Analysis of Free Surface Shape and Toss Width with a Broad-Crested Weir



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A broad-crested weir is a structure that directs and regulates flow of fluids. The specific goal of this study is to measure the toss width, specifically the slope of the water as it’s tossed off of the end of the weir, at designated points on the flume as flow velocity changes. We designed our experiment to measure quantitative data using a manometer for discharge height as well as the velocity meter to measure the fluid velocity. These measurements are used to qualitatively characterize the free surface shape, recognize patterns, and compare overshoot. The toss width is the priority of our experiment, with the heights and widths of the cavitation, which is the formation of an air bubble within the flow, being measured. As the toss width is influenced heavily by upstream characteristics, we will compute the upstream Froude number, which is characterized by a ratio from inertia to gravity as dominating forces. We predict that the results will show that as fluid velocity increases, our free surface shape will become more chaotic on the outflow and that our toss width will change, specifically the air bubble formed from our weir will have a larger height and smaller width. Broad-crested weirs are commonly used in nature as a dam that regulates flow. They can be used recreationally by keeping fish populations in specific areas along a river, encouraging fishing. Studying these weirs inside of a controlled environment can give us insight into how they can be used effectively in nature.


Dr. Terry Jo Leiterman, Mathematics

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mathematics, free surface shape

Analysis of Free Surface Shape and Toss Width with a Broad-Crested Weir