Print Email Facebook Twitter Air entrainment and free-surface fluctuations in A-type hydraulic jumps with an abrupt drop Title Air entrainment and free-surface fluctuations in A-type hydraulic jumps with an abrupt drop Author Luo, Maoyi (Sichuan University) Wang, Hang (Sichuan University) Zheng, Xiaohui (Sichuan University) Wüthrich, D. (TU Delft Hydraulic Structures and Flood Risk) Bai, Ruidi (Sichuan University) Liu, Shanjun (Sichuan University) Date 2023 Abstract In high dam construction projects in China, stilling basin design with an abrupt bottom drop is sometimes introduced to reduce the bottom velocity and pressure loads by generating A-type hydraulic jumps. Although the stilling basin design is not new, A-type hydraulic jumps have not been studied taking into account the air entrainment and evolution of internal air–water flow structures. This paper presents an experimental study of self-aerated A-type jumps in terms of bubble transport and free-surface fluctuations over the bottom drop. Four Froude numbers from 4.1 to 10.3 are tested for three drop heights, in addition to the flat-bottom case. Compared to the classic hydraulic jumps, A-jumps are observed with longer jump lengths and weaker free-surface fluctuations. The downward deflection of the jet-shear flow and formation of a bottom roller in the step cavity require a modification to the analytical expression of velocity and void fraction distributions. The relationship between the bubble diffusivity and jump spreading rate differs from that in classic hydraulic jumps, suggesting a faster expansion of the bubble diffusion layer than the turbulent shear flow downstream of the drop, especially for large drop heights. At large approach velocities, the reattachment of the deflected jet-shear flow to the lowered bed may cause a local rise in bubble counts downstream the bottom roller. Further increase in drop height results in a W-jump with overwhelming bottom roller over the surface roller and an arced surface jet, which is beyond the scope of this study. Subject A-jumpabrupt dropair entrainmentbottom rollernegative step To reference this document use: http://resolver.tudelft.nl/uuid:8852ee21-5f8c-43be-b7d5-d29c2274fb69 DOI https://doi.org/10.1080/00221686.2023.2239193 Embargo date 2024-03-19 ISSN 0022-1686 Source Journal of Hydraulic Research, 61 (5), 720-734 Bibliographical note Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public. Part of collection Institutional Repository Document type journal article Rights © 2023 Maoyi Luo, Hang Wang, Xiaohui Zheng, D. Wüthrich, Ruidi Bai, Shanjun Liu Files PDF Air_entrainment_and_free_ ... t_drop.pdf 3.04 MB Close viewer /islandora/object/uuid:8852ee21-5f8c-43be-b7d5-d29c2274fb69/datastream/OBJ/view