基于流固耦合方法的柴油机排气管热机疲劳寿命研究

Thermomechanical Fatigue Life of Diesel Engine Exhaust Manifold Based on CFD-FE Coupling Method

由于高功率大缸径柴油机的排气管处于高温、高压、强冲击的工作环境,承受复杂恶劣的热机载荷,使得疲劳失效问题日渐突出。为解决工程中的排气管疲劳失效故障,基于流固耦合仿真分析的方法,研究了多通排气管在热载荷、机械载荷和热机耦合载荷三种不同条件下的疲劳损伤机理以及低周疲劳寿命。结果表明,单纯交变热载荷不足以造成排气管低周疲劳失效,交变的热机耦合载荷导致排气管寿命急剧下降,其中内壁压力和端面推力重要度分别为4.34和0.88;在排气温度不变,排气压力增大60%的高增压设计条件下,排气管的塑性应变进一步增加,疲劳寿命减小至3710次,仅为原来的29%。

Because the exhaust manifold of the high-power and large-bore diesel engine is in a high-temperature,high-pressure and high-impact working environment,it is subjected to complex and harsh thermomechanical loads,making the problem of fatigue failure increasingly prominent. To solve the exhaust manifold fatigue failure in engineering design,the fatigue damage mechanism and low cycle fatigue life of a multiple exhaust manifold under three different conditions of thermal load,mechanical load and thermomechanical coupled load are studied through the method of CFD-FE coupling simulation. The results show that the pure alternating thermal load is not enough to cause low-cycle fatigue failure of the exhaust manifold,and the alternating thermomechanical coupled load causes the exhaust manifold life to drop sharply. The importance of the inner wall pressure and the end thrust are 4.34 and 0.88. The plastic strain of the exhaust manifold is further increased,and the fatigue life is reduced to 3710 times,which is only 29% of the original,under the design condition of high boost pressure where the exhaust pressure is increased by 60% and the temperature is unchanged.