The turbulent character and pressure loss produced by periodic symmetric ribs in a circular duct

The structural character and steady-state statistics of the turbulence inside a rib-wall circular duct is investigated by the large-eddy simulation (LES) methodology. The impetus of this study is to gain an understanding of the principle physics attributing to minimizing the pressure recovered (or maximizing the pressure loss) within the core flow. For a rib periodicity with height (h) to pitch (p) ratio p/h=5, the computational results show that the majority of turbulence produced due to the rib’s presence is concentrated near the rib crest leading edge. Pairs of counter-rotating streamwise vortices form soon after the leading edge that are quickly convected radially toward the core flow. The turbulent activity within the duct trough region is negligible compared to the turbulence levels of the core flow. At this rib periodicity, the separated shear layers from the trailing edge of each rib nearly reattach to the trough floor before reaching the next rib. The resultant irrecoverable pressure loss in the form a centerline frictional coefficient is verified by an ‘at-sea’ test on board a US Navy submarine. Based on the duct diameter, their Reynolds numbers are ReDLES=8×103 and (ReDexp)avg=4×106, respectively.