Thermal Analysis of a Wind Tunnel Model with an Integrated CFRP-Heating-Layer

Kurzfassung

This report contains basic information on the new TSP-insert with an integrated CFRP heating, an exchangeable part of the wind tunnel model 1000 mm-profile for the application of TSP-technique (compare to figures 1.1 and 2.1). Aside the documentation of the design and manufacturing process of the TSP-insert the focus of this report is set to the thermal analysis of the wind tunnel model. Since the inhomogeneity of surface temperature distribution is a common problem for the application of thermographic methods, the thermal behaviour of the model is a main aspect of its design. The estimation of the heat transfer needs to be accounted in the conceptual design and the embodiment design phases. To approach this matter, a calculating method was developed and evaluated on the case of the 1000 mm-profile and the TSP-insert 3. The calculating method is based on a computer aided thermal FEM-analysis on bar-shaped model sections. Therefore the sections are chosen in the way to represent the variations in model structure ([2]). The effectivity of this method was investigated by comparing the results to FEM-analysis on bigger model sections (i.e., slice-shaped sections). Though, analysing bigger model sections reveal a more detailed view of heat transfer and therefore may show surface temperature deviation that is not detectable on bar-shaped model sections, it is very time consuming. The general temperature distribution through the model does not provide significant difference in results. To evaluate the prediction of the thermal behaviour of a model via FEM in general, the calculated results were compared to experimental data from model testing. The testing conditions in the wind tunnel and in the laboratory were taken into account by documenting the surface temperatures from TSP-data and thermocouples integrated within the model. Each measurement obtained at least 30 s of heating process at a defined heating power. The TSP-results reveal about 20% to 30% higher surface temperatures than predicted by FEM. Further investigations reveal that the temperature measured with thermocouples differs significantly from TSP-results due to the way they were integrated into the TSPinsert. The surface temperature variation of the FEM-results is observed when varying the thermal parameters of the materials and convection. Hence, the experimental thermal property values of used materials and flow conditions are usually unknown and have to be estimated, a deviation to experiments has to be expected and accounted for during model design. However, the FEM-analysis on bar-shaped model sections has proven to be a fast way to estimate the electrical power of the heating layer. To approach the possible temperature deviation between the calculation and reality, an operation range according to possible power variation has to be provided for the heating layer.