Study On Hydraulic Character Of Water-measuring Column With Round Head In Small Channels

Measuring water in channels is a key technology of irrigation water management as wellas planning of water in irrigation district, and is an effective means to promote waterconservation. Small channels in Irrigation Areas of North China have an gently slope, siltationproblems seriously affect the performance of water measuring facilities, and it has good valueand scientific significance to develop suitable water measuring facilities for small channelswith gently slope and sediment-laden water in Irrigation Areas of North China, which hashigh accuracy, low loss, small backwater height and removable. Based on the cylinder watermeasuring flume, this paper puts forward mobile water measuring column with round head,which is a new water measuring facility. Experimental study on its hydraulic characteristicswas conducted in the rectangular, trapezoidal, and U-shaped channels, use the softwareFlow-3D and the RNG k-ε turbulence model to simulate the water flow movement of watermeasuring column with round head in U-shaped channel，the main The main contents andconclusions are as follows:(1) To study the general flow measurement theory of water measuring column withround head, and deduced its critical depth theoretical flow calculation formula in therectangular, trapezoidal and channels based on critical flow principle.(2) A series of experimental studies for different contraction ratios, different waterdownstream lengths of water measuring column with round head were carried out in differentsection form channels, to explore the variation of backwater, Froude number, criticalsubmergence degree and water head loss, etc, about the water measuring column with roundhead in different shape. The results showed that suitable contraction ratios ε range ofwater-measuring column with round head in rectangular channels is0.45~0.60; suitablecontraction ratios ε range in trapezoidal channels is0.65~0.75; suitable contraction ratios εrange in U-shaped D40channels is0.62~0.72; suitable contraction ratios ε range in U-shapedD60channels is0.60~0.70. Suitable downstream length of water-measuring column with roundhead is: L=3/2D～2D.(3) The relationship between stagnation-point depth and discharge of water-measuringcolumn with round head is very well and the correlation coefficient reached more than0.98. Due to the location of critical depth is unstable and difficult to measure, replace the criticaldepth with stagnation depth to calculate discharge has a good accuracy. Based on test data,relationship formula of discharge related to stagnation-point depth and contraction ratios inrectangular, trapezoidal and U-shaped channels were obtained, which could meet with a goodflow measurement accuracy. The average critical submergence S of water-measuring columnwith round head is greater than0.84, the critical submergence of channels is larger, which illustrate that downstream water level of water-measuring column with round head does notaffect the upstream in free flow range and not easy to result submerged flow.(4) Use the software FLOW-3D and the RNG k-ε turbulence model to simulate thethree-dimensional water flow movement of water measuring column with round in U-shapedD40channel, to verify the simulation studies with the test results, and to determine thereliability of the model and validity of the simulation results by comparing the flow pattern,the water line changes and velocity distribution. To simulate water measuring column withround head in a larger flow range, determined the resulting flow formula from the test has agreater scope, and provide a theoretical basis for the widely use of water measuring columnwith round head.