1、鼓風(fēng)式機(jī)械通風(fēng)冷卻塔空氣動(dòng)力特性數(shù)值模擬研究趙順安、李紅莉、毋飛翔（中國(guó)水利水電科學(xué)研究院，北京 100038）Numerical research on aerodynamic characteristics of the forced draft mechanical cooling tower Zhao Shunan、Li Hongli、Wu Feixiang(China Institute of Water Resource and Hydropower Research, Beijing 100038 )摘要：鼓風(fēng)式機(jī)械通風(fēng)冷卻塔常用于核電廠的重要廠用水系統(tǒng)，但相關(guān)設(shè)計(jì)規(guī)范并沒有給出

2、冷卻塔的空氣動(dòng)力特性計(jì)算公式。本文采用Fluent軟件對(duì)鼓風(fēng)式機(jī)械通風(fēng)冷卻塔的空氣動(dòng)力進(jìn)行了數(shù)值模擬計(jì)算，對(duì)冷卻塔的設(shè)計(jì)布置進(jìn)行了優(yōu)化，分析總結(jié)給出了冷卻塔阻力計(jì)算公式。結(jié)果表明，填料安裝位置對(duì)鼓風(fēng)式機(jī)械通風(fēng)冷卻塔整塔阻力影響不大，但會(huì)影響填料斷面風(fēng)速分布均勻性，填料安裝高度越低，風(fēng)速分布越均勻；出口收縮段的高度越高，整塔阻力越小，風(fēng)速分布越均勻；出口收縮段與水平的夾角越大，整塔阻力系數(shù)越小，但變化趨勢(shì)不明顯，收縮角基本不影響填料斷面風(fēng)速分布均勻性。關(guān)鍵詞：鼓風(fēng)式冷卻塔；塔型；阻力系數(shù)；風(fēng)速均勻性Abstract: The forced draft mechanical cooling tow

3、er is always used in a nuclear power plant, while the relevant design specifications have not formula about the aerodynamic characteristics of cooling tower. This paper uses FLUENT software to simulate and study the aerodynamic characteristics of the forced draft mechanical cooling tower, and optimi

4、ze the design of the cooling tower, and analysis to summarize the cooling tower resistance calculative formula. The results show that the height of the fill has little effects on the whole tower resistance coefficient, but it influences the wind velocity distribution uniformity of the fill section,

5、the lower the position is, the more uniform the wind velocity distribution is; the convergent section height is higher, the whole tower resistance is smaller and the wind velocity distribution is more uniform. The angle between convergent section and horizon is bigger, the whole tower resistanc

6、e is smaller, while this trend is not obvious, it does not affect the wind velocity distribution uniformity on the fill section.Keywords: the forced draft mechanical cooling tower, tower shape, resistance coefficient, wind velocity distribution uniformity1研究背景內(nèi)陸核電廠的重要廠用水的水量不大，但卻影響核電廠的安全。鼓風(fēng)式機(jī)械通風(fēng)冷卻塔能較

7、好地適應(yīng)核電對(duì)安全性和抗震性能的要求而常被內(nèi)陸核電廠采用。鼓風(fēng)式機(jī)械通風(fēng)冷卻塔不僅在通風(fēng)方式上有別于常規(guī)的抽風(fēng)式機(jī)械通風(fēng)冷卻塔，在塔型結(jié)構(gòu)布置上也有明顯差異。我國(guó)的相關(guān)設(shè)計(jì)規(guī)范和資料對(duì)鼓風(fēng)式機(jī)械通風(fēng)冷卻塔沒有明確的設(shè)計(jì)計(jì)算方法15。為了解塔內(nèi)氣流特性并對(duì)塔型進(jìn)行優(yōu)化，需要通過(guò)相關(guān)的研究來(lái)確定其空氣動(dòng)力特性。通過(guò)物理模型試驗(yàn)來(lái)研究冷卻塔空氣動(dòng)力特性是一個(gè)十分有效的手段，但是由于鼓風(fēng)式機(jī)械通風(fēng)冷卻塔模型本身的復(fù)雜性及系統(tǒng)試驗(yàn)的塔型的變化，使模型試驗(yàn)研究工作量和投資都很大。本文利用Fluent軟件建立鼓風(fēng)式機(jī)械通風(fēng)冷卻塔空氣動(dòng)力計(jì)算的數(shù)學(xué)模型，經(jīng)過(guò)與試驗(yàn)結(jié)果對(duì)比驗(yàn)證，確定模型參數(shù)和網(wǎng)格數(shù)量。研究了不

8、同塔型條件下塔內(nèi)氣流分布及阻力特性，最終分析總結(jié)出了鼓風(fēng)式機(jī)械通風(fēng)冷卻塔的阻力計(jì)算公式以及塔型與配風(fēng)均勻性的關(guān)系。阻力系數(shù)計(jì)算公式與試驗(yàn)結(jié)果相比偏差小于5%，可為設(shè)計(jì)提供參考。1research backgroundThe water quantity of important water system of inland nuclear power plant is not big, but it affects the security of nuclear power plant. The forced draft mechanical cooling tower can satisfy

9、 the requirements of equipment security and earthquake resistance, so it will be used more and more in inland nuclear power plant.The forced draft mechanical cooling tower is not only different from the conventional induced draft mechanical cooling tower in ventilation way, but also has distinct dif

10、ference in tower shape and structure layout. China's relevant design specifications and information on the forced draft mechanical cooling tower have no clear design method. For understanding the airflow characteristics of the tower and optimizing the tower shape, it's necessary to do some r

11、elevant research to realize the aerodynamic characteristics. It's a very effective way to establish a physical model to study the aerodynamic characteristics of the cooling tower, however, due to the forced draft mechanical cooling tower model's complexity and variability, the workload of ex

12、periment and investment is very big.This paper uses FLUENT software to build a mathematical model of the forced draft mechanical cooling tower to study the tower aerodynamic characteristics, and after comparing with the experimental results to determine the model parameters and grid number. It studi

13、es the airflow distribution and resistance characteristics in the conditions of different tower shapes, and analysis to summarize the cooling tower resistance calculative formula and the relationship between tower shape and airflow distribution uniformity. The difference of computational resistance

14、coefficient and the experimental results is less than 5%, it can provide a reference for design.2數(shù)學(xué)模型及計(jì)算方法2.1 空氣流場(chǎng)控制方程塔內(nèi)外流場(chǎng)為等溫、不可壓流動(dòng)，其控制方程包括連續(xù)方程、動(dòng)量方程，并選用雙方程湍流模式對(duì)方程進(jìn)行封閉，各方程可寫為統(tǒng)一形式： （1）式中：為空氣密度，kg/m3；為空氣流速，m/s。各控制方程的變量、擴(kuò)散系數(shù)項(xiàng)與源項(xiàng)如下表1。表1 控制方程中各變量代表參數(shù)控制方程連續(xù)方程100動(dòng)量方程（流速），湍能方程耗散方程其中生成項(xiàng)；為空氣分子粘性系數(shù)；為壓力；為紊流粘性系數(shù)

15、，由動(dòng)能和紊動(dòng)耗散率求出：，為經(jīng)驗(yàn)常數(shù)；和分別為和的紊流普朗特?cái)?shù)。2 Mathematical models and calculative methods2.1 Air flow governing equationsThe tower flow field is isothermal and incompressible. Its governing equations include continuity equation, momentum equation, which can be closed with two-equation turbulence model, these e

16、quations can be written as a unified form: (1)Where: is air density, kg/m3; is air velocity, m/s. All governing equations' variable 、diffusion coefficient term and source term are shown as Table 1 below.Table 1 , and of every governing equationGoverning equationsContinuity equation100Momentum eq

17、uation（Velocity of flow），Turbulent energy equation Dissipation equation Generated item , is viscosity coefficient of the air molecules; is pressure, Pa; is the turbulent viscosity coefficient, which is can be calculated by the turbulent kinetic energy and dissipation rate : , is an empirical constan

18、t; and are turbulent Prandtl number of and .2.2 邊界條件底部為固壁無(wú)滑移邊界條件，四周及頂部采用壓力出口邊界條件，塔殼采用固壁邊界條件。進(jìn)風(fēng)口及塔的出口都設(shè)置成內(nèi)部邊界；填料區(qū)域設(shè)置成多孔介質(zhì)邊界條件，并根據(jù)實(shí)測(cè)填料阻力系數(shù)設(shè)置各方向阻力系數(shù)；風(fēng)機(jī)采用Fluent風(fēng)扇邊界條件，也可采用第一類邊界條件。2.2 Boundary conditions The bottom of the computational domain is solid wall boundary condition with no-slip, all around and

19、top is pressure outlet boundary conditions, the tower shell is solid wall boundary condition. The boundaries of the air inlet and outlet are defined as interior; the porous model is used to simulate the fill and according to the measured resistance coefficient to set the fill resistance coefficient

20、in each direction; the FLUENT fan model is used to simulate the fan of the tower, first boundary condition can also be used.2.3 冷卻塔阻力系數(shù)及風(fēng)速分布均勻性計(jì)算鼓風(fēng)式機(jī)械通風(fēng)冷卻塔，氣流經(jīng)由風(fēng)機(jī)鼓入塔內(nèi)，依次經(jīng)過(guò)塔進(jìn)風(fēng)口，雨區(qū)、填料等，并經(jīng)由出口排入到大氣中，氣流經(jīng)過(guò)各部分的阻力為該區(qū)域前后斷面的全壓差，一般表示為阻力系數(shù)與填料斷面平均氣流速度頭之積： （2）式中為氣流經(jīng)過(guò)某區(qū)域前后斷面的全壓差（Pa）；為空氣密度（kg/m3）；為填料斷面平均風(fēng)速（m/s）。填料斷

21、面處風(fēng)速分布狀況影響冷卻塔的熱力特性，一般將填料斷面風(fēng)速分布均勻性作為一個(gè)設(shè)計(jì)指標(biāo)，用風(fēng)速分布均布系數(shù)表示: （3） 式中為填料斷面風(fēng)速分布均布系數(shù)；為填料斷面各點(diǎn)風(fēng)速（m/s）；n為風(fēng)速統(tǒng)計(jì)點(diǎn)的個(gè)數(shù)。2.3 Computational methods of the cooling tower resistance coefficient and wind velocity uniformity For the forced draft mechanical cooling tower, airflow is blown into the tower by the fan, sequentia

22、lly through the tower inlet, rain zone, fill etc, and is discharged into the atmosphere through the outlet finally. The resistance of each part is the pressure loss of the region, which is generally expressed as the resistance coefficient multiply the average flow velocity head: (2)Where is the pres

23、sure loss of the region（Pa）; is air density（kg/m3）; is the average wind velocity of the fill section（m/s）.Distribution of wind velocity at the fill section affects the thermodynamic characteristics of the cooling tower, generally put the wind velocity distribution uniformity of the fill section as a

24、 design index, it can be expressed with a velocity distribution uniformity coefficient: （3）Where is the velocity distribution uniformity coefficient; is the velocity at the measure point in the fill section（m/s）; n is the velocity statistical points number. 模型的驗(yàn)證對(duì)已具有試驗(yàn)結(jié)果的某抽風(fēng)式機(jī)械通風(fēng)冷卻塔的空氣動(dòng)力特性模型試驗(yàn)6作對(duì)比驗(yàn)證

25、計(jì)算，冷卻塔如圖1示，首先對(duì)冷卻塔進(jìn)行網(wǎng)格的敏感性分析，然后再將計(jì)算結(jié)果進(jìn)行對(duì)比分析。圖1 抽風(fēng)式機(jī)械通風(fēng)冷卻塔模型試驗(yàn)布置示意圖不同填料阻力條件下模型試驗(yàn)實(shí)測(cè)與計(jì)算結(jié)果對(duì)比如圖2所示，圖中橫坐標(biāo)L0/L為距其中一側(cè)塔壁的相對(duì)距離， V/為相對(duì)風(fēng)速，V為測(cè)點(diǎn)風(fēng)速，為測(cè)點(diǎn)風(fēng)速的平均值。進(jìn)風(fēng)口氣流流態(tài)作對(duì)比如圖3所示，從圖中可以看出，試驗(yàn)結(jié)果與數(shù)值計(jì)算結(jié)果規(guī)律較為一致，吻合良好。圖2 試驗(yàn)與計(jì)算填料斷面風(fēng)速分布對(duì)比（a）模型試驗(yàn)結(jié)果 （b）數(shù)值計(jì)算結(jié)果圖3 試驗(yàn)與計(jì)算進(jìn)風(fēng)口上沿氣流流態(tài)分布對(duì)比進(jìn)風(fēng)口區(qū)域冷卻塔阻力系數(shù)試驗(yàn)與計(jì)算結(jié)果對(duì)比見表2，二者相差不大于5%，吻合較好。表2 模型試驗(yàn)與數(shù)值計(jì)算進(jìn)

26、風(fēng)口區(qū)域阻力系數(shù)對(duì)比結(jié)果填料阻力系數(shù)進(jìn)風(fēng)口區(qū)域阻力系數(shù)相差(%)試驗(yàn)結(jié)果計(jì)算結(jié)果10203036.12.4 Model validationTo do validation with the experimental results of aerodynamic characteristics of an induced draft mechanical cooling tower model, the layout drawing of the cooling tower is shown as Figure 1, Firstly, analysis the grid sensitivity

27、, then compare and analyze the results.Fig. 1 Layout drawing of the induced draft mechanical cooling tower model In the conditions of different fill resistance coefficients, the results of the comparison between experimental and computational are shown in Figure 2, Abscissa L0 / L is the relative di

28、stance from one side to the wall, V/is relative wind velocity, V is the velocity at the measure point, is the average measure points wind velocity. The results of the comparison between experimental and numerical inlet air flow state are shown in figure 3, as can be seen from Fig.3, experimental res

29、ults is consistent with the results of numerical calculation.Fig. 2 Comparison between experimental and computational fill section wind velocity distribution（a）Experimental results （b）Numerical resultsFig. 3 Comparison between experimental and Numerical inlet air flow distributionComparison between

30、experimental and Numerical cooling tower air inlet area resistance coefficient are shown in table 2，the difference is not greater than 5%，the results tally well.Table 2 Comparison between experimental and computational cooling tower air inlet area resistance coefficientFill resistance coefficientInl

31、et resistance coefficientDifference (%)Experimental resultsNumerical results1020303 計(jì)算結(jié)果及分析鼓風(fēng)式機(jī)械通風(fēng)冷卻塔不同的塔型尺寸，如填料的安裝高度、塔出口收縮段的高度、角度等，都會(huì)影響塔內(nèi)氣流阻力特性及風(fēng)速分布，本文分別研究了不同塔型對(duì)冷卻塔氣流特性的影響。鼓風(fēng)式機(jī)械通風(fēng)冷卻塔立面布置如圖4所示，塔的平面尺寸為×，風(fēng)機(jī)直徑為。HCHF圖4 鼓風(fēng)式機(jī)械通風(fēng)冷卻塔立面布置圖3 Results and analysisDifferent tower shapes for the forced draft

32、 mechanical cooling tower, such as installation height of the fill、the convergent section height and angle, will affect the tower airflow resistance characteristics and wind velocity distribution. This paper studies the influence of different tower shapes on the air flow characteristics. The forced

33、draft mechanical cooling tower elevation, tower plane size is ×, fan diameter is . The forced draft mechanical cooling tower elevation3.1 計(jì)算模型的建立及網(wǎng)格劃分流體仿真計(jì)算域范圍的選取影響計(jì)算的速度和精度，根據(jù)經(jīng)驗(yàn)，當(dāng)計(jì)算域到達(dá)一定的大小時(shí)，塔內(nèi)的流場(chǎng)就不再受計(jì)算域大小的限制。假定塔高為H，寬為W，進(jìn)風(fēng)口高為H1，經(jīng)過(guò)試算分析，計(jì)算域進(jìn)風(fēng)口上下游寬度取為3H1、寬度取為4W、高度取為2H時(shí)再增大計(jì)算域范圍對(duì)計(jì)算影響不大。數(shù)值模擬計(jì)算與計(jì)算網(wǎng)格的劃

34、分密切相關(guān)，本文進(jìn)行了網(wǎng)格相關(guān)性分析計(jì)算，結(jié)果如圖56所示。當(dāng)網(wǎng)格數(shù)量達(dá)到50萬(wàn)時(shí)，塔內(nèi)氣流特性受網(wǎng)格數(shù)量的影響已經(jīng)很小，計(jì)算區(qū)域網(wǎng)格圖如圖7所示。圖5 網(wǎng)格數(shù)量對(duì)冷卻塔阻力系數(shù)影響圖6 網(wǎng)格數(shù)量對(duì)填料斷面風(fēng)速分布影響圖7 塔內(nèi)及計(jì)算域網(wǎng)格示意圖3.1 Establishment of calculative model and mesh generationThe scale of fluid computational domain affects the calculative velocity and accuracy, based on experience, when comput

35、ational domain reaches to a certain scale, flow field in the tower is no longer limited by computational domain scale. Assume that the tower height is H, width is W, air inlet height is H1, according to the results of the trial computation, it makes little difference to increase the computational do

36、main when the length of upstream and downstream of air inlet is 3H1, the width of the whole computational domain is 4W and the height is 2H.Numerical simulation is closely related to grid partition, this paper analysis grid correlation, the results are shown in Figure 5 and 6. It is known according

37、to the two figures that the grid number has little effect on air flow characteristics in the tower when the grid number reaching 500000, computational domain grid is shown as Fig.7.Fig 5 The influence of grid number on the cooling tower resistance coefficient Fig 6 The influence of grid number on th

38、e fill section velocity distributionFig 7 The tower and computational domain grid schematic diagram 填料安裝高度對(duì)冷卻塔氣流特性影響不同的淋水填料安裝高度時(shí)，冷卻塔的阻力系數(shù)與填料斷面風(fēng)速分布計(jì)算結(jié)果如圖8和圖9所示，圖中橫坐標(biāo)HF/L為填料底至進(jìn)風(fēng)口上沿距離與塔寬之比，結(jié)果表明，填料安裝高度對(duì)整塔阻力系數(shù)影響不大，但填料安裝高度離塔進(jìn)風(fēng)口遠(yuǎn)時(shí)，填料阻力較小者風(fēng)速分布均勻性變差。圖8填料安裝高度對(duì)整塔阻力系數(shù)的影響圖9填料安裝高度對(duì)填料斷面風(fēng)速分布均勻性的影響3.2 The influence

39、of the fill installation height on the cooling tower aerodynamic characteristicsIn the conditions of different fill installation height, the computational results of cooling tower resistance coefficient and fill section wind velocity distribution are shown in figure 8 and figure 9, abscissa HF/L is

40、the distance from fill bottom to top of the air inlet divides tower width, it turns out that the bottom height of the fill has little effect on the whole tower resistance coefficient, but when fill installation height is higher, the smaller the fill resistance coefficient is ,the wors

41、e the wind velocity distribution uniformity is. The influence of fill installation height on the cooling tower resistance coefficient The influence of fill installation height on the fill section velocity distribution冷卻塔出口收縮高度對(duì)冷卻塔氣流特性的影響調(diào)整冷卻塔出口收縮高度，冷卻塔的阻力系數(shù)與填料斷面風(fēng)速分布計(jì)算結(jié)果如圖10和11所示，圖中橫坐標(biāo)HC/L為收縮段至進(jìn)風(fēng)口上沿距

42、離與塔寬之比。由圖可以看出，隨著塔出口收縮高度的增加，冷卻塔阻力系數(shù)降低，當(dāng)HC/L達(dá)到后，阻力系數(shù)變化減小，大于后基本不再變化，填料斷面風(fēng)速分布均布系數(shù)亦有相似的規(guī)律。圖10 收縮高度對(duì)整塔阻力系數(shù)的影響圖11 收縮高度對(duì)填料斷面風(fēng)速分布均勻性的影響 The influence of the outlet convergent section height on the cooling tower aerodynamic characteristicsAdjusting the cooling tower outlet convergent height, the computational

43、 results of cooling tower resistance coefficient and fill section wind velocity distribution are shown in figure 10 and figure 11, Abscissa HC/L is the distance from the convergent section to the top of the air inlet divides tower width. As can be seen from the two figures, with the increase of the

44、tower outlet convergent height, the whole cooling tower resistance coefficient decrease, when HC/, the resistance coefficient change becomes slowly, when HC/L is greater than 0.90,it's no change, fill section wind velocity distribution uniformity coefficient also has the similar laws. The influe

45、nce of convergent height on the cooling tower resistance coefficient The influence of convergent height on the fill section wind velocity distribution冷卻塔出口收縮角度對(duì)冷卻塔氣流特性的影響調(diào)整冷卻塔出口收縮角度，冷卻塔的阻力系數(shù)與填料斷面風(fēng)速分布計(jì)算結(jié)果如圖12和13所示, 圖中橫坐標(biāo)為收縮段與水平的夾角。隨著塔出口收縮角度的增加，冷卻塔阻力系數(shù)降低，但趨勢(shì)不明顯。填料斷面風(fēng)速分布均布系數(shù)基本不受塔出口收縮角度的影響。圖12 收縮角度對(duì)整塔阻力

46、系數(shù)的影響圖13 收縮角度對(duì)填料斷面風(fēng)速分布均勻性的影響 The influence of convergent angle on the cooling tower airflow characteristicsAdjusting the cooling tower outlet convergent angle, the computational results of cooling tower resistance coefficient and fill section wind velocity distribution are shown in figure 12 and fig

47、ure 13, Abscissa is the angle between convergent section and horizon. With the increase of tower outlet convergent angle, the cooling tower resistance coefficient decrease, but this trend is not obvious. Fill section wind velocity distribution uniformity coefficient is not affected by tower outlet c

48、onvergent angle. The influence of convergent angle on the cooling tower resistance coefficient The influence of convergent angle on the fill section wind velocity distribution3.5 冷卻塔阻力系數(shù)計(jì)算公式按式（2）對(duì)不同塔型尺寸的計(jì)算結(jié)果進(jìn)行分析總結(jié)，可獲得以下冷卻塔自風(fēng)機(jī)進(jìn)口到塔出口相對(duì)于填料斷面速度頭的阻力系數(shù)計(jì)算公式。公式整理時(shí)塔的出口段收縮角為27º，收縮段相對(duì)高度為0.50.92。 （4） 式中為填料

49、阻力系數(shù)；為冷卻塔淋水面積（）；為冷卻塔出口面積（）。3.5 Calculative formula of cooling tower resistance coefficient In the condition of summarizing the results of different tower shapes according to equation (2), it can obtain the cooling tower resistance coefficient calculative formula which is from tower inlet to outlet r

50、elative to the fill section wind velocity. The convergent angle is 27º, the convergent section relative height HC/L is when finishing the formula. (4) Where is the fill resistance coefficient; is tower's rain area (m2); is outlet area (m2)。4 結(jié)論本文對(duì)鼓風(fēng)式機(jī)械冷卻塔在不同填料安裝高度、不同收縮高度與角度等條件下的塔的空氣動(dòng)力特性進(jìn)行了數(shù)

51、值模擬，結(jié)果表明，填料安裝高度對(duì)冷卻塔整塔阻力系數(shù)影響不大，在填料阻力小時(shí)，安裝高度高時(shí)均勻性變差；出口收縮段相對(duì)高度越大，阻力越低，填料斷面風(fēng)速分布也越均勻，當(dāng)其大于時(shí)所獲的收益已經(jīng)很小；出口收縮段與水平夾角增大時(shí)，冷卻塔阻力系數(shù)降低，但趨勢(shì)不明顯，填料斷面風(fēng)速分布均布系數(shù)基本不受塔出口收縮角度的影響。本文還分析總結(jié)了鼓風(fēng)式冷卻塔的阻力系數(shù)計(jì)算公式，計(jì)算方法經(jīng)過(guò)類似模型試驗(yàn)對(duì)比，與試驗(yàn)結(jié)果偏差在5%之內(nèi)，可供冷卻塔設(shè)計(jì)計(jì)算參考。4 Conclusions This paper establishes a numerical model to study the aerodynamic cha

52、racteristics of the forced draft mechanical cooling tower in the conditions of different fill installation heights、different convergent heights and angles, it turns out that the bottom height of the fill has little effects on the whole tower resistance coefficient, but when fill installation height is higher, the smaller the fill resistance coefficient is ,the worse the distribution uniformity is; with the increase of the tower outlet convergent height, cooling tower resistance coefficient decrease, the fill section velocity distributi