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You are here : eLibrary : IAHR World Congress Proceedings : 35th IAHR Congress - Chengdu (2013) : THEME 3 - WATER ENGINEERING AND CIVILIZATION : Water Surface Profiles in a Tunnel Bend with High Velocity
Water Surface Profiles in a Tunnel Bend with High Velocity
Author : Bo Wang, Ping Wu, Yun-liang Chen, Chao Wu and Qin Zhou
It is widely believed that a bend in horizontal plane is not suitable for a free-surface tunnel. It is also a strict rule in Specification for Design of Hydraulic Tunnel (SL279-2002) that a horizontal curve should not be adopted in the free-surface tunnel with high velocity. Due to the high veloctiy and large Froude Number, the bend in free-surface tunnels is hardly used in hydraulic engineering; and the hydraulic characteristics of which rarely is investigated intensively. The bend in free-surface tunnels has outstanding features different from that of spillways and rivers. In this article, the flow regimes of the bend and its downstream reach were observed in a physical model at the approach Froude Number 4-8, and the water surfaces were obtained. The following findings are concluded from the experimental results, which may be helpful for dealing with the problems produced by the tunnel bend.The water depth on both banks is essentially equal upstream the entrance of the bend. The flow moves ahead both in the tangential direction and in the transverse direction from the inner to the outer wall. The surface along the inner wall drops while the one along the outer wall climbs. The flow on the inner bank finally becomes a water-layer. The flow on the outer bank exceeding the vertical wall will cling to the arch and continue the tangential movement. The directon of the tranverse motion becomes from the outer wall to the other. The wall-attached flow will slip down the vertical wall on the inner bank as it passes the apex of arch, forming a waterfall and supplementing the flow on the inner bank. The flow upstream of the bend entrance characterises two-dimensional, and becomes a swirling flow containing an air cavity in the bend. The hollow swirling flow out from the bend develops into a shock wave with a fluctuating surface in the straight tunnel because of the boundary change. The crest of surface along both walls alternately arises.
File Size : 726,772 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 35th IAHR Congress - Chengdu (2013)
Date Published : 18/07/2016
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