塑料大棚气流场模拟及作物蒸腾量计算

为了分析塑料大棚内气流场的特征和计算与作物蒸腾量有关的通风参数,该文通过计算流体动力学模拟了塑料大棚内自然通风量,建立了华东地区常见塑料大棚内平均风速和外部风速之间的线性关系,根据能量平衡和紊流扩散模型建立了一个计算作物蒸腾量的数学模型,并利用棚外的常规气象资料和棚内的实测温度计算了棚内作物蒸腾量。通过将作物蒸腾量的计算值和实测值进行比较,结果发现作物蒸腾量的计算值与实测值比较一致,逐日蒸腾量间的决定系数为0.7756,累积蒸腾量间的决定系数为0.9983,模拟累计值与实测累计值之间标准误差为1.16 mm,最大绝对误差为4.82 mm;结果表明,所建立的计算方程参数较少,推求的风速参数比较适用于普通塑料大棚。该研究可满足大棚内作物水分管理、温室大棚设计规划和区域水资源管理等方面的需要。     

Airflow and microclimate patterns in a one-hectare Canary type greenhouse: An experimental and CFD assisted study

This study presents an analysis of air circulation and microclimate distribution during daytime in a 1-ha Canary type tomato greenhouse in the coastal area of southern Morocco. The investigation of the climate inside the greenhouse is based on a numerical simulation using a finite volumes method to solve the mass, momentum and energy conservation equations. The main novelty of this simulation lies in the realism of the 3D modelling of this very large agricultural structure with (i) a coupling of convective and radiative exchanges at the surface of the plastic roof cover, (ii) simulation of the dynamic influence of the insect screens and tomato crop on airflow movement, using the concept of porous medium, (iii) simulation, in each grid cell of the crop canopy, of the sensible and latent heat exchanges between the greenhouse air and the tomato crop, and (iv) detailed simulation of climate parameters in a 1-ha real-scale commercial greenhouse.The model simulations were first validated with respect to temperature and relative humidity fields measured inside the experimental greenhouse for fairly steady-state outside conditions marked by a prevailing sea breeze around the solar noon. A good agreement was observed between the measured and simulated values for inside air temperatures and specific humidity. It was next used for exploring the details of the inside air temperature and humidity fields and plant microclimates and transpiration fluxes throughout the greenhouse space. Simulation for a wind direction perpendicular to the side and roof openings shows that the insect screen significantly reduced inside air velocity and increased inside temperature and humidity, especially in the vicinity of the crop canopy. It revealed the details of the flow field within the greenhouse. At the windward end of the greenhouse, the flow field was marked by a strong windwise air current above the tomato canopy which was fed by the windward side vent, and a slow air stream flowing within the tomato canopy space. Then, from the first third of the greenhouse to the leeward end, the flow field was marked by the combination of wind and buoyancy forces, with warmer and more humid inside air which was evacuated through the upper roof vents, while colder and dryer air was penetrated through the upper roof vent openings. Based on these simulations, design studies of the greenhouse crop system were performed to improve inside air temperature and humidity conditions by simple modifications of orientation of the crop rows.     

利用CFD模型研究日光温室内的空气流动

在温室内空气流动对室内环境具有重要调节作用,因此有必要研究日光温室内空气流动特性。基于计算流体动力学CFD(computational fluid dynamics)方法,运用大型计算流体动力学软件Fluent对日光温室建立模型,采用标准湍流模型对日光温室内气流分布进行了三维稳态求解。模拟时将日光温室内外空气作为研究对象,并且温室内空间连同其周围的一部分室外空间一起作为CFD模拟的计算领域。对日光温室内气流变化及分布进行了数值模拟,并在温室内进行了气流试验测试,对测量值和计算所得的风速值进行了比较,结果表明,二者最大误差小于9%,说明风速的实测值和模拟值吻合良好,CFD模型有效,且得到了日光温室内部流场速度分布。通过气流流场模拟结果分析表明,直观显示了日光温内的流场特性和流动状态,气流从窗户进入沿着底部通风口流出日光温室,并且气流在底部通风口速度分布较均匀,在温室下部形成了较为明显的涡流。该文模拟结果可为东北地区日光温室的优化设计以及温室环境调节等方面提供理论依据。     

作物冠层微气象仪器研制与应用

研制成适用于测定作物冠层内部微气象(温度、湿度和风速)的观测仪器。应用4组温度与湿度感应器和热球式风速传感器于实验室进行标定,并在大田自然条件下进行平行对比检验。玉米观测试验结果符合小气候的基本规律,并给出更加精确和实时测量。     

日光温室主动蓄热后墙传热CFD模拟及性能试验

中国的日光温室实现了高效的能量利用,在中国北方地区的冬季农业生产中发挥了巨大的作用。但在实践生产中日光温室存在巨大的能量不平衡,给北方冬季的农业生产造成很大的损失,同时也限制了日光温室的高效应用。为了实现了日光温室对太阳能的高效利用,该文提出了一种能够将白天富裕能量进行有效存储的主动蓄热后墙日光温室。该文对主动蓄热后墙日光温室的室内温度和通风蓄热风道蓄热特性进行理论分析和试验,并与传统9m跨的被动蓄热日光温室进行了对比分析。试验结果表明,主动蓄热后墙日光温室的温度指标有了较明显提高。在晴天和多云采光天气条件下,主动蓄热后墙日光温室室内的温度较9m跨被动蓄热日光温室均有较大幅度的增加,在晴天夜间保温时段(16:00~次日09:00),主动蓄热后墙日光温室温度提高最小为1.8℃,最大为2.8℃,平均提高2.2℃;在多云天夜间保温时段(16:00~次日09:00),主动蓄热后墙日光温室温度提高最小为1.6℃,最大为4.2℃,平均提高2.2℃。该文利用CFD数值模拟对温室蓄热后墙的20℃等值面进行了分析,分析结果表明在定常条件下,通风主动蓄热的高效范围在10m以内,有效长度在20m以内。通过该试验,结合温室建筑的实践构造要求,确定的蓄热风道合理长度为20m。     

Understorey microclimate and crop performance in a Grevillea robusta-based agroforestry system in semi-arid Kenya

The influence of dispersed trees on microclimatic conditions, gas exchange and productivity of maize (Zea mays L.) in a Grevillea robusta-based agroforestry system in semi-arid Kenya was examined to test the hypothesis that the benefits of shade seen in savannah ecosystems may be outweighed by competition for below-ground resources. Meristem temperature, cumulative thermal time, intercepted radiation, spatial distribution of shade and gas exchange were determined for maize grown as sole crops, in an agroforestry system, or under shade nets providing 25 or 50% reductions in incident radiation to discriminate between effects of shade and below-ground competition. The major benefit of shade was to reduce exposure to the supra-optimal temperatures experienced in many tropical regions, and which are predicted to become increasingly common by climate change models. However, although trees decreased photosynthetic photon flux density (PPFD) incident on understorey maize by ca. 30%, the yield reduction was much greater than in the 25% shade net treatment in four seasons providing contrasting rainfall. Maize yield was unaffected by 50% artificial shade in the driest season (168 mm) but decreased with increasing shade when rainfall was high (628 mm). Shade reduced meristem temperature and delayed flowering by 5–24 days depending on treatment and seasonal rainfall. Thermal time to flowering in the agroforestry system doubled from 600 to 1200 °C day as rainfall decreased. Photosynthetic and transpiration rates for understorey maize were similar to the 25 and 50% shade treatments when rainfall was high, but were ca. 10% of those for unshaded sole maize in dry seasons. PPFD-saturated photosynthetic rate was initially similar in all treatments but fell sharply in the agroforestry system as the season progressed. Radiation conversion coefficients did not differ between unshaded sole and understorey maize. The results suggest that the ameliorative influence of tree shade was greater in low rainfall seasons, as in savannah systems, but that potential benefits were outweighed by below-ground competition. This may be managed by root-pruning trees.     

基于CFD的两连跨日光温室热环境模拟

相比单跨日光温室,两连跨日光温室具有单位面积建造成本低,土地利用率高等优势,为深入了解两连跨日光温室热环境性能,该研究基于计算流体动力学(computational fluid dynamics,CFD)构建了相同结构参数和构造材料的单跨和两连跨日光温室热环境模型。通过试验测试两连跨日光温室内的环境温度和各围护结构表面热流,并与CFD模拟的温度场进行对比,结果表明模拟数据与实测数据吻合度较高。在此基础上,基于该CFD模型分别对两连跨和单跨日光温室热环境进行模拟,并提取各围护结构表面热流和温度、土壤温度和空气温度进行对比分析。结果表明,在相同外界气候条件下,两连跨日光温室比单跨日光温室夜间气温高1.7～3.8 ℃,土壤温度高2.9～3.0 ℃,墙体内表面温度高2.9～7.9 ℃;两连跨日光温室的土壤和墙体在夜间,持续向南侧棚室放热,热流稳定,热流密度分别为7.11～8.59、12.65～15.19 W/m²,分别比单跨日光温室土壤、墙体表面热流密度高0.76～2.42,9.71～14.36 W/m²。相比单跨日光温室,两连跨日光温室地表土壤温度和室内气温波动较小,热环境调节能力明显提升。该研究结果为两连跨日光温室的结构优化、耕种管理等提供参考。     

面向控制的温室系统小气候环境模型要求与现状

以往的温室作物生长和小气候环境模型,主要是从面向研究而不是面向实际生产的温室获得的,这二者的最大不同是:面向研究的模型主要考虑的是得到作物生长高产所需的"最优"的温室内部气候环境参数设定值,而较少考虑温室内控制设备的能力（控制动态过程）、生产过程中温室外气候变化情况和达到"最优"所需付出的能量等代价;而后者在面向实际生产的自动化控制的温室系统模型中是必不可少的。当前温室系统自动化控制面临的一个最大困难,就是缺乏一个这样的可靠的温室系统模型,而只能采用面向研究的温室系统模型去进行实际生产的温室系统控制,这种忽视实际生产条件下的温室系统模型与理想条件下的模型之间差异的"纸上谈兵"的做法,必然导致温室控制技术水平低、达不到预期效果。该文介绍了温室系统的整个控制过程,对一个实际生产的温室系统中各种变量和参数作了简要描述,并概括了面向实际的温室生产控制要求的温室系统模型的基本结构,对温室环境模型、作物生长模型和能耗及CO₂消耗模型的研究现状作了详细的回顾。从满足控制需求出发对现有的温室系统模型所存在的问题进行了分析,并指出了其中的不足和局限性。探讨了未来温室系统的建模方法和需要解决的关键问题,提出了面向控制需求的温室系统建模要满足的要求,为温室系统的建模研究提供了一种新的思路和方向。     

主动蓄热日光温室不同气流方向后墙传热CFD模拟

日光温室是一种能源高效利用型的温室结构,在中国北方的设施园艺产业中起到了非常重要的作用,其中主动储热日光温室结构是最近该领域研究的热点问题之一。针对高效主动储热风道的研究问题,该文构建了3种不同气流运动方式的主动蓄热日光温室后墙模型,分别是顶进顶出气流运动方式的主动蓄热日光温室后墙(W1)、侧进侧出气流运动方式的主动蓄热日光温室后墙(W2)、侧进顶出气流运动方式的主动蓄热日光温室后墙(W3)。在W1工况下对比试验数据及数值模拟数据发现,平均相对误差为6.7%,最大相对误差为13.4%,说明该文所建模型的数值模拟与试验数据有很好的一致性;进一步模拟结果表明,进口条件一致的情况下,W1、W2、W3在主动蓄热循环系统运行阶段的有效蓄热范围分别为700～800、500～600、600～700 mm;W1、W2、W3的出口平均温度分别为17.3、18.9、18.2℃,进一步计算得到,3种工况下,内部空气流的努塞尔特数分别为40.95、35.25、35.30;3种不同气流循环运动方式下,温室后墙的对流换热强烈程度表现为W1最大,W3其次,W2最小。该研究为设计主动蓄热日光温室墙体气流循环运动方式提供了理论依据和试验参考。     

长江中下游Venlo型温室番茄蒸腾模拟研究

该文针对目前国际上计算作物蒸腾速率的通用Penman-Monteith方程(P-M方程)存在的所需参数即作物叶片气孔阻抗不易获取的问题,首先通过春季和冬季Venlo型温室小气候和番茄(Lycopersicon esculentum Mill.)叶片气孔阻抗以及植株蒸腾量的实验观测,分析并量化番茄叶片气孔阻抗与温室小气候因子之间的关系。然后将其与P-M方程结合,模拟计算了春冬两季温室内番茄作物的累积蒸腾量,并用实测植株蒸腾量检验了模拟的效果。结果表明,在长江中下游地区的春季,两个供试番茄品种叶片气孔阻抗r_s与光合有效辐射PAR的关系为11205/(5.28+PAR)。将该函数关系与P-M方程相结合模拟计算的春冬两季温室内番茄的蒸腾量与实测值的吻合度较高。春季番茄蒸腾量模拟值与实测值之间的决定系数为0.97,标准误为5.50 mm,冬季番茄蒸腾量的模拟值与实测值之间的决定系数为0.99,标准误为1.21 mm。本研究建立的番茄叶片气孔阻抗与太阳辐射的定量关系,解决了在长江中下游地区用P-M方程计算番茄蒸腾速率时所需模型参数(叶片气孔阻抗值)难以获取的困难,为P-M方程在温室番茄水分管理中的实际应用奠定了基础。     

背负式喷雾器雾滴分布特性的CFD模拟与试验

为了解决不同喷雾条件对背负式喷雾器雾滴分布的影响问题,采用CFD离散相粒子跟踪模拟方法,研究了距喷嘴垂直高度分别为0.4、0.55和0.7m,喷雾压力分别为0.15、0.2、0.3和0.35MPa,风速分别为0、1、2、3m/s情况下,雾滴沉积分布和粒径分布特性,并进行试验验证。结果表明:沉积率受风速影响显著,随风速增大而降低,但沉积率受喷雾压力影响不显著。模拟与试验结果回归决定系数R2和标准误差SE分别为0.9424、0.039,表明CFD离散相粒子跟踪模拟法可用于评估雾滴沉积分布。雾滴粒径分布模拟结果与试验结果相关性差,CFD模拟法不宜用于评估雾滴粒径分布情况。该研究为后续各类喷雾器数据测量提供参考。     

不同种植密度下温室间作玉米的水分利用情况与其营养元素吸收特征的关系

Dent corn, as a catch crop used for salt removal, was cultivated at different densities, i.e., 7.3 （low density）, 59.7 （normal density）, and 119.5 plants m-2 （high density）, during a 50 d fallow period after cultivation of a commercial crop in a greenhouse, to analyze the characteristics of nutrient salt （N, K, Mg, and Ca） uptake by roots and to study the effect of plant density on the characteristics associated with crop water use. Leaf area index for the high and normal density treatments reached extremely high values of 24.3 and 14.9, respectively. These values induced higher transpiration rates that were estimated using the Penman-Monteith model with the incorporation of specific parameters for crop and greenhouse conditions. The total N, K, Mg, and Ca contents in the crop canopy at harvest were 26.8, 13.0, 1.0, and 1.7 g m-S, respectively, under the high density treatment. The dynamics of salt uptake rates for high, normal, and low density treatments were evaluated by assessing weekly changes in salt content, and were subsequently compared against the transpiration rate. A positive linear relationship was obtained between these 2 parameters for all 3 density treatments and all tested salts. Hence, higher transpiration rates caused higher salt uptake rates through water absorption. On the other hand, salt uptake efficiency per unit water use by cultivation was lower in the low density treatment. Therefore, management procedures with dense planting that induce higher transpiration rates and lower evaporation rate are extremely important for the effective cultivation of corn catch crops.     

基于Penman-Monteith方程的温室番茄蒸腾量估算模型

作物的蒸腾是作物生命过程中十分重要的组成部分。为寻求适合于温室栽培条件下番茄植株蒸腾量的计算模型,本文以Penman-Monteith方程为基础,针对温室特定的小气候环境,对番茄冠层整体气孔阻力、空气动力学阻力等参数进行合理修正,建立了包含气象数据、番茄叶面积指数和冠层高度为主要参数的温室番茄蒸腾量估算模型。分别采用2009年5月2-13日（开花坐果期）和2009年6月9-20日（成熟采摘期）2个时段内的实测蒸腾量对模型模拟结果进行验证,2个时段内模型模拟结果的平均相对误差分别为8.48%和9.20%,表明所建模型可以较好地的计算温室番茄的蒸腾量。本研究提出的蒸腾量估算模型对温室番茄作物水分关系的深入研究具有重要参考价值。     

靶标周围流场对风送喷雾雾滴沉积影响的CFD模拟及验证

该文主要探讨在温室环境中用气流辅助方式喷施农药时,施药对象(靶标)周围的流场对雾滴飞行轨迹及雾滴附着行为产生的影响,以期为精准施药技术提供参考。该文基于CFD模拟,用离散相粒子跟踪法模拟流场中的雾滴运动轨迹,在此基础上探寻雾滴附着靶标的条件,并采用试验手段验证模拟结果的可靠性。研究表明,在靶标附近区域,对区域内的雾滴轨迹进行分析后,得出了雾滴在靶标上表面实现附着的时间条件,即雾滴从进口处运行到靶标边缘所需的时间必须比雾滴从进口处运行到靶标上表面等高位置所用时间长,雾滴才能实现附着;喷雾过程中靶标下方存在雾滴不能到达的遮挡区域,靶标对雾滴运动的遮挡长度与喷雾角度有关;气流速度与雾滴粒径是雾滴附着靶标的关键因素,在雾滴粒径为50μm,喷雾角度为60°的情况下,喷雾速度越高,流场中靶标上表面压力越大,喷雾雾滴的沉积率越低。     

Nutritional changes in petiole sap over space and time in a tomato crop greenhouse

The aims of this trial were to determine the spatial and temporal variability of the nutrients in petiole sap in a tomato crop under greenhouse and to determine the number of sub-samples for a representative sample. The experiment consisted of the selection of 20 sampling points. Petiole of fully expanded leaf was collected weekly in order to determine Cl, NO₃-N, H₂PO₄-P, SO₄-S, Na, K, Ca and Mg concentrations. Our results showed that variations of NO₃-N, Na, Ca and K concentrations in sap were affected by the spatial distribution, whereas SO₄-S and Mg concentrations in sap were affected by their temporal distribution. The spatial variability of our experiment could be related to radiation, yield and antagonism between nutrients, whereas the time variability could be related to the phenological stage of the plant and the antagonism between nutrients. The suggested number of petiole sub-sample ranging from 25 to 113 depending on nutrient.     

温室内密闭小环境降温除湿效果及蒸腾水循环利用

为探索密闭小环境对其内部温湿度及蒸腾水循环利用的影响,该研究对温室内盆栽做全密闭处理,基于“温差”热交换原理,通过调控盆栽小环境内的温湿度,降温除湿的同时回收利用蒸腾水。结果表明,利用“水-气温差”对密闭盆栽进行降温除湿回收蒸腾水,降温除湿效果显著,正午12:30左右,相比密闭对照盆栽,温度降低3℃左右,相对湿度下降7%;其他时间降温除湿效果虽不及正午,但白天平均降温2.4℃,相对湿度平均下降5%,蒸腾水最终都回收到U型管中。而利用“地-气温差”进行热交换、利用气泵使水汽循环,对密闭盆栽进行降温除湿回收利用蒸腾水。试验过程中,夜晚的降温除湿效果不显著。白天气泵运行期间,地-气热交换处理盆栽相对于密闭对照盆栽温度平均下降2.5℃左右;相对湿度平均下降10%。正午时分,降温除湿效果最为显著,相比密闭对照盆栽气温降5℃以上,与温室内的温差只有1.5℃;此时湿度下降15%。降温后凝结而成的水珠在高速气流的带动下重复利用于盆栽。由此可见,利用水-气、 地-气温差对密闭盆栽小环境可实现降温、除湿并实现蒸腾水的回收利用。     

长江中下游地区Venlo型温室空气温湿度以及黄瓜蒸腾速率模拟研究

根据温室能量和质量平衡的物理学原理,建立了一个以温室外气候条件(太阳辐射、温度、湿度、风速等)为驱动变量,以温室结构、温室覆盖材料、温室内作物(高度、叶面积指数)为参数的温室小气候模拟模型,并利用上海Venlo型温室的三季试验数据对模型进行了检验。结果表明：模型能较好地预测中国长江中下游地区Venlo型温室内夏季和冬季空气温度、湿度以及作物蒸腾速率。模型对该地区夏干季节(2001年8月,三伏天)、夏湿季节(2002年6月下旬至7月中旬,梅雨季节)和冬季(2002年1月27日~2月5日)温室内空气温度、湿度以及作物蒸腾速率预测值与实际观测值的决定系数(R²)和标准误(SE)分别为：0.89,0.75,0.52;1.1℃,4.4%,0.040 g·m^-2·s^-1;0.80,0.84,0.77;1.5℃,4.4%,0.018 g·m^-2·s^-1;0.84,0.59,0.73;1.6℃,6.0%,0.012 g·m^-2·s^-1。该研究为进一步探讨温室环境的优化调控提供了理论依据和决策支持。     

Carbon distribution and variations in nitrogen-uptake between catch crop species in pot experiments

Chicory (Cichorium intybus L.) and perennial ryegrass (Lolium perenne L.) are seen as suitable catch crops species in Sweden. Pot experiments were conducted to study C distribution and variations in nitrogen uptake between several varieties of chicory and perennial ryegrass for comparison.A soil amended with Ca(¹⁵NO₃) (109 and 145 mg N kg⁻¹ soil) and glucose (2.5 g C kg⁻¹ soil) was incubated for 10 days to promote the immobilization of added ¹⁵N; therefore, N was supplied to plants through the remineralization of the immobilized ¹⁵N. In experiment 1 four varieties of chicory and one variety of perennial ryegrass were grown for 60 days in greenhouse conditions. In experiment 2, only two varieties of chicory and one ryegrass were grown in soil with high-N rate of fertilization. In the later experiment, pots were moved from greenhouse to a growth chamber with ¹⁴CO₂ atmosphere for a pulse labelling of the plants 7–10 days before harvest.At both levels of N supply, dry weights of taproots were higher in the chicory cultivars Cassel and Fredonia than in cultivars Puna and Salsa. The opposite was found for dry weights of small roots. There were significant differences in N uptake between chicory varieties. Cassel and Fredonia together with the ryegrass were significantly more effective in securing nitrate than the other two varieties. Significantly higher amounts of labelled-N were found in taproots of Cassel than in Puna. The opposite trend was found for small roots. Similar results were measured for amounts of radioactivity (kBq pot⁻¹) of newly fixed C transferred to roots. Amounts of labelled-N measured in soil residues for both crop species were significantly higher at the low level of N supply than at the high level of N. There was no significant increase in plant uptake of soil-N (native-N) either between chicory varieties or between chicory and ryegrass, when the high level of N was supplied.The importance of these results is discussed in relation to the suitability of chicory species as catch crop and as plant material for breeding.     

基于气候阻力的温室黄瓜蒸腾速率模拟

在北方地区玻璃温室内,观测黄瓜生长期叶温与温室内微气象因子,利用基于能量平衡方程和水汽扩散理论的叶-气温差方程计算植株气孔阻力(ri),结合同期气候阻力(r^*)和边界层阻力(re)进行分析,结果发现：不同天气条件下ri/re的比值与r^*/re比值之间呈极显著正相关关系,晴天时：ri/re=1.207(r^*/re)-0.326(n=328,r=0.8055),阴天时：ri/re=0.169(r^*/re)+0.278(n=222,r=0.8076)。根据此拟合方程,以r^*/re代替ri/re代入修正后的P-M公式中计算温室黄瓜的蒸腾速率,与直接代入ri值的计算结果比较,结果晴天与阴天条件下的相对误差均<10%,一致性指数达0.96以上,说明利用拟合方程建立的模型模拟效果很好。此模型能够直接利用气象数据计算温室作物气孔阻力并进而计算蒸腾速率,使温室作物蒸腾速率的计算更简单方便,该文结果对同类温室和作物有参考价值。