Drag Reduction on a backward-facing step: Effect of tabs and their spacing

The effect of vortex generators (tabs) on the drag and reattachment behind a backward-facing step was investigated using computational fluid dynamics (CFD) through StarCCM+. The 3D CFD simulations utilized a Realizable K-Epsilon turbulence model for a Reynolds-Averaged-Navier-Stokes (RANS) simulation. The simulation used a variable mesh size that was finer around the step and coarser in the free stream. The CFD was run for ten different configurations of the backward-facing step: one with no tabs, one with a single tab, and eight with various tab spacing. The simulations were run for a 12 m/s free stream velocity which ensured a turbulent Reynolds number of 24000. Once these simulations were run, the drag and lift coefficients were determined and the reattachment length of the flow was found for each configuration. The results were verified against existing experimental studies. The addition of vortex generators significantly altered the drag coefficient, mean flow field, and turbulent kinetic energy. Additionally, the reattachment length was found to vary in the spanwise direction when tabs were introduced.