Civil Engineering and Architecture 3(6): 172-188, 2015 DOI: 10.13189/cea.2015.030602 http://www.hrpub.org A raphic Method to Etimate the Wind Speed under Urban Canopy Layer Manoureh Tahba School of Architecture and Urban Planning, Shahid Behehti Univerity (SBU), Iran Reearch Centre of Landcape and ernacular Deign, SBU, Iran Copyright 2015 by author, all right reerved. Author agree that thi article remain permanently open acce under the term of the Creative Common Attribution Licene 4.0 International Licene Abtract Thi article i baed on a graphic method introduced by the author to determine the wind peed around the building for the level le than 10 meter. By the help of the graph produced in thi reearch the architect i able to etimate the wind peed in every urban terrain and every height le than 10 meter above the ground - that i deferent from the height and terrain of the meteorology tation - without being involved with calculation procedure. According to the importance of the turbulent wind in urban pace, thi article produced a table by uing equivalent teady wind peed ( ) upporting the graphic method to determine the acceptable wind peed around the building. Thi table will be ued by the help of a CFD imulation to etimate the proportion of the equivalent teady wind peed around the building ( ) to the mean wind peed ( ) in the ame level of the urban terrain ( / ). It will help the architect to predict important threhold of the acceptable wind peed around the building in hi/her own deign to prevent unpleaant condition. Referring to the meteorology data of the place, the graph will how the duration, time and direction of the wind that may caue unpleaant condition. Therefore it will lead the deigner to correct the deign and reduce uncomfortable ituation. Keyword Mean Wind Speed, Urban Terrain, Turbulence Intenity, Equivalent Steady Wind Speed, Numeric Method, raphic Method 1. Introduction One of the climatic element that can be controlled and modified by urban deign i the urban wind. When wind flowing over an open area approache the boundarie of the built-up area, it encounter a higher roughne of the urface, created by the building. The increaed reitance reulting from the higher roughne reduce the wind flow at the level of the urban canopy. In thi way a tranitional one i created between the ground and the unditurbed wind flow above the urban air dome, which i called the urban boundary layer. The unditurbed flow i called the gradient wind and it velocity i called the gradient velocity. The wind variation with height i divided into two pecific ub-layer [1]. The obtructed ub-layer or urban canopy ub-layer which extend from the ground urface up to the building height; and the free urface layer or urban boundary layer which extend above rooftop. The flow in the obtructed or canopy ub-layer i driven by the interaction of the flow field above and i influenced by the local effect of topography, building geometry and dimenion, treet, traffic and other local feature uch a the preence of tree. In the general way, wind peed in the canopy layer i much lower when compared to the unditurbed wind peed [2]. The wind field i characteried by two parameter: the vertical profile of the mean wind peed and the turbulence pectrum. Both are affected and modified by the profile of the terrain and, in an urban etup, by the urban tructure [3]. Thi article i more concentrating on the firt parameter: the vertical profile of the mean wind peed and it i uppoed to achieve a graphic method to etimate the wind peed in a terrain according to the turbulence occur around the building by the help of CFD imulation. 2. Etimating the Wind Speed in a Study Site Many building ite are located far from the nearet long-term wind recording ite, which i uually an airport. To etimate wind condition at uch ite, the terrain urrounding both the anemometer ite and the building ite hould be checked. The anemometer in meteorology tation i ettled in the height of 10 meter above the ground level in a flat and completely open area. In lower level the wind peed will be reduced becaue of the friction of the earth urface. The amount of the wind peed reduction depend on the terrain condition. Reduction of the wind peed on the
Civil Engineering and Architecture 3(6): 172-188, 2015 173 large area of water urface i the leat and in the dene urban area with low and high rie building i the mot (Table 1). So the data of the wind peed reported by the meteorology tation i different from the wind peed in urban area. Architect and planner need to make thee data uitable for deign. To etimate the appropriate wind peed there are ome experimental and numerical method. 2.1. Numerical Method In modelling the urban effect on the wind peed, the vertical profile of the wind, from the gradient wind level down to the ground i ued. The imple formula developed by Davenport (1960) how the profile of the wind peed in different height of an area. The logarithmic model predict a ero wind velocity at the height of the roughne under any wind condition, while in reality variou wind peed, ometime very trong, can be experienced at that level. The power model of Davenport (1960) doe not have thi theoretical limitation becaue it predict a certain wind peed even very near the ground level [14, pp. 265-266]. It how that the wind peed vary with height according to the power law [4, p. 37 and 3, p. 262]: Z Z Table 1 how the typical value of (1) Z and for mean wind peed over four type of terrain. The value and terrain categorie in Table 1 are conitent with thoe adopted in other engineering application, for example ASCE Standard 7 [5]. Formula (1) will be developed to formula (2) which help to calculate wind peed in the ame terrain for every tudy height. Z 10 10 Z To etimate the wind peed in different urban area with different denity and terrain roughne, formula (3) i introduced [6]: met 10 10 met met Z Z 10 10 2.2. Reliability of the Numerical Method Equation 1, 2 & 3 give the wind peed at height Z above the plan area-weighted average height of local obtacle, uch a building and vegetation. At height at or below thi average obtacle height (e.g., at roof height in denely built-up uburb), the peed depend on the geometrical arrangement of the building, and the equation are le reliable [5]. met (2) (3) Terrain Category Table 1. Suggeted alue of Decription Z and for ariou Terrain Condition [5] Exponent Layer Thickne Z (meter) 1 Large city centre, in which at leat 50% of building are higher than 21.3 m, over a ditance of at leat 0.8 km or 10 time the height of the tructure upwind, whichever i greater 0.33 460 2 3 4 Urban and uburban area, wooded area, or other terrain with numerou cloely paced obtruction having the ie of ingle-family dwelling or larger, over a ditance of at leat 460 m or 10 time the height of the tructure upwind, whichever i greater Open terrain with cattered obtacle having height generally le than 9 m, including flat open country typical of meteorological tation urrounding Flat, unobtructed area expoed to wind flowing over water for at leat 1.6 km, over a ditance of 460 m or 10 time the height of the tructure inland, whichever i greater 0.22 370 0.14 270 0.10 210
174 A raphic Method to Etimate the Wind Speed under Urban Canopy Layer 3. raphic Method In the numerical method for each change of the wind peed, all calculation mut be repeated; thi make the calculating proce difficult and confuing. To eae the etimating proce of wind peed, a graphic method wa recommended by the author [7]. By thi method, without being involved with calculation, the mean wind peed in every terrain and every tudy height will be etimated eaily and rapidly. There are 3 graph that are produced by the author. The explanation of the graph are a below: The graph in Fig 1 - which i drawn by uing formula (3) - how the relationhip between oberved mean wind peed in the meteorology tation at the tandard height 10 meter and the mean wind peed in four type of terrain in Table 1 at the ame height. method for every change of reported wind peed, the wind peed of the tudy urban terrain will be etimated eaily and quickly [7]. Figure 2. The relationhip between height above the ground and the percentage of wind peed in different terrain Figure 1. The relationhip between meteorology wind data and the tudy train at 10 meter height The graph in Fig 2 - that i drawn by uing formula (2) - how the relationhip between height above the ground and the percentage of wind peed in different terrain. Thi graph i prepared for height le than 10 meter and how the exponent for different kind of terrain. The graph in Fig 3 i drawn by uing formula (2). It how the relationhip between wind peed at the height of 10 meter and the percentage of wind peed at the lower height. It how the wind peed at the tudy height. All the graph are compacted in Fig 4 that will be ued for graphical method etimation of wind peed. Uing thee graph, without being involved with calculation procedure, the wind peed in the tudy terrain at each deire height will be etimated for every reported wind peed data by the meteorology tation at 10 m height. By thi Figure 3. The relationhip between wind peed at the height of 10 meter and the percentage of wind peed at the lower height
Civil Engineering and Architecture 3(6): 172-188, 2015 175 Terrain Category 1 2 3 4 Decription Large city centre, in which at leat 50% of building are higher than 21.3 m, over a ditance of at leat 0.8 km or 10 time the height of the tructure upwind, whichever i greater Urban and uburban area, wooded area, or other terrain with numerou cloely paced obtruction having the ie of ingle-family dwelling or larger, over a ditance of at leat 460 m or 10 time the height of the tructure upwind, whichever i greater Open terrain with cattered obtacle having height generally le than 9 m, including flat open country typicalof meteorological tation urrounding Flat, unobtructed area expoed to wind flowing over water forat leat 1.6 km, over a ditance of 460 m or 10 time the height of the tructure inland, whichever i greater Exponent Layer Thickne (meter) 0.33 460 0.22 370 0.14 270 0.10 210 Z Figure 4. The graph to etimate wind peed in tudy terrain at tudy height [7] Table 2. Summary of wind effect on people baed on the Beaufort cale [4, p. 40] Type of wind Wind peed (m/) Effect Name Dangerou wind peed uncomfortable wind peed Acceptable wind peed 8 More than 24.4 Damage building and tree 7 17.1 24.4 People blown over by gut, generally impede progre, great difficulty with balance in gut Strong gale 6 13.8 17.1 Inconvenience felt when walking Near gale 5 10.7 13.8 4 5.4 10.7 Umbrella ued with difficulty, difficult to walk teadily, wind noie in ear unpleaant Raie dut, dry oil and looe paper, hair diarranged, force of wind felt on body, limit of agreeable wind on land Strong breee Moderate and freh breee 3 3.3 5.4 Wind extend light flag, hair i diturbed, clothing flap entle breee 2 1.5 3.3 Wind felt on face Light breee 1 Le than 1.5 Calm, no noticeable wind calm
176 A raphic Method to Etimate the Wind Speed under Urban Canopy Layer 3.1. Wind Quality The graph produced by the author (Fig 4) implified the procedure of etimating the wind peed in the urban area but it i not clear for the deigner how to ue thi information in architectural and urban deign. The Beaufort cale (Table 2) can be ued for thi reaon. Thi table how the relationhip between the wind peed and the condition caued by it. According to the acceptable wind peed in urban area that i le than 5 m/ [4, p. 37]; it i poible to claify the wind peed in 3 main group: 1. The wind peed le than 5 m/, that i acceptable in urban area (light breee to gentle breee) 2. The wind peed between 5 to 17.5 m/, that will caue difficultie for paenger (moderate breee to near gale) 3. The wind peed more than 18 m/ that will caue damage for the building and uprooted the tree (gale to trong gale) To ditinguih thee group, 8 area are hown on the graph at bottom right of Fig 4 which help to predict the quality of the wind peed for urban deign deciion. In thi cae the graph of the Fig 4 i completed and can be ued by urban deigner a a guideline. 3.2. Benefit of the raphic Method Uing the graph in Fig 4 it i poible to predict the wind peed in every tudy height and in every urban area according to the meteorological reported wind peed only by drawing ome line. In uing Equation 1, 2 & 3, cae may be encountered where, for a given wind direction, the terrain upwind of either the building ite or the recording ite doe not fall into jut one of the categorie in Table 1. The terrain immediately upwind of the ite may fall into one category, while that omewhat further upwind fall into a different category. Thi difference in terrain alo occur when a building ite or recording ite i in an urban area near open water or at the edge of town [5]. In thee cae, the uggeted approach i to ue the terrain category that i mot repreentative of the average condition. If the average condition i omewhere between two categorie decribed in Table 1, the value of and Z can be interpolated from thoe given in the Table 1. One of the advantage of graphic method i eay interpolating between the terrain categorie. 3.3. Limitation of the raphic Method The recommended graphic method ha all the reliability limitation of the numerical method. In order to deign for the effect of airflow around building, wind peed and direction frequency data hould be obtained. The implet form of wind data are table or chart of climatic normal recorded in meteorology tation, which give hourly average wind peed, prevailing wind direction, and peak gut wind peed for each month of the year. In cae where the only ignificant difference between the airport recording ite terrain and the building ite terrain i urface roughne, the mean wind peed can be adjuted, uing Equation 1, 2 & 3 and Table 1, to yield approximate wind velocitie at the building ite. A rough guideline i that only wind peed 4 m/ at the building ite can be etimated reliably uing thee equation for the condition that the building and meteorological tation are in different terrain categorie. In addition, everal other factor are important in cauing the wind peed and direction at a building ite to differ from value recorded at a nearby meteorology tation [5]. Another limitation i that all the mathematical model of the vertical wind profile aume a mooth curve from the level of the gradient wind down to the ground or the roughne parameter height. Thi form repreent the wind peed pattern to the top of the urban canopy (ueful for the pollution and wind loading on high building). In a city near ground level, turbulent created by the building, caue a very complex wind field. So in urban canopy the wind field can not be defined by a imple mooth curve loping down to the ground [3, p. 265]. 4. Turbulent Wind in Urban Area The wind condition in the airpace between the building i very important from the view point of pedetrian comfort, building ventilation and energy demand. Often the wind peed near the ground (pedetrian level) may be higher than the wind peed in the middle height of the pace between the building. Air flow around iolated building i well characteried by a bolter eddy vortex due to flow down the windward façade, while behind i a lee eddy drawn into the cavity of low preure due to flow eparation from the harp edge of the building top and ide. Further downtream i the building wake characteried by increaed turbulence, but lower horiontal peed than the unditurbed flow [2]. In an urban area the wind peed may change by a factor three to five time over ditance of a few meter. To make into account the effect of turbulent wind, Aren (1981) reviewed the mechanical effect of wind on pedetrian, ranging from diturbance of clothing and hair to reitance to walking and lo of balance. By uing the concept of equivalent teady wind peed ( ) that i defined a a turbulent wind, he made a formula to etimate the ame perception or afety effect a a teady wind with mean wind peed of [15, pp. 296-297]. Local mean peed i another name for the concept of equivalent teady wind peed. The mean wind peed i a theoretical mean peed that i calculated at Z height from the free tream velocity according to the power law that give the mean peed vertical gradient [8]. In the recommended graph of thi article, the amount of mean wind peed i etimated by the down right graph of Fig 1.
Civil Engineering and Architecture 3(6): 172-188, 2015 177 T 2 i where 1 a T ) (4) ( i 2 i the root mean quare of the equivalent teady wind peed [8] (andemer, 1977, p.425) Different value for a coefficient are recommended by different tudie, ranging from 1.5 to 4 [9]. The effect of turbulence depend on the pecific criterion ued in it evaluation, and alo on the circumtance and the activitie of the pedetrian. Turbulence intenitie in area of trongly channelled flow are found to be relatively low (0.10-0.15) and probability by normal ditribution. Local turbulence intenitie near the ground in open country are typically around 0.2. alue in the order of 0.3 or even higher would be appropriate in urban area. Turbulence intenitie of 0.25-0.4 are more repreentative for other area with ignificant wind peed [10]. 4.1. Example for Uing Equation 4 To how the way of uing equivalent teady wind peed concept ome example are done here: Example 1 [3, p.297]: With an average wind peed of 4 m/ a turbulence intenity of 0.2 and an a value aumed at 3.0 the perceptible wind peed will be: 4(1 30.2) 6.4 m/ According to Beaufort cale and penwarden recommendation for pedetrian, it i poible to divide the urban wind peed to three categorie. It i ueful to mention that Hunt recommend imilar value to claify acceptable wind peed on pedetrian [11]. 1. The acceptable wind peed that i le than 5.4 m/: extend light flag, hair i diturbed and clothing flap. 2. Uncomfortable wind peed that i more than 10.7: caue umbrella ued with difficulty, difficult to walk teadily and wind noie on ear. 3. Dangerou wind peed that i more than 24.7: caue damage building and tree (Table 2). Uing equation 4, the wind peed in urban area will be divided to three group for different terrain with different denity and height of building (Table 3). Example 2: For the urban condition of example 1 aume =1.6, etimate the reported wind peed for three main category of wind effect on people (acceptable, uncomfortable, dangerou). In Table 3 for =1.6 by equivalent teady wind peed = 5.4, 10.7 and 24.4 m/, the mean wind peed are = 3.4, 6.7 and 15.3 m/ repectively. The graph in bottom left of Fig 4 how the mean wind peed in different terrain. In thi graph adding the curve line of 3.4, 6.7 and 15.3 m/, how the mean wind peed outcome of Table 3. For the terrain category 1 and 2 at the height of 2 meter (the height that affect the pedetrian), the reported wind peed in meteorology tation at 10 meter height will be claified according to the following part of thi article. It i ueful to mention that i equal 1.3 to 1.6 for building higher than 10-15 torie [8]. Citation to [12]. 4.2. CFD Simulation / Critical Wind Speed To etimate the proportion of in critical point of a building arrangement a CFD imulation for each pecific deign will be ued. By the help of the imulation it i poible to etimate the proportion of in every pecific location and find out the threhold of the mean wind peed which may caue an unpleaant or dangerou ituation (Fig 5). CFD imulation of ome building ettlement by different arrangement are hown in Fig 6-8. In thee example 1 the mean wind peed ( ) i defined a 5 m/ and the legend in the left part of the imulated figure - that how the current velocity vector around the building - etimate the equivalent teady wind peed ( ). Therefore the etimation of in critical part of building by different arrangement will be etimated with an acceptable approximation for the beginning tage of deign procedure. 4.3. erification of the CFD Simulation by an Experimental or Wind Tunnel Tet The that i propoed in table 3 and will be etimated by a CFD program, need to be verified by an extra tet uch a experimental tet in a real cae tudy or a wind tunnel tet by a model. Here a imple example i preented by a real cae tudy. 1 - The etup of the CFD and procedure of the CFD imulation mut be done according to a valid method of chooing the dimenion of the tet ection, model, the reference wind peed, the mehing hape and oftware that i ued.
178 A raphic Method to Etimate the Wind Speed under Urban Canopy Layer Table 3. Equivalent teady wind peed and mean wind peed for different denity and height of building mean wind peed in the urban area (m/) Equivalent Steady Wind Speed (m/) Acceptable Uncomfortable Dangerou Le than 5.4 m/ 10.7-24.4 m/ >24.4 0.2 1.5 3.3 5.4 10.7 13.8 17.1 24.4 1.2 0.2 1.3 2.8 4.5 8.9 11.5 14.3 20.3 1.3 0.2 1.2 2.5 4.2 8.2 10.6 13.2 18.8 1.6 0.1 0.9 2.1 3.4 6.7 8.6 10.7 15.3 1 at i or ( ) 1.8 0.1 0.8 1.8 3.0 5.9 7.7 9.5 13.6 2 0.1 0.8 1.7 2.7 5.4 6.9 8.6 12.2 2.5 0.1 0.6 1.3 2.2 4.3 5.5 6.8 9.8 3 0.1 0.5 1.1 1.8 3.6 4.6 5.7 8.1 3.5 0.1 0.4 0.9 1.5 3.1 3.9 4.9 7.0 4 0.1 0.4 0.8 1.4 2.7 3.5 4.3 6.1 15 ( ) 3 5
Civil Engineering and Architecture 3(6): 172-188, 2015 179 mean wind peed in the urban area 1 a T i or ( ) Equivalent Steady Wind Speed (m/) Le than 5.4 m/ 10.7-24.4 m/ >24.4 (m/) 0.2 1.5 3.3 5.4 10.7 13.8 17.1 24.4 1.2 0.2 1.3 2.8 4.5 8.9 11.5 14.3 20.3 1.3 0.2 1.2 2.5 4.2 8.2 10.6 13.2 18.8 1.6 0.1 0.9 2.1 3.4 6.7 8.6 10.7 15.3 1.8 0.1 0.8 1.8 3.0 5.9 7.7 9.5 13.6 2 0.1 0.8 1.7 2.7 5.4 6.9 8.6 12.2 2.5 0.1 0.6 1.3 2.2 4.3 5.5 6.8 9.8 3 0.1 0.5 1.1 1.8 3.6 4.6 5.7 8.1 3.5 0.1 0.4 0.9 1.5 3.1 3.9 4.9 7.0 4 0.1 0.4 0.8 1.4 2.7 3.5 4.3 6.1 Table 3: equivalent teady wind peed and mean wind peed for different denity and Figure 5. Uing CFD imulation in critical point around the building ettlement at pedetrian level Figure 6. Wind peed in critical point i approximately 3 time more than mean wind peed
180 A raphic Method to Etimate the Wind Speed under Urban Canopy Layer 10 ( ) 2 5 mean wind peed in the urban area 1 a T i or ( ) Equivalent Steady Wind Speed (m/) Le than 5.4 m/ 10.7-24.4 m/ >24.4 (m/) 0.2 1.5 3.3 5.4 10.7 13.8 17.1 24.4 1.2 0.2 1.3 2.8 4.5 8.9 11.5 14.3 20.3 1.3 0.2 1.2 2.5 4.2 8.2 10.6 13.2 18.8 1.6 0.1 0.9 2.1 3.4 6.7 8.6 10.7 15.3 1.8 0.1 0.8 1.8 3.0 5.9 7.7 9.5 13.6 2 0.1 0.8 1.7 2.7 5.4 6.9 8.6 12.2 2.5 0.1 0.6 1.3 2.2 4.3 5.5 6.8 9.8 3 0.1 0.5 1.1 1.8 3.6 4.6 5.7 8.1 3.5 0.1 0.4 0.9 1.5 3.1 3.9 4.9 7.0 4 0.1 0.4 0.8 1.4 2.7 3.5 4.3 6.1 Table 3: equivalent teady wind peed and mean wind peed for different denity and Figure 7. Wind peed in critical point i approximately 2 time more than mean wind peed (left)
Civil Engineering and Architecture 3(6): 172-188, 2015 181 9 ( ) 1.8 5 mean wind peed in the urban area 1 a T i or ( ) Equivalent Steady Wind Speed (m/) Le than 5.4 m/ 10.7-24.4 m/ >24.4 (m/) 0.2 1.5 3.3 5.4 10.7 13.8 17.1 24.4 1.2 0.2 1.3 2.8 4.5 8.9 11.5 14.3 20.3 1.3 0.2 1.2 2.5 4.2 8.2 10.6 13.2 18.8 1.6 0.1 0.9 2.1 3.4 6.7 8.6 10.7 15.3 1.8 0.1 0.8 1.8 3.0 5.9 7.7 9.5 13.6 2 0.1 0.8 1.7 2.7 5.4 6.9 8.6 12.2 2.5 0.1 0.6 1.3 2.2 4.3 5.5 6.8 9.8 3 0.1 0.5 1.1 1.8 3.6 4.6 5.7 8.1 3.5 0.1 0.4 0.9 1.5 3.1 3.9 4.9 7.0 4 0.1 0.4 0.8 1.4 2.7 3.5 4.3 6.1 Table 3: equivalent teady wind peed and mean wind peed for different denity and Figure 8. Wind peed in critical point i approximately 1.8 time more than mean wind peed (right)
182 A raphic Method to Etimate the Wind Speed under Urban Canopy Layer South facade north Wet facade The reference logger on the roof Figure 9. The cae tudy building in Tehran January 2013 The tet logger on the outh/wet facade Roof wind peed data 6th floor outh/wet façade data Figure 10. wind peed on the outh/wet 6 th floor i nearly 2 time more than wind peed on the roof Wind tunnel tet [4] Wind tunnel tet [4] CFD imulation Figure 11. The wind tunnel tet in thi model verifie the CFD imulation reult of the wind turbulent condition around the building To how the reliability of CFD imulation an experimental tet i done in a real condition. In thi example a 10 floor emi tall building in Tehran i examined in winter 2013. Some Ketrel data logger peronal weather tation were ued to collect the wind peed information in the roof, outh/wet façade and north façade of the building (Fig 9). The roof data i ued a the reference weather tation and other data logger log the critical point around thi building. The data were collected in five day from 11-15 January. The wind peed comparion for north/outh wind direction in critical part around the building how that when the wind peed on the roof i around 4-5 m/, the wind peed in the ixth floor of outh/wet corner of the façade i around 8-10 m/ (Fig 10). It mean that =2. Comparing the experimental or wind tunnel tet reult with CFD imulation reult will give the reliability and repeatability of our imulation for other critical point around the building in different time of the year. Fig 11 how the wind tunnel reult that i verifie wind turbulent and hape around two tall and hort building. 4.4. Reult of raphic Method for Deign Principle Uing thi method it i poible to determine the
Civil Engineering and Architecture 3(6): 172-188, 2015 183 uncomfortable or dangerou ituation according to the meteorology data. Table in the down ide of Fig 6-8 how the important threhold of critical mean wind peed ( ) for = 1.8, 2 and 3. Determining thee threhold on graph of Fig 4 and uing the graphic method, help to etimate the important threhold of meteorology wind peed data related to them according to terrain category. Table 2 that how the wind effect on pedetrian baed on the Beaufort cale i a good completion to thi graph. Fig 12 how the complete graph for etimating wind peed by graphic method. Specifying the important threhold of meteorology wind peed data that will caue uncomfortable and dangerou ituation around the imulated building, it will be clear how many time in a year the uncomfortable or dangerou ituation may happen. Therefore by modifying the deign at the critical point, it i poible to prevent problematic ituation around the building and achieve harmony between architectural deign and natural wind movement in the urban area. According to the reult obtained from example in Fig 13 it i clear that: 1. In terrain category 2 (uburban area around the citie) the airflow between building higher than 10-15 torie (with condition of example 1), when the meteorology wind peed i reported le met 10 than 6-7.5 m/, the equivalent teady wind peed around building at height of 2 meter i perceptible a gentle breee (le than 5.4 m/). For more met 10 than 13.5-15 m/ it i felt uncomfortable (more than 10.4 m/). For more than 31-32.5 m/ it will met 10 caue damage (more than 24.4 m/). 2. In a terrain category 1 (large city centre with condition of example 1), when the meteorology wind peed met 10 i reported le than 13 m/ the mean wind peed around building at height of 2 meter i perceptible a gentle breee (le than 5.4 m/). For more than 27 m/ it i felt met 10 uncomfortable (more than 10.4 m/). The data information from the meteorology tation related to the ite how the time, duration and direction of the wind that may caue problem. Table 4 how that in the example ite the wind from the wet in March, April and May at midday may caue uncomfortable condition for the example ettlement of the building. Therefore the reult below will be obtained for the primary tage of the deign procedure: Do not build lengthy building normal to the wet. Do not ettle erial layout building with mall pace in between parallel to the wet. Do not ettle che layout building with mall pace in between parallel to the wet. Impede the wet wind by ome natural or contructed wind break. 5. Concluion According to importance of climatic element in urban deign, thi article introduce a new graph and graphic method produced by the author, which will help to etimate the wind peed in urban area eaily and rapidly without being involved with calculation procedure. Although computer oftware may do the ame, the graphic method i another way to approach the reult and i appropriate for the condition that the uer i not familiar with oftware or he/he want to have a quick prediction of different ituation. Thi method give a comprehenive undertanding of different wind peed ituation which will be helpful in deign deciion making procedure.
184 A raphic Method to Etimate the Wind Speed under Urban Canopy Layer Wind peed Type of wind (m/) Effect 8 More than Damage building and tree Dangerou 24.4 wind peed 7 17.1 24.4 People blown over by gut, generally impede progre, great difficulty with balance in gut uncomforta ble wind peed Acceptable wind peed Name Strong gale 6 13.8 17.1 Inconvenience felt when walking Near gale 5 10.7 13.8 Umbrella ued with difficulty, difficult to walk teadily, wind noie in ear unpleaant 4 5.4 10.7 Raie dut, dry oil and looe paper, hair diarranged, force of wind felt on body, limit of agreeable wind on land 3 3.3 5.4 Wind extend light flag, hair i diturbed, clothing flap Strong breee Moderate and freh breee entle breee 2 1.5 3.3 Wind felt on face Light breee 1 Le than 1.5 Calm, no noticeable wind calm Figure 12. complete heet of graphic method for etimating wind peed in urban area
Civil Engineering and Architecture 3(6): 172-188, 2015 185 mean wind peed in the urban area (m/) 1 at i or Equivalent Steady Wind Speed (m/) Acceptable Uncomfortable Dangerou Le than 5.4 m/ 10.7-24.4 m/ >24.4 0.2 1.5 3.3 5.4 10.7 13.8 17.1 24.4 1.6 0.1 0.9 2.1 3.4 6.7 8.6 10.7 15.3 ( ) acceptable uncomfortable dangerou Figure 13. Threhold of mean wind peed that may caue problem in the pecific location of an example deign and the related meteorology wind peed data for terrain category 1 and 2
186 A raphic Method to Etimate the Wind Speed under Urban Canopy Layer Table 4. Time, duration and direction of the wind that may caue problem in critical point around the building [13, pp. 59-61]
Civil Engineering and Architecture 3(6): 172-188, 2015 187 The graph are baed on the power law formula that predict wind peed in a deire height above the ground according to the profile of the wind from the ground up to the gradient boundary layer for different terrain area. The graph help to etimate the wind peed for height le than 10 meter for a tudy terrain different from meteorology tation. To make the etimation of wind peed meaningful for deign tak, uing Beaufort Table, different part of the graph wa claified to 8 area that help architect to predict the condition which may happen by the wind peed in the tudy urban terrain. Turbulent that may occur by incident wind to obtacle uch a building in every urban area, can caue unpleaant gut with higher peed near the ground that i not acceptable for pedetrian comfort. Detail of the building and treet canyon in an urban area, like the dimenion and orientation, have a great effect on turbulent wind near the ground. To make into conideration the effect of the turbulence wind around building near the ground, the concept of equivalent teady wind peed i being ued. By uing thi concept it i poible to ue graphic method for claifying the reported wind peed in meteorology tation to 3 main categorie according to the effect on pedetrian (acceptable, uncomfortable and dangerou condition). Some example are preented to explain the method of uing the graph. Predicting the main threhold of the meteorology tation wind peed data help to recognie the duration, time and direction of the wind that may caue uncomfortable or dangerou ituation around the pecified building arrangement. Thi knowledge help the architect to make better deciion at the primary tage of deign proce. It i neceary to explain that the reliability of thi prediction depend on the reliability of the aumption that may be calculated by a CFD imulation. To verify the imulation an experimental cae tudy or a wind tunnel model tet i neceary to check ome critical location around the building. When the experimental cae tudy or wind tunnel tet howed the reliability of the imulation for the checked part, the imulation reult for the other part or other time will be verified and we can ue them in the graphic method. Lit of mathematical ymbol = mean wind peed at Z height in the tudy terrain (m/). In the recommended graph of thi article, the amount of mean wind peed i etimated by the down right graph of Fig 1. = mean wind peed at height Z ( gradient height) at the top of the boundary layer of the tudy ite, above which the peed i aumed to be contant, (m/) 10 = mean wind peed at the height of 10 meter in the tudy terrain (m/) met 10 = mean wind peed at height of 10 meter in the meteorology tation (m/) = equivalent teady wind peed (m/) Z = the height for which the wind peed (m) Z = the height at which gradient velocity i computed i firt oberved in the ame terrain (m) (radient layer thickne i introduced by ymbol in ASHRAE Handbook and ome other reference) Z 10 = the height of 10 meter in the ame terrain (m) = an empirical exponent which depend on the urface roughne, tability and temperature gradient. met = the exponent of the roughne of the meteorology tation met 10 = the tandard obervation height of 10 meter in the meteorology tation (m) met = gradient height at the top of the boundary layer of the meteorology tation T i = turbulence intenity level a = an empirically determined coefficient REFERENCES [1] Oke, T. R.: (1987) Street Deign and Urban Canopy Layer Climate, Energy and Building, ol 11, pp. 103-113. [2] eorgaki, Chria and Mat Santamouri: (2005). Wind and Temperature in the Urban Environment, Natural entilation in the Urban Environment, London, Earthcan,, pp. 81-102. [3] ivoni, Baruch: (1998). Climate Conideration in Building and Urban Deign, New york, an Notrand Reinhold. [4] Penwarden, A. D. and A. F. E. Wie: (1975). Wind Environment around Building, London, Building Reearch Etablihment Report. [5] ASHRAE Handbook Fundamental (SI): (2005). Chapter 16: Air Flow around Building. [6] Anley, R. M.; W. Melbourne & B. J. ickery: (1977). Architectural Aerodynamic, London, applied cience publiher Ltd. [7] Tahba, Manoureh: (2009). Etimation of the Wind Speed in Urban Area for height le than 10 meter above the ground, The International Journal of entilation, ol. 8, No. 1, pp. 75-84. [8] andemer, : (1977). Wind Environment around Building: Aerodynamic Concept, Pro. Wind Effect on Building & Structure, Cambridge Univerity Pre, pp. 423-433. [9] Iyumov, N., and A.. Davenport: (1978). Evaluation of the Effect of Tall Building on Pedetrian Level Wind Environment, Pro. American Society of Civil Engineering (ASCE), Annual Convention, Chicago, Illinoi, October 1978. [10] Iyumov, N: (1977). The round Level Wind Environment in
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