Numerical simulation of hydraulic performance for portable short-throat flume in field based on FLOW-3D

Abstract: Improvement of water management can encourage conservation and make best use of our limited water resources. The measurement of flow rates is an important element of water management. Many devices and structure have been developed for the measuring discharge but measuring flume is one of the most accepted and used structure. According to the practical situation of irrigated areas in northern China, use of portable short-throat flume in field to measure the discharge of water inlet in the field is an emerging technique developed for water discharge measurement of inlet in the field, which contributes to control of irrigation water consumption and water conservation. Based on FLOW-3D software in this study, 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 field with a 51 mm width throat under 18 working conditions. Experimental results about portable short-throat flume in field were also obtained based on a new test to validate the simulation results. It verified discharge capacity of the flume. The parameter settings and boundary conditions used in the CFD models provided an efficient approach for simulation of the flow through portable short-throat flume in field. Combined with hydraulic experiments, hydraulic performance was obtained from simulation analyses on water surface profiles, Froude number, velocity distribution and head loss. 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 gave a solid agreement between experimental and numerical simulation results. Hence, it can be used to 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. The simulation results showed that both Froude number and velocity accelerated along the flume with free flow condition, and in submerged flow condition increased at first and then decreased. The cross-section of critical depth was located at throat section by Froude number analyses. The flow surface profile in throat section of portable short-throat flume in field was highly curvilinear in both free and submerged outflow working conditions as the flow accelerated from the subcritical regime to the supercritical regime. Equations of upstream depth versus discharge under free and submerged outflow working conditions were fitted by regression analyses, respectively. The maximum relative error between measured discharge and calculated discharge by equations was -5.63%, which met the requirements of water measurement for irrigation. Further, maximum head loss of portable short-throat flume with a flat base for the field accounted for 12.10% of total upstream head. Compared with long-throat flume, the head loss of portable short-throat flume in field was less. The three-dimensional turbulence model along with the TruVOF technique allowed one to reproduce the hydraulic characteristics of flow through portable short-throat flume in field. Due to shorter time demand and lower cost of numerical simulations compared to experimental studies in predicting the hydraulic characteristics, simulation of the portable short-throat flume in field flows based on a properly validated model provided the flow characteristics of these flumes for various flow configurations encountered in the field. This study provides a reference for flow-measurement of final stage of canal in irrigation areas in North China.