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Mechanism of Flow Gauge and Structure Optimization for Airfoil-shaped Measuring Flume

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Tutor: LvHongXing
School: Northwest University of Science and Technology
Course: Water Resources and Hydropower Engineering
Keywords: canal flow measuring,airfoil-shaped,hydraulic characters,multi-objectiveopzimati
CLC: S274.4
Type: PhD thesis
Year:  2013
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Abstract:
In China, most irrigation water is delivered in canal from source to field. Development ofcanal water gauge technology is crucial for standard irrigation and improvement of irrigationwater use efficiency. In other word, it is important for water saving agriculture and a way toachieve efficient water use in agriculture. However, as restricted to the situations in diversityregions, the economic background, irrigation management, development level and fieldhydraulic character is different for irrigation area in China. Therefore, it is urgent to develop acanal water measurement technology which is suitable for all regions. In relation to the higheconomic profitability and stability, a flume measuring equipment is suitable for applicationin large parcels. The explosion of a flow gauge technology with flume structure plays asignificant role in sustained development of irrigation area. Under specific situation, tt shouldhave the advantages like simple structure, high measuring accuracy, high adaptability andconvenient manipulation.Airfoil-shaped measuring flume is a new technology applicable to irrigation region inour nation. The streamline structure makes water flowing smoothly along the flume withouthigh resistance. Compared with the traditional flow measuring method, it has the advantageslike smooth water flow, low cost and easy to build. Therefore, in this paper, modelexperiments and computational numerical simulation was combined to analyze mechanism offlow gauge and related hydraulic parameters under different structures of airfoil-shapedmeasuring flume. Then a multi-automatic optimizing method was developed to accomplish amulti-objective optimization of flume structure. The results obtained are as follows:(1) The experiment was conducted with3contraction ratios for airfoil-shaped measuringflume in a rectangle canal. The equation was proposed by dimensional analysis method tocalculate flow rate. The equation is with a simple form and the differences between calculatedand experiment results are small.3-dimensional numerical simulation was conducted byFluent software. The results was compared with model experiment and shows a highcoincident. Turbulent flow field and related hydraulic parameters were analyzed. Criticalsubmergence coefficient S in flume is relatively high. Upstream Froude number Fr is smallerthan0.5, which is satisfied flow measuring standard. (2) With two different experimental conditions, a last stage of irrigation canal renovationproject in a certain small irrigation area was taken as an archetype. Water jump in U-ShapedCanal Airfoil-shaped flume in three dimensions was simulated, with the turbulencemathematical model tracking the free surface of liquid based on TruVOF method and meshoptimization based on Favor. The hydraulic parameter were also analyzed such astime-averaged flow field, conjugate depth, occurring position, jump length, distribution ofhydraulic velocity in cross section and the loss of energy of hydraulic jump section.Simulation results were verified using model experiment data with a model ratio at1:1.Finally, the conjugate depths of experimental data and simulation results were analyzed, andthe calculation formula of conjugate depths for U-Shaped Canal Airfoil-shaped flume wasproposed. Turbulence characters and head loss was studied under different experimentcondition, which provides recommendation for determination of flow measuring flumestructure.(3) Taking airfoil-shaped flume in a rectangle canal as study objective. An optimizationmodel was established based on Isight platform. In this model, airfoil parameterization wasrealized by Hicks-Henne Shaped function. Parameters were selected and optimized byMulti-Island Genetic Algorithm. It is used to realize a multi-objectives hydraulic optimizationof airfoil-shaped flume. Taking two representative conditions of airfoil-shaped flume as studycases, optimization results were simulated and verified by Flow-3D. It was shown that, for theoptimum flume structure, there is an enhancement in side contraction capacity. Head loss issmaller, which leads to a more smoothly flow. It is benefit for improve the irrigationefficiency and more applicable for plain with gentle slope and weak hydraulic situation.(4) The application of Fluent and Flow-3D was compared in respect to explosion method,mesh divided and liquid free surface tracking method. The results show that, either of thesoftware is applicable to the study of hydraulics. However, convergence rate is better forFluent and it is more suitable for qualitative analysis with a massive calculation. Flow-3D isbetter at dealing with free surface. Simulation accuracy is higher and it is more suitable forverification of model experiment results.
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