계단형 보의 공기유입과 산소전달에 영향을 미치는 월류 흐름의 수리학적 영향 분석

Abstract

which is installed to raise the water level for water intake makes the deterioration of the water quality by the interception and storage of the river flow. Thus, it is necessary to improve the water quality by increasing oxygen transfer through air entrainment when the water flows the weir. The stepped weirs may be one typical example. This paper examines the air entrainment and the efficiency of oxygen transfer by the overflow characteristics of the stepped weir through the hydraulic experiments. Nappe flow occurs at low flow rates and for relatively large step height. Dominant flow features include an enclosed air pocket, a free-falling nappe impact and subsequent hydraulic jump on the downstream step. Air entrainment occurs from the step edge, but most air is entrained through a free-falling nappe impact and hydraulic jump. Air pocket also has an important role in the air entrainment. As the flow velocity and Froude number increases, flow condition changes from a nappe flow to a skimming flow. At larger flow rates, skimming flow occurs with formation of recirculating vortices between the main flow and the step corners. Oxygen transfer becomes smaller in the region of skimming flow but becomes larger in the region of nappe flow since the air entrainment is made mainly through a free-falling nappe impact, a hydraulic jump and an air pocket. The stepped weir was found to be efficient for water treatment associated with substantial air entrainment and oxygen transfer.