| Our country was an agricultural country, and we had to go the way of water-savingirrigation, because of the large agricultural water consumption and water shortages. Thecontradiction on the hydraulic calculation of fluid between the energy loss and the energysupply must be solved as far as possible, in order to made the safe operation and the economytransmitting in the design of irrigation pipe conveying came true. Main and branch pipeformed water distribution pipe network in irrigation system, and became the main body ofirrigation project. In irrigation pipe network, the local resistance loss of common deformationpart in main and branch pipes was important content in the pressure calculation and design ofpipe network. Correct calculation of the deformation resistance loss, could not only solve theunderpressure in pipeline and tube explosion, but generated great significance on theeconomic and reasonable design of pipe networks and reducing the project cost.The research on variable diameter pipe and bend at home and abroad was summarized inthis paper, according to the question and insufficiency of variable diameter pipe and bendresearch, the drag characteristic of common variable diameter pipe, the drag characteristic of90°bend, and hydraulic characteristics of45°elbow in irrigation pipe network were studied bythe method of experiment and numerical simulation.Common PVC adapter bonnet in irrigation pipe network is studied in this paper. Byusing FLUENT software and RNG k-epsilon turbulence model, the flow of fluid in pipeline isresearched by means of numerical simulation, under the condition of different flow velocity.Six kinds of PVC adapter bonnet is simulated, among this, four groups of the pipe is chose indoing test, the experiments results agree well with the results in simulation. The relationbetween coefficient of local resistance and pipe diameter ratio of upstream and downstream inadapter bonnet is fitted by MATLAB software, and the relational expression of the two isgiven, this can provide a reference for practical engineering applications to a certain extent.Meanwhile, the local energy loss mechanism of adapter bonnet is discussed in this paper, aswell as the analysis of unique fluent characteristic and energy dissipation mechanism ofadapter bonnet in irrigation pipe network.In order to study the flow resistance and water flow characteristics of elbow. A series ofexperiments and numerical simulation of water flow in two kinds of PVC90°socket elbowswhich include DN75and DN50,their flow characteristics have been studied in this paper. Thesimulation results are consistent with test results. The results show that the local resistancecoefficient in different pipe diameter of elbow firstly drops quickly with the Reynolds number increasing, while the Reynolds number reaches a certain value, the change with Reynoldsnumber is very small. The flow characteristics in the elbow is then studied with the CFDsoftware. Based on the simulation results, The expression that the local resistance coefficientand the pipe diameter was established. At the same time, by comparisoning and analysisingthe90°socket elbow velocity field and pressure field, the elbow flow diagram and thevelocity vector diagram, we draw the conclusion that the main reason for the bend energy lossis that Bend energy loss occurs mainly in the elbow downstream section, bend head lossmainly because of the change of flow direction and vortex.On the basis of the test and numerical simulation about90°elbow, the45°elbow wassimulated. The results showed that in the square area, the local resistance coefficient of45°elbow with different pipe diameter was between0.4and0.5basically. Compared with90°elbow, in45°bend, the diameter made smaller effect on resistance rule, and had betterresistance characteristic. |
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