Skin Friction Reduction Characteristics of Nonsmooth Surfaces Inspired by the Shapes of Barchan Dunes

Engineering Applications of Computational Fluid Mechanics

Zhang

et al. 2019

Self Cite

It is well known that drag reduction occurs when the flow is passing by a grooved circular cylinder at certain Reynolds numbers, which has been used as a powerful energy saving method in a broad range of circumstances. However, a challenge here is how to evaluate the combined effects of depth, width and location of a given triangular groove set covering half of the cylindrical surface area. A useful approach to quantitatively analyze the influence of these different factors on drag reduction using the response surface methodology is described here. The flow characteristics, including drag coefficient, flow velocity, turbulent kinetic energy and vorticity, were calculated by numerical simulation. The results showed a great drag reduction effect under the legitimate set of groove structure parameters at a super-critical Reynolds number providing a base for optimization process in various engineering applications. The drag reduction mechanism found from this research could extend to other cases and should provide insights into engineering applications like car grilles. ARTICLE HISTORY

Section: Achievementsmentioning

confidence: 94%

Application and optimization of drag reduction characteristics on the flow around a partial grooved cylinder by using the response surface method

Engineering Applications of Computational Fluid Mechanics

Zhang

et al. 2019

Self Cite

“…, where y is the normal distance between the fluid and the wall and  is the thickness of the boundary layer [41]. By disturbing the near-wall turbulent region with a nonsmooth unit cell, a new turbulent boundary layer will be generated.…”

Section: Model Of a Bionic Nonsmooth Surfacementioning

confidence: 99%

“…The total length was set to 1.5 m, and the length of the test section was set to 0.3 m. To form a fully developed turbulent boundary layer at the inlet of the test section, a smooth section with a length of 1 m was arranged upstream. The normal distance from the far field boundary to the wall was 0.2 m. Preliminary research has found that turbulent drag is most influenced by the near-wall turbulent region of the boundary layer, defined as y/δ ≤ 0.2, where y is the normal distance between the fluid and the wall and δ is the thickness of the boundary layer [41]. By disturbing the near-wall turbulent region with a nonsmooth unit cell, a new turbulent boundary layer will be generated.…”

Section: Computational Domain Selection and Grid Divisionmentioning

confidence: 99%

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Turbulent Drag Reduction Characteristics of Bionic Nonsmooth Surfaces with Jets

Zhang

2019

Applied Sciences

Self Cite

Aiming at aerodynamic drag reduction for transportation systems, a new active surface is proposed that combines a bionic nonsmooth surface with a jet. Simulations were performed in the computational fluid dynamics software STAR-CCM+ to investigate the flow characteristics and drag reduction efficiency. The SST K-Omega model was used to enclose the equations. The simulation results showed that when the active surface simultaneously reduced the skin friction and overcame the sharp increase of pressure drag caused by a common nonsmooth surface, the total net drag decreased. The maximum drag reduction ratio reached 19.35% when the jet velocity was 11 m/s. Analyses of the turbulent kinetic energy, pressure distribution, and velocity profile variations showed that the active surface reduced the peak pressure on the windward side of the nonsmooth unit cell, thereby reducing the total pressure drag. Moreover, the recirculation formed in the unit cell transformed the fluid–wall sliding friction into fluid–fluid rolling friction like a rolling bearing, thereby reducing the skin friction. This study provides a new efficient way for turbulent drag reduction to work.

“…In the initial stage of the occurrence of vortex, the variation of scale’s angle could prevent the vortex from further development and finally suppress the occurrence of vortex 12 – 14 . Inspired by shapes of barchan dunes in deserts, Song et al found trough numerical simulation that the maximum drag reduction rate of bionic non-smooth surface was 33.63% 15 . Kumagai et al studied the drag reduction effect of micro-bubbles by injecting airflow into the machinery’s surface to form a layer of micro-bubbles.…”

Section: Introductionmentioning

confidence: 99%

Drag reduction mechanism of Paramisgurnus dabryanus loach with self-lubricating and flexible micro-morphology

Wang

et al. 2020

Sci Rep

Underwater machinery withstands great resistance in the water, which can result in consumption of a large amount of power. inspired by the character that loach could move quickly in mud, the drag reduction mechanism of Paramisgurnus dabryanus loach is discussed in this paper. Subjected to the compression and scraping of water and sediments, a loach could not only secrete a lubricating mucus film, but also importantly, retain its mucus well from losing rapidly through its surface micro structure. In addition, it has been found that flexible deformations can maximize the drag reduction rate. this self-adaptation characteristic can keep the drag reduction rate always at high level in wider range of speeds. therefore, even though the part of surface of underwater machinery cannot secrete mucus, it should be designed by imitating the bionic micro-morphology to absorb and store fluid, and eventually form a self-lubrication film to reduce the resistance. In the present study, the Paramisgurnus dabryanus loach is taken as the bionic prototype to learn how to avoid or slow down the mucus loss through its body surface. This combination of the flexible and micro morphology method provides a potential reference for drag reduction of underwater machinery.