|Determination of the optimum parameters of hothouse fence|
|Written by Administrator|
|Tuesday, 02 November 2010 16:39|
The importance of hothouses is not in doubt. However, how to choose a construction site and the most optimal location of greenhouses? When you can reduce the cost of heating by installation fences against wind and how to install these fences better? Today, such questions can be answered visually.
DETERMINATION OF THE OPTIMUM PARAMETERS OF HOTHOUSE FENCE
Firstly airflows were modeled that arise at the vegetable factory territory (Fig. 1) for a fixed wind speed of 5 m/s (heading west) takes into account natural barriers (the wood). As is evident from the results of calculations (Fig. 1b,2), there is uneven distribution of the velocity of air masses. In the absence of the fences wind loads occur on the ends of greenhouses, which is why in winter, when strong wind can significantly cool greenhouses (20%). In the absence of fences wind loads occur on the ends of each greenhouses, which is why in winter, a substantial cooling (up to 20%) of the greenhouses can occur because of strong wind.
Fig. 1. Hothouses placement scheme (a). Velocity scalar field distribution (horizontal section at 2,5m height, wind velocity equals 5m/s) (b)
Fig. 2. The distribution of velocity of air in the horizontal section at a height of 2,5 m
To eliminate the cooling greenhouses was suggested to use a fence to protect the western part of the greenhouses from wind. As a criterion for the effectiveness of fence, were used wind speed measurements at several points at the end of the greenhouses (p1, p2, p3) (Figure 3).
Fig. 3. Points for velocity magnitude determination
In the analysis a solid fence of varying heights (H = 2m, 2.5m и 3m) was considered At different distances from the greenhouses (L = 1m, 3m, 5m, 10m и 15m). Wind speed: 5m/s. As the results of simulation, the wind speed at the end of the hothouses decreased with increasing height of the fences , and at a distance of 3 to 5 feet were obtained the best results. For distances greater than 5 meters observed increase in wind speed. For a point p1 results can be explained by the presence of the dead zone in the lower end of the greenhouses (in the absence of barriers) due to uplift of the incoming air stream by greenhouse. increase the speed at a given point for models with fencing 2 and 2.5 m are explained by the presence of a small vortex behind the fence. Therefore, the main criterion for choosing the optimal configuration of the fence is the maximum lift of the air flow over the end face of the greenhouses, i.e. minimum wind speed at the points at the top of the greenhouse (p2, p3).
Fig. 4. The distribution of air velocity in cross sections for fence height H = 2.5 m at a distance of 5 meters in front of the end face of the greenhouses
In solving such problem arises a natural question: whether to use solid fencing or in order to save material to install a fence with gaps? On this question also can try to answer by simulation. Figure 5 shows the distribution of the velocity modulus around obstacles with different values of the gap in comparison with solid fence. As can be seen, this type of fence reduces wind speed and vorticity in the area between the fence and the greenhouse, although perhaps not so well raises airflow.
a b c
Fig. 5. Distribution of wind speed over the fence with the gap width 33% (a), 50% (b) and 0% (c) of construction period
|Last Updated on Wednesday, 24 November 2010 20:18|