Numerical Simulation Of Soil Water And Heat Transfer Under Vertical Pipe Surface Drip Irrigation

Desertification with high wind and sand flow,arid climate and high surface temperature are not conducive to the survival of sand fixing plant seedlings,and there are many problems with plant sand fixation.In order to solve the damage of soil drought and high surface temperature to the sand fixing plant seedlings simultaneously,a vertical pipe surface drip irrigation system is designed.As a newly developed irrigation technology,the practical application of vertical pipe surface drip irrigation system still lacks a certain theoretical basis and needs further research.In this paper,the method of combining numerical simulation and experimental verification was used to study the soil water and heat transfer in vertical pipe surface drip irrigation system.When the soil temperature and water temperature are constant,the soil water movement characteristics of four kinds of aeolian sandy soil with two scenarios of vertical pipe water accumulated infiltration and vertical pipe surface drip irrigation under different influencing factors of saturated hydraulic conductivity,drip discharge,vertical pipe diameter,and vertical pipe buried depth.Based on this study,the changes of soil temperature during low-temperature water irrigation under the same drip discharge were studied,and the effects of different drip discharge and water temperatures on soil temperature were analyzed,as well as the effects of water temperature and soil temperature on soil water movement.The main research contents are as follows:(1)When the soil temperature and water temperature are constant,the numerical simulation of soil infiltration rate under the situation of vertical pipe water accumulated infiltration and the wetting front transport distance under the situation of vertical pipe surface drip irrigation agree with the experimental data and have a high degree of affinity;During the low temperature water irrigation process of vertical pipe surface drip irrigation,the error between the measured values of soil temperature and moisture at the observation points in the laboratory test and the simulated values of HYDRUS-2D is small.The established mathematical model for soil water movement and water heat transfer of vertical pipe surface drip irrigation is correct,and the simulation of water movement and water heat transfer process of vertical pipe surface drip irrigation system with HYDRUS-2D software is feasible.(2)For vertical pipe water accumulated infiltration,the soil stable infiltration rate increases with increasing saturated hydraulic conductivity and vertical pipe diameter.On the other hand,it decreases with increasing vertical pipe buried depth.An estimation model of the i_fincluding the vertical pipe buried depth,vertical pipe diameter and vertical pipe buried depth,was established(power function multiplication form).The power function exponents were 0.87,1.89,and-0.37,respectively,and the power function coefficient was 0.17.Experiments verify the reliability of the model.The RMSE is 0.05 L/h,and the NSE is 0.98.The model can provide a reference for selecting drip discharge for vertical pipe surface drip irrigation systems.(3)Under vertical pipe surface drip irrigation,the soil wetting front transport distance conforms to the rule of downward direction>horizontal direction>upward direction.The soil wetting front transport distance is positively correlated with the saturated hydraulic conductivity and drip discharge and negatively correlated with the vertical pipe diameter and vertical pipe buried depth.The saturated hydraulic conductivity and drip discharge significantly affect the wetting front transport distance in the three directions.In contrast,the vertical pipe diameter only substantially impacts the wetting front transport distance in the horizontal and upward directions.The vertical pipe buried depth has a relatively small effect on the wetting front transport distance in the three directions.The time for the wetting front to reach the surface is shortened with increasing saturated hydraulic conductivity and drip discharge and prolonged with increasing vertical pipe diameter and vertical pipe buried depth.(4)The calculation formula for the time required for irrigation water to reach the bottom of the vertical pipe was determined.A model for estimating the wetting body size of vertical pipe surface drip irrigation was developed,including saturated hydraulic conductivity,drip discharge,vertical pipe diameter,vertical pipe buried depth,and irrigation time.Experimental data were used to evaluate the reliability of the estimation model.The RMSE was between 0.17 and 0.41 cm,with an average of 0.31cm.The NSE was between 0.88 and 0.95 cm,with an average of 0.92.The model had an excellent prediction effect and can provide a theoretical basis for the practical application of vertical pipe surface drip irrigation systems.(5)There are significant differences in temperature changes at different depths of soil.At the horizontal distance of 0 cm,the shallower the burial depth,the more obvious the soil temperature change,the earlier the time of temperature change,the lower the soil temperature after the end of irrigation,the larger the peak of the temperature change curve with time;at the horizontal distance of 10 cm,the shallower the burial depth,the higher the soil temperature,the larger the temperature change.There are differences in soil temperature changes at different horizontal distances at the same burial depth,the greater the horizontal distance,the higher the soil temperature;there is a big difference between soil temperature changes inside and outside the vertical pipe at the same burial depth;different burial depths,the variability of soil temperature in the horizontal direction between the observation points are different.(6)Drip discharge affects the soil temperature change during the irrigation process of vertical pipe surface drip irrigation.The higher the drip discharge,the lower the soil temperature at the end of irrigation,and the earlier the temperature change;the influence of drip head flow rate on temperature change is greater when the soil is shallow,and less when it is deeper.Irrigation water temperature also affects soil temperature,the same observation point under different water temperature soil temperature change curve is basically the same;the lower the irrigation water temperature,the lower the soil temperature after the end of irrigation,soil depth and horizontal distance,the water temperature on the soil temperature influence degree of different size.(7)Irrigation water temperature has a certain influence on soil moisture movement.The higher the water temperature,the lower the water content of the observation point at the end of irrigation;when the soil is buried deeper,the effect of water temperature on soil moisture is subtle,and soil moisture is positively correlated with water temperature.Soil temperature also affects soil moisture movement,and the degree of influence of soil temperature on soil moisture increases with soil depth and then decreases;the higher the soil temperature,the lower the soil moisture content of each observation point at the end of irrigation;the soil moisture change curves of each observation point under different soil temperatures have intersection points,before the intersection point,soil moisture is positively correlated with soil temperature,and after the intersection point,soil moisture is negatively correlated with Before the intersection point,soil moisture was positively correlated with soil temperature,after the intersection point,soil moisture was negatively correlated with soil temperature.