| Low-pressure pipe irrigation is an efficient water-saving irrigation technology.It has gradually become one of the most important forms of agricultural irrigation water conveyance projects in China due to its advantages such as water saving,land saving,energy saving,easy management,and increased production and income.With the development of water-saving agriculture,implementing water metering in irrigation districts,strengthening agricultural water management,and achieving total irrigation water control have become important tasks in the construction of irrigation districts in China.Therefore,it is necessary to study the economical and suitable water measuring facilities for low-pressure pipe irrigation systems.The low-pressure pipe irrigation system using surface water as the water source which has many impurities and coarse particles inside.In order to solve the problem of clogging on the upstream side of ordinary Venturi flowmeters,this paper improves the design of traditional Venturi flowmeters and proposes an eccentric Venturi flow measuring device.Through FLOW-3D numerical simulation and combined with real-flow test,analyzing the flow measurement performance of the device.The specific research content is as follows:1.In order to meet the needs of low-pressure pipe irrigation with surface water as the source of water,a new type of flow measurement device,namely the eccentric Venturi flow measuring device,is proposed.The eccentric Venturi tube shrinks eccentrically towards the bottom,and the bottom remains straight without bulge.This flow measuring device maintains the characteristics of small head loss of traditional Venturi flowmeter,and at the same time,the problem of bed mass accumulation is not easy to occur on the upstream side.2.The paper conducts real-flow tests and numerical simulations of DN100 eccentric Venturi tubes.By comparing and analyzing the result data,it is concluded that the pressure difference between the two and the discharge coefficient are basically similar,thus proving the feasibility of FLOW-3D simulation of the eccentric Venturi3.The numerical simulation method was used to study the hydraulic characteristics of the eccentric Venturi and the appropriate diameter reduction ratio.The effects of the reduction ratio and Reynolds number changes on the flow measurement performance of the eccentric Venturi tube was systematically studied.By analyzing the relationship between the flow and pressure difference of the eccentric Venturi,the discharge coefficient,permanent pressure loss and flow field distribution characteristics,have a preliminary understanding of its current measurement accuracy,energy loss,and flow pattern change law.The research results show that in the range of low Reynolds number,the relationship between the flow rate of the eccentric Venturi and the head difference is consistent with the general theoretical formula of the differential pressure flowmeter,and the stability of the discharge coefficient is good.The suitable diameter reduction ratio is initially determined to be 0.40?0.60.4.The numerical simulation method was used to compare the hydraulic characteristics of eccentric Venturi and standard Venturi.Models of eccentric Venturi tube and standard Venturi tube with equal diameter reduction ratio are established,and the flow measurement characteristics of the two Venturi tubes are compared and studied through numerical simulation under constant flow conditions.The simulation results show that the discharge coefficient of the eccentric Venturi is slightly smaller than that of the standard Venturi,but both have good stability and the accuracy of the flow measurement can meet the requirements;the permanent pressure loss of the eccentric Venturi is slightly higher than that of the standard Venturi,but its pressure loss ratio can also be controlled below 20%,which is still a low-pressure loss water measuring device.Therefore,the eccentric Venturi flow measuring device can meet the water measurement requirements of the low-pressure pipe irrigation system. |
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