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1.
《国际水土保持研究(英文)》2014,2(2):67-78
Rainfall simulators have been used for many years contributing to the understanding of soil and water conservation processes. Nevertheless, rainfall simulators’ design and operation might be rather demanding for achieving specific rainfall intensity distributions and drop characteristics and are still open for improvement. This study explores the potential of combining spray nozzle simulators with meshes to change rainfall characteristics, namely drop properties (drop diameters and fall speeds). A rainfall simulator laboratory set-up was prepared that enabled the incorporation of different wire meshes beneath the spray nozzles. The tests conducted in this exploratory work included different types of spray nozzles, mesh materials (plastic and steel), square apertures and wire thicknesses, and positions of the meshes in relation to the nozzles. Rainfall intensity and drop size distribution and fall speed were analysed. Results showed that the meshes combined with nozzles increased the mean rainfall intensity on the 1 m2 control plot below the nozzle and altered the rain drops’ properties, by increasing the mass-weighted mean drop diameter, for example. 相似文献
2.
Sílvia C. P. Carvalho Joo L. M. P. de Lima M. Isabel P. de Lima 《Land Degradation \u0026amp; Development》2016,27(4):1295-1302
Rainfall simulators are an important tool in studying soil erosion, which is a key process contributing to land degradation. The kinetic energy of simulated rain is central to these studies and it is used as an indicator of the raindrops' ability to detach particles from the soil surface. The main purpose of this experimental work was to explore the usefulness of incorporating meshes underneath pressurised nozzles' rain simulators that intercept the drops sprayed out by the nozzles and change the simulated rain characteristics, namely by increasing the rainfall kinetic energy. The laboratory experiments included testing four types of spray nozzles (discharge from 2·3 to 11·9 L min−1), combined with a high‐density polyethylene mesh (square aperture of 20 mm). The effect of the mesh was studied for three vertical distances between the nozzle and the mesh (0·20, 0·40 and 0·60 m). A laser disdrometer was used to measure the diameter and fall speed of the simulated raindrops. For the mesh‐free simulations, the nozzles produced drops having on average a mean equivalent diameter of around 0·6 mm and a mean fall speed of about 1·5 m s−1. The mesh increased the formation of bigger drops (>2·5 mm) and, consequently, increased the rainfall kinetic energy of the simulated rain; the magnitude of this increase varied with the spray produced by the nozzles. Results show that meshes can be useful for increasing the kinetic energy of the rainfall simulated by nozzles within soil erosion studies. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Methodologies for interrill soil erosion studies 总被引：1，自引：0，他引：1
Due to wide range of experimental techniques reported in the literature for determining interrill erodibility and soil loss values, meaningful comparisons between experiments often cannot be made. Furthermore, inaccurate concepts are developed because erosion processes are dependent upon methodologies. The purpose of this paper is to discuss problems related to both laboratory and field rainfall simulator experiments. Rainfall simulators cannot duplicate a wide range of rainfall intensities and, at the same time, have similar energies as natural rainstorms, unless several different nozzles are used. Rainfall intensity in most simulators is created by varying the frequency of spray oscillation. This intermittent spray characteristic of most simulators, and the constant drop size characteristic of other simulators, greatly affects results. Erosion pan design for laboratory studies and preparation of soil samples placed in the pans also can influence erosion results. We conclude that standardization of rainfall simulator design and test procedures will allow better comparison of erosion results to be made among researchers. 相似文献
4.
相邻喷头喷洒重叠区域内的射流来自不同喷头,喷射过程中往往产生冲撞等相互作用。为研究组合喷头喷洒过程中相邻喷头间射流相互作用对组合喷洒特性造成的影响,选取Nelson D3000锯齿状喷盘喷头和R3000旋转式喷头,对其单独喷洒和以2.5 m组合间距进行喷洒时的水量分布以及雨滴谱信息进行了测试与比较。结果表明:喷头之间相互影响的强弱程度受喷头几何结构的影响,R3000喷头受组合喷洒时喷头间射流的影响作用不明显;Nelson D3000喷头(锯齿状喷盘)受组合喷洒时喷头间射流的影响作用剧烈,水量分布集中点的位置因射流轨迹的变化而产生偏移,喷灌强度最大点向靠近喷头侧偏移约0.5 m。组合喷洒条件下测点MP5处的降水强度、能量通量密度以及水滴数目较单独射流分别增长91.27%、107.58%和239.29%,其中粒径大于0.9 mm水滴数目的增加对该测点水量和能量提升的贡献率达到40.89%和58.83%。变异性分析结果表明水量和能量的重分布主要是由组合喷洒时增加了水滴之间相互碰撞的机率所引起。在Nelson D3000锯齿状喷盘喷头这类喷头进行水量叠加计算时,应考虑相邻喷头间水滴互相碰撞、结合或碎裂等相互作用对组合后的水量分布形式产生的影响,采用单喷头水量分布直接叠加的方法可能会导致计算精度较低。 相似文献
5.
Hans H. Becher 《植物养料与土壤学杂志》1990,153(6):409-414
Using a drop impact transducer, the relative energy and distribution of rains simulated by five different field simulators at almost the same rainfall intensity were monitored along runoff plots. Evaluation of the impact pulses registered with a highly-resolving X-t-recorder indicated that the rainfall energies of all simulators varied with time and position. Despite this variability, in many cases differences between the different rainfall simulators were significant. It was also found that the energy of one simulator was not typical for natural rainstorms and that that of another one was sensitive to wind conditions. Rainfall simulators with moving nozzles as dropformers showed characteristic periodicities in their energy distribution. 相似文献
6.
蒸发式冷凝器喷嘴喷淋性能的数值模拟及试验 总被引：2，自引：1，他引：1
为了研究蒸发式冷凝器喷嘴工作时性能变化情况,该文建立了喷嘴喷淋二维模型,利用计算流体力学计算软件对2种不同喷嘴出水口的喷淋效果进行了模拟,在测试平台上对喷嘴实际喷水效果进行了现场测试,并对其喷嘴结构和布置方式提出改进方案。试验及模拟结果显示:在满足蒸发式冷凝器最小喷淋量的前提下,喷嘴喷水出口处,由于流体运动轨迹发生变化,出口处动压存在不规则分布,喷嘴2局部动压明显高于喷嘴1,动压的不规则分布会直接影响出口处的速度分布情况。在2 m/s进水速度下,冷凝器内腔2种类型喷嘴喷水出口处动压分别为6 000和13 000 Pa,出口处局部最大速度达到3和5 m/s。在模拟中发现,与喷嘴1相比,喷嘴2外部流场静压更加均匀合理,拥有更大的流体出口动压,喷淋面积较大,流体迹线也简单明了,喷嘴2分流槽设计能够提高喷嘴的喷淋效果。在今后设计中,喷嘴1可以通过增设第二层分流平台,来提高内部喷淋水流场均匀性;喷嘴2在原来底座上增加分流槽,增大底座直径,可使喷淋水花更加均匀,增强了盘管液体薄膜传热特性,提高了换热效果。 相似文献
7.
为了深入理解喷嘴直径对旋转折射式喷头水量分布特性的影响规律,以R3000型旋转折射式喷头为研究对象,配备红色6槽的喷盘,选用36种不同直径（1.79～9.92 mm）的喷嘴,在室内无风环境下,采用雨量筒放射线布置法,开展了98、196和294 kPa 3种工作压力下的旋转折射式喷头水量分布特性试验。试验结果表明：在98 kPa工作压力下,使用喷嘴直径1.79～7.54 mm的喷头径向水量分布形式为双驼峰型曲线,使用喷嘴直径7.94～9.92 mm的喷头径向水量分布形式为单驼峰型曲线;在196和294 kPa工作压力下,使用喷嘴直径1.79～9.92 mm喷嘴的喷头径向水量分布曲线均呈现单驼峰型曲线。旋转折射式喷头的水量分布均匀性随工作压力增加而下降;在98 kPa工作压力条件下,除个别喷嘴直径（1.79、1.98 mm）以外,喷头的水量分布均匀性均在60%以上。喷头的喷洒半径范围为4～9 m。喷头的喷洒半径随喷嘴直径增加并非呈单调递增趋势;当喷嘴直径超过7.54 mm（对应38#喷嘴）,随喷嘴直径增加喷洒半径呈下降趋势;并根据试验数据分析结果,确定了喷洒半径随喷嘴直径变化的抛物线模型。喷头的喷灌强度最大值和平均值随喷嘴直径增大而增大,曲线拟合结果表明,喷灌强度最大值和平均值均与喷嘴直径呈明显指数关系,决定系数R2均在0.95以上。研究结果可为低压旋转折射式喷头优化设计、工程应用及促进产品国产化等提供技术依据和参考。 相似文献
8.
Comparison of German and Swiss Rainfall Simulators - Rain Structure and Kinetic Energy The drop size distributions of the investigated rain are significantly different. The rainfall simulators Swanson, Bonn, Basel and Trier culminate in the 2 - 3 mm drop diameter class (～40%) and thus simulate best the drop size distribution of natural heavy rainfall. The structure and the kinetic energy of the rains of eight rainfall simulators have been investigated. The data are compared to those registered during a thunder-shower at the research station of Mertesdorf near Trier/FRG. The results are summarized as follows:
- The impact velocity of artificial raindrops depends on the water pressure within the rainfall simulator, the initial velocity of the raindrops and the fall height. A correction factor to match the kinetic energy of natural rainfall, which is based on the percentage of deviation from the terminal velocity, can be applied only to some extend.
- With respect to various fall velocities of the artificial raindrops all tested rainfall simulators except one yield a rainfall energy between 19 and 27 J/m2 per mm of rainfall.
- The actual amount of precipitation measured at the end of the rainfall experiments sometimes differs significantly from the aimed value of 60 mm/h. Due to this variation, the total rainfall energy during the experiments accumulated to 9 - 15 MJ/ha.
- This high variability depends on the used rainfall simulator. But it also demonstrates the importance of precipitation measurements on the plot during simulations in order to exactly calculate the rainfall energy.
9.
针对传统喷杆喷雾机作业时需水量大、叶片背面雾滴沉积量不足和雾滴分布不均匀等问题,该研究提出一种静电喷雾与喷杆喷雾相结合的施药技术。为探究静电喷杆喷雾机的最佳工作参数,明确不同参数对雾滴雾化效果的影响,利用Fluent软件建立了流场、离散雾场和空间电场耦合仿真模型。仿真试验结果表明,多喷头的空间电场分布均匀性优于单喷头,静电喷雾的雾滴体积中径比非静电喷雾减小12.7%。搭建静电喷雾试验平台,以喷雾水压、充电电压和喷头间距为试验因素,以雾滴的荷质比、粒径、分布均匀性和沉积量为试验指标进行雾滴的荷电特性和沉积特性试验。试验结果表明,多喷头喷雾的雾滴荷质比最大值为0.26 mC/kg,比单喷头喷雾提高52.9%,雾滴均匀性变异系数比非静电喷雾减小32.1%,体积中径减小14.8%,上、中、下层叶片正面的雾滴附着率分别提高27.1%、37.3%和45.2%;静电喷雾的最佳作业参数组合为充电电压6 kV、喷雾水压0.4 MPa和喷头间距250 mm。田间试验表明,静电喷头与常规喷头喷雾施药的病虫害防治效果基本一致,静电喷头的施药用水量减少了60%。在满足防控效果的前提下,静电喷雾能增加雾滴在植株下层和叶片背面的沉积量,有效减少田间作业的需水量,研究结果可为静电喷雾技术在大型喷杆喷雾机上的应用提供参考。 相似文献
10.
PWM连续变量喷雾的雾滴速度和能量特性 总被引：4，自引：3，他引：1
作者研发了一种基于脉宽调制技术（PWM）的连续式变量喷雾装置,并针对平口扇形、中空锥形和实心锥形3种喷嘴研究了此装置的雾化特性。该文介绍了此种装置的喷雾动态特性,即雾滴速度、喷雾比能（SE）、和喷雾动能中值直径（KEMD）随喷雾流量变化的规律。研究中采用丹麦Dantec公司生产的相位多普勒粒子动态分析仪（PDA）、在喷嘴正下方50 cm处测量了雾滴粒径和速度。对测量结果进行统计分析,得到了雾滴速度、SE、KEMD和体积中值直径（VMD）随流量变化的规律。研究结论为：雾滴速度和喷雾比能都随喷雾流量的减小而减小,尤其当占空比小于75%,雾滴速度的减小很显著;KEMD随着流量减小而减小,且与VMD的变化率一致,表明KEMD与雾滴粒径相关。 相似文献
11.
负压反馈射流喷头(简称射流喷头)是中国自主研发的新型中程灌溉喷头。喷管是喷头的重要组成部分,对喷头水力性能影响重大。为针对性研究喷管参数(仰角、长度组合)对射流喷头水力性能的影响,寻找最优喷管参数,开展了不同喷管参数下射流喷头与PY_210摇臂式喷头水力性能对比试验。结果表明,在相同主喷嘴尺寸时,不同工作压力和不同喷管参数下,射流喷头均同比摇臂式喷头射程远1～2.5 m;射流喷头水量分布中近程呈现较好的"三角形"分布,远处出现水量"凸峰"。最后对试验数据采用综合评分法和熵权法进行分析,同时综合考虑实际喷头野外抗风性能和单一造价,确定最优综合评分下的主副喷管参数为:主副喷管长度组合4.2 cm×4.2 cm,工作压力为0.20～0.30 MPa时,主副喷管仰角40°×40°;工作压力为0.35 MPa时,主副喷管仰角30°×30°。 相似文献
12.
便携式人工模拟降雨装置的设计与率定 总被引：3，自引：2，他引：1
用人工模拟降雨研究径流,可以大大缩短试验周期,加速雨水入渗规律和土壤侵蚀规律的研究进程。目前的人工模拟降雨装置普遍存在体积庞大、操作复杂、试验成本高等问题,在现实应用中难以推广。该文针对以上问题设计了一种由喷淋系统和供水系统构成的便携式人工模拟降雨装置。该装置采用单喷头、下喷式模拟降雨结构,通过控制输水管道供水压力和改变喷头型号,实现了不同雨强、不同历时的人工模拟降雨过程。通过降雨特性试验表明,该装置可实现降雨强度为0～140mm/h的模拟降雨,降雨均匀性能保持在80%以上,雨滴直径主要分布在0.1～5.5mm之间,能够满足不同直径的雨滴获得2～2.9m/s的终点速度。试验结果与天然降雨有较高的相似性,可有效实现模拟降雨。 相似文献
13.
由于人工模拟降雨可以解决天然降雨耗时长、成本高以及难以取得精准控制数据等问题,越来越多的学者使用该方法进行科学研究。通过降雨量测量和计算分析方法,测定了Veejet80150喷头降雨特征参数,评价了改进后槽式下喷模拟降雨机的降雨均匀性。结果表明:Veejet80150喷头降雨面积为矩形,且随喷头高度增加而增加,中心点降雨强度随高度增加而减小,并从中心点向外呈规律性减小,便于多喷头组合,获得空间均匀降雨。多喷头组合降雨时,2.5 m高度下的降雨均匀系数在0.88~0.90范围内;4 m高度下的降雨均匀系数在0.94~0.95范围内,该降雨机均匀性好,喷头高度大于2.5 m时可满足试验要求。 相似文献
14.
喷雾助剂类型及浓度对喷头雾化效果影响 总被引：8，自引：5，他引：3
为达到农药减施增效的目的,助剂逐渐成为农药喷洒过程中必不可少的部分,其效果及浓度直接影响着施药过程中农药利用率。为探索不同助剂及浓度对喷头雾化效果的影响,该文利用激光粒度仪比较分析了IDK120-025型和LU120-015型喷头喷施不同浓度典型增效剂意欧、减量增产助剂激健、尿素时,其雾滴体积中径及雾滴分布相对跨度差异。两款喷头应用广泛,喷雾角度相同、喷腔雾化结构相异。结果表明：3种助剂溶液对IDK120-025型喷头的影响效果相比于LU120-015型喷头更为显著,但是LU120-015喷头喷雾雾滴均匀性较优于IDK120-025。激健溶液配比为1:3 000时,在0.4 MPa喷雾压力条件下,与水相比可将IDK喷头雾滴体积中径增加20.43%,粒径分布相对跨度减小1.74%;意欧溶液配比为1:2 000时,在0.4 MPa喷雾压力条件下,与水相比可将IDK喷头雾滴体积中径增加11.10%,粒径分布相对跨度减小8.86%;意欧溶液配比1:3 000时,在0.2 MPa喷雾压力条件下,与水相比可将LU喷头雾滴体积中径减小5.99%,粒径分布相对跨度增大1.56%;尿素溶液在配比1:2 000时,在0.4 MPa喷雾压力条件下,与水相比可将IDK喷头雾滴体积中径增加16.92%,粒径分布相对跨度减小6.92%。该试验可为田间农药施用中助剂及喷头的选择提供依据,为进一步研究喷头及助剂提供数据基础。 相似文献
15.
述评悬线式、针头式、管网式、喷头式4种降雨模拟器的特性及其应用现状与前景。悬线式和针头式降雨模拟器具有降雨强度下限低、均匀性好等优点,但在模拟降雨时,控制面积小,雨滴粒径偏大而且单一,所以应用渐少。管网式与喷头式降雨模拟器所产生的雨滴粒径与能量分布与天然降雨更为接近,广泛应用于土壤侵蚀试验研究中。目前,智能化、自动化、大型化的降雨模拟大厅不断涌现,同时根据雨滴发生基本原理搭建的手控、简易的降雨模拟器仍有其强大的生命力。 相似文献
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针对阻尼喷头外流场水力学特性研究较少的问题,该文研究了单位体积动能、动能强度与有无散水齿、不同喷嘴直径之间的关系。在工作压力分别为175、200、250和300 k Pa,喷嘴直径分别为3.6、4.0、4.4和4.8 mm下,采用激光雨滴谱仪对Nelson R33阻尼喷头的水滴直径、速度和数目等参数进行试验测试,并对试验结果分析及模型建立。结果表明:有无散水齿条件下的单位体积动能均有逐渐增大的趋势;距喷头相同测点处,单位体积动能随喷嘴直径的增大而减小;给出了有无散水齿下不同喷嘴阻尼喷头单位体积水滴动能分布模型,相关系数均在0.94以上;在距喷头0~4 m,不同喷嘴直径的动能强度较小且差值不超过0.002 W/m2,在距喷头较远处,不同喷嘴直径的动能强度差值较大,最大差值达到0.006 W/m2。有散水齿时,动能强度在不同压力下波动均比较小,差值不超过5%。该结果为进一步研究阻尼喷头外流场水力学特性提供理论依据。 相似文献
18.
Spatial variability of throughfall under a single tree: Experimental study of rainfall amount, raindrops, and kinetic energy 总被引：2，自引：0，他引：2
Kazuki Nanko Yuichi OndaAkane Ito Hiromu Moriwaki 《Agricultural and Forest Meteorology》2011,151(9):1173-1182
To evaluate the spatial variability of throughfall amount, raindrops, and erosivity under a single canopy during calm meteorological conditions, indoor experiments were conducted using a 9.8-m-tall transplanted Japanese cypress (Chamaecyparis obtusa) and a large-scale rainfall simulator. Drop size distribution, drop velocity, and kinetic energy of throughfall varied spatially under a single canopy as did throughfall amount and rain rate. Compared with throughfall rain rate, the variability was similar in drop size distribution, lower in drop velocity, and higher in kinetic energy. The results suggest that the spatial distribution of throughfall amount was dominated by the canopy shape and position of branches inside the canopy, and thus the spatial distribution was correlated with the radial distance from the trunk. Throughfall amount and rate were lower at the midway point between the trunk and the canopy edge. Throughfall drop size indices (drop size distribution, drop velocity, and unit kinetic energy) varied spatially while did not differ significantly. On the other hand, time-specific throughfall kinetic energy was correlated with the radial distance from the trunk. The dependence the throughfall kinetic energy on the radial distance from the trunk was dominated by the spatial distribution of throughfall amount. The trend in the spatial distribution of throughfall revealed in this study will aid in modelling canopy water processes and in predicting soil erosion on the bare forest floor. 相似文献
19.
Volker Prasuhn 《植物养料与土壤学杂志》1993,156(1):33-37
Comparison of German and Swiss Rainfall Simulators - Influence of Rainfall Characteristics on Soil Surface Roughness Six different field rainfall simulators were compared. Soil surface roughness was tested by a simple field method before and after rainfall simulation. Preparation of the test site with a rotary cultivator inadvertently entailed spatial variability of roughness and aggregate size. Thus, the plots with finer seedbed showed higher runoff and soil loss. The relative decrease of roughness could best be correlated with the total kinetic energy as well as with the R factor of the different simulators (r = 0.87 resp. 0.91). Thus, the degree of soil surface leveling was shown to be due to the rainfall characteristics of the different simulator types. However, there was no relation between change of soil surface roughness and runoff. The relative classification of the kinetic energy of the rainfall simulators explained the leveling of the soil surface better than the classifications previously used in many studies (r = 0.91 as against r = 0.73). 相似文献
20.
能量相似是降雨模拟的基本原则。通过对雨滴粒径、雨滴击溅速度、降雨均匀度等能量相似要素的分析和探讨,提出实现降雨模拟能量相似的重要手段,即在降雨高度、雨滴发生器等条件不变的情况下,通过调节雨强来实现降雨能量的相似;通过加大供水压力等手段可提高降雨动能,所以在降雨模拟实践中,降雨高度不一定需要达到使所有粒径的雨滴均达到终速所需的高度。 相似文献