轮式装载机动力舱热管理系统数值仿真分析

1、轮式装载机动力舱热管理系统数值仿真分析ABSTRACT：INTRODUCTION：In recent years, construction machinery manufactures have attempted persistently to deliver high engine performance and controlled climate systems. However, both attempts have encountered design hardships due to geometrical and space restrictions in the under

2、 hood compartments. 随着工程机械行业的高速发展，人们对工程车辆安全性、舒适性、节能性和环保性的要求越来越高，如今的工程机械逐渐倾向于集成化、微型化设计，导致工程机械发动机舱内空间相对狭小以及零部件安放位置比较紧凑，舱内布置多个热源与散热器,在作业过程中,经常发生动力舱内散热器模块中,相应各系统发动机冷却系统、传动油冷却系统和液压油冷却系统温度过高,造成相应系统工作不正常,影响装载机使用效率,同时对发动机造成伤害。因此，研究高效可靠的装载机动力机舱热管理方法势在必行。The aforementioned facts formed components congestions

3、in vehicles underhood compartments, and therefore creating complex airflows and difficult air paths to take place within the compartments1-3. In Ref. 1 , engine cooling performance is studied by evaluating radiator heat dissipation and Top Hose Temperatures(THT) using 1D (KULI) and 3D (FLUENT, RADTH

4、ERM) simulation codes, various design modifications in underhood area are analysed through simulations. In Ref. 2, a hybrid method is presented using the principle of flow network modeling (FNM) and computational fluid dynamics (CFD), the entired flow domain in underhood is broken into various air f

5、low passages. Ref. 3 presents an analytical methodology developed to enhance passenger cars and trucks cooling and underhood thermal management process utilizing CFD technology. Ref. 4 assessed the consequence of the architectural arrangements of electrical and mechanical components on the aerotherm

6、al behavior in the underhood compartment, evaluated the qualitative impact of each individual component on the aerothermal environment of the underhood. In Ref. 5, Coupled radiation/convection simulations are performed to obtain the complete airflow and thermal map of the engine compartment using an

7、 interior-to-boundary method wherein the need for creating a water-tight surface mesh is not a pre-requisite for volume mesh generation. Ref. 6 developed a 3D CFD program which can be used by the development engineer to analyze the performance of the vehicle cooling system, and a method to predict t

8、he coolant inlet temperature of the radiator is presented. Ref. 7 expounded many individual topics which include numerical modelling of engine cooling system, under hood air flow, heat transfer at water jacket, heat transfer at radiator and coolants after-boiling phenomenon. Ref. 8 addressed the aer

9、othermal phenomena encountered in the vehicle underhood compartment by physical analysis of the heat transfer modes in complex internal flows. Ref. 9 finished with an overview of the method to link the 1-D system thermal model and the 3-D CFD model together with validation data. Ref. 10 reported a n

10、umerical investigation of spatial optimization of heat-exchanger by acting on its positioning in the vehicles cooling module, and elucidated how to act on the different parameters influencing heat-exchanger performance in order to optimize their functioning. Ref. 11 reported velocity and temperature

11、 measurements by Particle Image Velocimetry (PIV), by Laser Doppler Velocimetry (LDV) and by thermocouples, measurements are carried out for conditions simulating both the slowdown and the thermal soak phases with the fan in operation, and different fan rotational speeds, radiator water flow and und

12、erhood geometries have been experimented. However, all these attentions are focused on automobile industry. 工程机械的散热模块工作环境与汽车有所不同。汽车的散热器往往前置于车头部位，沉入动力舱且距离进气格栅较近，进气格栅的流通面积略小于散热器的迎风面，往往采用迎风面积较大、厚度较小的散热器。而工程机械中散热器布置特征则相反，在工作时需要保持行进方向的准确性，驾驶员需要实时观察路面情况，因此动力舱安装位置不应过高，几何尺寸不宜过大，更不允许采用类似汽车那种大迎风面的布置形式，动力舱内的散热

13、器通常采用与冷却风扇居中对齐的安装方式，迎风面积通常略小于动力舱截面大小，厚度较大。两种车辆散热器的工作状态也有所不同，由于汽车在行驶中具有较高的迎风速度，冷空气受冲压作用进入散热器，风扇直径较小。压路机在作业中往往不具有较高车速，散热模块主要依靠冷却风扇形成的压差，将冷空气送入散热器，冷却风扇直径通常与散热器的迎风面高度或宽度相当。Generally, there are two main sources of energy which contribute to the cooling air flow through under hood, one is the ram air and

14、another is radiator fan. As for a vehicle, the flow rate of it is determined by both fan rotational speed and vehicle proceeding speed, for the ram air, as a result of the latter, may have a considerable contribution to the magnitude of airflow blowing in. But the mass flow rate of a loader is contr

15、olled almost merely by the rotational speed of fan. Granted that a loader has the potential to move, the proceeding speed ,no more than 10m/s, is relative lower than that of a vehicle and under working condition it maybe even lower. So we just dismiss the effect of ramp air, and define a moving spee

16、d of 1m/s to consider the movement of ambient air.Compatible researches should carry on pertaining to construction machinery field where similar thermal management challenges are confronted. Whats more, 独立散热系统，quite different from the traditional heat sink system applied in loader, is seldom studied

17、 both structurally and thermally. 独立散热系统是一种应用在装载机上的相对新型的散热系统。其特点是将全部的四个散热器布置到动力舱的后端，并在散热器与发动机之间设置隔热板，thus，动力舱被分隔为两部分：one including风扇、散热器模块 called 散热器模块housing，the other one including 发动机及其他wind stymie blocks called motor housing。独立散热系统最大特点是风扇由液压马达驱动，其优势有二：其一，液压马达的存在避免了风扇主轴与发动机的直接机械连接，发动机与风扇的距离也就不受机械

18、连接的限制了，散热器模块的布置可以远离发动机，加之隔热板的影响，因此发动机的热辐射对散热器的影响大大降低了；其二，液压马达的转速可以通过温度反馈机制调节，温度数据来自各个散热器温度传感器的监视数据，此温度数据作为反馈数据，若某一温度过高，则通过此机制提高风扇转速，反之亦然，这就使得发动机负载较高，燃油消耗较大。本文重点关注独立散热系统的设置对动力舱结构的影响and the sequential influence of 散热效率。It is imperative to conduct a thermal analysis on the relatively new heat sink syst

19、em. Thus, 本论文综合运用一维和三维仿真方法，分析了4吨位轮式装载机动力舱的空气流动特性和散热特性，综合考虑了对流和辐射对散热系统温度场的影响，并对现有的动力舱结构形式进行了改进，得到了一个more optimal cooling systems 和动力舱布置形式。2. MODELING METHODS2.1 总体研究思路（Overall research methodology）动力舱冷却系统的散热性能由冷却系统的布置形式、空气和冷却液的参数决定，因此，仿真模型需要能够预测散热器外部空气侧（air side）和内部流体侧的流场和温度场分布。目前，大部分关于动力舱热管理系统的研究都是单

20、独基于一维或三维CFD商业软件的仿真研究，conventional CFD analysis for underhood thermal management is quiet involved and time consuming because of the complex geometry and flow distributions， 单一的一维仿真又由于数据的缺乏而难以保证系统仿真的准确性。因此，本篇论文采用三维CFD仿真和一维仿真结合的方法，综合运用两者的长处，对轮式装载机热管理系统进行仿真分析，总体研究思路如图？所示。首先建立动力舱的CAD模型，并进行适当的简化；之后进行网格的生

21、成，对重要的部位进行网格的细化；前处理完成之后，将模型导入FLUENT求解器，设置边界条件和初始条件，进行流场求解和分析；然后，根据流场仿真分析得到的一些数据（比如流量、压降），建立冷却系统一维仿真模型，分析散热器外部空气侧和内部流体侧的温度场分布；最后将仿真结果与实验结果进行对比，验证仿真结果是否合理，否则，再重新对仿真参数进行调节，以期获得准确可信的仿真结果，并在此基础上对动力舱冷却系统布置形式进行一定的改进，改善冷却系统的散热效果。CAD Model of UnderhoodCAD Model of UnderhoodModel SimplificationMesh Generation

22、 (HYPERMESH)CFD Modeling and Solving (FLUENT)Pressure difference and flow rate (Post-processing)1D Modeling (KULI)Characteristics Curves (Radiator, Fan, Water Circuit, Oil Circuit, Air Circuit)Air Side and Inner side Temperature DistributionComparison with different forms of layoutImprovement therma

23、l management structural styleComparison with experimental dataEndYESNORepeat with differentsetting methods2.2 整车布局（wheel loader layout）本论文以4吨位轮式装载机为研究对象，整车外观如图1所示，主要由底盘（包括驾驶室）、工作装置、动力系统和散热系统几部分组成，其中动力系统和散热系统的总体布局如图2所示，散热系统包括发动机冷却系统（水冷却系统、空气冷却系统）、液压油冷却系统和传动油冷却系统，对应的有水散热器water radiator (RAD)、中冷器charge

24、 air cooler (CAC)、液压油冷却器hydraulic oil cooler (HOC)和传动油散热器transmission oil cooler(TOC)四个散热器。Though our main interest is focused on the underhood parts, a few of auxiliary parts are reserved because of their blockage effect. The auxiliary parts include tires, guidingroom and 工作装置。2.3 specific featrues

25、When modeling the loader, some specific features should be 重视。For unlike traditional case, 独立散热系统的动力舱分为两部分: 发动机housing、散热器模块housing，如图1所示。散热的循环系统分为内循环和外循环。内循环即散热器内冷却质的循环，冷却质包括发动机冷却水、涡轮增压器排出的高温空气、液压油及传动油。外循环即冷却空气与散热器表面及发动机外表面的对流换热。若发动机的功率和效率一定，则废热一定。废热量会在两个housing之间分配。除通过发动机的冷却水内循环外，冷却空气在两者间的流动也会影响热量

26、的分配。这种分配会造成paradoxical effect，一方面，因散热器housing内的流体比较robust，the interaction有助于发动机舱内的热量挥散出，另一方面通过发动机舱由于流入散热器舱内的流体是高温流体，这不利于散热器舱内热量的散出。The comprehensive output of the effect is hard to decide. And 一个excellent的内循环系统就是一个尽可能把发动机的热量带入散热器模块的循环系统。这除了与散热器housing的散热效率有关外还和发动机的循环系统的配置有关。我们假设内循环系统excellent。Thus，a

27、ny cooling air flowing into exchanger package housing through motor housing is dispensable. The research is concentrated in the flow patterns in exchange package housing. And it seems preferable to isolate the two housing totally. But if so, a higher resistance to cooling air, and thus a lower flow

28、rate will be encountered. To evaluate this effect practically, a case comparison is conducted. 为研究散热器舱内的流场模式，必须distinguish冷却空气的入口和出口。在风扇吸风式冷却方式情况下。散热器舱的空气入口有：机罩两侧开口、机罩上部后排开口、hiatus in chassis、 隔热板与机罩间隙。Which can be classified as legitimate ones including机罩两侧开口、机罩上部后排开口, and illegitimate one， namely

29、隔热板与机罩间隙。 For隔热板与机罩间隙在减少流道阻力，增加流量的同时是会导致发动机舱内的高温空气的流入散热器舱。我们将重点关注legitimate 入口的流量，及总流量在两类入口间的分配情况。散热器舱的空气出口即机罩的后开口，将重点研究其对散热器舱所排出的热空气流动的阻碍作用，以及其面积大小对流量大小的影响。发动机舱的空气入口如图2所示，冷空气经由底盘及驾驶室流入发动机舱。发动机舱的空气出口有两个一个即散热器舱的illegitimate入口，一个是机罩上部前排开口。需要指出的是由于模型简化的原因，许多irrelevant的缝隙已被封堵，如机罩与底盘的间隙，由于此间隙较小，不会对流场模式及流

30、量产生太大影响，故在建立模型时将底盘与机罩连为一体。对于底盘底部的处理亦如此，原本在底盘内分布有若干层的垫板及supporting board，少量空气可由板层间的间隙流入，但是the effect is negligible，所以在散热器舱区域的底盘底部， a single boarded is implemented. 上述的入口和出口是在风扇吸风冷却的情况下demonstrated 的， 若风扇冷却形式改为吹风式，则入口变出口and verse vice。3. SIMULATION3.1 网格生成（Grid generation）Hypermesh 11.0 is used as a t

31、ool for grid generation in the present geometry which applies the mesh-generating category of Boundary to Interior (B2I) wherein, a “water-tight” surface mesh is needed before the interior volume mesh can be generated. This means T-connections are excluded when performing every single CFD-tetramesh

32、operation. A “watertight” geometry model including the outer surface CAD data for the overall loader body structure and the underhood components should be constructed first. And a cubic box is created around the submodel as a virtual wind tunnel in which the streamwise direction represents the x-dir

33、ection and the vertical represents the z-direction, as it is shown in Fig . It defines a computational domain and, meanwhile, represents a real-world wind tunnel test environment. The location of the truck and the size of the tunnel assure that the results are not affected by the boundaries. Triangu

34、lar surface mesh elements derived from the CAD model which allows discretization of complex geometries while maintaining low cell counts are employed to generate the body mesh elements. An unstructured mesh size of approximately 17 million cells generated for the entire fluid flow domain. The finest

35、 elements are concentrated to the fan region and measure approximately 0.001 m. Figure 3a shows a cut section of the mesh in Z-0 plane of the vehicle and 3b shows surface mesh on various underhood components. Mesh quality has such a bearing on the simulation result that it is imperative to pay due a

36、ttention to control it. Whats more, unlike that of structure mesh which depends only on the sizes and shapes, mesh quality of fluid cells requires also the cell size gradient Ref. The more likely cell size gradient resembles velocity gradient, the more precise simulation result will be achieved. 3.2

37、 三维CFD流场模型（3D CFD Air Flow Model）Ansys Fluent 14.0 is used as a CFD simulation code for fluid flow modeling and analysis. FLUENT is a commercial software package, from Ansys software products, available for fluid dynamics simulations and quite robust in solving complicated models. The NavierStokes e

38、quations are solved through iterative procedures to satisfy mass, momentum, and energy conservation by fluent using the finite volume method. 风洞入口定义为速度入口，入口为压力出口。风扇应用mrf 模型。The fan pressure rise over the blades was obtained from experimental data and was treated as a source term in the momentum equa

39、tion. The pressure rise curve from experimentally obtained data was modeled with dimensionlessSince the fan characteristics depend on the air density in the fan blade region, the dimensionless function was correlated to the air temperature at the estimated working condition in the vehicle.散热器被定义为多孔介

40、质模型，The exchanger cores were modeled as rectangular fluid domains with empirical correlations for the airside pressure drop. Four porous zones were defined for HOC, CAC, RAD and TOC. The resistance coefficients were determined from the pressure drop curve provided by the component calorimeter test.

41、In the momentum equation, this pressure drop was treated as a source term. All the vents on hood are mesh screen zones, and we define for each of them an independent cell zone which means fluid zone enveloped by identified faces, namely the inner face, the outer face and the peripheral face. Despite

42、 the fact that we reserve both the outer and inner faces of hood, the wall thickness of hood is too little to define porous zones, since its thickness measures several millimeters while its height and width measures hundreds millimeters. Thus, we applied 多孔阶跃模型 instead. To realize this model the inn

43、er faces of mesh screen zones are endowed the wall type of interior, while the outer faces endowed多孔阶跃模型. Similarly, resistance coefficients were determined from the pressure drop curve provided by the component calorimeter test.Monitor faces definingMore than one revised is evaluated and compared i

44、n this paper. Therefore a criterion should set for comparisons and optimizations. Although the ultimate goal of this research is reduction of operating temperature on exchangers, it is both inefficiency and unnecessary to obtain the temperature data about all the studied models. As can be seen from

45、the following study, the temperature difference of a certain exchanger obtained though cooling process is bound up with its mass flow rate and the inlet temperature of the mass flow. Thus we can appraise each revised and original models based on the mass flow rate and inlet temperature of their exch

46、angers. To get mass flow rate data and speculated inlet temperature, some monitor faces should setup before calculation. Among these are the front end face of hood to monitor the mass flow rate exhausted from underhood, the lateral vents and top vents of hood to monitor the mass flow rate inhaled in

47、to under hood and the vents, formed by the gaps between chassis and insulation plate and between hood and insulation plate, to monitor the mass flow rate of relative high temperature flowing from motor housing to cooling module housing.In the computation no effort has been made to fully resolve boun

48、dary layers, instead wall functions have been used for no-slip boundaries.The computational cases presented in this paper are described in Table 1. The first case is on the present loader configuration. Thereafter, only one installation parameter is changed and evaluated at each time. And, for some

49、cases more than one installation parameter is modified relative to the basic reference case and, hence, a different reference case, namely Case REF_SP, is used in the evaluation. Each simulation has been run to convergence of mass flow through the fan. Also criteria on mass flow on mesh screens have

50、 been considered. Air Flow and Thermal AnalysisIDNameDescriptionREF1Case REFBasic reference case_2Case EXDAs Case REF but air vents on hood extended13Case PSExtended insulating plate, reaching the chassis and hood14Case P+100Insulating plate moved 100mm nearer to cooling package15Case P-100Insulatin

51、g plate moved 100mm further from cooling package16Case REF_SPA simple model with only fan and cooling model reserved-7Case F+20Fan moved 20mm nearer to cooling package68Case F+40Fan moved 40mm nearer to cooling package69Case F-20Fan moved 20mm further from cooling package610Case BLCooling pattern ch

52、anged from suction to blast 13.3 一维PTC模型（1D Power Train Cooling（PTC）Model）4. RESULTS AND DISCUSSIONFig.1and 2 show the overall velocity distribution of the loader, including both inner and outer fluid field, in the form of velocity vector where the direction of the arrows represent that of the veloc

53、ity there, the color of the arrow represent the magnitude of velocity there and the density of the arrows represents that of the nodes there. The velocity ranges of these distributions can be seen from the color-maps on the left of these figures. Threshold values of these ranges are set to obtain a

54、more illustrative figure. Regions including nodes of velocity beyond these ranges are ignored, why some regions in the exist louvers of hood abutting fan are devoid of arrows in these figures.Fig.1 is velocity distribution in perpendicular face z=0, which is the z component of central point of the f

55、an. A number of observations came out regarding the air flow behavior in the underhood region and its effects on the exchanger performance.The blockage effect of working equipment, cab, wheels and other peripheral parts can be seen conspicuously. A higher (compared to far field velocity distribution

56、) turbulent density is observed around these blockage parts. And intense vortexes due to strong turbulences have a negative effect on the flow pattern of inlet airflow. Besides, a considerable potion of kinetic energy is dissipated and altered to heat energy which aggravates local thermal condition

57、even more. The cab cause vortexes right above hood top vents which are on downstream of it. In addition, wheels and working equipment generate considerable vortexes upstream the inlet of motor housing, namely the gap between chassis and cab. Thats why blockage parts should be taken into consideratio

58、n, though they are located faraway from cooling module.Fig.1 velocity distribution on face z=0Fig.2 is velocity distribution in horizontal face y=880, which is the y component of central point of cooling fan. Blockage effect is detected from wheels on lateral inlets of hood，therefore flow pattern on

59、 the lets is worsen. The tendency of airflow inhaled into cooling module housing through lateral inlets is salient. The airflow coincides with the one inhaled from top vents and the one from gap between chase and isolation plate, thats why airflow zone between R2 exchangers. Then the blended airflow

60、 from different vents passes though two rows of exchangers, finally exhausted from exist louvers of hood. As the flow passes through the inlets the flow becomes more unstructured. For the heat exchangers are modeled as porous media, the unsteady flow becomes of a more organized character. This is du