JPH0313122B2 - - Google Patents

Description

[Detailed description of the invention]

This description relates to a windbreak fence used to prevent the scattering of coal dust from the surface of coal storage in an outdoor coal storage area such as a thermal power plant, and relates to a fence that has an extremely high wind-blocking effect. In the above-mentioned coal storage yards, etc., as shown in Figure 1, coal dust is blown up and scattered by strong winds from the surface of the coal storage 1 piled up in a mountain shape, and falls outside the storage area, contaminating the surrounding area and becoming a problem. There is. Windbreak fences, for example, are useful in addressing such problems. A fence A is provided on the windward side of the coal storage 1 to block the blowing wind. However, windbreak fences have the following problems. In other words, in theory, the wind-shielding effect of a fence is that, as shown in the schematic explanatory diagram in Fig. 2, separation C is generated in the wind flow B by the upper end of the fence A, and the flow below the separation flow is Line D of wind speed 0
The so-called dead area (hatched area) surrounded by
The idea is to form a However, in reality, if a simple screen-like fence is used as a fence, many strong eddies E will occur in the dead area, especially near the fence, and the theoretical dead area may not be a sufficient wind speed reduction area. It's something that doesn't exist. The inventor of the present invention intended to develop a windbreak fence that can eliminate the vortices in the dead water area and secure the dead water area as a sufficient wind speed reduction area, and as a result of extensive experiments and research, the following facts were discovered. This is what we discovered. That is, as mentioned above, when a fence is installed, the strong vortices that form on the leeward side of the fence can be made weaker and smaller by making the fence itself into a net shape. In other words, in a net fence, this is the result of the wind blowing through the fence acting on the vortex on the leeward side of the fence. However, even in the case of this net fence, it is practically impossible to achieve both the effect of suppressing vortices on the leeward side of the fence and the original wind shielding effect, that is, the effect of reducing wind speed when the influence of vortices is ignored. In other words, in the case of a net fence, the conditions of its mesh greatly affect the flow on the leeward side of the fence. Specifically, the fullness rate of the fence surface, that is, the ratio of the mesh-filled part to the fence area is a major influencing factor, and if this fullness rate tends to be small,
Although the effect of suppressing vortex formation on the leeward side of the fence increases, the wind shielding effect becomes poor, and conversely, at a large filling ratio, the wind shielding effect itself improves, but the vortex formation becomes stronger and larger, and eventually The wind speed reduction ratio in the dead water area becomes lower. Because of this relationship, even in the case of a net fence, it is difficult to secure a sufficient wind speed reduction area on the leeward side of the fence. However, in this net fence, the net has a so-called double-layered structure, and this double-layered net is connected to both nets 2 and 2 as shown in FIG.
By arranging the meshes between 2' in a staggered manner in both the vertical and horizontal directions, it is possible to simultaneously ensure an excellent wind-shielding effect and an effect of suppressing vortices in the dead water region. In other words, in this double-layered net fence, the apparent fullness rate of the fence surface, that is, the discovered area of the fence and both nets 2, 2'
The ratio of the projected area of the full mesh part is the most important factor that influences the flow on the leeward side of the fence, and the relationship between this apparent fullness ratio and the wind shielding effect and vortex suppressing effect tends to be as described in 1 above. It is similar to the case of a single-walled netfence. In other words, if the filling ratio is small, the wind blocking effect will be poor, and if it becomes large, the rectifying effect on the leeward side of the fence will be reduced. However, in the case of double-walled panels, unlike single-walled panels, it is possible to maintain a high wind-shielding effect while ensuring an excellent rectifying effect. There is a range of rates. This is because when the wind passes through a double fence, it passes through the net twice, but at that time, the net functions as a rectifying grid, and at the same time has the dual effect of breaking down large turbulent vortices into smaller ones. This is thought to be due to the fact that the For this reason, in the case of a double-walled net fence, it is possible to ensure a wide wind speed reduction on the leeward side of the fence and a sufficient wind speed reduction ratio. That is, the present invention is based on the above, and
Two screen nets 2, 2' having the same mesh shape and arranged parallel to each other are provided, and the two nets are positioned so that each other's meshes are staggered in both the vertical and horizontal directions,
The apparent fullness rate of the wind shielding surface of the fence body consisting of both nets is 50 to 80%, and the distance L between both nets is 2 mm or more and within 5 times the lateral length l of the mesh opening. The gist is a windbreak fence that is characterized by the following. In the present invention, the positional relationship of the meshes of the double-strapped nets is staggered in both the vertical and horizontal directions as shown in FIG. 3, so that the double-strapped nets can function sufficiently as a rectifying grid. This is to enable effective elimination of the vortices immediately on the leeward side of the fence. Next, the apparent fullness rate of the fence surface of the fence body made of this double-strapped net was limited to 50 to 80%, based on the results of wind tunnel experiments described later. This is estimated based on numerical changes in the wind speed distribution and turbulence strength distribution (see Figures 6 and 7, especially A and C) when the wind speed is lower than 50%. If it becomes sufficient, the wind speed reduction ratio on the leeward side of the fence will be insufficient, and conversely, if the filling ratio is too large, exceeding 80%, the flow rectification immediately on the leeward side of the fence will not be sufficiently achieved, which poses a problem. Note that this apparent enrichment rate is particularly preferably about 55 to 65% in terms of effectiveness. Furthermore, the mutual separation distance L of the double-strung net shown in Figure 3 B (vertical side view) is set to be 2 mm or more and within 5 times the lateral length L of the mesh opening (see Figure 3 A). was determined by taking into consideration the mutual separation distance in the case of two sheets and the turbulence strength distribution based on the change in apparent filling rate based on the results of wind tunnel experiments, and L<
This is because 2 mm is functionally almost the same as a single-layer net, and the original meaning of double-layer netting is lost, and when L>5l, there is no mutual interference effect. As the net of the double-walled net fence of the present invention, any net can be used regardless of the shape, size, etc. of the mesh, as long as the above-mentioned apparent filling rate can be secured from 50 to 80%. In short, no matter which net you use, you can always expect the same effect as long as you maintain an apparent fulfillment rate of 50 to 80% as a fence. Said third
The nets 2 and 2' shown in the figure are of the so-called expanded metal type, which are made by making a slit in a single plate and expanding it, and this expanded metal type is the most common type of metal net. . Specifically, the fence of the present invention is constructed as shown in FIG. 4, for example. That is, in the figure, the fence body A has a large number of panel structures 3 using the above-mentioned nets arranged vertically and horizontally between pillars 4 erected at predetermined intervals at the fence installation location. It is installed and configured. The panel structure 3 is, for example, as shown in FIG. 5 (A is a front view, B is a side view), a rectangular net 2, 2' is stretched and fixed with presser parts 6 and 7 arranged along the edges to form a panel shape. Next, an experiment conducted to confirm the effectiveness of the fence of the present invention will be explained. Wind tunnel experiments were conducted using an Effel-type blowout boundary layer wind tunnel and the following three NetFence models. <Fence model>

[Table] No. 3 is a double-walled net fence based on the present invention, in which the distance L between the nets is 2 mm, and the filling rate of the net alone is 36%. The experiment was conducted as follows. A model fence is installed in the wind tunnel perpendicular to the main wind direction in the wind tunnel, and air is blown. The airflow in the wind tunnel is a uniform turbulent flow with a turbulence component given by a turbulence grid, and the wind speed is measured at a position at a height of 500 mm (boundary layer height) from the wind tunnel floor (fence installation floor). It is 10m/sec. While the air is being blown, the wind speed is measured using a constant temperature hot wire anemometer at each of a number of measurement points set on a vertical plane passing through the wind tunnel center line (Fuens center line) and parallel to the main wind direction. For each measurement point, the output of the constant temperature hot wire anemometer is linearized using a linearizer, and then converted to a digital quantity with a sampling interval of 0.01 seconds and a duration of 10 seconds, and its average value (average wind speed) and standard deviation are calculated. (Standard deviation of wind speed fluctuation √ ² ) is determined, and the average wind speed is converted into a complete element by the average wind speed r of the approaching flow at the same height as the measurement point, and is expressed in the form of wind speed ratio U/r, and the standard deviation of wind speed fluctuation is √
² is made dimensionless by the average wind speed of the approaching flow r ₅₀₀ at a height of 500 mm (height of the boundary layer) and becomes √
Each is expressed in the form of the so-called turbulence intensity of U ² /r ₅₀₀ . The results of the experiment are shown in FIGS. 6 and 7. 6th
The figure shows the vertical distribution of the wind speed ratio/r, and Figure 7 shows the vertical distribution of the turbulence strength. In both figures, I to C indicate that the Fuens model used is I...No.
1. B... No. 2, C... No. 3. In both figures, the vertical axis shows the height position, the horizontal axis shows the position in the main wind direction, and the vertical axis shows the height Z from the wind tunnel floor surface Z/ N, and the horizontal axis is X/H, which is the distance X taken from the fence position as a reference (the main wind direction is positive and the opposite direction is negative), which is also made dimensionless by the height H of the fence.
, respectively. The wind speed ratio distribution in Figure 6 shows how many times the wind speed at a certain height is compared to the wind speed of the approaching flow, and the turbulence strength distribution in Figure 7 shows the strength of flow separation from the top of the fence. It is something that can be done. In addition, for ease of understanding, the sixth
In the figure, the area where the wind speed ratio is 0.6 or less is shown as a sufficient wind speed reduction area, and in Figure 7, the area where the turbulence strength is 0.1 or more is hatched as an indicator of the strength of separation. From the results in both figures, the following can be said. First, with regard to single-layered fences, in the case of fence model No. 1 with a small filling ratio, the separation of the flow from the upper end of the fence becomes weak, and the wind speed on the leeward side of the fence cannot be sufficiently reduced. Similarly, when the enrichment ratio is set high as in No. 2, the wind speed reduction ratio on the leeward side of the fence increases overall, but the turbulence strength immediately on the leeward side of the fence also increases, and sufficient wind speed reduction is not achieved in this area. I can't hope. It goes without saying that the large turbulence strength means that the wind speed fluctuations are large, which means that the maximum instantaneous wind speed may become large. On the other hand, with a double-walled fence based on the present invention like No. 3, the turbulence immediately on the leeward side of the fence can be effectively eliminated, and the wind speed on the leeward side of the fence can be sufficiently reduced. Incidentally, in the experiment, the airflow in the wind tunnel was a uniform turbulent flow with a turbulence component given by the turbulence grid as described above, but in reality, a slight boundary layer was observed to form in the vertical wind speed distribution. , its power index was α≒1/10.3. According to many actual measurement results,
The atmospheric boundary layer on the coast and other open areas is
The power index has a value of approximately 1/10≦α≦1/7, and therefore the wind tunnel airflow used in the experiment can be considered to roughly reproduce the actual atmospheric boundary layer in an open area. The above experimental results can be recognized as being in accordance with the actual situation. As is clear from the above description, the windbreak fence of the present invention can secure a wide wind speed reduction area with a sufficient wind speed reduction ratio on the leeward side of the fence, and is therefore particularly useful in outdoor coal storage fields. It can exhibit excellent effects in preventing stored coal from scattering and also in protecting agricultural crops.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of the use of a fence in an outdoor coal storage yard, Fig. 2 is a diagram illustrating the wind-shielding effect of the fence, and Fig. 3 is an example of a double-lined net of the fence of the present invention. A front view, and (b) a vertical side view. FIG. 4 shows a specific example of the overall structure of the fence of the present invention, in which A is a front view and B is a longitudinal side view. FIG. 5 shows a panel structure used in the fence according to the present invention, in which A is a front view and B is a side view. Figures 6 and 7 show the results of wind tunnel experiments regarding various types of fences, with Figure 6 being a vertical distribution diagram of wind speed ratio, and Figure 7 being a vertical distribution diagram of turbulence strength. In the figure, 1: Coal storage, 2, 2': Net, 3: Panel structure, 4: Strut, 5: Spacing material, 6,
7: Pressing member.

Claims (1)

[Claims] 1. Two screen nets 2, 2' having the same mesh shape and arranged in parallel to each other are provided, and the two nets are positioned so that each other's meshes are staggered in both the vertical and horizontal directions. The apparent fullness rate on the wind-shielding side of the fence body is 50 to 80%, and the spacing L between both nets is 2 mm or more and is within 5 times the lateral length l of the mesh opening. Windproof fence.