Study On Hydraulic Performance Of Portable Short-throat Flume In The Field

Flow measurement is a key technique of planned use, conservation and quota management of water. In terms of economical practicality and reliability, flumes, compared to other existing flow-measuring devices, are more suitable for flow measurement in open channels and easier to be widely applied. Much research has studied different kinds of flumes, providing a variety of adjustments of the channels. But there is not much work attempting for small-size flume or flume set in the field to measure discharges of water inlet in the field. Hence, the flume, measuring the discharge of flow into the field, needs to meet the requirements of simple structures, cheap prices and a reasonable accuracy.Originated from the Parshall flume, portable short-throat flume in the field, consisted of a flat-bottom flume with converging, throat and diverging sections, is a device for flow-measurement of inlet in the field to control the discharge into the field accurately in North China. Portable short-throat flume in the field was evaluated by laboratory experiments and FLOW-3D software in two types, different outflow and different discharge conditions. The main research contents and conclusions are as follows.(1) General flow-measurement theory of portable short-throat flume in the field was studied, and theoretical equations of depth versus discharge were deduced according to the principle of critical flow.(2) Experimental programs of portable short-throat flume in the field with 51 and 76 mm width throat were developed. Experiments of portable short-throat flume in the field with a 51 mm width throat were conducted on 16 discharges with free outflow conditions and 8 discharges with submerged outflow conditions. Experiments of portable short-throat flume in the field with a 76 mm width throat were conducted on 8 discharges with free outflow conditions and 8 discharges with submerged outflow conditions. Hydraulic performance of portable short-throat flume in the field is obtained from experimental analyses on flow capacity, water surface profile, cross-section velocity distribution, Froude number and head loss. Location of critical depth section was determined. Regression analyses developed for upstream depth versus discharge under free outflow condition and submerged outflow condition are satisfying with the relative error of within 10%, which meets the common requirements of flow measurement in irrigation areas.(3) Based on FLOW-3D software, RNG k-ε three-dimensional turbulence model, TruVOF technique and FAVOR(fractional area volume obstacle representation) method were employed to simulate three-dimension flow field in portable short-throat flume in the field. A few experimental results about portable short-throat flume in field were also obtained to validate the simulation results. Comparison between experiments and simulations showed that measured and simulated flow capacity, flow field and flow depth have a good consistency, and relative errors were less than 10%, and yielded a solid agreement between experimental results and numerical simulation results. Hence, it can simulate flow state of portable short-throat flume in field effectively and visually. On the basis of reliable numerical simulated consequents, analyses of hydraulic performances in detail were carried out.(4)Model selections among different flumes with different throat length by FLOW-3D software. Hydraulic performances were obtained by simulations, such as flow pattern, head loss and so on. Simulated results showed head loss of short-throat flume was less than others, and flow pattern was steady. It concluded that the length of portable short-throat flume in the field was more reasonable than others for flow measurement of discharges into the field.