基于流固耦合方法排气歧管热机械疲劳分析

Exhaust Manifold Thermal-Mechanical Fatigue Analysis Based on CFD-FEA Coupling Method

柴油机功率的不断提升,排气温度也相应升高,排气歧管须承受更高的热负荷,从而可能导致其热机械疲劳失效。在设计初期阶段可通过计算机辅助工程(CAE)分析工具执行一系列虚拟模型仿真验算以验证设计方案的可行性和潜在风险,而非花费高额成本和大量时间针对实际样品进行测试验证。采用瞬态传热计算流体动力学(Computational Fluid Dynamics,CFD)分析和实体壁面温度相映射的方法模拟排气流经排气歧管时流动分离情况,经CFD和有限元分析(Finite Element Analysis,FEA)之间的耦合迭代后,根据热机械计算结果,即温度场、应力和塑性应变参数监测歧管结构设计缺陷,然后选择合适的材料属性和评估关键位置潜在开裂风险,最后依据各方案计算结果制造出排气歧管样件,在试验台架上进行整机耐久性测试,试验中未出现开裂失效,研究结果表明采用热机械疲劳分析方法可有效预测排气歧管疲劳潜在失效并为结构设计变更提供指导。

The increased exhaust temperature due to bringing up diesel engine power causes higher thermal load in an exhaust manifold,and then possibly leads to the risk of thermal-mechanical fatigue. In the initial stage of design,compared with physical prototypes,a series of virtual model verifications with modern analytic tools seem to be cost effective and timely manners. The phenomenon of exhaust gas flow separation through tailpipes was analyzed using transient CFD heat transfer and solid wall temperature mapping methods. The structural design defects were possibly detected according to the results such as temperature field,stress field and plastic deformation parameters after several iterations of CFD and FEA simulations. The appropriate material characteristics were chosen and the cracking risk was evaluated at a critical position of exhaust manifold. Finally,a physical prototype of exhaust manifold was fabricated and validated on a test bench based on the calculated results. There is no crack failure occurred for this exhaust manifold prototype during the entire durability test. The application of thermo-mechanical coupling can be qualified to efficiently predict fatigue failure of exhaust manifold.