A prediction of drag reduction by entrapped gases in hydrophobic transverse grooves

Wang, Bao; Wang, Jiadao; Chen, Darong

doi:10.1007/s11431-013-5395-y

Cited by 13 publications

(6 citation statements)

References 33 publications

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“…The numerical simulation is of great help to understand the characteristics of flow field. For some complex problems, it is difficult to present the analytical solutions and numerical simulation is a kind of effective method [15,16]. Here, the numerical simulation was chosen to study the boundary layer structure when liquid flows over the transverse microgrooved surface.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…The grid spacing increased from the walls by aspect ratio of less than 1.1 to get a structured mesh. A renormalized group (RNG) -model, which had an additional term in its equation that significantly improves the accuracy [15], was used for turbulence modeling [15,16]. An implicit solution scheme was used in combination with an algebraic multigrid method to achieve faster convergence.…”

Section: Numerical Simulationmentioning

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: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

Drag Reduction by Microvortexes in Transverse Microgrooves

Bao

Wang

Zhou

et al. 2014

Advances in Mechanical Engineering

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“…However, when the grooved structure is optimized to minimize the extra pressure, a stable drag reduction can be achieved for a long time because the entrapped gas cannot be easily discharged from the surface. Wang et al [92,93] proved that a transverse grooved surface could achieve underwater drag reduction based on theoretical and experimental investigations; more than 10% drag reduction rate was achieved at an optimized surface structure.…”

Section: Drag Reduction Of Other Surfacesmentioning

confidence: 99%

Underwater drag reduction by gas

Wang

Chen

2014

Friction

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Publications on underwater drag reduction by gas have been gathered in the present study. Experimental methods, results and conclusions from the publications have been discussed and analyzed. The stable existence of gas is a requirement for underwater drag reduction induced by slippage at the water-solid interface. A superhydrophobic surface can entrap gas in surface structures at the water-solid interface. However, many experimental results have exhibited that the entrapped gas can disappear, and the drag gradually increases until the loss of drag reduction with immersion time and underwater flow. Although some other surface structures were also experimented to hold the entrapped gas, from the analysis of thermodynamics and mechanics, it is difficult to prohibit the removal of entrapped gas in underwater surface structures. Therefore, it is essential to replenish a new gas supply for continued presence of gas at the interface for continued underwater drag reduction. Active gas supplement is an effective method for underwater drag reduction, however, that needs some specific equipment and additional energy to generate gas, which limits its practical application. Cavitation or supercavitation is a method for passive gas generation, but it is only adaptive to certain vehicles with high speed. Lately, even at low speed, the evaporation induced by liquid-gas-solid interface of a transverse microgrooved surface for continued gas supply has been discovered, which should be a promising method for practical application of underwater drag reduction by gas.

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“…However, the Ni-P alloy prepared by traditional electrodeposition with low limit current densities has relatively slow deposition rate and low production efficiency, therefore cannot satisfy the need of modern production 1,2 . Jet electrodeposition, which has been developed in recent years, may significantly increase the deposition rate because it can accelerate the transfer process of electrodeposition material, augment the maximum current density and improve the cathodic polarization effects 3 . Changing the parameters of jet electrodeposition would alter the deposition rate and coating quality.…”

Section: Introductionmentioning

confidence: 99%

“…Changing the parameters of jet electrodeposition would alter the deposition rate and coating quality. Studying electrochemical kinetics can help people figure out how to control reaction conditions 3 and to improve the reaction speed and production efficiency. So far, most of the studies on kinetics have focused on the electroless coating of Cu, Ni-B alloy and Co-B alloy 4,5 .…”

Section: Introductionmentioning

confidence: 99%