Drag reduction through flow around ribbed superhydrophobic cylindrical structures inspired by the giant saguaro cactus

doi:10.7523/j.ucas.2024.033

Abstract

Abstract:

The cylindrical structure finds extensive applications in ocean engineering， where the shedding of wake vortices can generate fluctuating drag that may induce vortex-induced vibrations， which can lead to equipment instability. Reducing the flow drag around the cylinder can help suppress vortex-induced vibrations. In recent years， the use of cactus-inspired riblets and superhydrophobic coatings has emerged as two efficient passive control strategies for drag reduction. This study combines these two methods to conduct experiments on drag reduction in underwater cylindrical flow. The experimental results demonstrate that surface riblets can decrease the drag on the cylinder， and the addition of superhydrophobic surfaces can further enhance drag reduction. Surface riblets extend the recirculation region while superhydrophobic surfaces shorten it. By utilizing Proper Orthogonal Decomposition to compute the phase-averaged flow field， it is found that， compared to hydrophilic cylinders， superhydrophobic surfaces lead to a reduction in the cylinder’s wake shear layer and cause the vortex to form closer to the cylinder， thereby shortening the recirculation region. Overall， the combination of surface riblets and superhydrophobic coatings effectively reduces the flow resistance around the cylinder， offering potential applications in flow control and drag reduction technologies.

Key words: drag reduction, cactus-inspired ribs, superhydrophobic, recirculation region, vortex structure

CLC Number:

O357

Xiaolong GONG, Zhaohui YAO. Drag reduction through flow around ribbed superhydrophobic cylindrical structures inspired by the giant saguaro cactus[J]. Journal of University of Chinese Academy of Sciences, 2026, 43(1): 23-32.

Figures/Tables 10

Fig.1 Cactus section model and cylinder design

Fig.2 Experimental model and flow field measurement

Fig.3 Distribution of time-averaged velocity streamwise component U at two streamwise positions

Fig.4 Time-averaged velocity U-profile on the centerline

Table 1 Recirculation region length Lr of different cylinders

	L_r
	光滑	12肋	24肋
亲水	1.031	1.115	1.188
超疏水	0.804	1.015	0.946

Fig.5 Velocity field statistics at different streamwise positions

Fig.6 Average drag coefficient CD and its component

Fig.7 The first ten POD modes and their energy proportions

Table 2 Vortex shedding frequency ofdifferent cylinders

	脱涡频率
	亲水	超疏水
光滑	2.85	2.61
12肋	3.23	3.15
24肋	3.23	3.23

Fig.8 Comparison of phase-averaged vorticity field between hydrophilic and superhydrophobic cylinders

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