发动机排气歧管热负荷数值模拟

某发动机运行期间，由于不合理的结构设计导致排气歧管关键部位的热疲劳失效，为此采用CFD技术模拟排气歧管工作时的外流场；通过热力学计算得到排气歧管的入口和出口边界条件。计算排气歧管的三维瞬态内流场；将内外流场计算的等效传热边界条件影射到排气歧管的内外表面生成传热边界条件，计算出结构温度场；将固体边界的温度作为流场边界条件重新进行内外流场计算，反复迭代多次，最后，求解结构的热应力．对原方案提出了改进意见，结构改进后，排气歧管热疲劳失效得到排除．

Numerical simulation of thermal loads for engine exhaust manifold

The thermal fatigue failure of an engine exhaust manifold happened design during its working because of the incorrect structure.In the paper,the computational fluid dynamic(CFD) technology was employed to calculate the external fluid of the exhaust manifold.The 3-D transient internal fluid of the exhaust manifold has been simulated with the inlet and outlet boundary conditions calculated by the thermodynamics.The heat transfer boundary conditions of the structure were gotten by mapping the time-averaged equivalent CFD boundary conditions on the interior and exterior surfaces.The initial temperature field of the exhaust manifold was calculated with the former boundary conditions.Then,the surface temperature of the structure is used as the CFD boundary conditions and the fluid field is calculated again.This iterative analysis was done several times.At last,the thermal stress of the exhaust manifold was calculated and the original exhaust manifold was improved according to the results.The thermal fatigue failure of the new exhaust manifold was eliminated.