Drag enhancement by turbulence on a fixed cylinder: Effects of aspect ratio and inclination angle

Direct numerical simulations are conducted to investigate the effects of height-to-diameter aspect ratio (H/D) and inclination angle on turbulence-induced drag enhancement for fixed cylindrical particles in laminar and turbulent flows. When the cylinder axis is perpendicular to the flow, drag enhancement decreases with decreasing aspect ratio due to the competing effects of (i) turbulence-induced pressure reduction on the rounded surface and (ii) reduced drag enhancement near the sharp edges. The trends in pressure and viscous drag enhancements are consistent with those of the total drag, with the downstream low-pressure region contributing more significantly to drag enhancement when it is located away from the sharp edge. Among various inclination angles, the influence of aspect ratio is most pronounced when the cylinder axis is normal to the flow. When the axis is aligned with the flow, drag decomposition reveals distinct trends depending on the aspect ratio: for short cylinders, pressure drag enhancement dominates due to the streamwise advection of low-pressure regions along the rounded surface; for long cylinders, viscous drag enhancement prevails, driven by the accumulation of large velocity gradients along the streamwise direction.