On the maximum velocity profile of wave boundary layer flows in the very rough turbulent regime

• Published in: Applied ocean research Vol. 145; p. 103937
• Main Authors: Teng, Yunfei, Tong, Feifei, Liu, Yi, Jia, Lusheng, Chen, Zhanjie, Gao, Zhe, Cheng, Liang, Tang, Guoqiang, Lu, Lin, Li, Chen
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2024
• Subjects: Defect function; Velocity overshoot; Wave boundary layer; Velocity overshoot; Defect function; Wave boundary layer
• ISSN: 0141-1187; 1879-1549
• DOI: 10.1016/j.apor.2024.103937

•The maximum overshoot in WBL flow increases with the decreasing A/ks, and this trend is neither affected by the irregularity of waves nor by the non-uniformity of the seabed elements.•The kinetic energy trapped by roughness elements and transferred to the main flow is responsible for the large overshoot at small A/ks values.•A three-parameter defect function is proposed that describes the overshoot well in the maximum velocity WBL profile. The maximum velocity profile in turbulent wave boundary layer flows has been experimentally investigated under both regular and irregular wave conditions. Four types of seabed models are adopted, i.e., smooth, sand-covered, uniform-sphere-covered and nonuniform-stone covered. The results show that the maximum overshoot increases with the decreasing A/ks (A is the semi-excursion of fluid particles in the free stream and ks is the bottom roughness), but it is not notably influenced by the irregularity of the waves nor the nonuniformity of bottom roughness elements. Two-dimensional numerical simulations are carried out to reveal the physics behind the large overshoot behavior. It is found that the gap flow accelerates around roughness elements and subsequently contributes to the overshoot. A three-parameter defect function is proposed that well describes the maximum velocity profile, and all three model parameters are correlated with the governing flow parameter A/ks.