LES study of windward-face-mounted-ribs’ effects on flow fields and aerodynamic forces on a square cylinder

Abstract

Building-façade-mounted appurtenances are found to be effective for reducing wind loads on high-rise buildings. In this study, large eddy simulations (LES) are performed to investigate the effects of windward-face-mounted ribs on aerodynamic forces acting on a square cylinder of width D under smooth flow. The flow fields, wind pressure distributions and aerodynamic forces on different models are examined to clarify the underlying mechanism of the mitigation of wind load caused by vertical ribs. It is found that local recirculation forms in the front corner region, which greatly influences the flow separation and modifies the behavior of shear-layer flow. Three typical flow patterns around cylinders with different rib depths d are identified: full separation flow (0<d/D ≤ 0.105), periodic attachment flow (0.105<d/D ≤ 0.12), and steady attachment flow (d/D > 0.12). The wake vortex structures, vortex shedding frequency and wind pressure distribution are significantly different under these three flow patterns. The flow field changes result in remarkable mitigation of mean drag C‾d and fluctuating lift C'l. Optimal combinations of location b and depth d of ribs are also investigated. In these optimal cases, the shear layer first separates from the rib's leading edge and then passes by the cylinder's leading edge. The maximum reduction ratios of C‾d and C'l reach 50% and 86%, respectively, when d/D = 0.12 and b/D = 0.10. An empirical configuration equation of the vertical ribs is finally proposed by fitting results of optimal combinations.