Energetic mechanism for wake modulation and reduced fluid-dynamic loads in saguaro-inspired wall-mounted cylinders

The saguaro cactus survives high winds due to a resilient trunk geometry that inspires aerodynamic drag reduction. While previous studies focused on idealized two-dimensional cylinders, this work experimentally investigates the more relevant case of a finite wall-mounted (or cantilevered) cylinder to unravel the aerodynamic roles of its longitudinal ribs and domed top. Using a combination of load-cell force measurements, hot-wire anemometry, and particle image velocimetry, we analyse the flow around four configurations: smooth circular cylinder (SC), domed-top cylinder (DC), ribbed cylinder (RC), and cactus-like cylinder (CC, with both morphological features). We first perform a Reynolds-number sweep of forces and shedding frequency over 5 × 10³ ≤ Re ≤ 5.5 × 10⁴. A detailed wake diagnostics is then presented at Re = 2 × 10⁴ and aspect ratio Ar = 5. The cactus-inspired geometry (CC) attains up to 14% drag reduction and an ≈ 32% increase in shedding frequency, effects primarily attributable to the ribs. In contrast with two-dimensional cylinders, the ribs do not primarily delay separation; rather they redirect the downwash. A redirected downwash aerates the cylinder base, reduces turbulent kinetic energy in the near wake and stabilises the flow. The domed top enhances this control synergistically near the free end. These features modulate the wake by disrupting large-scale shear layers, shortening the vortex-formation length, and suppressing turbulent kinetic energy. They also lead to a more periodic but energetically weaker vortex shedding, evidenced by a higher Strouhal number yet attenuated Reynolds stresses.