Numerical investigation of quasi-periodic flow and vortex structure in a twin rectangular subchannel geometry using detached eddy simulation

Abstract

The hybrid Unsteady Reynolds-Averaged Navier–Stokes (URANS)/Large Eddy Simulation (LES) methodology was used to investigate the flow dynamics and associated gap vortex structure in compound rectangular channels for isothermal flows. The specific form of the hybrid URANS/LES approach that was used is the Strelets (2001) version of the Shear Stress Transport (SST) based Detached Eddy Simulation (DES). The DES-SST model was used to study quasi-periodic flow across a gap connecting two rectangular sub-channels on which extensive experiments were conducted by Meyer and Rehme (1994). It was found that the DES-SST model was successful in predicting the characteristics of the flow field in the vicinity of the gap region. The span-wise velocity contours, velocity vector plots, and time traces of the velocity components showed the expected cross flow mixing between the sub-channels through the gap. The dynamics of the flow field were quantitatively described through temporal auto-correlations, spatial cross-correlations and power spectral functions. The numerical predictions were in general agreement with the experiments. Predictions from the model were used to identify different flow mixing patterns. As expected, the simulation predicted the formation of a gap vortex street which results in a quasi-periodic flow through the gap. Coherent structures were identified in the flow field to be comprised of eddies, shear zones and streams. Eddy structures with high vorticity and low pressure cores were found to exist near the vicinity of the gap edge region. A three dimensional vorticity field was identified and found to exist near the gap edge region. The instability mechanism and the probable cause behind the quasi-periodic fluid flow across the gap was identified and related to the inflectional stream-wise velocity profile.