【作者】 王飞；

【导师】 秦四成；

【作者基本信息】 吉林大学 ， 机械设计及理论， 2010， 博士

【摘要】 随着我国装载机行业的发展,装载机在国民经济基础建设中的应用更加广泛。在实际工程应用中,装载机相应系统工作温度过高、影响正常使用的问题经常发生。本文建立了ZL50型装载机动力舱虚拟风洞模型,采用CFD仿真分析与试验测试相结合的方法,对动力舱空气流动与换热规律进行研究。本文通过CFD软件求解散热器模块中管片式与板翅式散热器单元冷却空气阻力特性与换热特性,并以此作为多孔介质模型边界条件,将多孔介质模型与散热器分布参数法相结合建立散热器模块中各散热器整体计算模型。通过虚拟风洞仿真分析,研究动力舱外流场、内流场冷却空气流动规律和散热器模块换热规律。计算结果表明,冷却风扇结构特征,在散热器模块冷却空气侧入口表面,形成冷却空气速度与压力的不均匀分布,降低了散热器模块换热性能；动力舱内大量热空气回流及动力舱后部形成的热空气滞留,影响了散热器模块换热质量。通过对装载机典型工况的整车试验,试验结果与仿真结果吻合良好。在此基础上,分别从冷却空气侧与热流体侧,对动力舱散热器模块换热性能影响因素进行分析,优化出系统综合改进方案。本文创新之处在于采用CFD计算方法求解散热器单元冷却空气阻力特性与换热特性,采用多孔介质模型与散热器分布参数法相结合,求解动力舱空气流动与换热规律的新途径。更多还原

【Abstract】 Title:ZL50-Type Wheel Loader Engine Compartment Air Flow and Heat Transfer AnalysisThe wheel loader industry of China started in the sixties of the twentieth century. After about half a century of development, a large wheel loader industry with the dominant product ZL50 and annual production reached nearly 200 thousands has been established in our country. The scale of the formation of a good development has made us become one of the world’s largest countries in production and sales of wheel loader.With the development of national economy, the urban and infrastructure construction has been developed in large scale. The total demand for a variety of wheel loader is increasing. In urban construction and infrastructure construction, all kinds of operating environment are harsh and complex. The space of wheel loader engine compartment is limited and the cabin layout over several heat sources and radiators. In engineering operation, the overheating problem often occurs in those radiators used for cooling transmission oil and hydraulic oil in engine compartment. The overheating problem will cause a high temperature in system fluid within the radiator module, including water cooling radiator, transmission oil cooler and hydraulic oil cooler. It will cause system malfunction and damage to the engine.Aiming at the overheating problem of radiator module in wheel loader ZL50 engine compartment, the air-side resistance and radiator behavior of tube-fin and plate-fin radiator have been analyzed with computational fluid dynamics method and radiator distributed parameter model together. According to the whole structure of ZL50 wheel loader, the virtual wind tunnel model was built. As for radiator module of engine compartment, the inner and outer fluid field of ZL50 engine compartment and the law of air flow and heat transfer in its inner radiator module have been acquired with porous medium model and radiator distributed parameter model. The studies of this paper are as follows:1. Numerical simulation of air flow and heat transfer in radiator unitRadiator is generally symmetrical in structure. According to the property of structural symmetry, two different kinds of radiator characteristic units have been analyzed in the chapter 2 of this paper. And along the direction of cooling air flow, we have intercepted two radiator characteristic units in accordance with the symmetrical structure respectively. The characteristics of air flow resistance and heat transfer of two radiator units were solved at different wind speed entrance boundary conditions with the CFD software. As results, the velocity distribution of cooling air flow is uniform in the entrance. Because of the disturbance of fin structure on cooling air and the small size of flow tunnel, the cooling air will be accelerated in the core section of radiator characteristic unit. Due to the viscous layer effect, the velocity of cooling air in the near wall, diaphragm and fin is low. As for the temperature distribution at cooling air side, the entrance cooling air temperature distribution is uniform. The secondary heat transfer surface of radiator characteristic unit fin and cooling air were applied in the core section. And the exit cooling air temperature will reach maximum. As for the distribution of turbulence intensity at the cooling air side, the fin plays an important role on the turbulence intensity. Compared to the fin of tube-fin radiator, the cooling air flow path of plate-fin radiator fin is staggered back and forth and the cooling air flow turbulence intensity will be increased better.By calculation, the flow velocity of cooling air and the curves of pressure loss and the heat transfer factor can be acquired. The results show that the cooling air pressure loss is increased as the increase of the entrance cooling air velocity. Moreover, the shaped cooling air resistance and the radiator characteristic unit heat transfer factor are also hoisted. Finally, the heat transfer performance of radiator characteristic unit will be improved.2. The analysis of inner and outer air flow of wheel loader engine compartmentBased on the whole structure of ZL50 wheel loader, the virtual wind tunnel model of engine compartment has been constructed in the chapter 3 of this paper. In engine compartment, the radiator module is arranged in series. The first one is water radiator, and the second one is the parallel radiator for cooling transmission oil and hydraulic oil. The porous medium model is adopted by the parallel radiator in calculation. In virtual wind tunnel, the CFD simulation analysis have been made for the three classic working conditions of ZL50 wheel loader, namely shovel geotechnical condition, high speed running condition and push geotechnical condition. Due to the small change in vehicle speed, the outer flow law of engine compartment of ZL50 wheel loader in the three classic working conditions is nearly uniform in results. There is no room for air pre-intake, the cooling fan plays an important role on the inner flow law of engine compartment. Through the two sides and the bottom of engine compartment, the cooling air enter into the engine compartment and make heat transfer with radiator module, then flow out. The tangential speed of cooling fan’s blade is different along the radial direction. There exists ring distribution of velocity and pressure on the air-side section of radiator module for cooling air. The father off the center, the greater the value is. The uneven distribution of cooling air makes the heat transfer of radiator uneven. Meanwhile, due to the bottleneck effect of the cooling air exit in engine compartment, the large recirculation of hot air between the bottom, two sides and radiator module occurs. It makes the heat transfer performance of radiator module lower.3. The analysis of wheel loader engine compartment radiator thermal moduleWith the help of CFD computation method, the porous medium model and distribution parameter method, the heat transfer law of engine compartment and its inner radiator module have been studied for the three classic working conditions of wheel loader in the chapter 4 of this paper. The results show that the air is heated by muffler and engine block in engine compartment. Because of the different tangential speed on the cooling fan’s blade, the distribution of air velocity and pressure is uneven in the front of radiator module. The uneven distribution makes the heat transfer of radiator module uneven too. Meanwhile, due to the bottleneck effect of the cooling air exit in engine compartment, the large recirculation of hot air between the bottom, two sides and radiator module occurs. The re-circulated air will reflow into the radiator module and increase the air temperature of radiator module on the front-end. Finally, it will lower the heat transfer performance of radiator module.Except for hot air recirculation, the bottleneck effect will also produce a stranded region for hot air and reheat the plate-fin radiator on the back of radiator module. It will lower the ability of heat exchange for transmission oil radiator. Compared the heat transfer power of hydraulic oil radiator with its designed value, it was concluded that the unreasonable design on flow distribution of hydraulic oil in system loop makes the hydraulic oil quantity of its radiator too low to realize the effective heat transfer.4. Wheel loader test and the analysis and improvement of radiator modulebehavior. The wheel loader field testing have been proceeded for the three classic working conditions, which are shovel geotechnical condition, high speed running condition and push geotechnical condition. The entrance and exit liquid temperature of water radiator, transmission oil radiator, hydraulic oil radiator and the air temperature of radiator module and the temperature of engine block have been measured. The result shows that the simulation model is verified correct.On the condition of different cooling fan speed, the properties of resistance and heat transfer of radiator module have been acquired with simulation. It can be concluded that the pressure loss and cooling air flow increase as the cooling fan speed increases and the heat transfer power of the three radiators in radiator module will increase accordingly. The increase of cooling fan speed can improve the heat transfer ability of radiator module. However, the increase of air flow resistance and cooling fan power can occur. Meanwhile, the spacing of radiator module has an impact on the heat transfer power of radiator. In the limited spacing, the heat transfer power of the three radiators increase as the spacing increasing. when the spacing reaches a certain value, the heat transfer power will not increase effectively.According to the above simulations, it can be concluded that the hot-air recirculation, inner hot source, air pre-heating, bottleneck effect of exit structure of engine compartment, intake structure character of engine compartment and hot-air stranded region between air flow exit of engine compartment and back-end of radiator module are the factors which have an impact on the heat transfer ability of engine compartment radiator module. For improving those factors, we have compared many results each other and set up a synthesized system plan. Based on the plan, the speed of cooling fan has been matched reasonably.更多还原