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温室窗帘和窗户通风设备的物理模型 我们采用实践与理论相结合的方法研究了温室的通风设备，主要是研究温室卷帘与开窗设备在低气压下的使用寿命及其在不同风速和气压下的波动情况。这些波动与平均风速有关，而平均风速是通过能量谱分析得来。由此推知，气压与平均风速有关，而气体紊流对平均风速的估算有很大影响。温室通风设备与启动电位之间的关系是基于对流体机械的突破性研究。关于气流与风压和气温的变化相对应这个预测符合实验得出的数据，大体上看，他们之间差异小于 20%.符号标志符号标志 A 面积 z 高度，mCc 对流影响系数 z0 表面粗糙度，mCkl kolmogorov 常量（0.5） Cwf 摩擦系数 希腊字母符号希腊字母符号Cu 紊乱动能常量 开窗下垂面与框架间的角度，度F(n) 能量谱密度，m2/s 热能膨胀系数，K-1g 重力加速度，m/s*s 孔积率 h 高度，m 冯.卡曼常量（0.4）H 溶度参量，m 动力黏度，NsKp 渗透率，m2 密度，千克/立方米L 长度参量，m 气压系数 n 频率，HzP 大气压，PaP0 绝对气压，PaPst 相对气压，Pa 下标符下标符Pw 风压，Pa fr 循环运动Q 流速，立方米、秒 I 内侧面ru 动能消耗比率，平方米、秒 l 超长度T 绝对温度，K rmsw 平均风速的平方根u 流体速度，立方米/平方毫秒 s 次长度u* 摩擦速度，m/s st 静态V 容积，立方米 w 风Y 惯性系数1.绪论绪论温室的自然通风设备是一个极其复杂的过程，这一过程取决于温室的所有参数（额定值，位置和窗户的几何形状以及漏孔面积等等）和外部环境条件。这种现象持续不断的利害关系会导致自然通风设备在质量和能量上的不平衡，并进一步严重影响室内环境。自从 1954 年 Morris 和 Neale1 第一次对温室开窗设备中的自然通风设备进行实验性研究以来，人们越来越多地考虑到潜在的物理现象对通风设备影响。几十年后，Baiely2和 Cotton3以及 Miguel 以及其他 4 的实验论证了在植物和温室顶棚之间使用遮阳网的潜在好处。近期以来，在开窗设备5处采用幕帘下是为了防止昆虫进入，这样即可减少用化学杀虫剂。所以，幕帘表面的气流研究同样是一门重要的课题。现有的对这个课题的分析方法大致可以分为以下两种：（1）：经验主义和半经验主义的研究方法研究穿过6.13和幕帘2.5.14的气流。（2）：以流体机械公式为指导数字化的解决问题。15.17 属于第一种类型的所有模式基于的理论思想是在气流与驱动气流循环运动的潜在物之间有一种简单的非线性关系。这种分析认为温室室内的空气是不可压缩的，这一分析纯碎根据经验或贝努利方程所得。尽管简单的假设是与具体实验下得到的改正系数结合在一起的，还是大大限制了这项研究成果的有效范围。 第二种模式中，采用一种数字化模拟程序来解决惯性方程，动能和能量方程，决定速度，温度及压力和温室内最终气流循环模式。 本文介绍的这项研究有以下两个方面：（1）加深了解气流通过带孔卷帘（保温，遮光，防虫）和天窗的交换过程中的物理特性。更重要的是论述带孔卷帘和天窗使用寿命的影响因素以及启动差位的各项参数。（2）推出一种简单而精算的计算风与温室框架对卷帘和天窗的影响的公式。2.理论理论 无约束的和约束的流体运动经过有孔设备和天窗的物理现象表明这种现象与天窗或带孔设备的特征参数和驱动循环运动势差的特征参数有关。公式精确描述这个现象必须考虑到这些因素。附录 A 中附有该公式。根据附录所示，穿过任何一天窗或带孔卷帘的气流与驱动势差有关，如下：（/）Q/ t + Kp-1Q +YA-1Kp-1/2QQ+0.5(AHCc2)-1QQ= -A(pw/H+pst/H) (1)和 Q=A其中，Q 是流量， 是气体密度，A 是工作面积， 是气体动力黏度， 是材料的孔积率（单位体积容纳流体的体积） ，Kp 是材料的渗透度（流体通过媒介体的能力） ，Cc表示对流影响系数，H 是渗透参数，pw 是风压差，pst 是与温度相关的压力差，Y 在附录 A 中有定义。为了便于计算气流通过多层次密封箱或天窗的空间时的运动，必须建立计算机联网服务。薄膜温室是一个分为两层的密封区域（如图 1） ，图 2 说明了气流的联网计算原理。 自然通风设备物理模型自然通风设备物理模型 在只有一个天窗和卷帘的温室内，网络对循环运动的控制由三个接点组成，这三个接点由两个电阻连接在一起（图 2 a） 。当卷帘有空隙时，网络控制也是由三个接点组成，但这三个接点由三个电阻串接在一起。 2.1 天窗与带孔卷帘设备的气流特征参数天窗与带孔卷帘设备的气流特征参数 可渗透材料的气流特征参分为孔积率和渗透度。18. 19 孔积率表示单位材料容纳气体的体积与总材料容纳气体体积之比，大小在 0 至 1 之间（01） 。对一个孔隙来说，孔积率规定为 1（=1） ，因为整个孔隙都充满气体。 任何一种可渗透材料都能透过气体，这种能力的度量衡称之为渗透度且符合气体运动原理渗透度不仅与流体运动黏度有关还与粒子扩散时与阻碍物的碰撞频率有关。18.20 就孔隙材料而言，气体分子的碰撞频率大于 103Hz，因为气体运动黏度的数值为 10-5，渗透度的数值即小于 10-7.而对于开口设备（窗，门）来说，碰撞频率接近于零所以渗透度 Kp- 。与以上一致，连接两个接端（毛细孔与大开口）的数量即为渗透度 Kp。对于空隙材料来说气体可认为是不可压缩的（1/Cc20） 。由公式（1）推出：（/）Q/ t + Kp-1Q +YA-1Kp-1/2QQ=-A(pw/H+pst/H) （2）对于开口（=1）材料的渗透度 Kp- ,公式（1）的左边第二和第三项可忽略，导出：Q/ t+0.5(AHCc2)-1QQ=-A(pw/H+pst/H) （3）公式（2）即为著名的 Forchheimer 公式，适用于多孔隙材料。对于微弱气体可舍去二次项，得出 Darcy 定律。当气流静止时公示(3)简化为贝努利方程。2.2 驱动势差驱动势差 引起气流的驱动势差是因为温差（静因素）或风速（导致风压变化）或两者同时作用时产生的。任何一种原因都可以产生一种梯度势差引起稳定循环。风速的波动会产生一种额外的循环运动。通过温室天窗的气流波动可以分为震动循环运动和旋窝型穿透运动。震动循环运动是由于风的波动和室内气体的可压缩性。旋窝型穿透运动是由于热气流的涡流对密封室内的气流造成转动的影响。2.2.1 温室对气流运动的影响温室对气流运动的影响 当多孔薄膜或天窗的内外有温差时，就会产生一种静态压力，这种压力可以导致气流运动。设想两边温度不同，根据以下公式，两边压力也不同：st=gh （4）和 = T其中， T 表示多次测量的绝对温度差，g 表示重力加速度，h 表示垂直高度差， 表示热膨胀系数。2.2.2 风速对气流运动的影响（风压）风速对气流运动的影响（风压）测量时风速是一个不定量。在 t 时刻的瞬时值可以人为是组成部分的平均值和波动值的总和，那就是 w和uw。一段时间间隔内的平均风压与风速有关（附录 B）： Pw=0.5( 2w +uwuw) (5)其中， w表示平均风速，uw表示风速的波动值。有一些风速计可以直接读出平均风速和平均风速的平方根。假设uw有一个 Gaussian 概率分布，可以简便用下面的公式代替公式（5）：Pw=0.5 2w+-1urmsw-1 (6)其中 urmsw 表示平均风速的平方根。普通情况下的风速计仅仅提供平均风速的读数，因此，不仅能显示平均风速，而且不忽略风的波动产生的影响的风速测量计是非常有用的。因此要将动态风速的平均值与静态风速的平均值联系在一起。动能消耗比率() 根据 Kolmogorov 定律21： r2/3=0.75ckl-1F(n)( w/2)2/3n5/3 (7)其中，F（n）为能量谱密度，n 表示频率，ckl为 kolmogorov 常量（0.5） 。再利用离表面 z 距离的动能湍流与动能消耗比率21之间的关系0.5 uwuw=c-0.5rk(z+z0)2/3 (8)风速波动的平方根值和平均值的关系如下：uwuw=3 F(n)( w/2)2/3n5/3 c-0.5rk(z+z0)2/3 （9）其中，k 是冯.卡曼常量（0.4） ，c是常量（0.99） ，z 为测量风速的高度，而z0为表面粗糙度（z0的值在参考文献 22 处可寻） 。为了获得 ，弄清楚 F(n)和 n 是必要的，而且需要实施一种能量谱分析的方法。这种能量谱分析法23是用来测量频率连续不断变化的摆动过程中变量方差的。这种分析不仅可以确定 值，而且可以获得一些阐明和刻划湍流波动结构的额外信息，并且可以确定风域内主要涡流的频率。风速通常在一个参考高度测量。应该导出一个面积系数，该系数与相对基本风域的参考高度的风域有关。这个系数是由大气风界层的纵断面上的风速决定的并遵循风向定位封闭室（温室） 。这些数值都由风道分界层的多次测量所得。3.实验研究实验研究为了证实波动存在的潜能，同时也检验模型的可适用性，我们进行了如下实验。实验是在两个向东（E-W）方位建造的温室中进行的。两个温室尺寸相同（如图 3）：屋檐高 4.5米，屋顶坡角 22 。 ，宽 4.1 米，长 6.6 米。每个温室内在离地面 2.9 米处的水平面装有一个LS11 型号的隔热板（Miguel 以及其他等等18验证渗透度 7*10-10m2，孔积率 0.99） 。在实验的第一部分，每个温室内的薄膜都是合格的。实验的第二部分，在卷帘薄膜的中间打开了 0.20 米*3.80 米细小的口子，看上去像一条水平裂缝。 图 3.两个尺寸相同的玻璃温室图解每个温室内部都被牢牢密封住，墙上装有绝热板条，地面盖有聚苯乙烯泡沫绝热层，除了屋顶的窗户，每两个窗户间装有 2.05 米*0.90 米大小的活动板条。开窗斜度可升高 30度。装有铝制表面的水平圆柱形电加热器（8 个 3.80 米，直径为 0.05 米的柱面，成对排列，每两个间隔 0.35 米，每队间隔 1.15 米） ，如图 4 所示。在实验中，隔热板上下方的温度会不同，加热器被用来抑制这种温度的不断变化。图 4. 加热系统排列的俯视图在每个温室中安装 25 个铜制镍铜合金温差电偶，用来测量隔热板上下及户外的温度。它们被均匀分布：10 温差电偶被分布在隔热板下方，10 个分布在上方，还有 5 个曝露在室外。为了保证获得一个快速响应8（响应频率大约为 12Hz） ，温差电偶都是用非常细的电线（直径约为 2.5*10-5米）做成。用带有薄膜层的压力转换器来测量压力，室内测量板的上部和下部（每个部分测量三次） 。室外瞬时风压的测量位置在天窗上 0.20 米处。风速的测量用一个快速响应的风速计（响应频率为 9.5Hz）,把它安置在距天窗 0.20 米处，同时也可测方向。气流的测定用到一种自动扫描气体的仪器。在实验中，用到了恒定流速和衰减率9.25.穿过隔板狭缝的气流量用总波动量减去通过隔板的波动量。每个温室中，在地面上用两个小鼓风机和打满孔的桶把扫描气体（N2O）分离出来。在实验中，每个温室内部空气取样检验都要在 18 个不同的位置获得（9 个在隔板上层，9个在隔板下层） ，并在红外线下进行分析。 两个取样检验在 1996 年 2 月至 3 月之间的 32 天进行：（1） 气流会穿过温室天窗和卷帘是由风速产生的。实验必须在室内室外温差少于2.00.5oC，风速高于 1.5 米每秒下进行。（2） 气流会穿过多孔卷帘和卷帘上的矩形狭缝（0.02 米*3.80 米）仅仅是由于卷帘上部和下部的温差产生的（稳定条件下） 。为了减小风压的影响，测定时要关闭所有窗户（背风面的窗户可开 2o） 。实验的第一部分（气流的产生是风的作用） ，在风速和室内外温差存在下收集的数据频率 10 分钟内都为 8HZ 。实验的第二部分（气流的产生是缓慢聚集起来的） ，在卷帘上部和下部温差稳定（T1 oC）下采集的数据频率为 1.66*10-2HZ（每 60 秒内） ，稳定情况下获得。4.结果和论述结果和论述4.1 风速和风压 谱分析是在风速的采集在 10 分钟内的频率都为 8HZ的条件下进行的。取样频率是通过对可获得的最高频率分析测定的，即取样频率的一半（Nyquist 频率）在本实验中为4HZ。由于风力的特征在背风面和迎风面会有不同，9所以谱分析要分别在两处进行。关闭温室内窗户所得的结果绘制成图，如图 5 和 6 所示。图 5. 三种不同风速下的风速能量谱密度：1.27m/s(*)，3.49m/s(o)，5.50m/s(+)，在迎风面距屋顶 0.20 米处测得（-为-5/3 的斜度）图 5 所示为三种不同风速下的风速能量谱密度：1.27m/s，3.49m/s，5.50m/s，在迎风面距屋顶 0.20 米处测得。图 6. 风速为 0.52m/s(*)，2.24m/s(O)，3.37m/s(+)时，在背风面距屋顶 0.20 米处测得能量谱密度（-倾斜度为-5/3）图 6 所示为背风处测得的相应风速能量谱密度（风速为 0.52m/s，2.24m/s，3.37m/s，在背风面距屋顶 0.20 米处测得） 。如图 5 和图 6 中所描绘的，能量谱均衡的分布，频率/能量为-5/3 的范围，符合Kolmogorov 定律。类似的可获得迎风面和背风面的风速能量谱。两处能量谱的主要波动最高点在频率低于 0.1，0.2HZ 处，频率高于 1HZ就没什么特别作用了，即低频在风域中占主要地位。事实上，风速中主要的能量大的涡流就发生在这个低频范围内。这证实了 Kaimal等26和 Bot.8的研究学说。参数 可以从 图 5 图 6 中能量谱密度和频率值计算出。计算中的表面粗糙度为 0.04米22，结果如表 1.4.2 穿过卷帘和天窗的气流穿过卷帘和天窗的气流对于气流仅仅因为温差所引起（即对于稳定温度条件下 Q/t0）的如图 7 和图 8所描绘的（P w0） 。图 7. 气流穿过卷帘对应于用公式（2）和（4）预算的卷帘温度差值（测量数据（*） ）图 8. 气流穿过卷帘中心的矩形狭缝对应于用公式（3）和（4）预算的卷帘温度差（测量数据（*） ）图 7 所示为实验中气流穿过卷帘对应于用公式（2）和（4）预算的卷帘温度差值。图8 所示为实验中气流穿过卷帘中心的矩形狭缝对应于用公式（3）和（4）预算的卷帘温度差。对于气流仅仅因为风速引起的（0）,如图 911 所示。在这些图中，气流穿过天窗或卷帘与多孔隔板由公式（2）得出的值，天窗由公式（3）得出的值相对应。图 9. 预测气流穿过迎风面（*）和背风面（O）时与迎风面的相对压力（开窗度为4o）图 10. 预测气流穿过迎风面（*）和背风面（O）时与背风面的相对压力（开窗度为4o）图 11. 预测气流穿过隔板与迎风面的相对压力（任意面有一扇窗打开，开窗度为20o）迎风面（*）,背风面（O）图 12. 预测气流穿过隔板中心狭缝与迎风面的相对压力（任意面有一扇窗打开，开窗度为20o） 迎风面（*）,背风面（O）图 9 所示为实验中预测气流穿过迎风面（*）和背风面（O）时与迎风面的相对压力（开窗度为 4o）图 10 所示为实验中 预测气流穿过迎风面（*）和背风面（O）时与背风面的相对压力（开窗度为 4o）图 11 所示为实验中预测气流穿过隔板与迎风面的相对压力。其中，温室中迎风或背风面的一扇窗户要打开（开窗度为 20o） 。图 12 所示为实验中预测气流穿过隔板中心狭缝与迎风面的相对压力。其中，温室中迎风或背风面的一扇窗户要打开（开窗度为 20o） 。图 7 和图 11 描绘了由于存在温差，各自的风域推动气流穿过有孔的隔板，它们显示出了两种不同的波动规律：Darcy 波动规律（如图 7）和 Forchheimer 波动规律（如图 11） 。这些发现归功于 Bear,Bachmat19和 Bailey2。对于 Reynolds 数据（Re=uKp1/2/）小于整体值时，气流与推动势成比例，即温室与周围空气间正常温差范围（T25K）内产生的情形。对于 Reynolds 数据大于整体值时，必须加上气流的二次项（Forchheimer 波动规律） ，即波动是由风速高于 0.25m/s 时产生的。 实验气流值与模型预测等效的气流值相比较，所得的误差总是小于 20%，出了图 12 之外。图中显示的大部分分散值是由于气流穿过裂缝所致，这些气流是从总的波动量中减去穿过隔板的波动量获得。由于差别很小，所以误差相应就很大。5.结论结论1. 对于换气设备起重要作用的、能量大的涡流是由频率低于 0.10.2HZ范围内湍急的风速下引起的。2. 据估计，这种湍急的风速在平均风速中占 13%至 52%，也就是说在总风压中占了重要地位。3. Forchheimer 方程式方程（2）描述了气流穿过有孔的隔板（孔集中在隔板中间） 。可是，对于温室与周围空气间温差在正常范围内所引起的气流波动，气流的二次项可忽略，所以方程就缩写成了 Darcy 法则（Kp-1Q=-Ap/HP） 。4. 通过理论预测的穿过隔板和通风口的气流与实验值很接近，大体上它们之间的差别小于20%。参考文献参考文献1 Morris L G; Neal F E the infra-red carbon dioxide gas analyzer and its use in greenhouse research. National Institute of Agricultural Engineering Report，Silsoe，UnitedKingdom，19542 Bailey B J Glasshouse thermal screens: air flow through permeable materials. Departmental Note no. DN/G/859/04013. National Institute of Agricultural Engineering, Silsoe, United Kingdom, 19783 Bailey B J; Cotton R F Greenhouse thermal screens: influence of single and double screens on heat loss and crop environment. Departmental Note no. DN/G/982/04013. National Institute of Agricultural Engineering, Silsoe, United Kingdom, 19804 Miguel A F; Silva A M; Rosa R Solar irradiation inside a single span greenhouse with shading screens . Journal of Agricultural Engineering Research, 1994, 59, 61-725 Kosmas S R; Riskowski G L; Christianson L Force and static pressure resulting from airflow through screens. Transactions of ASAE, 1993, 36, 1467-14726 Okada M; Takakura T Guide and data for greenhouse air conditioning. 3: heat loss due to air infiltration of heated greenhouses. Journal of Agricultural Meteorology (Tokyo), 1973, 28,223-2307 Kozai T; Sass S A simulation natural ventilation for a multi-span greenhouse. Acta Horticulturae, 1978, 87, 39-498 Bot G P A Greenhouse climate: from physical processes to a dynamic model. PhD dissertation, Agricultural University of Wageningen, The Netherlands, 19839 De Jong T Natural ventilation of large multi-span greenhouses. PhD dissertation, Agricultural University of Wageningen, The Netherlands, 199010 Montero J I; Anton A; Biel C Natural ventilation in polyethylene greenhouses with and without shading screens. Proceedings of the International Seminar and British-Israel Workshop on Greenhouse Technology, Bet Dagon, Israel, 1990, 65-7111 Fernandez J E; Bailey B J Measurements and prediction of greenhouse ventilation rates .Agricultural and Forest Meteorology, 1992, 58, 229-24512 vans Ooster A Using natural ventilation theory and dynamic heat balance modeling for real time prediction of ventilation rates in naturally ventilated livestock houses. Ag. Eng. 94 Milano, Report N. 94-C-012, 1994 13 Bullard T; Menses J F; Merrier M; Papadakos G The mechanisms involved in the natural ventilation of greenhouses. Agricultural and Forest Meteorology, 1996, 79, 61-7714 Batemans L Assessment of criteria for energetic electiveness of greenhouse screens. PhD dissertation. University of Ghent, Belgium, 198915 Okushima L; Sass S; Nara M A support system for natural ventilation design of computational aerodynamics. Alta Horticultural, 1989, 248, 129-134 16 Outworker E N J; Voskamp J P; Alaskan Y Climate simulation and validation for an aviary system for laying hens. Ag. Eng. 94 Milano, Report N.94-C-063,199417 Mastitis A; Bot G P A; Pacino P; Scarascia-Mugnozza G Analysis of the decency of greenhouse ventilation using computational fluid dynamics. Agricultural and Forest Meteorology, 1997, 85, 217-22818 Miguel A F; Van de Barak N J; Silva A; Bot G P A Analysis of the airflow characteristics of greenhouse screening materials. Journal of Agriculture Engineering Research, 1997, 67, 105-11219 Bear J; Bathmat Y Theory and Applications of Transport Phenomena in Porous Media. Dordrecht: Kluwer Academic20 LeBron G; Clout A thermo dynamical modeling of fluid flows through porous media: application to natural convection. International Journal of Heat and Mass Transfer, 1986, 29, 381-39021 Tenneco H; Lumley J L A First Course in Turbulence. Cambridge, MA: MIT Press, 197222 Euro code ENV 1991-2-4. Basis of design and action on structures: wind action. NNT Delft, 199523 Turkey J W The sampling theory of power spectrum estimates. Symposium on Application of Autocorrelation Analysis to Physical Problems. Washington, Office Naval Research 1950, 47-6724 Clarke R M Observational studies in the atmospheric boundary layer. Quarterly Journal Royal Meteorology Society, 1970, 96, 91-11425 Sherman M H Tracer-gas techniques for measuring ventilation in a single zone. Building and Environment, 1990, 2526 Kemal J C; Wynyard J C; Izumi Y; Cote O R Spectral Characteristics of surface-layer turbulence. Quarterly Journal Royal Meteorology Society, 1972, 98, 563-58927 Miguel A F; Van de Barak N J; Silva A; Bot G P A Forced fluid motion through openings and pores. Building and Environment 1998(in press)28 Walker I S; Wilson D J Evaluating models for superposition of wind and stack elect in air infiltration. Building and Environment, 1993, 28, 201-21029 Peixoto J P; Fort A Physics of Climate. New York, USA: American Institute of Physics, 1992附录附录 A: 穿过通风口和气孔的流速运动方程 对于呈线性的气流穿过一个可渗透的材料，其运动方程可描述为18.27(/)u/t+Kp-1u+YKp-1/2uu+(/2)uu/j（/） （2u/j2）=-pt0/j (A1)其中 Y=4.3610-2-2.12总压力28 Pt0=Pw+Pst 公式中，u 是变速度， 是密度，Pw 压力是由风或力学原因造成，Pst 压力是累积作用的产生的（热气压） ，Pt0 是总压力，pt0/j 是在 j 方向的压力梯度变化， 是动力黏度， 和 Kp 分别是孔积率和渗透度。 公式中包含了在固定地点，变化流动的当地加速度（左边第一项） ，粘性阻力是在流体基质分界面处的动量转换来的（左边第二项） ，穿过气孔的惯性作用（左边第三项）,对流惯性作用（左边第四项）和变化流动的粘性阻力（左边第五项） 。因而，这个描述流速穿过气孔以及孔隙的理论是正确的18.27对于有孔材料，u/j 接近于零19。当基质中固体的占有量大于液体占有量，液体流动产生的粘性阻力项可以忽略，公式（A1）变成 (/)u/t+（Kp-1+YKp-1/2u）u=-pt0/j +Fej (A2)对于孔隙，第四项可以写成27p uu/j=0.5（Hcc2）-1u2 (A3)公式中 Cc 是表明对流作用的系数，H 是孔隙深度。对于圆孔或方孔，271/Cc2=2.7-0.04203exp3.7(A/Afr)1/21-2.7-0.04203exp3.7(A/Afr)1/2(A/Afr)2.51/2 (A4)对于框架一边的孔隙装有遮板27， （90）,1/Cc2=1.75+0.7exp-(L1/LS)sin/32.52sin1+0.60(L1/Ls)(cos-2(90-)/360)sin)2 （A5） 。其中，是指框架和遮板夹角，A 是孔隙面积，Afr 是波动面积，L1 是大孔隙长度，Ls 是小孔隙长度。根据以上公式，无粘性流动的运动方程可写成(/)u/t+Kp-1u+YKp-1/2uu+0.5（HCc2）-1uu=-Pw/H-Pst/H （A6） ，其中，对于无孔材料，1/Cc2=0,对于有孔材料，1/Cc2由公式（A4）或（A5）得来。附录 B：风力引起的外部压力对于稳定流动，在 j 方向的流动方程（Navier-Sttokes 方程）可写成 u（u/j）=p/j+（2u/j2） （B1） 。风是由于物理量的波动不定、加速度和压力产生的急骤气流。这些变风区的急骤风波可用统计学的方法估算。用 Reynids 分解原理，瞬时量可以写成由平均量（-）和不定量（， ）组成。对于速度 Uw= w+U，w （B2）,和 w=-1uwdt其中，比有效波动时期长，但是比平均流动时期短，UW 是风速。把公式（B2）代入公式（B1）中得 w（w/j）=Pw/j+(2 w/j2)- （U，w U，w）/j (B3).右边第三项表示由急骤冲量产生的剪切应力。对前面的公式求积分，我们可以得到Pw=0.5 w2-（ w/j-0.5U，w U，w ）+w (B4),其中 w 是积分常量。如果考虑没有风的情况， w=0, U,w=0. 因此，w 必为零，Pw=0.5 w2-（ w/j-0.5U，w U，w ） （B5） 。 在低层大气的边界面29w/j=u*/(kh) (B6),公式（B5 就变为Pw=0.5（ w2+ U，w U，w）-cwf1/2/(kh) （B7）其中，Cwf=（u*/ w）2，Cwf 是摩檫系数，h 是离地面的高度，u*是摩檫速度，k 是冯卡曼常量。如果忽略粘性作用cwf1/2/(kh)0，公式（B7）就缩写为 Bot8和 Jong9 所做实验的假设与证实之间的关系。 J.agric.Engng Res. (1998) 70,165-176Article Number. Ag970262Physical Modelling of Natural Ventilation Screens and Windows in GreenhouseWe use a combination of practice and theory research on greenhouse ventilation equipment, is to study greenhouse shutter and Windows service life of the device under low pressure and under different wind and pressure fluctuations. These fluctuations associated with the mean wind speed, average wind speeds are obtained by energy spectrum analysis. It follows that a pressure associated with the mean wind speed, and estimation of gas turbulence on mean wind speed has a big impact. Start the potential relationships between greenhouse ventilation equipment and is based on the groundbreaking research of fluid machinery. On air flow and air pressure and temperature correspond to change this prediction corresponds with data from experimental, by and large, the difference between them is less than 20%.NotationA area,m2 Z height, mCc coefficient accounting for convective effect Z0 surface roughness legth,mCkl Kolmogorov constant （0.5） Cwf friction coefficient Greek symbolCu turbulent kinetic energy constant window angle betwwen the flap of windowand the frame,degF(n) power spectral density ，m2/s confficient of thermal expansion g gravitational acceleration，m/s*s porosity h height ，m k von Karmans constant（0.4）H characteristic depth，m dynamic viscosity,Ns/ m2 L characteristic length ，m wind pressure coefficient n frequency ，HzP pressure of air ，PaP0 mean absolute pressure of air in enclosure ，PaPst stack pressure ，Pa SubscriptsPw wind pressure ，Pa fr flow field Q airflow ，m3/s I inside ru turbulent kinetic energy dissipation rate,m2/s l larger length T absolute temperaturw ，K rmsw root-mean-spure wind velocityu flaid velocity, s smaller length u* friction velocity，m/s st stack V volume w wind Y inertial factor1.Introduction Natural ventilation of greenhouse is an extremely complex process, all parameters of this process depends on the greenhouse (rated value, location and geometry of the window as well as leak areas, and so on) and the external environmental conditions. This phenomenon continued interest can cause natural ventilation in mass and energy imbalances and further serious effects of indoor environments. Since 1954, Morris and Neale1 first on natural ventilation in greenhouse ventilation equipment for experimental studies, it is increasingly taking into account the potential physical effects on ventilation equipment. A few decades later, Baiely2 and Cotton3, and Miguel, along with 4 other experiments demonstrated the plant and greenhouse roof with sunshade NET potential benefits. In recent times, in the fenestration equipment 5 curtain is in order to prevent the entry of insects, thereby reducing use of chemical pesticides. So, research on surface air curtain is also an important issue. Existing on the subject of analysis methods can be broadly classified into the following two ways: (1): the empiricism and semi-empirical methods of research studies on airflow through the 6.13 and curtain 2.5.14. (2): guided by the fluid mechanical formulas of digital solutions. 15.17 belongs to the first type of all models based on the theory that the movement of air driven air circulation between the potential of there is a simple linear relationship. This analysis finds that the greenhouses of indoor air is not compressed, plain pieces of this analysis or based on experience derived from the Bernoulli equation. Despite the simple assumption that in conjunction with specific experiments under the corrective coefficient, is also greatly limits the range of the study results. In the second model, using a digital simulation program to solve the equation of inertia, momentum and energy equations, decision speed, temperature and pressure, and eventually air circulation patterns within the greenhouse. Described in this study are two-fold:(1) Understanding of airflow through the shutter with holes (insulation, shading, pest control) and physical properties of skylights in the Exchange. More important deals with shutter and skylight with holes of factors affecting the service life of the parameter and the poor start.(2) Offer a simple actuarial calculation of the wind and the greenhouse effect formula frame shutter and skylight.2.Theory Unconstrained and constrained fluid movement through hole equipment and physical phenomena indicate that this phenomenon of skylights and skylights or equipment with holes and drive circular motion potential difference of characteristic parameters characteristic parameters. Formula accurately describe this phenomenon must take account of these factors. With the formula in Appendix a. As shown in the Appendix, a skylight or curtain with holes through any airflow and drive potential difference of about, is as follows: (/) Q/ t+ Mu Kp-1Q+ YA-1Kp-1/2| Q| Q+0.5(AHCc2)-1| Q| Q=-A ( pw/H+ pst/H) (1) and Q=A which, Q is flow, is gas density, a, is work area, is gas power viscosity, is material of hole product rate (units volume holds fluid of volume), Kp is material of penetration degrees (fluid through media body of capacity), Cc said convection effect coefficient, h is penetration parameter, PW is wind pressure poor, pst is and temperature related of pressure poor, y in Appendix a, in the has defines. In order to facilitate the calculation of air flow through multi-level sealed box or blank space movement, computer networking service must be established. Film sealing area of the greenhouse is a two-story (Figure 1), Figure 2 illustrates the flow theory of networked computing. Physical model for natural ventilation In only one window and roller shutter in greenhouses, network control of the circulating movement is made up of three points, the three contact consists of two resistors are connected together (Figure 2-a). When the roller shutter when there are gaps, network control is made up of three points, but the three points by three resistance threaded together.2.1 Skylights and roller shutter device with holes air flow characteristic parametersAirflow characteristics of permeable materials are divided into porosity and permeability. 18. porosity materials hold the volume of a gas and total material to accommodate gas volume ratio of size between 0 to 1 (0 1). A pore, porosity is 1 ( =1), because the pores are filled with gas. Any permeable material can make use of the gas, the weights and measures of the ability to call it penetration and are consistent with principles of gas motion penetration is not only related to the fluid viscosity and particle diffusion and obstructions when the collision frequency. 18.2 in terms of porous materials, gas molecules of the collision frequency is larger than 103Hz, because gas kinetic viscosity values for 10-5, penetration value that is less than 10-7. and for opening device (Windows, doors), the collision frequency is close to zero so the penetration Kp-. Consistent with the above, connect the two ends (the pores with the larger opening) number is the penetration of Kp. For gap materials, gases can be considered incompressible (1/Cc2 0). By the formula (1) available: (/) Q/ t+ Mu Kp-1Q+ YA-1Kp-1/2| Q| Q=-A ( pw/H+ pst/H) (2) opening ( =1) material penetration Kp-, the formula (1), second and third on the left can be neglected, exporting: Q/ t+0.5 (AHCc2) -1| Q| Q=-A ( pw/H+ pst/H) (3) of the formula (2) is the famous Forchheimer equation, applied to porous materials. Weak gases can be rounded down second and concluded that Darcys law. When the air is stationary publicity (3) simplified Bernoulli equation.2.2 Driving PotentialDriving potential difference is because of airflow caused by temperature difference (static) or wind (causes the air pressure changes) or both roles at the same time. Any one cause can produce a gradient potential stability caused by poor circulation. Wind speed fluctuations will give rise to an additional cycle of movement. Through a greenhouse roof air flow fluctuations can be divided into vibration cycle and Rotary Wo penetration movements. Vibrating circular movement is due to the fluctuation of the wind and indoor air can be compressed. Rotary-Wo penetrating movement is due to the thermal air currents cause rotation of the vortex to seal indoor air impacts.2.2.1 Greenhouse effect on air movementWhen the porous films or blank when there is a temperature difference between inside and outside, there will be a static pressure, which can lead to air movement. Envisage different temperatures on both sides, according to the following equation, pressure on both sides is different: St= g h (4) and = t, expressed many times absolute measurement of temperature difference t and g the gravitational acceleration, h represents a vertical height difference, coefficient of thermal expansion.2.2.2 Effect of wind speed on the air movement (wind)Wind speed is measured does not quantitative. At t time averages and fluctuations of the instantaneous value can be man-made is an integral part of the sum of the values, its w and uw. Within a time interval of average wind speed and wind pressure on (Appendix b): Pw=0.5 ( 2W+uwuw) (5), w and the average wind speed, uw wind speed fluctuations in value. Some anemometer can be read directly out of the square root of the mean wind speed and average wind speed. Say uw have a Gaussian probability distribution, you can simple use the following formulas instead of formula (5): Pw=0.5 2W+ -1urmsw-1 (6), where urmsw is the square root of the mean wind speed. Ordinary cases the anemometer provided only average wind speed readings, therefore, can not only display the average wind speeds, and do not ignore the impact of fluctuations of the wind wind speed meter is very useful. So to average static dynamic wind speed average of the wind speed associated with. Kinetic energy consumption rate ( ) according to the law of Kolmogorov 21:r Mu 2/3=0.75ckl-1F (n) ( w/2 ) 2/3n5/3 (7), f (n) for the energy spectral density, n indicates the frequency, CKL-Kolmogorov constants ( 0.5). Again uses away from surface z distance of kinetic energy turbulence and kinetic energy consumption ratio 21 Zhijian of relationship 0.5 uwuw=c -0.5r k (z+Z0)2/3 (8) wind speed fluctuations of square root value and average of relationship following: uwuw=3 f (n) ( w/2 ) 2/3n5/3 c -0.5r k (z+Z0)2/3 (9) which, k is Mr Frederick FUNG. Kaman constants ( 0.4), c is constants ( 0.99), z for Measure the height of the wind speed, and Z0 is the surface roughness (22 to find value of Z0 in the reference literature). In order to obtain the gamma, make sure f (n) and n is necessary, and the need to implement an energy spectrum analysis method. 23 this energy spectrum analysis method is used to measure the frequency swing variable variances in the process of continuous change. This analysis not only to determine the gamma value, and you can get some extra information to clarify characterization and structure of turbulent fluctuations, and you can determine the frequency of wind field within the main vortex. Wind speed is usually at a reference height measurement. Should export one area coefficient, the coefficient and relative wind wind Domains domain reference high. This coefficient is determined by the atmospheric boundary layer wind speed on the vertical section of the wind decided to follow the wind direction positioning to close .3.Experinmental studyIn order to confirm the potential of fluctuations, while also testing the applicability of the model, we came up with the following experiment. Experiment is to the East in two (E-W) direction construction of greenhouses. Two greenhouse sizes the same (Figure 3): eaves height of 4.5 m, the roof slope angle 22. , 4.1 meters wide, 6.6 meters long. Inside each greenhouse from the ground 2.9 metres with a LS11 insulation panels (Miguel, and the other 18 verify that penetration 7*10-10m2, porosity of 0.99). In the first part of the experiment, each film in greenhouse is qualified. Second part of the experiment, shutter film opened 0.20 m *3.80 m a very small hole in the Middle, which looks like a horizontal crack.Each greenhouse is firmly seal on the wall with insulation Strip, the ground covered with polystyrene foam insulation, in addition to the Windows on the roof, between two Windows each equipped with *0.90 m active strips the size of 2.05 metres. Windows tilt can rise by 30 degrees. Equipped with an aluminum surface of horizontal cylinder-shaped electric heater (two 8-meter, 0.05 m diameter cylinders, arranged in pairs, each of two interval 0.35 meters, each interval of 1.15 m), as shown in Figure 4. In the experiment, heat insulation below the temperature will be different, heaters were used to suppress such temperature changing.Installed in each greenhouse 25 brass nickel-copper alloy thermocouple to measure heat shield and outdoor temperature up or down. They are evenly distributed: 10 thermocouple is distributed below the insulation panels, distribution of 10 at the top, there are 5 exposure outdoors. In order to ensure a fast response 8 (response frequency is approximately 12Hz), thermocouple is made of very fine wires (diameter of about 2.5*10-5 m). Pressure transducers to measure the pressure with a film layer, indoor measurement of upper and lower (each measured three times). Instantaneous measurement of wind pressures on outdoor locations on the skylight 0.20 metres. Measurement of wind speed anemometer with a fast response (response rate of 9.5Hz), skylight 0.20 metres it is placed at a distance, but also measurable. Flow determination using an automated scan of gas equipment. In the experiment, using a constant flow rate and decay rate of 9.25. through the slit air partition amount minus the total fluctuation through the divisions of the fluctuations. In each greenhouse, on the ground with two small fans and barrels full of holes to scan gases (N2O) separated. In the experiment, each within the greenhouse air samples have to be tested in 18 different locations (9 in partition top, 9 screens below), and under the infrared analysis. Two sample test conducted in 32 days between February 1996 and March: (1) flow through the greenhouse roof and curtain is produced by the wind. Trials should be indoor and outdoor temperature difference less than 2 0.5oC, under the wind speed is higher than 1.5 meters per second. (2) flow through the porous rectangular slits on the shutter and the shutter (0.02 m *3.80 m) simply because the shutter of the upper and lower temperature (under steady conditions). In order to reduce the effects of wind pressure, determination to close all the Windows (the Lee side of window opening 2O). First part of the experiment (air is the role of the wind), wind speed and temperature difference between indoor and outdoor gathering in the presence of data 8HZ in the frequency within 10 minutes. Second part of the experiment (air is slowly gathering), shutter upper and lower temperature stability ( t 1 oC) data collection frequency is under 1.66*10-2HZ (per 60 seconds), acquired under stable conditions.4.Results and discussion4.1 wind velocity and wind pressureAcquisition of spectrum analysis is the wind speed in 10 minutes frequencies are under 8HZ conditions. Sampling frequency is available through the determination of the highest frequency, that is half the sampling frequency (the Nyquist frequency) in this experiment, the 4HZ. Due to the characteristics of wind in the Leeward and Windward will be different, spectral analysis to 9 respectively in two places. Findings of the window in the closed greenhouse painted figure, as shown in figures 5 and 6.Figure 5. Three different wind speeds of power spectral density of wind speed: 1.27m/s (*) 3.49m/s (o), 5.50m/s (+) on the windward side measured from the roof of 0.20 metres (-five-thirds angle) as shown in Figure 5 for the three different wind speeds of power spectral density of wind speed: 1.27m/s,3.49m/s,5.50m/s, Windward 0.20 metres measured from roofs.Figure 6. Wind of 0.52m/s (*) 2.24m/s (O), 3.37m/s (+), on the Leeward side away from the roof of 0.20 metres measured power spectrum density (inclination- -5/3) As shown in Figure 6 to Lee the power spectral density of wind speed measured (wind of 0.52m/s,2.24m/s,3.37m/s, measured in the Lee side away from the roof of 0.20 metres). As depicted in Figure 5 and Figure 6, balanced distribution of energy spectrum, frequency/energy-five-thirds range, in line with the law of Kolmogorov. Similar access to windward and Leeward wind energy spectrum. Two major fluctuations in the energy spectrum at frequencies below 0.1,0.2HZ of the highest point, more frequently than 1HZ nothing special, low frequency domain dominated by the wind. In fact, the wind speed in the major energy vortex in the low frequency range. Proving the Kaimal Bot.8 and 26 research theory. Parameter can be Figure 5 figure 6 energy spectral density and frequency values calculated. Calculation of surface roughness: 0.04 m 22, results as shown in table 1.4.2 Through the curtain and window airTo flow just as caused by the temperature difference (that is, for stable temperature conditions Q/ t 0) as depicted in the figure 7 and Figure 8 (p w 0).Figure 7. Air through the shutter corresponding to the formula (2) and (4) budget rolling temperature difference (measurement data (*)Figure 8. Air through the rectangular slit shutter Centre corresponds to the formula (3) and (4) budget rolling temperature difference (measurement data (*) as shown in Figure 7 to air through the shutter corresponding to the formula in the experiment (2) and (4) shutter temperature difference of the budget. Figure 8 shows the experiment in the air through the rectangular slit shutter Centre corresponds to the formula (3) and (4) shutter the temperature difference of the budgets. Caused by airflow just because the wind speed ( 0), as shown in Figure 9-11. In the diagram, air through the skylight or curtain and porous partition by the formula (2) value of the skylight by the formula (3) corresponds to the value.Figure 9. Prediction of air through the Windward (*) and the Lee side (O) with the Windward relative pressure (window-4O)Figure 10. Prediction of air through the Windward (*) and the Lee side (O), as opposed to the Lee side of pressure (open the window-4O)Figure 11. Predict the relative pressure of air through the barricades and Windward (any one window open, window-20o) Windward (*), the Lee side (O)Figure 12. Forecast airflow through clapboard Center narrow sewing and upwind surface of relative pressure (any surface has a fan window open, opened window degrees for 20o) upwind surface (*), Leeward surface (O) Figure 9 by shows for experimental in the forecast airflow through upwind surface (*) and Leeward surface (O) Shi and upwind surface of relative pressure (opened window degrees for 4O) Figure 10 by shows for experimental in the forecast airflow through upwind surface (*) and Leeward surface (O) Shi and Leeward surface of relative pressure (opened window degrees for 4O) Figure 11 shows the experimental forecast relative pressure of air through the barricades and Windward. Greenhouse in the Windward or Leeward side of a window you want to open (window-20o). Figure 12 shows the slit and experimental Center for forecasting air through the clapboard Windward relative pressure. Greenhouse in the Windward or Leeward side of a window you want to open (window-20o). Figure 7 and Figure 11 depicts due to temperature, the wind field driving air through the holes in clapboard, which showed two different kinds of fluctuations: Darcy fluctuations (Figure 7) and Forchheimer fluctuations (Figure 11). These findings due to Bear,Bachmat19 and Bailey2. Reynolds data (Re= uKp1/2/) is less than the overall value, the flow and promote potential proportional to the greenhouse and normal ambient air temperature range (T25K). Reynolds when the data is larger than the overall value, must be added to air second (Forchheimer fluctuations), that is, when volatility is determined by the wind speed is higher than 0.25m/s. Experimental gas value compared with the forecast flow equivalent to the value of the model and the resulting error is always less than the 20%, beyond the figure 12. Diagram shows most of the dispersion value is attributable to air through cracks, the airflow is subtracted from the total amount of volatility fluctuations obtained through the clapboard. Because there is little difference, so error is very large.5. Conclusion1. For ventilation devices, energy plays an important role within the Vortex is less frequently than 0.10.2HZ caused by turbulent wind speeds.2. It is estimated that this turbulent winds 13% per cent of the mean wind speed, which means that occupy an important position in the total air pressure.3. Description the air through holes in clapboard (concentration of holes in clapboard middle). 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