The hydraulic effect of filter materials around gappy non-ideal field drains

The analyses of Widmoser and of Kirkham for flow into gappy non-ideal drain pipes with longitudinal slits and circumferential openings, respectively, were modified to take into account the hydraulic effect of filters when the boundary between filter material and soil is an equipotential surface. Upper and lower bounds were found for the effective drain radii of the drain pipes when surrounded by a cylindrical filter, by calculating the effective drain radii of the drain pipes with filter surrounds whose outer boundaries are the equipotential surfaces just contained within and without the outer cylindrical surface of the filter. The calculated bounds are close to each other for large filter thicknesses, but become further apart as the filter thickness is decreased. These calculated bounds for the effective radius were used to calculate, by the hodograph method, lower and upper bounds for the maximum water-table height for parallel lines of drain pipes installed in an infinitely deep soil. These show that the maximum water-table height in drained land is considerably lowered in the presence of a filter more permeable than the soil surrounding a gappy nonideal drain, and that a thin filter of high hydraulic conductivity relative to the soil is hydraulically more beneficial than a thicker filter of hydraulic conductivity only slightly more than that of the soil. An exact analysis, useful only for large filter thicknesses, is also given for the flow towards pipe drains with circumferential openings when surrounded by permeable material with hydraulic conductivity varying inversely with radial distance.     

BPX型排水泵内流分析及降噪方案

为了研究泵内流动诱导噪声源分布规律,从内部流动角度,运用计算流体动力学方法对一台典型的BPX型排水泵的内流场进行了数值计算,得到了在不同工况下泵内的速度、压力及涡量场分布特征.计算结果表明：泵过滤室内液流呈低速缓流状,异物过滤装置后盖板附近有环状非对称切向旋涡产生;过流通道面积突变使得叶轮吸入口入流条件较差;出液管内部流动出现明显的流动分离,由贯通流和低速回流区域组成;叶轮流道内部,特别是在叶轮轮毂周边及流道内靠近叶片背面附近,涡量分布密集,在叶尖附近也存在较强的涡量分布,出液管内有涡条带形成.同时,对模型泵进行了空气噪声测试,根据测试结果将泵运行过程划分为启动初期、正常运转期和空排期3个阶段,分析了各阶段的噪声特性,并提出了3种具有代表性的降噪方案,认为开设回流孔方案可行性较大.     

Entrance resistance of enveloped drainage pipes

The entrance resistance and the effective radius of corrugated PVC drain pipes without envelope and with six different prewrapped envelopes were evaluated in a sand tank experiment.By applying the theory of resistances, the entrance resistance of the naked pipe was found to be 0.0136 days/m. With envelopes, the values were 0.0024 to 0.0067 days/m, depending on the types of envelope.The effective radius of the naked pipe was found to be 0.47 cm for a drain pipe with an actual radius of 3.0 cm. This value increased to between 1.20 and 2.50 cm when envelope material was used. Then the values of the calculated entrance resistances were substituted in the steady state drainage equations under normal field conditions to evaluate the effect on drain spacing. In all equations, a tendency towards increasing the drain spacing was observed when envelope material was used.     

文丘利管在增压中冷柴油机EGR系统中的应用

针对增压中冷柴油机EGR系统,设计了3组不同的文丘利管,试验研究了不同文丘利管产生的效果及对增压中冷柴油机经济性能的影响。试验结果表明,文丘利管的进口截面、喉部截面以及出口截面之比不同,所产生的压降和扩压效果不同,而且对柴油机经济性能的影响也不同。同时还分析了试验过程中出现的激波现象和倒灌现象以及消除措施。     

Research and developments in selecting subsurface drainage materials

Subsurface drainage requires appropriate materials to ensure a proper functioning of the drainage system. The materials normally applied for subsurface drainage are drain pipes and envelopes. Besides a review of the materials used for drain pipes, their hydraulic characteristics — discharge capacity and entrance resistance — have been treated. Much attention is paid to subsurface drainage envelope materials because of practical problems and a serious gap in knowledge, in spite of considerable research efforts. After treating the aim of drainage envelopes, a review of the used materials is given. Practical experience with gravel envelopes, still often used in irrigated areas, shows serious shortcomings. Since organic envelopes are vulnerable to deterioration, the only possible alternative are synthetic envelopes. Their property to retain soil particles is characterized by the so-called filter criteria. Laboratory research and field experiments to evaluate the blocking and clogging aspects of synthetic envelopes are discussed and selection criteria given.     

设有复式空气阀的管道充、放水过程

为了研究长距离有压管道充水和放水过程中管内气体压力的变化情况,并保证其运行中的安全,针对长距离有压管道的特点,对其充水和放水过程,采取了对整个管道进行分段处理、依次充水和放水的策略.对于分段后的每一段管道,建立了圆形管道内水体体积与水深关系的数学模型.按照小流量充水的原则,运用理想气体状态方程,结合复合式空气阀的进气和排气性质,在空气阀和泄水管布置情况已知的前提下,根据不同的充水流量和放水流量,计算各管段气体压力的变化情况.整个数值计算过程采用自编Fortran程序计算求解.计算结果表明：充水和放水的流量越大,对应管段的气体压力越大和越小,管道越危险;在不影响管道安全性的前提下,为了使管道尽快充满和放空,应采取较大的充水流量（16 m3/s）和放水流量（泄水阀全开）.     

气力辅助静电雾化的PIV试验研究

为了研究气力辅助作用下静电雾化的流场特性,采用粒子图像测速技术（PIV）对风速、荷电电压及通气管与喷头间距等参数影响下的喷雾流场进行测量,并结合Tecplot后处理软件对所储存图片进行处理和分析,获得了不同参数下的静电喷雾流场特性.结果表明：通气管和喷头的间距以及风速一定时,不同的荷电电压形成不同程度的卷吸,且电压越大,卷吸现象越明显,卷吸区域沿着喷雾的轴向逐渐向下延伸;通气管和喷头的间距以及荷电电压一定时,随着风速的增大,气动力的主导作用越来越明显,在气流区的卷吸程度逐渐减弱,卷吸现象逐渐消失,卷吸区域逐渐向喷雾核心区收缩;风速以及荷电电压一定时,随着通气管与喷头间距的拉大,雾滴的漂移现象越来越严重,同时喷雾流场的卷吸现象越来越明显并逐渐向喷雾核心区靠近.     

Use of the Hooghoudt formula for drain spacing calculations in homogeneous-anisotropic soils

Cases of groundwater flow in anisotropic soils can be transformed to equivalent isotropic cases, and then be solved with the Laplace equation. On the basis of this principle, the Hooghoudt formula, developed for isotropic soils, has been used for calculating drain spacings in anisotropic soils. However, the Hooghoudt formula is only an approximate solution of the Laplace equation so that extension to anisotropic soils may not a priori be justified under all conditions. Results obtained with the Hooghoudt formula were compared to those obtained by numerical solutions of the Laplace equation. On the basis of this comparison, it is concluded that the Hooghoudt formula may indeed be used with reasonable confidence for drain spacing calculation in homogeneous-anisotropic soils.     

BPX型排水泵内流分析及降噪方案

为了研究泵内流动诱导噪声源分布规律,从内部流动角度,运用计算流体动力学方法对一台典型的BPX型排水泵的内流场进行了数值计算,得到了在不同工况下泵内的速度、压力及涡量场分布特征.计算结果表明：泵过滤室内液流呈低速缓流状,异物过滤装置后盖板附近有环状非对称切向旋涡产生;过流通道面积突变使得叶轮吸入口入流条件较差;出液管内部流动出现明显的流动分离,由贯通流和低速回流区域组成;叶轮流道内部,特别是在叶轮轮毂周边及流道内靠近叶片背面附近,涡量分布密集,在叶尖附近也存在较强的涡量分布,出液管内有涡条带形成.同时,对模型泵进行了空气噪声测试,根据测试结果将泵运行过程划分为启动初期、正常运转期和空排期3个阶段,分析了各阶段的噪声特性,并提出了3种具有代表性的降噪方案,认为开设回流孔方案可行性较大.     

土工织物反滤层对多孔管汇流量影响的试验研究

为了探究土工织物反滤层对多孔管汇流量的影响,以室内试验为主结合理论分析进行探究.设置5种面密度的短纤针刺非织造土工布、4种层数,共20组试验.观测记录不同工况下多孔管汇流量的情况.通过量纲分析土工织物反滤层对多孔管汇流量的关系函数式,对其进行回归分析,得到土工织物反滤层参数与多孔管汇流量之间的关系表达式,计算所得的汇流量与试验值误差较小,具有较高的准确度,可用于指导实际工程;在多孔管参数一定时,土工织物反滤层下多孔管的汇流量与土工织物的面密度和层数有关.通过试验数据分析可知:土工织物反滤层面密度一定时,多孔管汇流量随着土工织物层数的增加而减小,且速率降低;在土工织物层数一定时,多孔管汇流量随着面密度的增加而减小,因此在实际工程中合理地选择土工织物的面密度和层数可达到更好的技术效果和经济效果.     

外包滤料对暗管排水与土壤脱盐效果的影响

为了探究不同外包滤料条件下的暗管排水性能和土壤脱盐效果,基于室内试验研究成果,在田间设置4种暗管排水系统(各系统中暗管埋深均为80 cm,间距均为20 m),所用外包滤料分别为68 g/m²土工布(L)、砂滤料(S)、68 g/m²土工布+砂滤料(LS)和无外包滤料(W),以当地常规明沟排水(CK)作为对照,通过田间试验分析了春灌过程中各暗管系统的排水性能指标及土壤脱盐效率.结果表明:相比处理W,处理L,S和LS平均排水速率提升了7.44%,12.55%和15.75%,平均流量衰减度降低4.07%;处理S和LS累积排水量提高了5.11%和8.31%(P<0.05).各暗管处理春灌后平均土壤脱盐率均达47%以上,较CK提升显著,其中处理LS效果最优,为50.94%.综上,应优先选择处理LS作为河套灌区暗管排水系统外包滤料布设方案.该研究结果可为河套灌区暗管排盐技术的推广应用提供理论支撑和科学指导.     

毛细透排水带渗滤取水对比试验

通过环形毛细透排水带渗管、立式毛细透排水带渗管和普通PVC渗管的渗滤取水试验,对比了在不同反滤层环境下3种渗管的集水能力和滤净能力。结果表明,在单一均质反滤层条件下,立式毛细透排水带渗管能同时兼顾集水和滤净性能,取水效果达到最优。并首次提出新型毛细透排水带渗管可用于傍河取水的渗渠取水工程,研究成果对毛细透排水带在渗渠取水工程中的应用提供了理论依据和设计参考。      

气力辅助静电雾化的PIV试验研究

为了研究气力辅助作用下静电雾化的流场特性,采用粒子图像测速技术（PIV）对风速、荷电电压及通气管与喷头间距等参数影响下的喷雾流场进行测量,并结合Tecplot后处理软件对所储存图片进行处理和分析,获得了不同参数下的静电喷雾流场特性.结果表明：通气管和喷头的间距以及风速一定时,不同的荷电电压形成不同程度的卷吸,且电压越大,卷吸现象越明显,卷吸区域沿着喷雾的轴向逐渐向下延伸;通气管和喷头的间距以及荷电电压一定时,随着风速的增大,气动力的主导作用越来越明显,在气流区的卷吸程度逐渐减弱,卷吸现象逐渐消失,卷吸区域逐渐向喷雾核心区收缩;风速以及荷电电压一定时,随着通气管与喷头间距的拉大,雾滴的漂移现象越来越严重,同时喷雾流场的卷吸现象越来越明显并逐渐向喷雾核心区靠近.     

Calculation of non-steady flow towards a drain in saturated-unsaturated soil by finite elements

The problem of two-dimensional non-steady flow of water towards a drain in saturated—unsaturated soil is solved by a Galerkin-type finite element approach. Special emphasis is placed upon the type of boundary conditions to be used at the circumference of the drain, the hydraulic conductivity of the soil and the discretization scheme of the finite element network. Numerical solutions are compared with the Thiem—Dupuit well formula and with hodograph solutions given by Van Deemter (1950) and Childs (1959).     

微灌用自清洗网式过滤器自清洗结构流场分析与优化研究

自清洗过滤器是灌溉节水系统关键设备,随着微灌系统自动化程度提高,对该设备要求也越来越高。为此,在概述了过滤器特点及原理的基础上,运用FLUENT流体软件对自动清洗结构进行流场分析,得出速度矢量分布图,在此基础上,根据吸管流速相对方差与相对极差的计算结果,改变排污管、吸管部位的直径,使各个吸管的流量基本保持一致,达到吸污...     

暗管与鼠道组合排水改造渍害稻田试验

对湖积平原区的粘土渍害稻田,采用暗管与鼠道双层组合排水,在小麦、油菜生育期的雨季中,鼠道能有效地排除稻田的耕层滞水,减小田间地下水位上涨幅度;雨停后,在暗管排水作用下,地下水能迅速回降到离田面0.6～0.7m;稻田淹灌期,鼠道排水可增加两暗管之间的入渗强度,排泄土壤中有害物质。在渍害稻田改造中,适当加大暗管间距(24m),中间辅以鼠道排水,可起到工程投资省,改土效果明显,增产效益大的作用。     

农田不同排水措施地下排水效果模拟试验研究

在地下水位较高、地表易于形成积水的中国南方地区,通过农田排水措施可以及时排除多余地表积水,快速降低地下水位,以达到排涝降渍、协同调控的目的.文中基于室内砂槽试验,揭示暗管排水、明沟排水、不同反滤体高度的反滤体排水及改进暗管排水等措施的地下排水规律及效果.结果表明:将暗管周围土体置换为高渗透性土体介质的改进暗管排水可明显提高排水流量,当土体置换高度达2 cm时(对应于田间条件40 cm),其排水流量均高于相同埋深条件下的其他排水措施,达暗管排水的1.59~1.66倍;改进暗排在地表积水消失时仍保持较大的排水流量,可达相同埋深暗管流量的2倍以上,在积水层消失后,能迅速降低农田土壤水的渍害胁迫,将地下水位降低至暗管埋设高度;各种排水措施,在地表积水即将消失时,出现了流量与水头变化幅度较大的现象.相对于各种地下排水措施,改进暗管排水在除涝降渍中存在明显优势.研究结果可为涝渍灾害易发地区高效除涝降渍减灾工程设计和建设提供参考.     

滴灌条件下暗管滤层结构对排水、排盐效果的影响

为解决滴灌农田非饱和条件下暗管排水困难的问题,设置2种暗管滤层铺设方式,以常规暗管滤层进行排水为对照,基于室内土槽试验,分析了滤层铺设方式对暗管排水排盐效果的影响及其机理。T1处理为常规暗管滤层铺设方式,暗管四周铺设细砂滤层,T2处理为暗管上部铺设细砂,T3处理为细砂斜垫层斜铺连接体积质量分界层与暗管。结果表明,T1处理受土壤水滞后效应影响显著,暗管不排水,土壤水、盐积聚于暗管底部;T2、T3处理可在暗管上部产生局部饱和区,促使暗管排水。T2处理排水时所需历时较长,排出的水盐总量较少;T3处理可使暗管最早排水,排水时暗管下部土壤积盐最少,排水流量和排水盐总量最大。     

卧式自清洗网式过滤器排污时间试验及计算

通过对型号为8GWZ-200的卧式自清洗过滤器排污时间进行试验,获得了4种流量(220,200,180,160 m³/h)、6种含沙量(0.006,0.013,0.015,0.018,0.027,0.063 kg/m³)这2种条件下排污口含沙量随排污时间变化的试验结果.分别分析了相同流量不同含沙量以及相同含沙量不同流量条件下,排污口含沙量随排污时间的变化规律,结果表明:排污口含沙量均随排污时间先增大后减小,最后趋于稳定,进而得到排污时间的最小值应为14 s.根据质量守恒建立了排污时间的计算方法,并根据试验结果,对排污时间进行了计算,结果表明:计算得到的过滤器排污时间为15~47 s.结合排污时间试验结果,最终确定卧式自清洗过滤器排污时间为15~30 s.该结果与已有过滤器试验结果和实际工程运行结果均一致,完全可以用于实际工程中卧式自清洗网式过滤器排污时间的确定.     

Effect of perforation shape and pattern on the performance of drain pipes

In earlier calculations of the entrance resistance of perforated drain pipes, the basic assumption was made that no important error is introduced by not taking into account the presence of the pipe wall as an impermeable surface. This assumption was tested using an electrolytic model, and it was shown that the calculated values were approximately one half of the measured entrance resistance values. By adding a central source of strength which is half the total strength of the sinks that simulate the perforations, an impermeable wall is simulated and exact results are obtained, as shown by accurate mathematical calculation for particular cases. Based on these experiments, modified formulae have been derived for continuous longitudinal slits, circular perforations and discontinuous longitudinal slits.