滴灌灌水器水力特性及抗堵塞研究

节水中心2009届博士研究生喻黎明，在导师吴普特研究员、牛文全副研究员的指导下，经过三年努力完成了滴灌灌水器水力特性及抗堵塞研究。

研究方向：节水灌溉新技术

摘  要

迷宫流道结构灌水器的抗堵塞性能与水力性能主要受流道结构参数与固体颗粒特性的影响。本文以齿形流道、梯形流道为主要研究对象，以流道转角、流道高，流道宽、偏差量及梯形流道上底宽为主要结构参数，首先应用CFD单相流数值模拟技术对不同结构参数灌水器流道水力性能进行模拟，分析了不同结构参数对流态指数和流量系数的影响，其次，应用CFD两相流（含沙量为1%）数值模拟技术分析了结构参数对含沙量分布规律和抗堵塞性能的影响，然后，应用PIV可视化测试方法测试了固体颗粒在流道内运行轨迹及速度，分析了影响固体颗粒运动特性及流道内流体流态的基本因素，最后，对上述流道结构形式通过模具加工及滴灌带试制，进行了标准化测试（GB/T 17187-1997 农业灌溉设备 滴头技术规范和试验方法与ISO标准 ISO /TC23 /SC18 /WG5N4短周期堵塞测试程序），测试结果验证了CFD模拟结果，并提出了迷宫结构流道灌水器的抗堵塞设计方法。通过上述研究，本文取得了以下主要结论：

1、梯形流道上底宽对流量系数和流态指数影响显著，且与流态指数和流量系数呈正相关关系；流道转角对流态指数的影响显著，且与流态指数和流量系数呈负相关关系。其它参数如偏差量、流道高、流道宽等对流量系数和流态指数的影响不显著，流道宽、偏移量与流态指数呈负相关关系，流道高与流态指数呈正相关关系；流道宽、偏移量、流道高与流量呈正相关。

2、流道内最大含沙量的数值随结构参数的变化而变化，当最大含沙量增加时，增加了灌水器被堵塞的几率，降低了正常灌水天数。CFD模拟结果与样品试验结果具有较高的一致性，说明CFD固液两相流数值分析灌水器抗堵塞性能是可行的。在流道结构参数中，流道转角对灌水器的水力性能和抗堵塞性能有显著影响，当转角为60°时，灌水器流态指数相对较小，而抗堵塞能力相对较强，建议迷宫流道灌水器设计时宜采用60°转角。

3、按照流道内较小含沙量等值线修改流道结构，消除部分含沙量较高的迎水面、背水面等流道拐角部位，并对修改的流道进行标准化，比较流道尺寸和水力性能，选择最优流道作为新的流道结构，能大幅下降流道内部的含沙量，增加灌水器有效灌水天数，提高了灌水器的抗堵塞性能，而且与修改前的流道相比，其水力性能也有所改善，此方法对提高灌水器抗堵塞性能提供了新的思路。

4、对比分析不同直径和不同密度的固体颗粒运动轨迹线、速度线和路程的CFD模拟和PIV观测结果，表明CFD模拟和PIV观测流道内的颗粒运动规律比较接近，PIV观测颗粒运动时更加靠近水流的主流区因而可以获得较长时间的高速，但无法观测到整个流道的固体颗粒运行轨迹，而CFD却能对整个流道进行模拟。因此，对于流道内的颗粒运动分析应当结合两者的特点。通过PIV观测可知随着流道转角、流道宽增加，颗粒运动越紊乱，颗粒在流道内的运动时间、平均速度和路程越长；而偏差量对颗粒运动的影响与转角的影响接近，只是当偏差量较大时，颗粒可直接从两齿尖直接通过，而很少进入漩涡区，而颗粒一旦进入漩涡区，则其运动时间将大大加长，平均运动速度下降；流道高对颗粒运动的影响不明显。

关键词：迷宫流道灌水器，CFD数值模拟，PIV颗粒观测，结构优化, 抗堵塞性

STUDY ON HYDRAULIC AND ANTI-CLOGGING PERFORMANCE OF DRIP EMITTER

ABSTRACT

Geometrical parameter and characteristic factors of solid particles have great influence on the hydraulic and anti-clogging performance of labyrinth flow path of drip emitter. This paper studies the main geometrical parameter such as angle, height, width, stagger and the upper width in dentation and trapezoid flow path, firstly, uses the single-phase numerical simulation of the computational fluid dynamics (CFD) technique to analyse the influence of different geometrical parameter on discharge coefficient and flow state exponent of drip emitter. Secondly, uses the two-phases numerical simulation of CFD (1% sand content ) to analyse the influence of the above mentioned geometrical parameter on the contribution regulation of sand and anti-clogging performance. Thirdly, uses the PIV（particle Tracking Velocimetry） technique which can see the small-scale flow path to observe and test the trajectories and velocities of solid particles in labyrinth flow path, and analyses the basic factors which can influence the movement characteristic of solid particles and the flow state in flow path. Finally, makes the mould to produce the drip emitter and manufacture the drip tape according to the above mentioned geometrical measurement, and tests all aspects performance under the conditions of standardization(GB/T 17187-1997 Irrigation equipment in agriculture Technique criterion and experiment methods of drip emitter, and ISO short-period testing procedure, ISO /TC23 /SC18 /WG5N4), and validates the numerical simulation results of CFD, puts forward the design methods of anti-clogging about the labyrinth flow path emitter on the basis of the hydraulic performance, by the above mentioned analyze and study, and get the main results following:

1.The upper width in those parameters in trapezoid flow path is the biggest influence factor to flow rate and flow index, furthermore, the relationship each other is positive. Angle in flow path is the biggest influence factor to flow index, the relationship each other is negative, and the relationship between the discharge coefficient and angle is also negative. Other parameters such as offset value, height and width are not the biggest influence factors to flow rate and flow index, the relationship between  width, offset value and flow index is negative, the relationship between height and flow index is positive, the relationship between width ,height, offset value and flow index is positive.

2.The biggest sand content in flow path is changeable when the structural parameters change, when the value of the biggest sand content is increasing, the clogging ratio of drip emitters are increasing, the normal irrigation days are shorting, the results of numerical simulation and testing experiment have good consistency which testifies that it is possible to analyse the anti-clogging performance of drip emitter by the two-phases flow numerical simulation of CFD. The angle in flow path in those structural parameters is the biggest influence factor to the hydraulic and anti-clogging performance, when the angle is 60 degree, the flow index of drip emitter is smaller, and the anti-clogging performance is stronger, thus, designing the flow path it should be 60 degree.

3.Amending the structure of the flow path according to the isoline of smaller sand content, canceling the higher sand content part such as upwind surface, corner and so on, after standardization, comparing the measurements of flow path and hydraulic performance with the original one, and choosing the best one as the new flow path, this method can decrease rapidly the sand content, increase the effective irrigation time, enhance the anti-clogging performance of drip emitter, comparison with the original one, the hydraulic performance improved also, this method is one new thought thread to advance the anti-clogging performance of drip emitter. 

4. The velocity, path length and movement trajectories of the solid particles with different diameter and density simulated and observed by the numerical simulation technique of CFD and observation technique of PIV are close, it is feasible to CFD technique to simulate the movement regulation of solid particles in labyrinth flow path. But the movement of solid particles is more close the main stream by the PIV observation, and the time of higher velocity is more long, due to the observation points by PIV are lack, the trajectories and velocity curves are consist of beelines which connect the all observation points, this method can not descript the trajectories and velocity in any locations, but CFD can do, so, combines the CFD technique with PIV technique to analyse the movement regulation of solid particles.By PIV observation, with the increasing of the angle and width in flow path, the movement regulation of the solid particles are more turbulent, and the average movement speed and path length are longer, the influence of offset value on movement regulation of solid particles is near with the angles’, when the value of offset is bigger, the solid particles can go through the gap, but when solid particles enter into the vortex, the movement time is greatly long, and the average speed decrease greatly, it is not outstanding to solid particles movement regulation influenced by height.  

KEY WORDS: labyrinth emitter, CFD numerical simulation, PIV particle observation, structure optimize, anti-clogging performance