Mean velocity and turbulent characteristics of flow over half-cycle cosine sharp-crested weirs. (April 2019)

• Record Type: Journal Article
• Authors: Salehi, Saeed; Esmaili, Kazem; Azimi, Amir H.
• Is Part Of: Flow measurement and instrumentation. Volume 66(2019)
• Page Start: 99
• Page End: 110
• Publication Date: 2019-04
• Subjects: Flow discharge -- Flow measurement -- Hydraulics -- Cosine weir -- Sharp-crested weir -- Submerged flow -- Turbulence -- Turbulent kinetic energy; Fluid dynamic measurements -- Periodicals; Flow meters -- Periodicals; Fluides, Dynamique des -- Mesure -- Périodiques; Débitmètres -- Périodiques; 681.2805
• DOI: 10.1016/j.flowmeasinst.2019.02.002
• Languages: English
• ISSNs: 0955-5986

Abstract

Abstract: The classical sharp-crested weirs are not suitable to implement in irrigation canals with high suspended sediment flow. Over the time, sediment deposition occurs in the upstream of sharp-crested weirs and causes a time variant water level raise in the upstream and consequently variable discharge coefficients. A series of laboratory experiments was carried out to test the hypothesis of strong turbulent formation and three-dimensional flow in the upstream of half-cosine sharp-crested weirs to prevent sediment deposition. To verify this hypothesis, a series of laboratory experiment was carried out for different weir heights and top widths in free and submerged flow conditions. Mean flow structure and turbulent characteristics of half-cosine and rectangular sharp-crested weirs were measured using a micro-Acoustic Doppler Velocimeter (ADV) probe. It was found that the streamwise velocities of half-cosine weirs were higher than the corresponding rectangular weirs, however, the velocity fluctuations in this direction were similar for both types of weirs. Velocity fluctuations in vertical and transverse directions were found to be significant in half-cosine weirs. The results showed higher turbulent kinetic energy below the crest level for half-cosine weirs which made them capable of sediment resuspension and sediment removal. In was found that the introduced weir model are suitable structures for passage of small floating debris and sediments. A head-discharge formulation was also developed based on the geometry of half-cosine weir in free flow and a constant discharge coefficient was obtained by solving the Fresnel integrals. For practical purposes, semi-empirical formulations were also developed to estimate flow discharge in both free and submerged flow conditions. Highlights: Hydraulics of flow over half-cosine sharp-crested weirs was studied. Coefficient of discharge was estimated using data correlation and solving Fresnel integral. Transverse velocity fluctuation became a significant contributor of turbulent kinetic energy for half-cosine weirs. The location of the peak transverse velocity for half-cosine weirs is different from rectangular weirs. The average turbulent intensity for half-cosine sharp-crested weir is 19.2% higher than that of rectangular weir.