Journal of Irrigation and Drainage Engineering

This paper concerns efficiency improvement of an 8-in. mixed-flow irrigation pump by modification of discharge flow channel. First, computational fluid dynamics (CFD) modeling was validated with the experimental results using an available pump. Next, an investigation on the hydrodynamics structure was carried out by CFD. The investigation revealed large recirculation around the inner annulus area next to the impeller exit plane and jet flow around the pipe wall. This leads to formation of a strong shear layer between jet and recirculation flow. Improvements were realized by reducing the impeller size by 10% to increase the flow cross-sectional area between the impeller exit plane and the tube wall to slow down the jet flow. Bluff body was introduced at the inner annulus adjacent to the discharge flow channel to alleviate a recirculation wake region. The operating speed of the scaled-down impeller was increased from 900 to 1,100 rpm to compensate for the scaling effect, and the blade angle was modified to cope with the change of inlet relative flow angle. Experimental study suggested that more than 10% improvement could be achieved through these modifications. The maximum efficiency of the proposed model was 42%, compared with the maximum efficiency of 37% for the conventional model.

In this study, the hydraulic features of the $SCVW$ (a novel type of sharp-crested V-notch weirs) were scrutinized in the popular vertex angles $\theta$, i.e., 30°, 45°, 60°, 90°, 120°, 128°, and 150°, under aerated, steady and free overflow conditions in an open channel for large physical models. To assess the changes of the discharge coefficient of the $SCVW$ (i.e., $C_{\mathit{dSCVW}}$) versus weir height and $\theta$, widespread laboratory works were performed by measuring the water head over the crest of the weir and the discharge. Special formulas for the $C_{dSCVW}$ in the $\theta =60°$ were checked, and an appropriate empirical equation was recommended. The calculated $C_{dSCVW}$ by the proposed equation was within 0%–10% of the measured values. Three types of nonparametric artificial intelligence (AI) methods, namely, support vector regression ($SVR$), gene expression programming ($GEP$), and a robust hybrid model entitled hybrid ($SVR\text{-}ACO$) were developed to estimate the $C_{\mathit{dSCVW}}$. For the sake of modeling, 196 experimental datasets were applied in the mentioned methods to evaluate the $C_{dSCVW}$ by taking into consideration the dimensionless variables which impact the determining procedure of the $C_{dSCVW}$. In this modeling, by varying the architecture and core factors of the aforementioned methods, several scenarios were defined. The generated mathematical equation of $C_{dSCVW}$ by the best scenario of the $GEP$ was compared with the corresponding measured values in which the results were in 0%–10%. According to the attained statistical indices, scatter plots, and the values of the total grade ($TG$) technique, the hybrid $SVR(RBF)\text{-}ACO$ model was determined as the superior and optimal method to estimate the $C_{dSCVW}$ with high performance and accuracy.

U-flumes are a subset of long-throated flumes suitable for use in wastewater metering. Although their mathematical characteristics are well defined so that they can be readily analyzed with existing design tools for long-throated flumes, specific tests of their performance are sparse in the literature. This study compares rating curves developed using a half-scale physical model, a computational fluid dynamics (CFD) model, and an analytical model (WinFlume). The physical model and CFD model were also used to determine the effects of increasing tailwater and to make comparisons to WinFlume’s predictions of the limiting tailwater conditions for accurate flow measurement (modular limit). Based on the results obtained from the U-flume physical model, WinFlume estimated the rating curve for the study flume with an accuracy within 3%. The rating curve generated with the CFD model had a similar level of accuracy, corresponding to flow measurement errors of $-1.2\%$ to 3.8%. Both WinFlume and the CFD model gave reasonable estimates of the effect of high tailwater on the gauge level reading, but the limited CFD runs used in this study leave room for further work. The results of this portion of the study suggest that both WinFlume and CFD are useful tools for predicting the rating curves of long-throated flumes.

Non–pressure compensating (Non-PC) emitters are employed mainly in drip irrigation systems due to their structural simplicity and low manufacturing costs; however, they present high sensitivity to physical obstruction, even when using filtration. This research aimed to analyze the effects of pulsating pressure, constant pressure, and water exit position in terms of preventing clogging in Non-PC drippers with a labyrinth system. The tests were performed on a test bench, and each treatment had 68 drippers (repetitions). Quartz sand was added to the irrigation water at a $500\mathrm{mg}{\mathrm{L}}^{-1}$ concentration in two granulometric ranges (53–105 and 250–500 μm) to reproduce field conditions. The performance indicators were emitter flow rate ($\mathrm{L}{\mathrm{h}}^{-1}$) and relative flow rate ($q_r$). For the 250–500 μm granulometric range and the emitters positioned with the water exit facing downward, the 30 s constant pressure and 1 min pulsating pressure resulted in the obstruction of all emitters with only 2 h of operation. In the 53–105 μm granulometric range with the emitter hole facing downward, a pulsating pressure with a 1 min cycle was the most efficient at delaying emitter clogging, showing $q_r>75\%$ during the first 16 h of operation. When the dripper exit was positioned facing upward in the most critical situation (constant pressure), no clogging was observed within the two granulometric ranges during the 40 h test. For this emitter model, which is widely applied in horticulture, a water exit facing upward is recommended to prevent clogging by suspended solid particles.

Subsurface drip irrigation systems with water and fertilizer-aerated irrigation technology have helped improve crop yield and quality and are receiving increasing attention in the field of agricultural efficient irrigation. Venturi is an important part of water and fertilizer-aerated irrigation technology as a subsurface drip aeration device, but its performance is yet unknown. Consequently, to explore the working performance of the Venturi applicator as a subsurface drip aeration device, three different structures of DN20 Venturi applicators were selected, and the suction characteristics, working parameters, and stability of the Venturi aerators at five inlet pressure levels were measured according to a certain outlet pressure gradient. The results indicated that the gas injection flow of different Venturi aerators fluctuate in the form of peak–valley quasi periodic motion, and the fluctuation range is $20–300\mathrm{L}/\mathrm{h}$; under different inlet pressure levels, the average gas injection flows of the three Venturi aerators increase with the pressure difference, and the maximum average gas injection flow of the type plasson (PL) and type netafim (NF) types remains generally stable with the increase in inlet pressure. Furthermore, the standard deviation of gas injection flow is consistent with the gas injection flow. Under the same working condition, the type mazzei (MZ)-type Venturi device has the advantages of low working pressure range, large working flow, and high stability compared with PL and NF types, and thus it is suitable for use as the gas-filling equipment of subsurface drip irrigation systems. Furthermore, a suction estimation model related to the working inlet and outlet pressure is constructed, and the suction capacity can be estimated according to the inlet and outlet pressures of the Venturi aerator. The study findings can provide a reference for engineering application selection and help to improve the performance of Venturi.