射流三通产生的脉冲波对灌水器水力与抗堵塞特性的影响

该文应用CFD两相流模拟与水力试验相结合的方法,研究射流三通产生的脉冲水流对灌水器流道水力性能和抗堵塞性能的影响。进行射流三通水力性能试验,获取其脉冲参数(振幅、周期),用以生成波动压力,为数值模拟提供参考;对比射流三通、普通三通下定制灌水器出口流量的模拟值与实测值,验证模拟方法的可行性;数值模拟研究不同时刻脉冲条件下含沙量在流道的分布情况和不同密度、不同粒径颗粒的运动路径及速度变化。结果表明,射流三通产生的波形与同参数正弦波波形类似,可由正弦波代替射流三通波进行模拟。射流三通波形压力和恒压下的流量的实测值与模拟值之间的相对误差在7%以内;脉冲条件下灌水器流道的主流区和漩涡区都具有脉冲性能。脉冲条件下流道最大含沙量低于恒压条件下的22%。同一密度不同粒径条件下,恒压条件高于脉冲水流下颗粒路径的1.21%~26.9%,同一粒径不同密度条件下,恒压高于脉冲水流条件颗粒路径的3.25%~9.6%。综上,射流三通产生的脉冲波能够提高水流的挟沙能力和抗堵塞性能。

Effects of high frequency pulse produced by jet tee on hydraulic and anti-clogging characteristics of emitters

Abstract: The anti-clogging mechanism of pulsed water produced by jet tee in drip irrigation system is unclear. In this study, the influence of pulse wave generated by jet tee on hydraulic and anti-clogging properties was investigated. The flow depth of emitter used by the simulation and test was 1.87 mm, the dentation height was 2.17 mm, the tooth tip distance was 2.07 mm and the corner of runner was 16o. The hydraulic performance test of jet tee was carried out to obtain its pulse parameters (amplitude, period) and to verify the predictions of the computational fluid dynamics (CFD) simulations. The fluctuating pressure with the same pulse frequency as the jet tee was as the pressure inlet boundary condition of CFD. The internal flow of the emitter was described by CFD based on solid-liquid two-phase turbulent model established. The sediment concentration distribution and particles motion path in the emitter channels were obtained by CFD. The waveform produced by the jet tee was similar to the sine wave with the same parameters. A sine wave instead of a jet ternary wave was used for simulation. The relative error between the measured value and the simulated value of the pressure and constant pressure of the jet three-way waveform was samller than 7%. When the inlet water pressure was the same, the average flow rate of the dripper under pulsed water pressure was always smaller than that under constant water pressure. Under the pulse condition, the main flow area and the vortex area of the irrigation channel had pulse performance, and the maximum particle content of the flow channel was lower than 22% under constant pressure. Under the same particle density and different particle size conditions, the particle path in the constant pressure flow was from 1.21% to 26.9%, which was higher than that in the pulse flow. With the increase of particle size, the number of times of the minimum velocity increased, and the instantaneous velocity decreased with the same distance of particle movement. Under the same particle size and different particle density conditions, the particle path in the constant pressure flow was from 3.25% to 9.6%, which was higher than that in the pulse flow. The increase of particle path under the different particle density conditions was smaller than that under the particle size conditions. The comparative analysis above shows that the pulse wave generated by the jet tee would improve the sand-holding ability and anti-blocking performance of the water flow.