【作者】 张旭；

【导师】 蔡守华； 张福贵；

【作者基本信息】 扬州大学 ， 农业工程（专业学位）， 2019， 硕士

【摘要】 我国是一个农业大国,农业是我国的用水大户。由于人口增加,工业发展,城市化进程加快,非农业用水不断增加,对加强灌区用水管理、控制农业灌溉用水、提高灌溉水利用效率提出了更高的要求。灌区实行量水测水,是合理调度水资源,实现水资源高效、可持续利用的重要手段。随着灌区量水工作的逐步推进,对量水设备和量水技术提出了更高的要求。本文根据文丘里原理,提出一种适用于小型灌溉渠道量水的偏心孔板流量计,并研究了该设备用于灌区末级渠道量水的可行性。本文主要研究成果如下:(1)比较了 DN200涵管10cm孔径偏心孔板流量计现场试验率定数据与数值模拟结果,主要比较淹没出流情况下,试验与模拟所得的闸后水深、堰上水头、流出系数,结果表明两者吻合度均良好,证明了运用FLOW-3D进行数值模拟的可行性。(2)利用FLOW-3D进行模拟计算,对DN200、DN300、DN400涵管的偏心孔板流量计进行了不同孔板孔径条件下的测流数值模拟。主要讨论了流速变化和孔径比变化对流场的影响、流速变化和孔径比变化对流出系数的影响、同一孔板孔径的流出系数取平均计算管道过流流量的误差分析并选出最适宜安装的孔板孔径。数值模拟结果显示:①管内流速越快,孔板下游流态越紊乱,涡流越剧烈,造成的永久压力损失越大,同时随着流速的增大,孔板上游的压力越来越大,孔板下游的压力越来越小,所以流速增大孔板前后压差也随之增大;当孔板孔径较小时,流出系数随流速的变化幅度很小,基本保持稳定,当孔板孔径较大时,流出系数受下游淹没水头的影响整体趋势随流速的增大而逐渐增大;②孔径比增大,孔板下游流态越稳定,涡流区域越小,造成的永久压力损失降低,同时随着孔径比增大,孔板上游取压点的压力减小,下游取压点的压力增大,孔板前后流体的压差减小,而流出系数整体变化趋势为增大;③在一定孔径范围内,对于同一管径,同一孔板孔径,不同流速情况下渠道实际流量与通过管道底部孔板上下游D-D/2取压方式取得的压力差值计算得到的理论流量之比存在一固定系数,即不同流速所求的流出系数值近似为一常数;④通过误差分析发现测流误差总体随着孔径比的增大而增大,在本文所研究的孔径范围内,当0.5D≤d≤0.75D(d为孔径,D为管径)时,测流误差小于±5%;当d>0.75D时,测流误差超过±5%,因此实际渠道中运用时,可采用孔径比为0.75的偏心孔板,既满足测量精度又不产生明显的水头损失。更多还原

【Abstract】 China is a large agricultural country,and agriculture is a big household in China.With the increase of population,the development of industry,the acceleration of urbanization and the continuous increase of non-agricultural water use,higher requirements have been put forward to strengthen the management of water use in irrigation area,control agricultural water use and improve the efficiency of irrigation water use.Measuring and measuring water in irrigation area is an important means to rationally dispatch water resources and realize efficient and sustainable utilization of water resources.With the gradual advancement of water measuring work in irrigation area,higher requirements have been put forward for water measuring equipment and technology.Based on the Venturi principle,an eccentric orifice flowmeter for measuring water in small irrigation canals is presented in this paper,and the feasibility of using this device to measure water in the last stage of irrigation canals is studied.The main achievements of this paper are as follows:(1)Comparing the calibration data and numerical simulation results of DN200 culvert tube 10 cm orifice eccentric orifice flowmeter,mainly comparing the water depth behind the sluice,the head of weir and the effluent coefficient under the condition of submerged outflow.The results show that the goodness of fit is good,which proves the feasibility of using FLOW-3D for numerical simulation.(2)FLOW-3D was used to simulate the flow measurement of eccentric orifice flowmeters with DN200,DN300 and DN400 culverts.The influence of velocity change and aperture ratio change on the flow field,the influence of velocity change and aperture ratio change on the effluent coefficient,the error analysis of averaging the effluent coefficient of the same orifice plate to calculate the flow rate of the pipeline through the orifice are discussed,and the most suitable orifice plate diameter is selected.The numerical simulation results show that:① The faster the flow velocity in the tube,the more turbulent the flow pattern downstream of orifice plate,the more intense the eddy current,the greater the permanent pressure loss.At the same time,with the increase of the flow velocity,the pressure upstream of orifice plate becomes larger and larger,and the pressure downstream of orifice plate becomes smaller and smaller,so pressure difference before and after orifice plate increases with the increase of the flow velocity.When orifice diameter is small,the effluent coefficient varies little with the flow velocity and keeps stable basically.When orifice diameter is large,the effluent coefficient increases gradually with the increase of flow velocity;② With the increase of aperture ratio,the flow pattern downstream of orifice plate is more stable,the eddy region is smaller,and the permanent pressure loss decreases.At the same time,with the increase of aperture ratio,the pressure at the upstream of orifice plate decreases,the pressure at the downstream of orifice plate increases,the pressure difference decreases before and after orifice plate,and the overall variation trend of flow coefficient increases;③ Within a certain orifice plate aperture range,for the same diameter,the same orifice plate aperture,the ratio of the actual flow rate of the channel to the theoretical flow rate calculated by the pressure difference between the upstream and downstream D-D/2 through the orifice plate at the bottom of the pipeline has a fixed coefficient,that is,the flow coefficient value obtained by different flow rates is approximately a constant;④ The error analysis shows that the flow measurement error increases with the increase of the aperture ratio.In the range of the aperture studied in this paper,when 0.5D≤d≤0.75D(d is aperture,D is pipe diameter),the flow measurement error is less than ±5%,when d>0.75D,the flow measurement error is more than ±5%.Therefore,eccentric orifice plate with aperture ratio of 0.75 can be used in the actual channel,which not only meets the measurement accuracy but also does not produce obvious head loss.更多还原