1、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
2、 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
3、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 di
4、fference 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
5、,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
6、 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* f
7、riction 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 extern
8、al 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
9、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 equi
10、pment 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-em
11、pirical 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
12、 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 coefficien
13、t, 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 thi
14、s 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
