On the contribution of saguaro cactus biological features in its aerodynamic advantages - A wind tunnel study

Abstract: This study explores the impact of ribs and domed-top on modulating the turbulent wake of a saguaro cactus, excluding the influence of spines and lateral arms. We systematically examine the flow dynamics around morphologically inspired cylinders with an aspect ratio of Ar = 5 at Reynolds numbers of Re = 1.2x10^4, based on the free-stream U? and diameter a. Four configurations are analysed: (i) simple circular cylinder (SC), (ii) domed-top cylinder (DC), (iii) ribbed cylinder (RC), and (iv) cactus-like cylinder (CC). Extensive measurements are conducted to analyse aerodynamic forces, shedding frequencies and velocity fields. The results indicate that the CC configuration achieves up to a 14% drag reduction and that the Strouhal number increases for both RC and CC compared to the SC. Additionally, the vortex formation length is the shortest for the CC, and the peaks of Reynolds normal stress nearly disappear close to the free-end in this case. While both cactus-inspired features attenuate the strength of spanwise vortices, the ribs have a markedly more significant effect on wake modulation than the domed top. Keywords: Turbulent wake flow, Saguaro cactus, Particle image velocimetry, Oil visualization