIV) measurements, coupled with time-varying pressure measurements along the facility walls, are compared to the Unsteady Reynolds-Averaged Navier–Stokes (URANS) k − ω model and two variations of a Detached Eddy Simulation (DES) model. Spatial and temporal validation system response quantities (SRQs) on both the local and global scales were used for validation. The DES model accurately predicted frequencies present in the pressure along the walls next to the cylinders in the first and the last cylinder, yet predicted other dominant frequencies in the remaining cylinders that were not found in the experiment. As expected, the temporal behavior of the DES was generally far superior to that of the URANS model. A grid convergence study shows typical global quantities (such as pressure losses) converge well while temporal quantities converge poorly for the same grids.

► Unsteady validation of k − ω and DES models using high-speed PIV. ► Local validation SRQs, include frequency spectra, autocorrelations, and correlations, while global SRQs include rms values and distributions. ► The DES-NB model predicts good approximations for most unsteady validation SRQs. ► The k − ω and DES-B models predict oscillatory flow with amplitudes larger than the experiment. ► All CFD models are capable of accurately predicting global validation SRQs, such as the minor loss factor.