| The proposal of dynamic water pressure mode provides a new way to solve the problem of emitter clogging caused by the decrease of the water pressure of the drip irrigation system.The dynamic water pressure aggravates the turbulence of flow in the system,and improves the transport ability of the water to the particles,so as to enhance the anti-clogging performance of the system and the emitter.In this paper,the main research object was the tooth labyrinth channel,and the main research factors were the dynamic water pressure wave parameters,sand grain characteristic parameters and the structure characteristic parameters of labyrinth channel.By means of theoretical analysis,PTV observation test and numerical simulation method,the movement characteristics of water and sediment in the labyrinth channel under different operating conditions were studied;the passing rate of sands was used as the labyrinth channel anti-clogging performance evaluation index,the influence of dynamic water pressure wave parameters,sand grain characteristic parameters and labyrinth flow structure characteristic parameters on the anti-clogging performance of labyrinth channel was analyzed.The anti-clogging mechanism of dynamic water pressure was revealed.Finally,the dynamic water pressure mode and fluctuation parameters in the dynamic water pressure drip irrigation system were optimized,and the filtration requirements of the system and the optimization structure design of labyrinth channel were proposed.By the study above,the main conclusions were drawn as follows:(1)Dynamic water pressure improved the anti-clogging performance in the labyrinth channel effectively,and the trigonometric function waveform dynamic water pressure model can most effectively improve the anti-clogging performance in the labyrinth channel.Comparing with the constant water pressure,flow rates in the channel under dynamic pressure modes showed no significant decrease.At the same time,the retention time of tracer particles in the flow channel was shortened greatly.Therefore,dynamic water pressure could effectively improve the anti-clogging performance in the labyrinth channel.Among the dynamic modes with trigonometric function,triangular,step and rectangular wave forms,the trigonometric function type demonstrated the shortest particles residence time in the flow stagnation region.The deposition probability of particles was the lowest under this mode,indicating a better particles transport capacity in the channel.The fluctuation effect generated by the water under pressure of trigonometric function form produced impact on the low-speed swirl in the stagnation region,and aggravated the turbulence of flow in this region.Therefore,the trigonometric function waveform dynamic water pressure model could improve the anti-clogging performance in the labyrinth channel the most effectively.(2)The basic water pressure and the wave amplitude could significantly change the flow rate of labyrinth channel,the wave amplitude and the fluctuation period could significantly change the flow fluctuation of labyrinth channel.The movement characteristics of single-phase transient flow was simulated by CFD.The primary and secondary influence relationship of dynamic hydraulic fluctuation parameters on flow rate of labyrinth channel was the basic water pressure and the amplitude.The period of waves shows the minimal impact.The primary and secondary influence relationship of dynamic hydraulic fluctuation parameters on flow fluctuation of labyrinth channel wasthe wave amplitude and the fluctuation period.The basic water pressure had the least influence.During a pressure changing period,the pressure distribution structure,the flow velocity distribution structure,and the vorticity position in the labyrinthine flow channel did not change significantly.The value of dynamic hydraulic fluctuation parameters continued to occur greatly fluctuates,generating different insensitive pulsations at each timeline.The turbulence of the water flow in the channel was more intense,the water flow strongly impinged on the solid particles which deposited on the channel wall.The strong impact made the solid particles which stuck in the flow channel detached from the bottom easily and passed through the channel quickly.Thus,it greatly improved the particles transport capacity of the water flow in the labyrinth channel.(3)The basic water pressure and the wave amplitude could significantly impact the sand passing rate.When the basic water pressure was 4 m,the wave amplitude was 3 m,and the wave period was 30 s,the combination of dynamic water pressure fluctuation parameter was the most suitable.The influence of of the variation of the dynamic water pressure parameters on the sand passing rate follows the sequence: the basic water pressure,the ratio of the amplitude to the base water pressure,the amplitude,and the fluctuation period.Using the multiple regression model,a mathematical model was established between the dynamic water pressure fluctuation parameters and the sand passing rate.Based on the above model,the dynamic water pressure fluctuation parameters were optimized and obtained:When the basic water pressure was 4 m,the wave amplitude was 3 m,and the wave period was 30 s,it not only could ensure the high anti-clogging performance of the labyrinth channel,but also can reduce the working pressure of the drip irrigation system.To some extent,the implementation and operating costs of the drip irrigation system was reduced.(4)The application of dynamic water pressure drip irrigation could reduce the filtration demand of the head of the system properly,and the maximum sand content of irrigation water could be appropriately increased.With the continuous increase of the sand particle size,the sand in the labyrinth channel firstly decreased,then gradually increased which presenting a parabolic shape.The sand particle with diameter of 0.1 mm was the blockage-sensitive particle size section of the labyrinth channel under dynamic water pressure.Therefore,the application of dynamic water pressure drip irrigation could reduce the filtration demand of the head of irrigation system properly.With the increase of sand concentration,the passing rate of sand increased,however,the growth rate decreased gradually.The distribution structure of sand in the labyrinth channel showed no obvious variation,and the number of sand particles in the channel increased continuously.Therefore,the maximum sand content of irrigation water in dynamic water pressure drip irrigation could be extended appropriately.(5)The reduction of the channel angle could remarkably improve the sand passing rate in the Labyrinth channel.The angle of the labyrinth channel with the best anti-clogging performance was less than 60°.The sand movement characteristics in the labyrinth channel was simulated by CFD.The effect sequence of the variation of the channel structure parameters on the sand passing rate was angle,tooth height,channel width,upper base width,and tooth tip pitch.Using the multiple regression model,a mathematical model was established between structure parameters and the sand passing rate.It was concluded that the angle of the labyrinth channel with the best anti-clogging performance was less than 60°.(6)The anti-clogging performance of emitters under dynamic water pressure was better than that of constant water pressure.Under constant pressure,the average emitter flow rate only decreased to 63.5% of q0,and there were 15 emitters clogged in total,the uniformity coefficient was reduced to about 29.5% at the end of the irrigation.Under dynamic water pressure,the average emitter flow rate only decreased to 85.3% of q0,there were only 5 emitters clogged in total,and the uniformity coefficient was only reduced to about 75.3% at the end of the irrigation.It showed that the average flow rate and system uniformity of the emitter under dynamic water pressure were much higher than the average flow and system uniformity of the labyrinth channel under constant water pressure.Therefore,the anti-clogging performance of emitters under dynamic water pressure was better than that of constant water pressure. |
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