Date of this Version
Evans, Alexander, (2015) Velocity Distributions and Wall Pressures in a Scale Model Gated Box Culvert Control Structure, M.S. Thesis, University of Nebraska - Lincoln.
The South Florida Water Management District (SFWMD) manages a system of canals and structures that control the flow through several large storm water treatment areas (STA). The present project was initiated because of the partial failure of a three-barrel, gated box culvert structure that belongs to the system. The structure has a forebay with three sluice gates that control the flow into three 8 ft by 8 ft box culverts. Settling and partial failure of the culverts in the structure was presumably caused by piping of sediment through joints in pre-cast sections of culvert. It was hypothesized that both unsteady pressure fluctuations and pressure differentials between the outside and inside of the culverts led to the piping failure. To better understand flow characteristics in the culvert that may cause these adverse effects, a 1:8-scale model of one of the three gated culverts was constructed. The bed of the model culvert was instrumented with eight pressure tap transducers. In addition, a Particle Image Velocimetry (PIV) system was employed to record velocity distributions immediately downstream of the sluice gate, where piping and settlement was most prominent in the prototype. Eight experiments of varying gate settings and flow conditions were carried out in the flume model. Both pressure and velocity distribution data were gathered. PIV data provided visual depiction of the formation, travel path, and translation to the flume bed of turbulent flow structures originating in the hydraulic jump recirculation zone within the model. The pressure taps captured spikes in pressures associated with these flow structures as they were translated to the bed. Trends between pressure and velocity were observed in the data and indicated that low gate settings produced conditions that were more likely to cause the aforementioned adverse effects in the prototype. The flow jet in low gate settings produced strong negative pressure zones along the bed, downstream of the gate. It also generated a more pronounced recirculation zone above the jet where turbulent structures were observed to form and be translated to the bed causing spikes in pressure.
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