A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces.However,in previous experim...A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces.However,in previous experiments,the ultrahydrophobic surfaces were fabricated with micro-structures or nano-structures and the channels were on the microscale.For the drag reduction in macro-scale channels few reports are available.Here a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes.The drag reductions up to 36.3% were observed in the macro-channels with ultrahydrophobic surfaces.The micro-PIV was used to measure the flow velocity in channels.Compared with the traditional no-slip theory at walls,a significant slip velocity was observed on the ultrahydrophobic surfaces.展开更多
This paper presents a stress controlled boundary slip model and predicts the fluid-solid interface slip in a system of parallel sliding plates or a sphere approaching a smooth plane. The numerical simulation results a...This paper presents a stress controlled boundary slip model and predicts the fluid-solid interface slip in a system of parallel sliding plates or a sphere approaching a smooth plane. The numerical simulation results are in striking agreement with the existing experimental observations. This model assumes that there is a limiting shear stress. No slip occurs if the surface shear stress is smaller than the limiting shear stress, and slip occurs when the surface shear stress equals it. It is found that boundary slip dramatically decreases the hydrodynamic pressure if the two squeezed surfaces have the same slip property. Finally, the hydrodynamic force reaches a saturation status and almost does not decrease any more. Compared with the no-slip solution, hydrodynamic force is found to decrease by over two orders in the case of boundary slip. When the squeezed surfaces have different slip properties, however, the hydrodynamic pressure is mainly controlled by the surface having a smaller surface limiting shear stress, and reduces more slowly compared with the case of two surfaces having the same slip property. Even when one of the surfaces has a zero surface limiting shear stress, a considerable hydrodynamic force still exists.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 10872106)
文摘A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces.However,in previous experiments,the ultrahydrophobic surfaces were fabricated with micro-structures or nano-structures and the channels were on the microscale.For the drag reduction in macro-scale channels few reports are available.Here a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes.The drag reductions up to 36.3% were observed in the macro-channels with ultrahydrophobic surfaces.The micro-PIV was used to measure the flow velocity in channels.Compared with the traditional no-slip theory at walls,a significant slip velocity was observed on the ultrahydrophobic surfaces.
基金This work was jointly supported by the National Natural Science Foundation of China(Grant No.10272028)the Doctor Education Foundation of China Education Ministry(Grant No.20030141013).
文摘This paper presents a stress controlled boundary slip model and predicts the fluid-solid interface slip in a system of parallel sliding plates or a sphere approaching a smooth plane. The numerical simulation results are in striking agreement with the existing experimental observations. This model assumes that there is a limiting shear stress. No slip occurs if the surface shear stress is smaller than the limiting shear stress, and slip occurs when the surface shear stress equals it. It is found that boundary slip dramatically decreases the hydrodynamic pressure if the two squeezed surfaces have the same slip property. Finally, the hydrodynamic force reaches a saturation status and almost does not decrease any more. Compared with the no-slip solution, hydrodynamic force is found to decrease by over two orders in the case of boundary slip. When the squeezed surfaces have different slip properties, however, the hydrodynamic pressure is mainly controlled by the surface having a smaller surface limiting shear stress, and reduces more slowly compared with the case of two surfaces having the same slip property. Even when one of the surfaces has a zero surface limiting shear stress, a considerable hydrodynamic force still exists.
