| Water shortage is one of the problems that limit economic development in China.The water-measuring device in irrigation district is an important benchmark to measure the level of water management in irrigation district and the basic condition for monitoring and measuring water in irrigation district.Thus studying convenient and adaptable flow-measurement devices is particular important to save water in irrigation district and alleviate water shortage.Water-measuring accuracy of sharp-crested side weirs is higher than Water-measuring accuracy of flumes.Side weir,as a kind of water-measuring devices,is installed in the side of channels and connected directly with the small channels or water inlet in the field without changing the original cross section of channels.It is simple in shape,installed and removed easily and with high precision.It has enormous potential application value,but study on influence factors of side weir hydraulic characteristics and optimizing side weir shape is superficial.Experiments were taken on rectangular side weirs with four kinds of side weir widths and six kinds of heights and trapezoidal side weirs with seven kinds of side weir crest angles under different discharges in rectangular channel.And the hydraulic characteristics of side weirs were investigated by using the CFD code of FLOW-3D software.Water surface profiles near side weirs,head loss,backwater depths,velocity distribution,fraction of fluid and relation between discharge coefficient and its influence factors were analyzed.The main research contents and conclusions are as follows:(1)Based on dimensionless principle,theoretical discharge formula of side weirs was obtained combined theory analysis and experimental data.(2)Experimental and numerical results of rectangular side weir were analyzed.Variation of water profiles near rectangular side weirs and velocity distributions near rectangular side weirs were obtained.The effect of rectangular side weirs width and height on head loss and backwater height were obtained.Experimental and simulated results of water profiles and velocity distributions of rectangular side weirs were compared,which showed that these two methods had a good agreement.The fitted formula has a satisfactory with the maximum relative error 9.87% and average relative error 0.46%.(3)Experimental and numerical results of trapezoidal side weir were analyzed.Variation of water profiles near trapezoidal side weirs and velocity distributions near trapezoidal side weirs were obtained.The effect of trapezoidal side weirs crest angles on head loss and backwater height were obtained.Experimental and simulated results of water profiles and velocity distributions of trapezoidal side weirs were compared,which showed that these two methods had a good agreement.The fitted formula has a satisfactory with the maximum relative error-8.97% and average relative error-3.83%.(4)Based on experimental and simulated results of rectangular and trapezoidal side weirs,hydraulic characteristics of fluid fraction,head loss,backwater depth and measuring accuracy were comprehensively analyzed.The sizes of rectangular and trapezoidal side weirs were optimized.Rectangular side weir widths shouldn't be too small and heights shouldn't be too high.Side weir crest angles shouldn't be too big.For experiments in this paper,suitable range for rectangular side weir heights were selected from 10 cm to 15 cm,for rectangular side weir widths were selected from 30 cm to 40 cm,and for side weir crest angles is selected from-6° to 6°. |
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