Peiling Yang

CFD and digital particle tracking to assess flow characteristics in the labyrinth flow path of a drip irrigation emitter

It is necessary to have a comprehensive understanding of the flow mechanisms within drip irrigation emitters to design emitters that have a high anti-clogging performance. The use of computational fluid dynamics (CFD) to research the flow characteristics is appropriate because the labyrinth flow path is narrow and its boundary is complex. In this paper, a CFD for numeric model was developed for numerical simulation of the velocity distribution and turbulence intensity distributions within labyrinth emitters. A two-dimensional digital particle-tracking velocimetry (2D-DPIV) visual display system of the full flow fields was also constructed using plain laser inducement fluorescence velocity measurement technology, custom-made fluorescent particles and a plane model of the emitters. The object lens of a microscope was fitted to a conventional charge coupled device (CCD) camera to overcome the contradiction problems between the image viewing area and resolution power within the flow path. The measured turbulence and velocity distribution characteristics within the labyrinth flow path were in good agreement with the calculated CFD results. This enabled the optimal emitter design patterns to be determined based on the hydraulic characteristics and clogging resistance in the labyrinth flow path.

Hydraulic Characterizations of Tortuous Flow in Path Drip Irrigation Emitter

At present, the tortuous emitter has the most advanced performances in drip irrigation. But the theories and methods for designing its flow path have been strictly confidential and the researches on the function of practical guidance have seldom been published. Seven types of most representative tortuous emitting-pipes currently used in agricultural irrigation regions of China were chosen for investigating the geometric parameters of the flow path by means of combining high-precision microscope and AutoCAD technology. By the measurement platform developed by the authors for hydraulic performances of emitters, the free discharge rates from the 7 types of emitters were measured at 9 pressure levels of 1.5 m, 3.0 m, 5.0 m, 7.0 m, 9.0 m, 10.0 m, 11.0 m, 13.0 m and 15.0 m. Then the discharge-pressure relationship, manufacturing variation coefficient, average velocity on the cross-section of flow path and the critical Reynolds number for the flow regime transformation within the paths were analyzed in detail. The results show that both pressure-ascending work pattern and pressure-descending work pattern have some impacts on the discharge rates of tortuous emitters, but the impact level is not significant. The target pressure could be approached by repetitive applications of the two work patterns during pressure regulation. The operation under low pressures has some impacts on the hydraulic performances of emitters, but the impact level is also not significant. The classical model of the discharge-pressure relationship is suitable for the pressure range of 1.5 m –15.0 m. The Reynolds number for fluids within the 7 types of tortuous emitters ranges from Re =105 to Re =930. The critical Reynolds number for the flow regime transformation is smaller than that for the routine dimension flow path. The variation coefficient of emitter discharge rates is slightly fluctuating around a certain value within the whole pressure range.

Flow Characteristics in Energy Dissipation Units of Labyrinth Path in the Drip Irrigation Emitters with DPIV Technology

The energy dissipation mechanism and anti-clogging properties of drip irrigation emitters are closely related to flow characteristics of the fluid in its flow paths, and flow field tests using modern flow visual technologies were carried out by a large number of designers. The Digital Particle ImageVelocimetry (DPIV) system was built for un-disturbed flow tests in the labyrinth path. In this article, the flow field was measured in the flow path section, the structural unit and the local region near sawtooth. Under the pressure level of 10 Kpa, 50 Kpa, 100 Kpa and 150 Kpa, the flows in the two labyrinth paths were in the turbulence state, with flow stagnation regions and whirlpool regions in the structure of the labyrinth path sections. The flow stagnation regions should be eliminated as much as possible. But the vortex should be fully developed, which could increase the self-cleaning capacity and the anti-clogging capacity of the emitter. With respect to the anti-clogging performance and the energy loss efficiency of the emitter, the M-type flow path is better than the K-type flow path.

Simulation of the flow characteristics of a drip irrigation emitter with large eddy methods

Realizing the internal flow visualization inside the drip irrigation emitter is the basis of optimizing the labyrinth path structure and promoting its anti-clogging capability. The Computational Fluid Dynamics (CFD) method has become an effective approach to research the water movement in the labyrinth path of the drip irrigation emitter. In this paper, the standard k-epsilon model and the Large Eddy Simulation method (LES) were applied to analyze the flow characteristic in the drip irrigation emitter. The results showed that the LES model was more effective to simulate the flow characteristics in the flow path of drip irrigation emitters. Based on this model, the energy dissipation mechanism was explained with the velocity and pressure values from local regions to the whole flow path, and the study of the flow path anti-clogging performance was carried out by way of analyzing the velocity distribution characteristics in different cross sections of the same structure unit

Impact of Simulated Irrigation with Treated Wastewater and Saline-Sodic Solutions on Soil Hydraulic Conductivity, Pores Distribution and Fractal Dimension

Irrigation with treated wastewater which has the characteristics of higher salt content, larger sodium adsorption ratio (SAR), and more organic matter and suspended particles can cause the deterioration of the soil environment. Ordinary water, treated wastewater, and saline-sodic solutions with SAR = 3, 10 and 20 (mmolc·L− 1)0.5, respectively, were used as five irrigation water types, and the changes of soil saturated hydraulic conductivity (K s), soil pores distribution, and soil pores single fractal dimension (D m) were studied after simulated irrigation for 1 and 2 years with simulated irrigation systems, which consisted of soil bins and simulated evaporation systems. The results showed that soil K s in the following descending order: CK > SAR3 > WW > SAR10 > SAR20, and the adverse effects on soil K s caused by suspended solid particles and dissolved organic matter might play a more significant role than sodium in treated wastewater. The 0-5 cm soils had a smaller single soil pore area but larger pores quantity after simulated irrigation, the distribution of soil pores which was irrigated with treated wastewater had a smaller change compared with saline-sodic solutions treatments, and it showed the soil pores structure binary image was an effective method to analysis soil pores distribution. Soil D m increased after simulated irrigation, and the smallest was the soil simulated irrigation with treated wastewater for 1 year, because the plugging and filling of suspended particles and dissolved organic matter in treated wastewater made the soil pores well distributed, but the soil D m did not increase with increasing of SAR levels in irrigation waters. The relative SAR levels irrigation to soils and soil K s had a good linear correlation relationship, while the relationship between soil D m and the relative SAR levels irrigation to soils was very complicated. The soil D m which calculated from soil binary images could not well reflect the hydraulic conductivity of saturated soil. Irrigation with treated wastewater had a greater effect on soil K s than soil D m, comparing with saline-sodic solutions which had the similar SAR value. It was suggested that the future research should consider both the horizontal and vertical directions of soil D m to well reflect the soil K s.

The Vulnerability Assessment Method for Beijing Agricultural Drought

Drought is a major disaster which Beijing agricultural systems faced with, build drought warning mechanism we need in-depth analysis the causes and mechanism of the drought to provide a basis for scientific disaster reduction and prevention. VAM vulnerability assessment method, selected 15 factors represent drought exposure, sensitivity and adaptive capacity, based on improved analytic hierarchy process to determine the weight of each factors, use K-means clustering algorithm to generate the drought vulnerability index system of research district. Draw vulnerability zoning map based on ArcGIS.

An improved canopy transpiration model and parameter uncertainty analysis by Bayesian approach

In this paper, an improved canopy transpiration (Ec) model that considered the unidirectional influence of soil evaporation on Ec was presented by extending Penman-Monteith model for increasing accuracy of modelling in sub-humid regions, and a Bayesian approach was used to fit the transpiration model to half-hourly transpiration rates for the 14-year-old cherry (Prunus avium L.) orchard collected over 4-month period and probabilistically estimated its parameters and prediction uncertainties. The probabilistic model was extended by adding a normally distributed error term, and the Markov chain Monte Carlo simulation method was used to determine the posterior parameter distributions. Seasonal variation of the Ec was analyzed by the experiments of Sap Flow method in Sijiqing Orchard in Beijing, north of China. The result showed there were larger uncertainties of the parameter and transpiration. The average value of parameters was used for the model, and long series data from simulated value of the model were compared with the measured data, and it showed that the improved transpiration model possessed high accuracy.

Mathematical model of ammonium nitrogen transport with overland flow on a slope after polyacrylamide application

The nutrient loss caused by soil erosion is the main reason for soil degradation and environmental pollution, and polyacrylamide (PAM) as a common soil amendment has a great influence on runoff and erosion processes at the slope. In order to investigate the mechanism of nutrient transport with runoff, a field experiment was conducted and a simple mathematical model was developed in this study. Four PAM application rates (0, 1, 2, and 4 g·m−2) and two rainfall intensities (50 and 80 mm·h−1) were applied in the field experiment. The results revealed that runoff rate of 2 g·m−2 PAM application treatments decreased by 5.3%-10.6% compared with the control groups, but it increased by10.9%-18.7% at 4 g·m−2 PAM application treatments. Polyacrylamide application reduced ammonium nitrogen concentrations of runoff by 10.0% to 44.3% relative to the control groups. The best performance with correlation coefficient (R2) and Nash–Sutcliffe efficiency (NSE) showed that the ammonium transport with runoff could be well described by the proposed model. Furthermore, the model parameter of the depth of the mixing layer (hm) linearly increased with an increase in flow velocity, but exponentially decreased with an increase in PAM application rate.

A DNA Tracer System for Hydrological Environment Investigations

To monitor and manage hydrological pollution effectively, tracing sources of pollutants is of great importance and also is in urgent need. A variety of tracers have been developed such as isotopes, silica, bromide, and dyes; however, practical limitations of these traditional tracers still exist such as lack of multiplexed, multipoint tracing and interference of background noise. To overcome these limitations, a new tracing system based on DNA nanomaterials, namely DNA tracer, has already been developed. DNA tracers possess remarkable advantages including sufficient species, specificity, environmental friendly, stable migration, and high sensitivity as well as allowing for multipoints tracing. In this review article, we introduce the molecular design, synthesis, protection and signal readout strategies of DNA tracers, compare the advantages and disadvantages of DNA tracer with traditional tracers, and summarize the-state-of-art applications in hydrological environment investigations. In the end, we provide our perspective on the future development of DNA tracers.

Characteristics of E. japonicus stomatal conductance under water-deficit stress using a nonlinear Jarvis modified model

Abstract Stomas are important gateways in the photosynthesis and transpiration of plant leaves. The stomatal size directly influences the photosynthetic and transpiration rates. However, the stomatal size is closely related to environmental factors. This study aimed to reveal the response principle between the leaf stomatal conductance of Euonymus japonicus and related environmental factors under water stress using pot experiments. The present paper introduced the difference between the leaf and air temperatures ( Δ T ) based on the Jarvis model, as well as established the improved Jarvis model between stomatal conductance and environmental factors. After optimizing the model parameters by the least-square method, the parameters were verified by the crossing method. An artificial neural network model was then introduced and compared with the former two. The results showed that the simulation results of the improved Jarvis model were better than those of the Jarvis and artificial network models. Compared with the Jarvis model, the improved Jarvis model had RMS and MRE errors that were at least 65% smaller, as well as a correlation coefficient ( R 2 ) that was at least 10% higher. The improved Jarvis model simulation results were more uniformly distributed than the Jarvis model on both sides of the 1:1 regression line. Therefore, under a water stress condition, the improved Jarvis model is more appropriate to use in simulating the stomatal conductance relationship of E. japonicus with environmental factors.