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Wind tunnel tests of wind pressure on regularly aligned buildings
Journal of Wind Engineering and Industrial Aerodynamics, 41-44 (1992) 1799-1810
1799
Elsevier
Wind tunnel tests of wind pressure on regularly aligned buildings J. Tsutsumi', T. Katayamab and M. Nishida~ ' Tohwa Institute for Science, Tohwa University, 1-1-1 Chikushi-gaoka, Minami-ku, Fukuoka 815, Japan bDivision of Thermal Energy System, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816, Japan Department of Architecture, Kyushu Sangyo University, 2-327 Matsugadai, Higashi-ku, Fukuoka 813, Japan •
l,'
Abstract Model experiments are carried out in order to make the./charateristies of wind pressure on groups of buildings clear. The wind pressure is thougiit tO be a natural ventilation force and the model buildings are assumed to be apartment buildings. The approaching flow of the wind tunnel tests simulates the wind over a built-up ~rea. The main parameter of the layout of buildings is the building ',olume ratio. A stagger6d grid layout is compared with a normal grid layout. The effect of the wind direction is also examined. The results of the experiments are presented as the wind pressure coefficient difference between windward and leeward. The relations between the average wind pressure coefficient in a model and various layouts of buildings are mainly discussed. The distributions of the wind pressure coefficient in model buildings are also presented in this paper. 1. I N T R O D U C T I O N The layout of apartment buildings in a housing estate greatly influences the wind pressure on the wall surfaces of each building. The wind pressure is an essential source of power for natural ventilation. It is, therefore, necessary to investigate the wind pre~;sure for better planning of apartment buildings from the viewpoint of natural ventilation. If a building stands separately or is much taller than the surrounding ones, a lot is known about the behavior of the wind pressure on the building. However, there are only a few studies of wind pressure on groups of buildings which are of similar size[ 1, 2, 31. These are model experiments in wind tunnels, which provide a reasonable method to study the wind pressure for various layouts of buildings. However, several problems are still left unansweredly these studies, in which the buildings are of the same size and aligned regularly. The parameters of this layout of model buildings is not very practical for the actual planning of a housing estate, and the approaching winds of these st.udies do not correspond to the natural wind over a buR-up area where the apartment buildings are planned practically. The results of wind tunnel tests are expressed as the wind pressure coefficients. The representative wind speed for the representative wind pressure is not always adequate 0167-6105/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
1800 for the various layouts of buildings in these studies. Here we report the results of wind tunnel tests of the wind pressure on various layouts of buildings, considering several of the problems concerning the practical planning of apartment houses, mentioned above. The distributions of the wind pressure coefficients on model buildings are also discussed, as well as the relations between the layouts of buildings and the average wind pressure coefficient on a whole building. 2. E X P E R I M E N T A L
ARRANGEMENT
The model buildings and their layout in the wind tunnel are main factors of the wind tunnel tests in this paper. The wind tunnel tests need a large number of models to form long lines of models in the streamwise direction, because a model influences the wind pressure on the leeward model, and this influence changes along the line. The basic features of the models and their layout are discussed below. 2.1. M o d e l b u i l d i n g s Three types of model buildings were used in this study. They differ in height, which means that the models are regarded as buildings of different stories. The models are called Model A, Model B and Model C, which represent a 5-storied, a 10-storied and a 15-storied building, respectively. These models are simple rectangular blocks with smooth sides. The full-scale sizes of the models and their layout are shown in Table 1. The scale of the models is 1/400. The space between two models in the widthwise direction is taken to be proportional to the
Table 1 Geometry of apartment building~ Model A Stories, it 5 Height, h 15.0 Width, w 60.0 Depth, d 10,0 Space, b 10.0 n : Number of stories
ModelB
Model C
10 30.0 60.0 10.0 20.0 "
15 45.0 60.0 I0.0 30.0
Unit: m (Full seal )
Table 2 Intervals between buildings Building volume ratio, 4) (%)
Interval, a Model A
50 75 100 125 150
76.5 47.2 32.8 24.4 18.4
Model B ---89.2 65.2 50.0 40.0
~ffi. Model C 123.2 90.0 70.0 56.8
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1801
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Figure 1. Model buildings with measurement points. heights of the models. There are two kinds of models for each type of models. One is the sensor model for the measurement of wind pressure, and the other is the dummy model to make the alignments of the models. The former is made of acrylic plastic, and the latter is wooden model. Only one model of the former is used in each layout. The sensor models are shown in Figure I. Model A, Model B and Model C have 12, 16 and 20 measurement points on one half of both of their side surfaces, respectively. The positions of these measurement points are fixed in consideration of the average and the distribution of wind pressure. The maesurement points are 0.5mm diameter holes, which are connected with the measurement instruments through plastic tubes.
2.2. Layout of buildings A layout of model buildings consists of models of a single type. The models are aligned regularly with constant intervals in both the widthwise and the depthwise directions. The models are fixed directly to the floor of a wind tunnel test section. The widthwise direction of the models is usually perpendiculer to the wind direction, except when the effects of the wind direction are examined. A group of models aligned in the depthwise direction is called a "Row", and in the widthwise direction a "Line". Model A, Model B and Model C are aligned in 7, 6 and 5 rows, respectively. The sensor model is placed in the central row. Sample layout of Model A is shown in Figure 2. The lines are numbered from the windward side as shown in Figure 2. The main parameter of the layout is the building volume ratio, 4~, defined in Table 2. The building volume ratio means the ratio of the total floor area of a building to the lot area.
1802 4.3m
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Figure 2. Sample layout of models in the test section. It is controled by the intervals between models in the depthwise direction. Measurements are performed with 5 different values of ~ for Model A, and with 4 different values for Model B and Model C. The intervals between the buildings for these building volume ratios are shown in Table 2. The bulding volume ratio was ch~ged from 50% to 150% in steps of 25%. A single unit of each type of model, i.e. 4~-0%, was also tested. The maximum value of the building volume ratio is decided from the duration of sunshine. The building volume ratio indicates the total floor area of the apartment buildings in a certain lot. When a housing estate is planned, the total floor area is one of the most important factors. Therefore, the building volume ratio is thought to be the reasonable parameter for the layout of the model buildings. The model buildings were fixed to form normal grid patterns, however, some measurements were made with staggered grid layouts, as shown in Figure 2, and different wind directions. Staggered grid layouts of the three types of models were tested with ~100%. Two different wind directions were tested with Model A at4~100%. These wind directions were ~/6 and 7r/3 from the building surface.
3. WIND TUNNEL TEST Wind tunnel tests have to simulate the actual conditions. This mainly depends on the condition of the approaching wind. If an adequate turbulent shear flow is supplied, the eddy viscosity may be assumed to be proportional to the representative length, which means that the turbulence Reynolds number of the model automatically corresponds to that of the full-scale system.
3.1. Wind tunnel The wind tunnel in which the model tests were carried out is an open-jet type. Its total length is 25m and its test section is 4.3m in length, 1.5m in width and l.Sm in height. The test section is relatively short in comparison with the height of the test section. It is difficult to form the thick boundary layer by roughness elements. Therefore, the approaching wind is formed by a screen which is made of horizontal bars with variable spacing[4l, fixed at
1803
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0 0.1 0.2 0.3 Turbulence intensity,'~/U Figure 3. Profiles of mean wind speed and turbulence intensity of approaching wind. the inlet of the test section. The approaching wind is a turbulent shear flow, simulating the natural wind over a built-up area. The vertical distribution of the mean wind speed should be the power law profile with the exponent of 1/4. The actual speed profile is shown in Figure 3. The reference wind speed, Ur, is approximately 8m/s, measured 1.5m downstream from the inlet of the test section without the models. The m aa wind speed profile fits the expected profile reasonably well for Z/Zr>0.1. The turbulen~;e intensity is, however, about 25% near tunnel floor, which is slightly smaller than that of the natural wind over ,, :~uilt-up area.
3.2. Measurement system The main quantity measured in the wind tunnel tests is the wind pressure on the model surfaces. The representative wind speed for the representative wind pressure difference is also measured to find the wind pressure coefficient. It is the point to fix the measurement position of the representative wind speed for all the layouts of buildings, because the models influence the wind speed distribution above them. The wind speed profiles above the models were measured by a hot wire anemometer. The measurement heights are shown in the results, Figure 4. The measurements were recorded as analogue data. The data corresponding to 5 seconds at each height were converted into degital data at intervals of 2ms to calculate the mean wind speed aad turbulence intensity. All the wind tunnel tests were carried out with a wind speed at the height of 750ram above the floor of approximately 8m/s. This is somewhat larger than expected wind speed Co,"natural ventilation. However, the greater wind speed makes the wind pressure difference clearer, and the similarity of various wind speeds have been verified by pre-tests. At first, the sensor model was set on Line 1, and subsequently moved to leeward.
1804 Three measurements of wind pressure were measured simultaneously by three displacement micro manometers. The measurement point on the windward surface was connected to the high pressure side of the manometer, and the measurement point on the leeward surface just opposite to the windward point was connected to the low pressure side of the same manometer. Therefore, the measured wind pressure is the wind pressure difference between the windward and the leeward surfaces. The output data were directly recorded on a penrecorder to read the mean wind pressure. 4. R E S U L T S AND D I S C U S S I O N The wind pressure difference between the windward and the leeward surfaces is divided by the representative wind pressure difference to find the wind pressure coefficient. It is, in fact, the wind pressure difference coefficient. However, it is simply called the wind pressure coefficient in this study. It is a reasonable variable for the natural ventilation through a dwelling caused by the wind. The relations between the wind pressure coefficient and the layouts of buildings are discussed here. 4.1. R e p r e s e n t a t i v e w i n d p r e s s u r e d i f f e r e n c e The wind speed profiles which are measured above the roof of the models are shown in Figure 4. The upper figures, (a)-(c), show the mean wind speed profiles. The lower figures, (d)-(f), show the turbulence intensity profiles. The representative wind speed, Ur, is measured at the representative height, Zr=750mm. Panels (a) and (d) indicate dependence of the profiles on the position of the models in the streamwise direction. They are measured with a layout which consists of Model A with a building volume ratio is 100%. The results presented here are the profiles above the models of Line 1 and Line 5. The profiles above other lines are also measured. They are almost identical to those above Line 5. Thus, the profiles above Line 5 are thought to be representative of all lines except Line 1. Panels (b) and (e) indicate the dependence of the profiles on the building volume ratio. They are measured above the models of Line 5 in layouts of Model A with three different values of the building volume ratio, The model position, Line 5, was decided from the results shown in panels (a) and (d). Panels (c) and (f) indicate the dependence of the profiles on the model type for a building volume ratio of 100%. These are also measured above the models of Line 5. Neither the mean wind speed nor the turbulence intensity at the representative height seems to be influenced by the layout of the models, Therefore, the dynamic pressure, at the representative wind speed is used as the representative pressure difference in this study. 4,2. W i n d p r e s s u r e coefficient in n o r m a l g r i d l a y o u t s The changes of the wind pressure coefficients along the rows of the models in the streamwise direction are shown in Figure 5. The wind pressure coefficients presented in Figure 5 are the averages of all the measurement points for one model. The wind pressure coefficients for Line I are much larger than for the other lines, whereas they show a minimum for Line 2, except for layouts of Model C. Occasionally, the wind pressure coefficient for Line 2 even becomes negative. The wind pressure coefficients for layouts of Model A and Model B on the leeward side of Line 3 do not change greatly, while these for layouts of Model C on the leeward of Line 2 become roughly equal. The wind pressure coefficients become somewhat irregular to leeward. This is an effect of the short test section of the wind tunnel. When the building volume ratio is higher, the wind
1805
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Figure 7. Distributions of thewind pressure coefficient over the model surfavce in normal gnd layouts. pressure coefficient becomes s~aller in most sections of all the layouts. The wind pressure coefficient on Line 5 is thought to be the stable value in the leeward part. The relations between the stable wind pressure coefficients and the building volume ratio and the model type are shown in Figure 6. It also shows results for a single model. It is clearly seen that the wind pressure coefficient becomes greater when the building volume ratio is smaller and the models are taller. These tendencies persist in layouts of other model types or other building volume ratios. The wind pressure coefficient for a single model is similar to that of models in Line l, the most windward line. The distributions of the wind pressure coefficients in the models are sl~,)wn in Figure 7. Except for the single model, these data are all for models in Line 5. When the building volume ratio is 0%, the wind pressure coefficients in the central parts of all the models are larger than near the perimeter. However, this tendency is reversed, when the building volume ratio is 100% or 150%. The wind pressure coefficients for a building volume ratio of 100% are almost uniform in the models. The difference between the wind pressure coefficient in the central part and that near the perimeter for a building volume ratio of 150% is larger than that of 100%. These tendencies are common to all three types of models.
1808
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Figure 9. Distributions of wind pressure coefficient in the models of staggered grid layouts.
4.3. Wind pressure coefficient in staggered grid layouts Though there are many variations of the layout of buildings, the staggered grid layout is one of the most common pattern. Staggered grid layouts sometimes give variety on the plan of a housing estate. However, the difference of the wind pressure in staggered grid layouts from that in normal grid layouts is not well known. Therefore, we tested the wind pressure coefficients on the model buildings of staggered grid layouts, and compared the results with those of normal grid layouts. Three types of staggered grid layouts were tested. Each of
1899 ,., 0.4 Model A
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them consists of just one type of model with a building volume ratio of 100%. The average wi.ad pressure coefficients on the models of the staggered grid layouts are compared with those of the normal grid layouts in Figure 8. In the case of Model A, the wind pressure coefficients on the leeward of Line 3 in the staggered grid layout are clearly smaller than those in the normal grid layout. However, the differences are very small in the cases of Model B and Model C. The wind pressure coefficients at Line 2 and Line 3 change remarkably from those of the normal grid layouts. The wind pressure coefficient at Line 3 in the staggered grid layouts are smallest in the alignments of the models, whereas those at Line 2 are smallest in the normal grid layouts. When the models are set in the staggered grid pattern, the models of Line 2 are exposed to the direct wind through the space between the models of Line 1. When the model is taller, the space is wider as shown in Table 1, and the wind pressure coefficient at Line 2 is larger. The intervals between the models in the streamwise direction is smaller, if the height of the model is shorter at the same building volume ratio. And the space is not straight in the staggered grid layouts. These are the reasons why the wind pressure coefficient for the staggered grid layout of Model A is remarkably small. Therefore, the effects of the wind blowing through the space between buildings on the wind pressure are thought to be great, when the intervals between buildings in the streamwise direction is small.
1810
The distributions of the wind pressure coefficients for the staggere~i grid layouts are shown in Figure 9. They were measured at Line 7, because Line 7 is regarded as the stable line for the staggered grid layouts from Figure 8, while Line 5 is thought to be the stable line for the normal grid layouts. The distributions of the staggered grid layouts are more complicated than those of "~e normal grid layouts with the same building volume ratio, 100%, which are shown in Figure 7. Although the vertical distributions of the wind pressure coefficients resemble those of the normal grid layouts, the horizontal distributions show a different tendency. The wind pressure coefficients in the central parts of the models are close to those in the perimeter parts, and th.: wind pressure coefficients between them are larger than those of the central and the perimeter parts. However, tire ravges of the wind pressure coefficient values in the staggered grid layouts are similar to those .r, :'e normal grid layouts.
4.4. Effects of wind direction on wind pressure coefficient The direction of the natural wind is always changing, and the effects of the wind direction on wind pressure is not simple. Two different wind directions, shown in Figure 10, were used for the layout of Model A with a building volume ratio of 100% to examine the effects of wind direction on the wind pressure coefficient. The average wind pressure coefficients along a row of models in the streamwise direction are shown in Figure 10. The wind pressure at Line 1 with a wind direction of x/3 becomes small. The wind pressure coefficients at Line 2 and Line 3 with the wind direction of 7r/6 are larger than those with normaly incident wind. The wind pressure coefficients on the leeward of Line 6 become almost stable. The relations between the wind direction and the wind pressure coefficients are shown in Figure 11, which refers to Line 7. When the wind direction shifts further from the normal, the wind pressure coefficient becomes smaller. The distributions of the wind pressure coefficients for wind directions x/6 and ff13 are shown in Figure 12. The wind pressure coefficient on the windward side is evidently larger than that on the leeward side.
5. CONCLUSIONS This paper gives relations between the wind pressure coefficient and the layout of buildings which are assumed to be located systematically in a built-up area. The wind pressure coefficient changes greatly in the streamwise direction up to the third building to windward, and also depends on the grid pattern of the layout. The interval between buildings in the streamwise direction greatly influences the wind pressure coefficient, If the building volume ratio is constant, the intervals between taller buildings become larger, and the wind pressure coefficient increases. When the wind direction shifts from being normal to the buildings, the wind pressw:~ coefficient becomes smaller, and that on the windward side is clearly larger than that on the leeward side.
6. REFERENCES I :2 3 4
B. E. Lee, et al., ASHRAE Journal, (Feb. 1980) 35. B.G. Wiren, J. of Wind Engineering and Industrial Aerodynamics, 15 (1983). T. Shoda and S. Gore, Trans. of A.LJ, 53 (1956) 80 (Japanese). M. Nishida, et al., J. of Wind Engineering, 19 (1984) 53-62 (Japanese).
1799
Elsevier
Wind tunnel tests of wind pressure on regularly aligned buildings J. Tsutsumi', T. Katayamab and M. Nishida~ ' Tohwa Institute for Science, Tohwa University, 1-1-1 Chikushi-gaoka, Minami-ku, Fukuoka 815, Japan bDivision of Thermal Energy System, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816, Japan Department of Architecture, Kyushu Sangyo University, 2-327 Matsugadai, Higashi-ku, Fukuoka 813, Japan •
l,'
Abstract Model experiments are carried out in order to make the./charateristies of wind pressure on groups of buildings clear. The wind pressure is thougiit tO be a natural ventilation force and the model buildings are assumed to be apartment buildings. The approaching flow of the wind tunnel tests simulates the wind over a built-up ~rea. The main parameter of the layout of buildings is the building ',olume ratio. A stagger6d grid layout is compared with a normal grid layout. The effect of the wind direction is also examined. The results of the experiments are presented as the wind pressure coefficient difference between windward and leeward. The relations between the average wind pressure coefficient in a model and various layouts of buildings are mainly discussed. The distributions of the wind pressure coefficient in model buildings are also presented in this paper. 1. I N T R O D U C T I O N The layout of apartment buildings in a housing estate greatly influences the wind pressure on the wall surfaces of each building. The wind pressure is an essential source of power for natural ventilation. It is, therefore, necessary to investigate the wind pre~;sure for better planning of apartment buildings from the viewpoint of natural ventilation. If a building stands separately or is much taller than the surrounding ones, a lot is known about the behavior of the wind pressure on the building. However, there are only a few studies of wind pressure on groups of buildings which are of similar size[ 1, 2, 31. These are model experiments in wind tunnels, which provide a reasonable method to study the wind pressure for various layouts of buildings. However, several problems are still left unansweredly these studies, in which the buildings are of the same size and aligned regularly. The parameters of this layout of model buildings is not very practical for the actual planning of a housing estate, and the approaching winds of these st.udies do not correspond to the natural wind over a buR-up area where the apartment buildings are planned practically. The results of wind tunnel tests are expressed as the wind pressure coefficients. The representative wind speed for the representative wind pressure is not always adequate 0167-6105/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
1800 for the various layouts of buildings in these studies. Here we report the results of wind tunnel tests of the wind pressure on various layouts of buildings, considering several of the problems concerning the practical planning of apartment houses, mentioned above. The distributions of the wind pressure coefficients on model buildings are also discussed, as well as the relations between the layouts of buildings and the average wind pressure coefficient on a whole building. 2. E X P E R I M E N T A L
ARRANGEMENT
The model buildings and their layout in the wind tunnel are main factors of the wind tunnel tests in this paper. The wind tunnel tests need a large number of models to form long lines of models in the streamwise direction, because a model influences the wind pressure on the leeward model, and this influence changes along the line. The basic features of the models and their layout are discussed below. 2.1. M o d e l b u i l d i n g s Three types of model buildings were used in this study. They differ in height, which means that the models are regarded as buildings of different stories. The models are called Model A, Model B and Model C, which represent a 5-storied, a 10-storied and a 15-storied building, respectively. These models are simple rectangular blocks with smooth sides. The full-scale sizes of the models and their layout are shown in Table 1. The scale of the models is 1/400. The space between two models in the widthwise direction is taken to be proportional to the
Table 1 Geometry of apartment building~ Model A Stories, it 5 Height, h 15.0 Width, w 60.0 Depth, d 10,0 Space, b 10.0 n : Number of stories
ModelB
Model C
10 30.0 60.0 10.0 20.0 "
15 45.0 60.0 I0.0 30.0
Unit: m (Full seal )
Table 2 Intervals between buildings Building volume ratio, 4) (%)
Interval, a Model A
50 75 100 125 150
76.5 47.2 32.8 24.4 18.4
Model B ---89.2 65.2 50.0 40.0
~ffi. Model C 123.2 90.0 70.0 56.8
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Figure 1. Model buildings with measurement points. heights of the models. There are two kinds of models for each type of models. One is the sensor model for the measurement of wind pressure, and the other is the dummy model to make the alignments of the models. The former is made of acrylic plastic, and the latter is wooden model. Only one model of the former is used in each layout. The sensor models are shown in Figure I. Model A, Model B and Model C have 12, 16 and 20 measurement points on one half of both of their side surfaces, respectively. The positions of these measurement points are fixed in consideration of the average and the distribution of wind pressure. The maesurement points are 0.5mm diameter holes, which are connected with the measurement instruments through plastic tubes.
2.2. Layout of buildings A layout of model buildings consists of models of a single type. The models are aligned regularly with constant intervals in both the widthwise and the depthwise directions. The models are fixed directly to the floor of a wind tunnel test section. The widthwise direction of the models is usually perpendiculer to the wind direction, except when the effects of the wind direction are examined. A group of models aligned in the depthwise direction is called a "Row", and in the widthwise direction a "Line". Model A, Model B and Model C are aligned in 7, 6 and 5 rows, respectively. The sensor model is placed in the central row. Sample layout of Model A is shown in Figure 2. The lines are numbered from the windward side as shown in Figure 2. The main parameter of the layout is the building volume ratio, 4~, defined in Table 2. The building volume ratio means the ratio of the total floor area of a building to the lot area.
1802 4.3m
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Figure 2. Sample layout of models in the test section. It is controled by the intervals between models in the depthwise direction. Measurements are performed with 5 different values of ~ for Model A, and with 4 different values for Model B and Model C. The intervals between the buildings for these building volume ratios are shown in Table 2. The bulding volume ratio was ch~ged from 50% to 150% in steps of 25%. A single unit of each type of model, i.e. 4~-0%, was also tested. The maximum value of the building volume ratio is decided from the duration of sunshine. The building volume ratio indicates the total floor area of the apartment buildings in a certain lot. When a housing estate is planned, the total floor area is one of the most important factors. Therefore, the building volume ratio is thought to be the reasonable parameter for the layout of the model buildings. The model buildings were fixed to form normal grid patterns, however, some measurements were made with staggered grid layouts, as shown in Figure 2, and different wind directions. Staggered grid layouts of the three types of models were tested with ~100%. Two different wind directions were tested with Model A at4~100%. These wind directions were ~/6 and 7r/3 from the building surface.
3. WIND TUNNEL TEST Wind tunnel tests have to simulate the actual conditions. This mainly depends on the condition of the approaching wind. If an adequate turbulent shear flow is supplied, the eddy viscosity may be assumed to be proportional to the representative length, which means that the turbulence Reynolds number of the model automatically corresponds to that of the full-scale system.
3.1. Wind tunnel The wind tunnel in which the model tests were carried out is an open-jet type. Its total length is 25m and its test section is 4.3m in length, 1.5m in width and l.Sm in height. The test section is relatively short in comparison with the height of the test section. It is difficult to form the thick boundary layer by roughness elements. Therefore, the approaching wind is formed by a screen which is made of horizontal bars with variable spacing[4l, fixed at
1803
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0 0.1 0.2 0.3 Turbulence intensity,'~/U Figure 3. Profiles of mean wind speed and turbulence intensity of approaching wind. the inlet of the test section. The approaching wind is a turbulent shear flow, simulating the natural wind over a built-up area. The vertical distribution of the mean wind speed should be the power law profile with the exponent of 1/4. The actual speed profile is shown in Figure 3. The reference wind speed, Ur, is approximately 8m/s, measured 1.5m downstream from the inlet of the test section without the models. The m aa wind speed profile fits the expected profile reasonably well for Z/Zr>0.1. The turbulen~;e intensity is, however, about 25% near tunnel floor, which is slightly smaller than that of the natural wind over ,, :~uilt-up area.
3.2. Measurement system The main quantity measured in the wind tunnel tests is the wind pressure on the model surfaces. The representative wind speed for the representative wind pressure difference is also measured to find the wind pressure coefficient. It is the point to fix the measurement position of the representative wind speed for all the layouts of buildings, because the models influence the wind speed distribution above them. The wind speed profiles above the models were measured by a hot wire anemometer. The measurement heights are shown in the results, Figure 4. The measurements were recorded as analogue data. The data corresponding to 5 seconds at each height were converted into degital data at intervals of 2ms to calculate the mean wind speed aad turbulence intensity. All the wind tunnel tests were carried out with a wind speed at the height of 750ram above the floor of approximately 8m/s. This is somewhat larger than expected wind speed Co,"natural ventilation. However, the greater wind speed makes the wind pressure difference clearer, and the similarity of various wind speeds have been verified by pre-tests. At first, the sensor model was set on Line 1, and subsequently moved to leeward.
1804 Three measurements of wind pressure were measured simultaneously by three displacement micro manometers. The measurement point on the windward surface was connected to the high pressure side of the manometer, and the measurement point on the leeward surface just opposite to the windward point was connected to the low pressure side of the same manometer. Therefore, the measured wind pressure is the wind pressure difference between the windward and the leeward surfaces. The output data were directly recorded on a penrecorder to read the mean wind pressure. 4. R E S U L T S AND D I S C U S S I O N The wind pressure difference between the windward and the leeward surfaces is divided by the representative wind pressure difference to find the wind pressure coefficient. It is, in fact, the wind pressure difference coefficient. However, it is simply called the wind pressure coefficient in this study. It is a reasonable variable for the natural ventilation through a dwelling caused by the wind. The relations between the wind pressure coefficient and the layouts of buildings are discussed here. 4.1. R e p r e s e n t a t i v e w i n d p r e s s u r e d i f f e r e n c e The wind speed profiles which are measured above the roof of the models are shown in Figure 4. The upper figures, (a)-(c), show the mean wind speed profiles. The lower figures, (d)-(f), show the turbulence intensity profiles. The representative wind speed, Ur, is measured at the representative height, Zr=750mm. Panels (a) and (d) indicate dependence of the profiles on the position of the models in the streamwise direction. They are measured with a layout which consists of Model A with a building volume ratio is 100%. The results presented here are the profiles above the models of Line 1 and Line 5. The profiles above other lines are also measured. They are almost identical to those above Line 5. Thus, the profiles above Line 5 are thought to be representative of all lines except Line 1. Panels (b) and (e) indicate the dependence of the profiles on the building volume ratio. They are measured above the models of Line 5 in layouts of Model A with three different values of the building volume ratio, The model position, Line 5, was decided from the results shown in panels (a) and (d). Panels (c) and (f) indicate the dependence of the profiles on the model type for a building volume ratio of 100%. These are also measured above the models of Line 5. Neither the mean wind speed nor the turbulence intensity at the representative height seems to be influenced by the layout of the models, Therefore, the dynamic pressure, at the representative wind speed is used as the representative pressure difference in this study. 4,2. W i n d p r e s s u r e coefficient in n o r m a l g r i d l a y o u t s The changes of the wind pressure coefficients along the rows of the models in the streamwise direction are shown in Figure 5. The wind pressure coefficients presented in Figure 5 are the averages of all the measurement points for one model. The wind pressure coefficients for Line I are much larger than for the other lines, whereas they show a minimum for Line 2, except for layouts of Model C. Occasionally, the wind pressure coefficient for Line 2 even becomes negative. The wind pressure coefficients for layouts of Model A and Model B on the leeward side of Line 3 do not change greatly, while these for layouts of Model C on the leeward of Line 2 become roughly equal. The wind pressure coefficients become somewhat irregular to leeward. This is an effect of the short test section of the wind tunnel. When the building volume ratio is higher, the wind
1805
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1808
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4.3. Wind pressure coefficient in staggered grid layouts Though there are many variations of the layout of buildings, the staggered grid layout is one of the most common pattern. Staggered grid layouts sometimes give variety on the plan of a housing estate. However, the difference of the wind pressure in staggered grid layouts from that in normal grid layouts is not well known. Therefore, we tested the wind pressure coefficients on the model buildings of staggered grid layouts, and compared the results with those of normal grid layouts. Three types of staggered grid layouts were tested. Each of
1899 ,., 0.4 Model A
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them consists of just one type of model with a building volume ratio of 100%. The average wi.ad pressure coefficients on the models of the staggered grid layouts are compared with those of the normal grid layouts in Figure 8. In the case of Model A, the wind pressure coefficients on the leeward of Line 3 in the staggered grid layout are clearly smaller than those in the normal grid layout. However, the differences are very small in the cases of Model B and Model C. The wind pressure coefficients at Line 2 and Line 3 change remarkably from those of the normal grid layouts. The wind pressure coefficient at Line 3 in the staggered grid layouts are smallest in the alignments of the models, whereas those at Line 2 are smallest in the normal grid layouts. When the models are set in the staggered grid pattern, the models of Line 2 are exposed to the direct wind through the space between the models of Line 1. When the model is taller, the space is wider as shown in Table 1, and the wind pressure coefficient at Line 2 is larger. The intervals between the models in the streamwise direction is smaller, if the height of the model is shorter at the same building volume ratio. And the space is not straight in the staggered grid layouts. These are the reasons why the wind pressure coefficient for the staggered grid layout of Model A is remarkably small. Therefore, the effects of the wind blowing through the space between buildings on the wind pressure are thought to be great, when the intervals between buildings in the streamwise direction is small.
1810
The distributions of the wind pressure coefficients for the staggere~i grid layouts are shown in Figure 9. They were measured at Line 7, because Line 7 is regarded as the stable line for the staggered grid layouts from Figure 8, while Line 5 is thought to be the stable line for the normal grid layouts. The distributions of the staggered grid layouts are more complicated than those of "~e normal grid layouts with the same building volume ratio, 100%, which are shown in Figure 7. Although the vertical distributions of the wind pressure coefficients resemble those of the normal grid layouts, the horizontal distributions show a different tendency. The wind pressure coefficients in the central parts of the models are close to those in the perimeter parts, and th.: wind pressure coefficients between them are larger than those of the central and the perimeter parts. However, tire ravges of the wind pressure coefficient values in the staggered grid layouts are similar to those .r, :'e normal grid layouts.
4.4. Effects of wind direction on wind pressure coefficient The direction of the natural wind is always changing, and the effects of the wind direction on wind pressure is not simple. Two different wind directions, shown in Figure 10, were used for the layout of Model A with a building volume ratio of 100% to examine the effects of wind direction on the wind pressure coefficient. The average wind pressure coefficients along a row of models in the streamwise direction are shown in Figure 10. The wind pressure at Line 1 with a wind direction of x/3 becomes small. The wind pressure coefficients at Line 2 and Line 3 with the wind direction of 7r/6 are larger than those with normaly incident wind. The wind pressure coefficients on the leeward of Line 6 become almost stable. The relations between the wind direction and the wind pressure coefficients are shown in Figure 11, which refers to Line 7. When the wind direction shifts further from the normal, the wind pressure coefficient becomes smaller. The distributions of the wind pressure coefficients for wind directions x/6 and ff13 are shown in Figure 12. The wind pressure coefficient on the windward side is evidently larger than that on the leeward side.
5. CONCLUSIONS This paper gives relations between the wind pressure coefficient and the layout of buildings which are assumed to be located systematically in a built-up area. The wind pressure coefficient changes greatly in the streamwise direction up to the third building to windward, and also depends on the grid pattern of the layout. The interval between buildings in the streamwise direction greatly influences the wind pressure coefficient, If the building volume ratio is constant, the intervals between taller buildings become larger, and the wind pressure coefficient increases. When the wind direction shifts from being normal to the buildings, the wind pressw:~ coefficient becomes smaller, and that on the windward side is clearly larger than that on the leeward side.
6. REFERENCES I :2 3 4
B. E. Lee, et al., ASHRAE Journal, (Feb. 1980) 35. B.G. Wiren, J. of Wind Engineering and Industrial Aerodynamics, 15 (1983). T. Shoda and S. Gore, Trans. of A.LJ, 53 (1956) 80 (Japanese). M. Nishida, et al., J. of Wind Engineering, 19 (1984) 53-62 (Japanese).