A Research on Coupled Transient Analysis of Thermal Flow and Thermal Stress 2005-01-0516

In SAE paper 2004-01-1345, author focused on how to use a steady state temperature result obtained by a CFD analysis to conduct a thermal-stress analysis easily with 3 data transfer methods (Direct Conversion Method, Surface Mapping Method and Volume Mapping Method). The advantage and disadvantage of the 3 methods were compared in that paper and a steady state analysis of an engine exhaust manifold was used to show the accuracy, flexibility, efficiency and practicality.

In this paper, how to simplify data transfer in a transient coupling is introduced. In transient couplings, 3 troublesome operations always happen. They are 1) multisteps coupling, 2) change of element from low to high order, and 3) estimation of mid node temperature loads of high order elements. In this paper, CFD (Computational Fluid Dynamics) software adopted is SC/Tetra [1], which generates hybrid mesh consisting of tetrahedron, hexahedron, and prism as well as pyramid elements. Meanwhile, structure analysis software used in the study is NASTRAN and ANSYS, in NASTRAN second order tetrahedron or second order hexahedron must be used independently. So in the typical case, the sequences normally are: generating only tetrahedrons in solid part in CFD mesh, and then at every time step, transferring solid part temperature result of CFD to structure elements, executing thermal conduct analysis for getting mid node temperature loads and at last defining constrain conditions and performing thermal stress analysis. It is of great significance to simplify all these operations by preparing an input file as explained in the following paragraphs. Further more, author shows how to choose a few steps of transient temperature results as the loads of thermal stress analysis from a long list of CFD transient results to estimate the local maximum transient thermal stress. In this paper a T pipe and an exhaust manifold are used to describe simplification of data transfer procedures.