仿生二级微沟槽表面减阻特性数值模拟

Numerical simulation of drag reduction characteristics in bionic secondary micro-grooved surface

快速游动的鲨鱼,其皮肤表面布满沿流动方向的沟槽,这种沟槽能够减小鲨鱼游动过程中的阻力。通过仿生技术人们设计了一系列具有单一尺度的沟槽结构,如V型、L型、U型等(定义为原始沟槽),并获得了一定的减阻效果。然而通过仔细观察,发现鲨鱼皮肤表面的沟槽并非是单一尺度的。根据这一启发,通过在原始V型沟槽顶部两侧增加小尺度三角形突起,设计了一种二级沟槽表面。利用RNGk-ε湍流模型,对原始V型沟槽和二级沟槽表面进行了流场分析。讨论了在不同雷诺数的情况下,两种沟槽壁面对湍流边界层内速度分布、沟槽壁面切应力及减阻效果的影响。计算结果表明,在一定雷诺数范围,原始V型沟槽最佳减阻4.6%,二级沟槽结构最佳减阻8.07%,二级沟槽减阻效果明显优于原始V型沟槽。二级沟槽表面能够更有效地抑制边界层内湍流流动,减小了流体流动的黏性阻力,具有更好的减阻效果。

The skin surface of fast swimming shark＇s is covered with grooves along the flow direction, which is proved to be able to reduce resistance in swimming. Using bionic technology, a series of trench structures with single scale is designed, such as V- shaped, L-shaped, U-shaped, etc. （defined as the original trench）, and some drag reductions are acquired. Considering that the grooves covered on shark skin surface do not have a single scale, a secondary micro-grooved surface is designed in this paper by adding small-scale triangle on the top of the V-shaped grooves on both sides. Using RNG/e-e turbulence model, the flow field of original V-shaped grooves and secondary micro-grooved surface were analyzed. With different Reynolds numbers, the effects of two trench wails on the velocity distribution in the turbulent boundary layer, shear stress of the trench wall and drag reduction were discussed. The results show that, in a certain range of Reynolds number, secondary micro-groove reduce the resistance by 8. 07~, while the original V-shaped groove shorten the resistance by 4. 6%. The secondary micro-grooved surface is more effec tive in inhibit the turbulent flow in boundary layer and reduce the viscous resistance in fluid flow, and has a better drag reduction characteristics.