弧型迷宫流道灌水器颗粒运移状态分析

弧形迷宫灌水器的消能方式主要为沿程水头损失,弧齿形迷宫灌水器主要为局部水头损失;弧形迷宫流道抗堵塞性能优于弧齿形,但其水力性能较差;颗粒在流道中发生旋转的临界速度约为0.5 m/s,当小于此速度时,颗粒易在漩涡处发生旋转,当大于此速度时,颗粒容易逸出漩涡进入主流道。因此,在设计弧齿形迷宫流道时,借助AutoCAD建模和计算流体动力学CFD数值模拟以及低成本PIV试件观测,减少流道内颗粒速度在0.5 m/s以下速度场的分布,以提高灌水器的抗堵塞性能。     

涌泉根灌灌水器抗堵性能试验研究

为了研究大流道涌泉根灌灌水器的水力性能及抗堵性能,在微灌产品测试平台上对其进行了水力性能和短周期抗堵测试,并与常规迷宫流道灌水器进行比较。结果表明,涌泉根灌灌水器流态指数为0.517,制造偏差为3.5%,属优等产品;在含沙水条件下,其出水均匀性高于95%;经强制加沙试验验证,涌泉根灌灌水器与常规迷宫流道灌水器相比,具有较强的抗堵塞能力,并且该灌水器流量大,适合旱地经济林灌溉。     

迷宫流道偏差量对灌水器水力性能及抗堵塞性能的影响

以齿尖偏差量分别为-0.25、0、0.25和0.50 mm的齿形流道结构形式的灌水器为研究对象,应用CFD单相流流场速度数值分析、CFD两相流沙粒浓度分布数值分析、试验样品清水和浑水测试相结合的方法,研究了偏差量对灌水器水力性能和抗堵塞能力的影响.结果表明:偏差量与流态指数呈正相关关系,与流量系数呈负相关关系,而随着偏差量的增加灌水器的抗堵塞能力也在下降,综合分析偏差量对水力性能和抗堵塞性能的影响,认为在满足流态指数的要求下应尽量减小偏差量以提高抗堵塞能力.     

额定压力及低压下内镶片式滴头抗堵塞性能试验

依据ISO短周期滴头堵塞测试方法,测试了12种内镶片式齿型迷宫滴头在额定压力和低压情况下的抗堵塞性能.结果表明:滴头抗堵塞性能随着流道断面最小尺寸增加而提高,当滴头流道断面最小尺寸大于等于0.6 mm时滴头将获得较好的抗堵塞性能,但在0.04 MPa时滴头流道设计形式对滴头抗堵塞性能有更为明显的影响.在过滤器滤网孔径大小选择方面,压力为0.10 MPa时,可选用流道断面最小尺寸的1/5作为有效孔径,而压力为0.04 MPa时,则应按流道最小断面尺寸的1/7来选择.研究还表明,滴灌系统在低压运行时,可通过间歇灌溉的方式来预防和减少滴头的堵塞.     

新型微压侧翼迷宫滴灌带设计方法研究

利用计算流体动力学(CFD)技术对设计的一种新型微压滴灌带的水力特性进行了数值模拟,得到了灌水器内部的压力和流速分布,预测了压力流量关系。研究结果表明:该滴灌带灌水器的流量系数为0.4858,说明流道内为全紊流状态,有利于灌水器的消能,并可提高其抗堵塞性;灌水器进口及出口的压力变化很小,流道内沿水流前进方向压力均匀下降,流道单元相同时,压力变化幅度相同;流道内的流速可分为流道齿尖附近的主流区及齿脚附近的旋流区二个区,每二个单元之间的速度分布基本一致。采用CFD技术进行微压滴灌带结构设计是一种新方法,可快速准确地获得灌水器的水力特性,为其结构设计提供理论指导,同时大大缩短了研制周期,降低开发成本。     

不同工作压力下穿孔形灌水器内的旋涡作用分析

为探究穿孔形流道内的旋涡对灌水器的抗堵塞与消能性能的影响,基于试验验证的数值模拟方法,对4种工作压力下流道中的流场分布、旋涡区的几何特征、涡旋强度及压力分布进行了分析,同时分析了该灌水器内不同粒径泥沙颗粒的运动情况.结果表明:旋涡区可对流道边壁进行持续冲刷清洗并减缓颗粒在流道内部的聚积,旋涡区可发挥抗堵塞作用;旋涡区内不同流速的流层间、旋涡区与主流区间、旋涡区与流道边壁间的摩擦作用都会消耗能量,旋涡区可发挥消能作用;旋涡区可在不同压力下形态稳定.以上分析表明,旋涡区在不同压力下稳定存在,并可提高滴灌灌水器的抗堵塞与消能性能,为灌水器的抗堵塞及水力性能优化提供参考.     

单翼迷宫灌水器进口流场数值模拟与结构优化

针对单翼迷宫式滴灌灌水器工程应用中,大多数堵塞都发生在灌水器进口及其邻近区域的问题,对单翼迷宫式滴灌灌水器进口结构特性和水力性能进行分析,并对内部流场的计算流体进行动力学（CFD）数值模拟研究,发现目前广泛使用的单翼迷宫式滴灌灌水器的进口在实现灌水器多进口安全保障、过滤、抗堵塞等功能方面的设计存在不足之处.应用CAD-CFD技术改进单翼迷宫式滴灌灌水器进口的结构,优化其水力性能.改进后的灌水器5个进口流量基本相同,流速分布也较为均匀.不存在超低流速区,能有效减少灌水器进口的沉积和堵塞,提高灌水器的抗堵塞能力,实现了多进口的安全保障功能.     

Identification of the hydraulic conductivity using a global optimization method

A method to determine the soil hydraulic conductivity via an internal drainage experiment is presented. Identifying the parameters of the hydraulic conductivity is achieved by solving an inverse global optimization problem that uses the water contents measured at different depths and times as matching flow variables. The optimization procedure is combined with a recently developed analytical model for the water content propagation, which essentially assumes that the flow is gravity-driven. A crucial (from the identification point of view) parameter of such a model is the initial position z_W of the draining front, determining the interface between the wetted and dried zone. By using an evolutionary algorithm specifically developed for this problem, it is shown that if information upon z_W is not a priori available, the identification of the hydraulic conductivity is not possible. However, assuming that z_W is known (i.e. measured), and by dividing the model variables by z_W, the optimization is able to fully identify the soil hydraulic conductivity. Finally, in order to show the robustness of the proposed approach, it is shown that the method leads to very good estimates of the hydraulic conductivity even if data are noise-affected, provided that the optimization procedure is coupled to the (Tikhonov) regularization approach.     

迷宫流道转角对灌水器水力性能的影

为研究齿形、梯形以及矩形流道转角变化对水力性能的影响,采用Fluent软件对不同形状下不同转角的流道进行了数值模拟.研究结果表明:当其他条件相同时,转角的变化与流量系数、流态指数呈负相关,其变化对梯形流道灌水器的流量系数影响最大,最多下降了19.03%,齿形流道次之,下降了10.14%,矩形流道是梯形流道转角角度增加的延伸,具有相同的水力性能变化规律;随着角度的增加,梯形流道总的局部水头损失系数最多增加了32.5%,而齿形流道总的局部水头损失系数最多增加了23.4%,变化都很明显;压力较高时,摩阻系数基本保持不变,流体为紊流状态.     

齿型迷宫灌水器抗堵塞性能分析与结构优化模拟

【目的】揭示齿型迷宫流道灌水器物理堵塞的内在流动特性成因,同步优化提出高抗堵型齿型灌水器流道结构。【方法】基于CFD数值模拟技术中的Workbench数值计算平台,对5种不同齿型流道结构(含改进后流道结构)的灌水器进行水砂两相流数值模拟计算,分析了不同齿型结构水流流速、流道内湍动能、湍动能耗散率分布规律及物理颗粒运动轨迹等。【结果】提出了齿型流道结构优化改进方案,优化后的流道结构增加了灌水器内低速区域面积和低速区域湍动能值,区间湍动能范围同比最高提升了52%～200%,同时提高了物理颗粒的运移速率,减少了颗粒运移路程和滞留时间,提升了齿型迷宫灌水器的抗堵塞性能。【结论】齿型流道灌水器的抗堵塞性能与流道内低速区的流体速度及流道内湍动能大小分布密切相关,流速和湍动能较大的区域不易造成堵塞;湍动能最大值均出现在主流区,并且在齿尖迎水区达到最大;湍流动能耗散率分布与湍动能分布具有十分相似的规律,湍动能耗散最严重的区域分布在齿尖处,齿尖结构对灌水器的消能效果起关键性作用。     

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.     

齿间角对迷宫灌水器水力特性影响的数值模拟

为了探究迷宫流道齿间角对灌水器水力性能的影响,应用CFD流场和速度场的数值分析方法,研究齿间角度分别为50°,60°,70°和80°时正齿型和斜齿型迷宫灌水器的流场和速度场随齿间角的变化规律.研究结果表明:相比于RNG k-ε模型和SST模型,标准k-ε模型的计算结果与试验结果更加接近;正齿型和斜齿型迷宫灌水器通道内主要存在2处低速回流区,即齿型的左上侧低速回流区和右下侧低速回流区;相比于正齿型迷宫灌水器,斜齿型迷宫灌水器左上侧的低速区域较多,而右下侧的低速区域较少;随着齿间角度不断增加,灌水器内的流量不断增大,斜齿型迷宫灌水器内的流量增加受齿间角度的影响更为明显;正齿型迷宫灌水器的流量系数较大,但流态指数较小, 齿间角度为70°的正齿型迷宫灌水器的流态指数在所有灌水器中最小,其水力性能最好.     

迷宫流道内沙粒-壁面碰撞模拟与PTV实

以单个沙粒为对象，研究了沙粒与灌水器流道壁面的碰撞过程。采用计算流体力学CFD数值模拟方法，分析了沙粒与壁面碰撞反弹系数Rc对灌水器抗堵性能的影响。结果表明，反弹系数对灌水器抗堵性能影响较大。利用粒子跟踪测速技术PTV，观测了复杂迷宫流道内沙粒与壁面碰撞过程，测定了不同压力点下矩形流道的碰撞反弹系数，为灌水器数值模拟时反弹系数的设定提供了实验依据，从而可以更加准确评估灌水器抗堵性能。     

Modeling a weak turbulent flow in a narrow and wavy channel: case of micro-irrigation

The baffle-fitted labyrinth channel is commonly used in micro-irrigation systems. The flow in this labyrinth channel has a rather low-Reynolds number. In addition, emitter clogging, which is the major drawback of the micro-irrigation technique, is significantly related to flow characteristics. In order to design an anti-clogging emitter with a good performance, the hydrodynamics must be understood and analyzed. As CFD modeling is nowadays the most efficient approach for improving emitter geometry, this paper presents assessment of several k–\(\varepsilon\) turbulence models for computation of micro-irrigation emitter hydrodynamics. The objective is to determine the simplest and most efficient model to improve emitter conception, in terms of both discharge/pressure loss and limitation of the areas where low velocity is likely to generate emitter clogging. Low-Reynolds number k–\(\varepsilon\) models are often assumed to be more suitable for the labyrinth-channel flow since these models have no wall functions, they can take into account low turbulence levels and they account for the effect of damped turbulence. The low-Reynolds number k–\(\varepsilon\) models used in the present study are compared to high-Reynolds number k–\(\varepsilon\) models. Very different trends are observed between low-Reynolds number k–\(\varepsilon\) models. Some models reproduce a turbulent behavior, while others reproduce a laminar behavior. The head loss analysis reveals that, contrary to classical smooth pipe flow, the contribution of turbulent dissipation cannot be neglected since its contribution is larger than wall friction ones. This feature explains why different models can induce quite different flow behavior.     

Drip irrigation emitter clogging in Dutch greenhouses as affected by methane and organic acids

It is believed that the serious clogging of drip irrigation emitters in the Dutch greenhouse industry is caused by methane-oxidising bacteria and/or organic acids used as anti-clogging agents. In this study greenhouses with moderate to severe emitter clogging have been examined. High methane concentrations—up to 69 mg/l—were found both in ground water (GW) and in the water from reverse osmosis (RO); however, in the fertiliser-mixing tanks (MTs), methane concentrations were <0.01 to 9 mg/l.In trials, a methane concentration of 0.11 mg/l in the fertiliser-mixing tank (MT), giving 0.08 mg/l at the emitter outlet, caused severe clogging of tube emitters and after prolonged exposure, also of labyrinth emitters. Slime in the emitter with ‘methane treatment’ contaminated not only higher carbon and adenosine triphosphate, but also higher element concentrations than in the non-methane treatment. Biofouling increased the deposits of salts (scaling). To avoid emitter clogging, growers using ground water should carefully volatise the methane gas if it is present in the fertiliser-mixing tanks at concentrations higher than 0.01 mg/l, i.e. the detection limit.Organic acids, i.e. acetic acid and formic acid, were shown to increase the growth of Trichoderma, a fungus often isolated from emitter slime. Commercial anti-clogging agents containing organic acids were not effective in killing Trichoderma. It is likely that the carbon of the acids serve as a substrate for the micro-organisms. The use of anti-clogging agents without organic acids is advisable.     

滴灌灌水器三角形迷宫流道优化设计

为了研究三角形迷宫流道滴灌灌水器的水力特性,将其结构作为研究单元,以流道转角、流道宽度和齿高3个结构参数为因素,采用均匀设计方法设计出10个结构参数组合方案.对于每个参数方案,通过AutoCAD对灌水器流道进行三维造型设计,采用计算流体动力学软件Fluent 6.2对流道内部流体的流动状态进行数值模拟,并且模拟分析灌水器内部流道的水力性能和流场特性,得到流道内部流场可视化图像,同时计算不同压力对应的流量值,通过回归分析建立压力与流量之间的量化关系和回归曲线图,并获得其流态指数.在此基础上,根据10个组合方案数据,通过多元回归计算,建立流态指数与结构参数之间的数学关系.以流态指数最小为目标,采用遗传算法,获得结构参数优化设计方案,得到一种流道内速度均匀分布、压力变化均匀递减、流量大小控制在滴灌允许范围之内、水力性能优良的三角形迷宫流道灌水器,可为三角形迷宫流道灌水器的参数化结构设计、制造中的精度控制以及最终的研发提供理论依据.     

迷宫滴头CFD分析方法研究

利用计算流体动力学CFD软件对3种不同流道结构的迷宫滴头进行了水力特性的数值模拟,得到了滴头流道内部的压力和流速分布,预测了滴头压力流量关系,同时将预测值与实测值进行比较。分析了现有CFD方法在预测迷宫滴头水力性能方面的优势,以及导致预测结果存在一定偏差的原因。对比了不同湍流模型、不同网格密度等因素对滴头内部流场计算结果的影响,提出了今后开展滴头CFD研究的发展方向。     

滴灌灌水器流道设计理论研究若干问题的综述

灌水器是滴灌系统最关键的部件之一,其结构与水力性能的优劣对滴灌系统的灌水均匀性、抗堵塞能力以及寿命影响很大。在简要论述国内外滴灌灌水器流道发展现状的基础上,从灌水器流量压力关系、流道内流体流动机理、流道堵塞与防治三个方面详细阐述了灌水器流道设计理论的研究进展,最后提出了滴灌灌水器流道的发展趋势以及国内在灌水器流道设计理论研究中急需解决的问题。     

快速制作迷宫流道工艺研究

迷宫流道对滴灌灌水器的水力性能有较大影响,设计出合理的流道形式并快速制造出试验样件是加速开发新产品研制周期的关键。利用先进的计算机辅助设计(CAD)和数控加工技术(NC)制造出迷宫流道试验样件,通过改制加工刀具,用刀尖的结构尺寸来控制流道几何尺寸,从而解决了流道尺寸测量难的问题。采用微流控芯片的制作方法,对基片进行热键合,能快速将迷宫流道设计思想转化成试验样件,并完成水力性能实验,实现迷宫流道的快速定型。     

灌水器迷宫流道结构参数数值模拟与抗堵塞分析

借助Fluent6.2CFD流场软件对齿形迷宫流道滴头内部水流特性进行了数值模拟,研究了流道参数齿角、齿尖参差量对灌水器流量的影响。齿尖角与流量之间呈正相关关系;进行抗堵分析时发现,齿角越小,湍急小体积的漩涡越多,越有利于消能和自清洗抗堵塞,而齿尖角越大,水流流线越平滑,越有利于水中颗粒的排出,因此在进行流道抗堵塞结构优化时,应综合考虑这二者之间的矛盾,根据设计流量选择适当的齿尖角;齿尖参差量与流量之间呈负相关关系,即相同齿角及压力条件下,参差量越大,出口流量越小,齿尖参差量对灌水器流量大小的影响与齿尖角度的大小有着密切的关系,随着齿尖角的增大,增大参差量,流量的减小幅度越大;进行抗堵分析时发现,参差量越小,流道的实际过流断面越大,越有利于水中颗粒排出。