双向流滴灌灌水器消能机理PIV试验研究

Research on the energy dissipation regime of bidirectional flow channel in drip irrigation emitter with PIV

滴灌灌水器流道内部水流运动特性与其水力性能密切相关。该文以双向流滴灌灌水器为研究对象,利用粒子成像测速技术(PIV, particle image velocimetry),分别在30 kPa和130 kPa进口压力条件下,观测灌水器流道内部水流运动特征,获取水流流速和湍流强度等水流运动的分布特性,据此分析了流道的消能机理。结果表明:流道内正向和反向水流形成了双S型主流流动及漩涡流动,水流流动呈现为紊流状态;灌水器进口压力的增加并未显著改变流道水流运动特征及漩涡的分布位置;在流道分流处、转角处及混掺处水流流速变化较为剧烈,为流道主要消能位置;随着进口压力升高,正向和反向水流在混掺前与混掺后的流速差均显著增加,有利于提高流道对冲、混掺消能效果;反向水流在混掺前与混掺后的流速差均高于正向水流,且随着压力升高,两者的差距显著增加,说明反向水流在混掺消能过程中的作用大于正向水流;流道湍流强度大部分在0.1-0.4之间,紊流程度较高,有利于在流道中消除多余能量,以确保灌水器出流量稳定。研究结果从微观角度揭示了双向流滴灌灌水器在不同进口压力下的消能机理,可与宏观试验及数值模拟相结合,为进一步优化流道结构及提高双向流滴灌灌水器水力性能奠定理论基础。

The hydraulic performance of drip irrigation emitter is closely related to fluid field characteristics.Hence,to design emitters with high hydraulic performance,it is necessary to have a comprehensive understanding of the flow regime within the flow channel.Base on this,the PIV system had been built to realize the visual observation of fluid field in this paper.Some micro-characteristics,such as the flow velocity distribution an d turbulence intensity distribution,were measured under 30 kPa and 130 kPa.The results showed that the flow in the bidirectio nal flow channel moved along a double S-shaped path,with some whirlpool regions.During this process,the flow velocity chang ed very rapidly and energy exchanges continuously occurred to dissipate the pressured energy.Especially,a strong mixing phenom enon occurred at the mixing area,which resulted in a large loss of the local pressure.This was the main different form compare d to labyrinth emitter with respect to energy dissipation.The mixing extent increased significantly as a function of pressure increa sing.The backward flow played a more important role than the forward flow in mixing process.Therefore,much more attention s hould be paid to the flow velocity of forward flow in order to enhance the mixing extent of flow channel.It was also observed th at the turbulence intensity of the bidirectional flow channel mostly ranged from 0.1 to 0.4.Higher turbulence intensity indicated more energy consumption in the flow channel.The findings can provide a theoretical foundation for optimizing the structure and promote the hydraulic performance of the bidirectional flow channel emitter.