Parametric sweep assessment of cross-slit cylinders for passive drag reduction and wake modification.

This paper presents a detailed numerical investigation and parametric sweep assessment of cross-slit (CS) cylindrical configurations aimed at passive drag reduction and wake modification in low to transitional Reynolds number regimes relevant to marine and offshore applications. A series of two-dimensional laminar CFD simulations were performed at Reynolds numbers of 100, 150, and 300 to analyze the influence of slit width ratio (SWR = 0.10-0.25) and sweep angle on wake dynamics, drag, lift, and vortex shedding characteristics. . A systematic mesh-independence study with Grid Convergence Index estimates and time-step sensitivity analysis were conducted to ensure numerical reliability. The results reveal that intermediate sweep configurations (SWR = 0.15-0.20) effectively modify alternating vortex shedding and reduce wake by promoting early shear-layer reattachment. Compared to conventional and single-slit cylinders, the optimized CS designs achieved 26-32.5% drag reduction, up to 40-52.5% reduction in reattachment length,, and a 93.1% reduction in Strouhal number at Re = 100,, indicating weekened vortex shedding intensity, and modified wake topology Increasing Reynolds number enhanced flow instability, yet the optimized CS geometry retained improved hydrodynamic stability and reduced fluctuating lift amplitudes. Wake vorticity analysis confirmed that cross-slit perforations alter the coherent vortex street by delaying shear-layer roll-up and extending the near-wake region. The observed trends in drag reduction, wake stabilisation, and shedding frequency modification indicate that cross-slit cylinders serve as a promising passive hydrodynamic control mechanism with potential implications for offshore risers, underwater structural supports, and marine energy devices.