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Coupled Numeric Structure Analysis

Temperature distribution on a hot body flap with and without coupled analysis

The ideal design of high temperature structures requires a coupling of different numeric analysis tools, such as in the fields of structure (FEM) and flow analysis (CFD) in order to consider the mutual influence correctly. Particularly with regard to the high temperature range where the energy transferred by radiation plays a significant role, convergence problems in the analysis occur due to the radiation intensity dependence by a factor of 4 to the power of temperature.
In addition the convectional heat transfer from the hot gas stream changes when temperature rises. In case of transient process characteristics, coupled analysis is indispensable for correct results.

For instance a coupled simulation environment has been developed within the DLR-project IMENS which is used for the coupled analysis of thermal protection systems and other hot structures that are in an interaction with a hypersonic flow field. This coupled environment enables an exchange between the CFD solver TAU and the structure analysis using the Finite Element Program ANSYS.
The coupled analysis showed in particular in structural areas with high temperature differences (local gradients) that due to thermal conduction toward the temperature gradient the initially expected temperature increase is clearly reduced.
This result was particulary of great importance with regard to the project SHEFEX and its facetted surface.
A completely different problem represents the analysis of porous materials which are penetrated by fluids like the problem in case of an effusion cooled thrust chamber structure or in general when considering actively cooled structures via transpiration/effusion. Now such cooling processes can be simulated by a software extension with the FE-program PANDAS. The model is based on continuum mechanics of multi-phase materials and permits the coupled analysis of a distortable, porous thermally loaded structure where a fluid passes through.