Investigation of retention of gases in transverse hydrophobic microgrooved surfaces for drag reduction

Wang, Bao; Wang, Jiadao; Dou, Zhaoliang; Chen, Darong

doi:10.1016/j.oceaneng.2014.01.015

Cited by 26 publications

(20 citation statements)

References 35 publications

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“…The experiment was done with a high-speed water tunnel, which is a closed circulation system, as shown in Figure 7(a) [17,18]. Water was driven by the pump and firstly flowed through the antirevolving part, which primarily prevented the revolving of the flow.…”

Section: Methodsmentioning

confidence: 99%

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Drag Reduction by Microvortexes in Transverse Microgrooves

Bao

Wang

Zhou

et al. 2014

Advances in Mechanical Engineering

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A transverse microgrooved surface was employed here to reduce the surface drag force by creating a slippage in bottom layer in turbulent boundary layer. A detailed simulation and experimental investigation on drag reduction by transverse microgrooves were given. The computational fluid dynamics simulation, using RNG k-turbulent model, showed that the vortexes were formed in the grooves and they were a main reason for the drag reduction. On the upside of the vortex, the revolving direction was consistent with the main flow, which decreased the flow shear stress by declining the velocity gradient. The experiments were carried out in a high-speed water tunnel with flow velocity varying from 17 to 19 m/s. The experimental results showed that the drag reduction was about 13%. Therefore, the computational and experimental results were cross-checked and consistent with each other to prove that the presented approach achieved effective drag reduction underwater.

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Section: Methodsmentioning

confidence: 99%

“…The test section of the water tunnel can measure the friction force of the sample directly [18] as shown in Figure 7(b). The sample was located at the middle of the tunnel and was supported through the center axle.…”

Section: Methodsmentioning

confidence: 99%

Drag Reduction by Microvortexes in Transverse Microgrooves

Bao

Wang

Zhou

et al. 2014

Advances in Mechanical Engineering

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“…3 Hydrodynamic drag reduction by such intact gas layer on textured superhydrophobic surface is a topic of intense current research interest. [4][5][6][7] It is a dynamic analogue of the non-wetting Cassie-Baxter state of water on superhydrophobic surfaces 8,9 that stimulated recent studies on the combined effects of surface wettability and the Leidenfrost phenomenon. 3,[10][11][12] Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Leidenfrost vapour layer moderation of the drag crisis and trajectories of superhydrophobic and hydrophilic spheres falling in water

2014

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We investigate the dynamic effects of a Leidenfrost vapour layer sustained on the surface of heated steel spheres during free fall in water. We find that a stable vapour layer sustained on the textured superhydrophobic surface of spheres falling through 95 °C water can reduce the hydrodynamic drag by up to 75% and stabilize the sphere trajectory for the Reynolds number between 10(4) and 10(6), spanning the drag crisis in the absence of the vapour layer. For hydrophilic spheres under the same conditions, the transition to drag reduction and trajectory stability occurs abruptly at a temperature different from the static Leidenfrost point. The observed drag reduction effects are attributed to the disruption of the viscous boundary layer by the vapour layer whose thickness depends on the water temperature. Both the drag reduction and the trajectory stabilization effects are expected to have significant implications for development of sustainable vapour layer based technologies.

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“…The latter mechanism is particularly important for surfaces subjected to turbulent flow. Entrapped gas was observed on various rough and structured surfaces that were immersed in water under static conditions (Bobji et al, 2009;Wang et al, 2014), and the periods of retention of air were compared showing a high dependence of surface structure and the mean time for the air trapped to disappear, ranging from approximately 35 minutes for surfaces with pillars and 25 minutes for surfaces with ridges (Bobji et al, 2009), to 1 hour for micro-grooved surfaces (Wang et al, 2014). Super-hydrophobic surfaces with ridges have been shown to retain air pockets for more than 8 hours under very small static water pressure of 50 mm (∼ 490 Pa), where the main factor to maintain the Cassie-Baxter state was the minimized environmental fluctuations such as no variation in temperature (Xu et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Quantifying the Durability of a Friction-Reducing Surface with Recoverable Superhydrophobicity

et al. 2021

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The durability of super-hydrophobic surfaces in fully immersed conditions is a major obstacle to their application in engineering applications. We perform an experimental study to measure the friction factor f d as a function of time for a new super-hydrophobic surface that is capable of recovering the Cassie-Baxter wetting state. Values of f d were obtained by measuring the pressure drop and volume flux of a turbulent water flow in a 1.5 metre long duct containing one super-hydrophobic wall. The Reynolds number of the flow was approximately 4.5 × 10 4 for all experiments. Reductions in f d were 29-36 % relative to a hydraulically smooth surface. The Cassie-Baxter state could be recovered blowing air through the porous surface for 10 minutes. The durability of the drag-reduction, as quantified by the relaxation time T in which the surface loses its superhydrophobic characteristics, were measured to be between 10-60 minutes depending on the initial head. The relaxation time T was highly dependent on the pressure difference across the surface. In contrast to models based on Darcy flow through a porous medium, the study indicates that there seems to be a critical pressure difference beyond which the Cassie-Baxter state cannot be sustained for the material under consideration.

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Investigation of retention of gases in transverse hydrophobic microgrooved surfaces for drag reduction

Cited by 26 publications

References 35 publications

Drag Reduction by Microvortexes in Transverse Microgrooves

Drag Reduction by Microvortexes in Transverse Microgrooves

Leidenfrost vapour layer moderation of the drag crisis and trajectories of superhydrophobic and hydrophilic spheres falling in water

Quantifying the Durability of a Friction-Reducing Surface with Recoverable Superhydrophobicity

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