Flow dynamics around mesh wrapped wall-mounted circular cylinders

This study experimentally investigates the flow around emergent, wall-mounted circular cylinders wrapped in a nine-start bidirectional helical mesh. The motivation stems from the need to reduce local scour in hydraulic and offshore structures, where conventional porous coatings are prone to sediment clogging. The proposed bidirectional mesh acts as a passive flow control method to alter wake dynamics and also potentially enhance heat transfer in pin fin applications. Three mesh configurations with a fixed pitch of 2 d and varying heights, 0.01 d , 0.02 d , and 0.04 d (where d is the cylinder diameter), are evaluated. Experiments were conducted at a Reynolds number of 14,500 (based on cylinder diameter), using particle image velocimetry (PIV) to capture detailed velocity fields and analyze flow structures. At lower mesh heights, only minor deviations from the baseline (bare cylinder) flow are observed. However, the 0.04 d mesh notably reduces wake mean velocity, elongates the recirculation region, and distorts the near-bed wake structure. Instantaneous velocity fields and probability density function analysis reveal enhanced flapping of the separated shear layers at mid-wake for the 0.04 d case. Two-point correlation analysis shows that this configuration increases near-bed coherent structure size, while smaller mesh heights reduce spatial coherence. Upstream of the cylinder, the flow exhibits bimodal unsteadiness, marked by intermittent transitions between back-flow and zero-flow modes, indicating that the horseshoe vortex system is sensitive to mesh height. Reynolds stress distributions at the cylinder-bed junction further highlight that the 0.04 d mesh represents a threshold, beyond which significant changes in both upstream junction flow and downstream wake behaviour become apparent.