Author(s): Shuen-Jong Tsorng; Fong-Zuo Lee; Jihn-Sung Lai; Yih-Chi Tan
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Keywords: Sharp-crested weir; Velocity distribution; Discharge estimation; ADV; Surface velocity
Abstract: Water stage and velocity distribution of flow over a sharp-crested weir are measured using point gauge and three-dimensional Acoustic Doppler Velocimetry (16-MHz ADV), respectively. There are 6 sets o experiments with various (h o -h w) /h w =0.72–0.99 (h c /h w =0.60–0.85), where weir height h w =20cm. According to variation of the longitudinal velocity distributions, velocity field shows acceleration pattern above the elevation of weir height. Opposite patterns, in contrast, occur blow the elevation The maximum velocity at weir occurs near the crest, instead of water surface. Similar velocity distributions at the weir crest are summarized and normalized by water depth and free-surface velocity The maximum normalized longitudinal velocity is u/u s =1.61 and its corresponding elevation is (z-h w) /h c =0.18. Linear and 2nd-order polynomial regressions are performed to sketch the longitudina velocity distribution at weir crest. Direct integration of the regression formula provides more accurate discharge estimation within 0.5–10%than that by traditional discharge equations. The proposed method developed by experimental data not only estimate reasonable discharge but also provide information of the velocity distribution at weir crest.
Year: 2010