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首页> 外文期刊>International Journal of Heat and Mass Transfer >Drag-reduction in buoyant and neutrally-buoyant turbulent flows over super-hydrophobic surfaces in transverse orientation
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Drag-reduction in buoyant and neutrally-buoyant turbulent flows over super-hydrophobic surfaces in transverse orientation

机译：横向上超疏水表面上的浮力和中性浮力湍流的减阻

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摘要

The present study involves Direct Numerical Simulations (DNS) of a turbulent channel flow subject to passive-control of super-hydrophobic surfaces (SHS) employed in form of ridges/posts at the bottom-wall of the channel, oriented in transverse direction to the flow. The simulations have been carried out for a fixed friction Reynolds number Re_ι = 180 to investigate the effect of thermal forcing in tandem with SHS at a fixed friction Richardson number Ri_ι = 15. It is observed that on decreasing the width to depth (w/d) ratio of the ridge topology, the drag-reduction increases and this reduction is found to be maximum for the topology of SHS posts. A key effect of this control is reduction in cross-flow fluctuations in the buffer-layer (i.e. 10 ＜ z~+ ≤ 50) which lead to generation of weaker and more stable low-speed streaks which results in reduction in bursting of these near-wall streaks. This eventually causes considerable reduction in turbulent kinetic energy (TKE) which leads to turbulent skin-friction drag reduction at the controlled wall generally of the order of 10-22%. Unstable-stratification of the SHS flow results in the wall-normal convection of turbulent-vorticity which enhances cross-flow fluctuations leading to an increase in Reynolds shear-stresses near to the bottom-wall. In total the effect of heating is found to mitigate the net-reduction produced in turbulent drag by 6-7% for different cases employing ridge/post topology.
机译：本研究涉及湍流通道的直接数值模拟（DNS），该通道受超疏水表面（SHS）的被动控制，采用超疏水表面（SHS）的形式，位于通道底壁上的脊/立柱形式，横向于通道的横向。流。已经针对固定摩擦雷诺数Re_ι= 180进行了仿真，以研究在固定摩擦力Richardson数Ri_ι= 15的情况下热力与SHS协同作用的影响。观察到，将宽度减小到深度（w / d ）脊形拓扑的比率，减阻增加，并且此减少对于SHS帖子拓扑最大。此控制的关键作用是减少缓冲层中的横流波动（即10 ＜z〜+≤50），从而导致产生较弱且更稳定的低速条纹，从而减少这些附近区域的爆裂。墙条纹。这最终导致湍动能（TKE）的显着降低，这导致受控壁处湍流的皮肤摩擦阻力减小，通常约为10-22％。 SHS流动的不稳定分层导致湍流涡流的壁法向对流，这加剧了错流波动，导致靠近底壁的雷诺剪切应力增加。总的来说，发现加热的效果对于采用脊/后拓扑的不同情况将湍流阻力产生的净减少量减少了6-7％。

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