caa a22 4500 606197435 CHVBK 20210128100929.0 cr unu---uuuuu 210128e20150901xx s 000 0 eng 10.1007/s00348-015-2047-y doi (NATIONALLICENCE)springer-10.1007/s00348-015-2047-y Mechanisms of drag reduction of superhydrophobic surfaces in a turbulent boundary layer flow [Elektronische Daten] [Jingxian Zhang, Haiping Tian, Zhaohui Yao, Pengfei Hao, Nan Jiang] The drag-reducing property of a superhydrophobic surface is investigated along with its mechanism. A superhydrophobic surface with micro-nanotextures is fabricated and tested using SEM and contact angle measurement. Velocity distributions in the turbulent boundary layer with a superhydrophobic surface and a smooth surface are measured by particle image velocimetry at Re θ =810, 990, and 1220. An upward lift effect on the velocity profile caused by the rugged air layer on the superhydrophobic surface is observed, which indicates drag reduction. Estimated by the wall shear stress, a drag reduction of 10.1, 20.7, and 24.1% is observed for Re θ equal to 810, 990, and 1220, respectively. The drag reduction is caused mainly by slip on the interface and modifications in the turbulent structures, and the latter plays a more important role as Re θ increases. Suppressions are observed in turbulence intensities, and reductions in the total Reynolds shear stress T turb + are 2.5, 18.5, and 23.1% for Re θ =810, 990, and 1220, respectively. Vortex fields above the superhydrophobic and smooth surfaces at Re θ =990 are investigated. Vortexes are weakened and lifted upward by the superhydrophobic surface, and the position of the maximum swirling strength is lifted 0.17δ (δ is the boundary layer thickness) upward in the wall-normal direction. This modification in turbulence structures contributes significantly to the drag reduction in the turbulent boundary layer flow. Springer-Verlag Berlin Heidelberg, 2015 Zhang Jingxian Department of Engineering Mechanics, Tsinghua University, Beijing, People's Republic of China aut Tian Haiping School of Mechanical Engineering, Tianjin University, Tianjin, People's Republic of China aut Yao Zhaohui Department of Engineering Mechanics, Tsinghua University, Beijing, People's Republic of China aut Hao Pengfei Department of Engineering Mechanics, Tsinghua University, Beijing, People's Republic of China aut Jiang Nan School of Mechanical Engineering, Tianjin University, Tianjin, People's Republic of China aut Experiments in Fluids Springer Berlin Heidelberg 56/9(2015-09-01), 1-13 0723-4864 56:9<1 2015 56 348 https://doi.org/10.1007/s00348-015-2047-y text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-2047-y text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Zhang Jingxian Department of Engineering Mechanics, Tsinghua University, Beijing, People's Republic of China aut NATIONALLICENCE 700 1- Tian Haiping School of Mechanical Engineering, Tianjin University, Tianjin, People's Republic of China aut NATIONALLICENCE 700 1- Yao Zhaohui Department of Engineering Mechanics, Tsinghua University, Beijing, People's Republic of China aut NATIONALLICENCE 700 1- Hao Pengfei Department of Engineering Mechanics, Tsinghua University, Beijing, People's Republic of China aut NATIONALLICENCE 700 1- Jiang Nan School of Mechanical Engineering, Tianjin University, Tianjin, People's Republic of China aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/9(2015-09-01), 1-13 0723-4864 56:9<1 2015 56 348