Abstract
Rigid flow deflectors are usually used on water flow beds to protect engineering structures such as breakwater in coasts and to regulate flow routes in open channels. To reduce its side-effects, i.e., local scour at the toe of deflectors, a flexible flow deflector is proposed, and the corresponding local scour was investigated in this study. A flume experiment was conducted to investigate local scour. To show the advantage of flexible deflectors, a control experimental test was also conducted using a traditional rigid deflector under the same blockage area configuration and the same flow conditions. The flow field near the flexible deflector was also measured to reveal the local flow field. The results show that the bed-scour develops near the toe edges of both flexible and rigid deflectors, but the maximum and averaged scour depths for the flexible deflector are smaller. This advantage of flexible deflector in scour depth is mainly caused by its prone posture, which induces the upward stretching and enlarging horizontally rotating vortex and the upward shifted vertically rotating vortex. The former dissipates more turbulent energy and the latter results in smaller bed shear stress, which lead to smaller scour depth directly. In addition, the up- and down-swaying movement of the flexible deflector can also assistant to dissipate more turbulent energy, thereby damping the intense of the horseshoe vortices and thus weakening scour depth as well. The results of this study provide an elementary understanding on the mechanisms of a flexible flow structure and an alternative deflector-device to reduce scour depth.
Highlights
Underwater engineering structures, such as breakwater and cylinder in coastal areas [1,2,3], are usually exposed to the toe-scour damage and instability risk. To protect these underwater structures, rigid flow deflectors are widely used in the upstream section of these engineering structures
A new flexible flow deflector is proposed as a device to protect the underwater engineering structure, and the local scour depth at its leeside was investigated in this study
A rigid deflector of the same effective height and width was conducted under the same flow condition
Summary
Underwater engineering structures, such as breakwater and cylinder in coastal areas [1,2,3], are usually exposed to the toe-scour damage and instability risk. To traditional protect the measures underwater rigid engineering structures, deflectors,[16], fromrubble-mound scour-caused failure, generally include ripraps [14,15],including flexible mattresses failure, traditional measures generally include ripraps [14,15], flexible mattresses [16], rubble-mound structures [17], permeable structures [18,19], and protective spur dikes [20]. These methods structures permeable structures and protective spurarea dikesnear [20].the.
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