【作者】 李向阳；

【导师】 周以齐；

【作者基本信息】 山东大学 ， 机械工程（专业学位）， 2015， 硕士

【摘要】 目前国内推土机散热系统的传统设计以经验方法为主,适用于简单散热系统,但是难以满足日益复杂的现代推土机产品设计要求。计算流体动力学(CFD)方法可以较好的展现推土机机舱内影响传热的温度、流速、压力等物理量的变化情况,本文研究了基于CFD的发动机舱热管理系统,建立了机舱数值计算模型,分析确定了CFD计算边界条件和求解策略,进行了流场和温度场仿真计算和分析,得出了发动机部件表面温度过高和风扇与散热器距离偏近的结论,指导结构设计改进的工程实践,并完成了试验验证。研究工作主要包括以下方面：建立了某型推土机散热系统主要部件的三维几何模型,分别完成了发动机机体、排气后处理器、空滤器等部件的几何模型简化；风扇、散热器等关键部件的精确几何模型。模型导入和网格划分采用HyperMesh软件,对于风扇和散热器,进行了小尺寸网格细致划分,网格形式为非结构化的四面体网格单元。选择FLUENT作为求解器,计算模型为κ-ε模型,设定边界条件时,根据样机测试情况进行了修正。求解采用有限体积法对流体偏微分方程进行离散,利用求解压力关联方程的半隐式算法(SIMPLE)对机舱内的流动与传热方程完成了数值计算。仿真计算结果以速度矢量图和温度梯度云图输出。通过对计算结果结合产品设计参数分析,并考虑了实施改进的工程要求,提出影响该推土机散热性能的两个关键因素：(1)发动机舱内存在不合理的高温分布区域,这些高温表面导致散热器入口处空气温度升高；(2)风扇与散热器距离偏小,造成风扇气流紊乱,导致风速降低,散热效率下降。针对CFD仿真分析发现的问题,对发动机舱进行了整改：(1)更换轴向尺寸更短的风扇液压马达,增大风扇与散热器距离,以降低风扇紊流,提高通过散热器的风速；(2)对排气管和涡轮增压器用铝箔隔热板进行了隔热处理,以降低机舱内高温热辐射,降低散热器入口气流温度。然后,对改进后的车辆进行了实测验证,其最低环境适应温度为46.2℃,达到了散热系统的设计要求,也证明了本文方法的有效性。本文采用CFD方法对推土机散热系统进行分析并改进设计,是国内推土机研发领域的一次有益尝试,验证了其在推土机热管理系统优化中的作用,对今后的产品研发有一定的工程参考价值。更多还原

【Abstract】 Currently, the main method of the domestic tractor cooling system designed by experience is difficult to meet the increasingly complex requirements of modern bulldozers product design. Computational fluid dynamics (CFD) method can better analyze the inside changes of underhood temperature, flow rate, pressure and other physical quantities of the bulldozer. Based on the CFD method, this paper studies the bulldozer’s underhood thermal management, the establishment of a numerical model of the underhood and analyzes the CFD boundary conditions identification, solving strategy, the flow field and temperature field simulation and analysis, and makes the conclusion of that the surface temperature of the engine components is a litter higher and the fan is partial close to radiator. This findings can be used to guide the structural design and improved engineering practices as well as completed the experimental verification.Research work mainly includes the following aspects:A three-dimensional geometric model of bulldozer’s main components of the cooling system was established, the geometric model simplification of the engine block, air filter, after treatment and other components are completed; the precise geometry models of the fan, radiator and other key components the affect the thermal performance. Model import and meshing software using HyperMesh, which the fan and radiator is divided into small dimension meticulous grid with the grid in the form of unstructured tetrahedral grid cells.FLUENT is selected as a computational model solver, the boundary conditions are is corrected by prototype testing data using the κ-ε model when it is set. SIMPLE algorithm is used to solving the discrete fluid partial differential equations of flow and heat transfer underhood and complete numerical calculation. The simulation results are showed by speed and temperature gradient vector cloud graph.By combined analyze the calculation results and the product design parameter, and taking into account the implementation of improved engineering requirements, two key factors affecting the thermal performance are proposed:(1) high-temperature engine compartment unreasonable distribution areas, which leads to air temperature rise at the radiator inlet; (2) the distance between the fan and the radiator is too small, which resulting in fan turbulence and decrease the wind speed and cooling efficiency.After CFD simulation analysis for the problem, the rectifications to the engine compartment are:(1) the distance between the fan and the radiator is too small, which result in the disorder of the fan flow and decrease the wind speed and cooling efficiency; (2) there exist unreasonable high temperature distribution area in the underhood, this high temperature surface lead the air temperature raise of the radiator’s inlet.For the problem of CFD simulation analysis, the unerhood is certificated (1) replace the fan hydraulic motor with shorter axial dimension, increase the distance between the fan and the radiator to reduce fan turbulence and increase wind speed pass the radiator; (2) The heat insulation treatment of the exhaust pipe and the turbocharger is processed by aluminum foil insulation board to reduce the high-temperature thermal radiation inside the underhood and decrease the airflow temperature of the radiator inlet. And then, test and verify the vehicle after improvement, the LAT is 46.2℃, which is not only meet the design requirements of the cooling system, but also demonstrate the effectiveness of the paper method.This article adopts the CFD method to analyze and design improvement, which is a beneficial attempt. The result verified the effect of this method in optimization of the bulldozer thermal management system, which has certain engineering reference value in the future product research and develop.更多还原