中英整理内陆核电厂用水系统冷却塔空气动力特性数值模拟汇总.docx

1、中英整理内陆核电厂用水系统冷却塔空气动力特性数值模拟汇总鼓风式机械通风冷却塔空气动力特性数值模拟研究赵顺安、李红莉、毋飞翔（中国水利水电科学研究院，北京 100038）Numerical research on aerodynamic characteristics of the forced draftmechanical cooling towerZhao Shunan、Li Hongli、Wu Feixiang(China Institute of Water Resource and Hydropower Research, Beijing 100038 )摘要：鼓风式机械通风冷却塔常

2、用于核电厂的重要厂用水系统，但相关设计规范并没有给出冷却塔的空气动力特性计算公式。本文采用Fluent软件对鼓风式机械通风冷却塔的空气动力进行了数值模拟计算，对冷却塔的设计布置进行了优化，分析总结给出了冷却塔阻力计算公式。结果表明，填料安装位置对鼓风式机械通风冷却塔整塔阻力影响不大，但会影响填料断面风速分布均匀性，填料安装高度越低，风速分布越均匀；出口收缩段的高度越高，整塔阻力越小，风速分布越均匀；出口收缩段与水平的夹角越大，整塔阻力系数越小，但变化趋势不明显，收缩角基本不影响填料断面风速分布均匀性。关键词：鼓风式冷却塔；塔型；阻力系数；风速均匀性Abstract: The forced dr

3、aft mechanical cooling tower 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

4、 cooling tower, and optimize 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 unifor

5、mity of the fill section, 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

6、whole tower resistance 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研究背景内陆核电厂的重要厂用水的水量不大，但

7、却影响核电厂的安全。鼓风式机械通风冷却塔能较好地适应核电对安全性和抗震性能的要求而常被内陆核电厂采用。鼓风式机械通风冷却塔不仅在通风方式上有别于常规的抽风式机械通风冷却塔，在塔型结构布置上也有明显差异。我国的相关设计规范和资料对鼓风式机械通风冷却塔没有明确的设计计算方法15。为了解塔内气流特性并对塔型进行优化，需要通过相关的研究来确定其空气动力特性。通过物理模型试验来研究冷却塔空气动力特性是一个十分有效的手段，但是由于鼓风式机械通风冷却塔模型本身的复杂性及系统试验的塔型的变化，使模型试验研究工作量和投资都很大。本文利用Fluent软件建立鼓风式机械通风冷却塔空气动力计算的数学模型，经过与试验结

8、果对比验证，确定模型参数和网格数量。研究了不同塔型条件下塔内气流分布及阻力特性，最终分析总结出了鼓风式机械通风冷却塔的阻力计算公式以及塔型与配风均匀性的关系。阻力系数计算公式与试验结果相比偏差小于5%，可为设计提供参考。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 coo

9、ling tower can satisfy 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

10、 also has distinct difference in tower shape and structure layout. Chinas 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, its necessary

11、to do some relevant research to realize the aerodynamic characteristics. Its 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 models complexity and variability, the workload of

12、experiment 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 stu

13、dies 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 resistanc

14、e coefficient and the experimental results is less than 5%, it can provide a reference for design.2数学模型及计算方法2.1 空气流场控制方程塔内外流场为等温、不可压流动，其控制方程包括连续方程、动量方程，并选用k-双方程湍流模式对方程进行封闭，各方程可写为统一形式：()（1） + V=+S t式中：为空气密度，kg/m；为空气流速，m/s。各控制方程的变量、扩散系数项与源3项S如下表1。表1 控制方程中各变量代表参数其中生成项Gk=t(uiujui；为空气分子粘性系数；p为压力；t为紊流粘性系+

15、)xjxixjk2，C为经验常数；k和分别为k和的紊流数，由动能k和紊动耗散率求出：t=C普朗特数。 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 k- two-equation turb

16、ulence model, these equations can be written as a unified form:()+ V=+S t (1)Where: is air density, kg/m3; V is air velocity, m/s. All governing equations variable、diffusion coefficient term and source term S are shown as Table 1 below.Table 1 , and S of every governing equationGenerated itemuiujuiG

17、k=t(+)xjxixj, is viscosity coefficient of the airmolecules; p is pressure, Pa; t is the turbulent viscosity coefficient, which is can becalculated by the turbulent kinetic energy k and dissipation rate : an empirical constant;2.2 边界条件t=Ck2,C isk and are turbulent Prandtl number of k and .底部为固壁无滑移边界条

18、件，四周及顶部采用压力出口边界条件，塔壳采用固壁边界条件。进风口及塔的出口都设置成内部边界；填料区域设置成多孔介质边界条件，并根据实测填料阻力系数设置各方向阻力系数；风机采用Fluent风扇边界条件，也可采用第一类边界条件。2.2 Boundary conditionsThe bottom of the computational domain is solid wall boundary condition with no-slip, all around and top is pressure outlet boundary conditions, the tower shell is s

19、olid wallboundary 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 in each direction; the FLUENT fan model is used to simulate the f

20、an of the tower, first boundary condition can also be used.2.3 冷却塔阻力系数及风速分布均匀性计算鼓风式机械通风冷却塔，气流经由风机鼓入塔内，依次经过塔进风口，雨区、填料等，并经由出口排入到大气中，气流经过各部分的阻力为该区域前后断面的全压差，一般表示为阻力系数与填料断面平均气流速度头之积：P=V （2） 232f式中P为气流经过某区域前后断面的全压差（Pa）；为空气密度（kg/m）；Vf为填料断面平均风速（m/s）。填料断面处风速分布状况影响冷却塔的热力特性，一般将填料断面风速分布均匀性作为一个设计指标，用风速分布均布系数表示:=

21、(Vi/Vf-1)2n （3）式中为填料断面风速分布均布系数；Vi为填料断面各点风速（m/s）；n为风速统计点的个数。2.3 Computational methods of the cooling tower resistance coefficient and wind velocity uniformityFor the forced draft mechanical cooling tower, airflow is blown into the tower by the fan, sequentially through the tower inlet, rain zone, fil

22、l 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: Vf P= (2) 2Where P is the pressure loss of the region（Pa）; is a

23、ir density（kg/m3）; Vf 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 design index, it can be expre

24、ssed with a velocity distribution uniformity coefficient: 2=(Vi/Vf-1)2n （3）Where is the velocity distribution uniformity coefficient; Vi is the velocity at the measure point in the fill section（m/s）; n is the velocity statistical points number.2.4 模型的验证对已具有试验结果的某抽风式机械通风冷却塔的空气动力特性模型试验作对比验证计算，冷却塔如图1示，

25、首先对冷却塔进行网格的敏感性分析，然后再将计算结果进行对比分析。 风机6风机进口过渡段收水器配水装置填料支撑结构图1 抽风式机械通风冷却塔模型试验布置示意图不同填料阻力条件下模型试验实测与计算结果对比如图2所示，图中横坐标L0/L为距其中一侧塔壁的相对距离， V/V 为相对风速，V为测点风速，V 为测点风速的平均值。进风口气流流态作对比如图3所示，从图中可以看出，试验结果与数值计算结果规律较为一致，吻合良好。图2 试验与计算填料断面风速分布对比（a）模型试验结果 （b）数值计算结果图3 试验与计算进风口上沿气流流态分布对比进风口区域冷却塔阻力系数试验与计算结果对比见表2，二者相差不大于5%，吻

26、合较好。表2 模型试验与数值计算进风口区域阻力系数对比结果2.4 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 isshown as Figure 1, Firstly, analysis the grid sensitivity, then compare and ana

27、lyze the results. FanDrift eliminatorFig. 1 Layout drawing of the induced draft mechanical cooling tower modelIn 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 dista

28、nce from one side to the wall, V/V is relative wind velocity, V is the velocity at the measure point, V 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 re

29、sults is consistent with the results of numerical calculation.Fig. 2 Comparison between experimental and computational fill section wind velocitydistribution（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 arearesistance coefficient3 计算结果及分析鼓风式机械通风冷却塔不同的塔型尺寸，如填料

31、的安装高度、塔出口收缩段的高度、角度等，都会影响塔内气流阻力特性及风速分布，本文分别研究了不同塔型对冷却塔气流特性的影响。鼓风式机械通风冷却塔立面布置如图4所示，塔的平面尺寸为9.0m9.0m，风机直径为6.0m。图4 鼓风式机械通风冷却塔立面布置图3 Results and analysisDifferent tower shapes for the forced draft mechanical cooling tower, such as installation height of the fill、the convergent section height and angle, wi

32、ll 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 draft mechanical cooling tower elevation is shown as Fig.4, tower plane size is 9.0m9.0m, fan diameter is 6.0m. Air outletWater distribution systemAir