| Drip irrigation is one of the most efficacious water-saving irrigation methods with the merits of high uniformity of irrigation,water-saving and fertilizer-saving,improved crop quality,and increased yield and income at present.It is a water-saving irrigation technology developed by modern agriculture and a measure of clogging of the irrigation device.Blocked irrigation is one of the main problems that constrain the application of this technology.The study indicated that the jet tee structure model invented by using the jet attachment wall and load switching principle can be directly used as a pulse generator to generate intermittent fluctuating water flow in the capillary tube,which has the excellence of strong water turbulence,high irrigation uniformity and reduced system maintenance cost.In this paper,the jet tee element was utilized as the pulse generator of dynamic water pressure drip irrigation system,the performance parameter test platform of the pulse drip irrigation system was constructed,the experimental study of the convective index and the uniformity of irrigation under pulse pressure was carried out,the decay law of the pulse characteristics along the drip irrigation belt was summarized,and the structure was optimized for the improvement of the pulse characteristics of the capillary jet tee,and the test prototype was processed for test verification.The content and results of the study are as follows.(1)Conduction of experimental studies on the flow index and irrigation uniformity of pulse parameters under pulse pressure.The results declare:1)The expressions of the irrigator flow pressure relationship between wave peaks and troughs and average pressure under pulse pressure conditions were explored.By comparison,it was discovered that the pulse wave average pressure could more accurately reflect the dynamic water pressure irrigator flow pressure relationship expression,and the flow state index under this condition can be exploited as the flow state index x under the pulse drip irrigation system condition.2)The variation of pulse parameters on the uniformity of irrigation water was investigated to find the pulse parameters corresponding to the optimal uniformity of irrigation water.It was found that when the optimal irrigation water pressure was 80 kPa,the uniformity was98.69%,the pulse frequency was 4.2 Hz,and the head amplitude was 49 kPa.3)Compared with the condition of constant pressure,the inlet flow rate of drip irrigation belt is the same as that of pulse wave peak pressure and constant pressure at the inlet of drip irrigation belt.Meanwhile,the pulse pressure of both test schemes can reduce the flow index of the emitter and improve the uniformity of irrigation water.In the first scheme,the uniformity of irrigation was increased by 0.19%~1.80%,and the deviation rate of flow was reduced by 2.18%~6.47%.(2)Exploration of pulse and hydraulic characteristics along drip irrigation zones.By calculating the flow pressure distribution at each monitoring point along the 60 m long drip irrigation zone,the attenuation law of the pulse characteristics along the drip irrigation zone was determined and the head loss under pulse and constant pressure conditions was compared and analyzed.The results reveal that:1)The flow threshold for the determination of the jet tee to produce pulsed water flow is 0.2~0.8 m~3/h.2)The pulsed attenuation law demonstrates that when the inlet head amplitude is greater than 10 kPa,there is a mutation point in the attenuation rate of the head amplitude along the route and a peak point in the attenuation of the pulse frequency along the route,and the mutation point and the peak point correspond to each other in the attenuation position along the route.3)The variation of water head loss along the 60m long drip irrigation belt was studied.The water head loss along the pulse drip irrigation capillary was smaller than that of constant pressure drip irrigation.When the inlet flow of the tee is 0.5~0.8 m~3/h,the head loss of drip irrigation under pulse pressure is 5.0~8.5 kPa,and the head loss is reduced by 62.5%~83.3%compared with the constant pressure condition.(3)Taking the optimal pulse parameters and head loss as the evaluation indexes to carry out the structural optimization test of the three-way jet for the uniformity of irrigation water.Six structure size parameters that affect the pulse characteristics were selected as the main influencing factors,and the influence rules of structure size parameters on the pulse characteristics were explored by adopting the method of orthogonal design and CFX numerical simulation technology.The primary and secondary order of each influencing factor is determined by the range method,and the significance analysis of the influencing factor is performed by the variance method.The results manifest that the optimal structure of the jet tee is 3.8 mm nozzle width,10 mm nozzle depth,2 mm control tube width,1.6 mm differential,34 mm split length and 24°sidewall angle.Under the inlet pressure of 50~120 kPa,the flooding uniformity was significantly improved compared with the ordinary tee,the flooding uniformity coefficient was improved by 2.82%~3.05%and the flow rate deviation was reduced by 4.27%~9.17%. |
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