Projection Method for Irreversible Thermochromic Paint Post-Processing Using Endoscope Images on Turbine Blade Surfaces

Abstract In order to achieve higher thermal efficiency levels, gas turbines are increasingly being pushed to their performance limits. This results in high thermal loads for the turbomachinery components. Even small changes in temperature have an impact on the service life of the highly stressed components. For this reason, precise measurement of temperature values is crucial for the design process validation of gas turbines. Irreversible thermochromic paints are a suitable and proven measurement method for this purpose. The analysis of thermochromic paints is currently a manual task for experts and therefore a cost-intensive process. For this reason, the automation of thermochromic paint post-processing using colored turbine blade surfaces would be an important milestone. If it is feasible to measure and evaluate the projected thermochromic paint data, the test engine does not require disassembly for analysis, and further testing can be performed afterward. In this paper, a process chain for projecting endoscope images onto a geometric surface of a turbine blade is set up. Firstly, the alignment method is presented, which is impaired by inhomogeneous illumination, no vertical recording angles and no coded reference points. The color information is then transferred to the geometry surface and the projection result is presented. Finally, an approach that identifies temperature distributions on the 3D surface is introduced. The integration of thermochromic paint information enables a more accurate and efficient assessment of the service life and performance characteristics of the engines as well as the possibility of transfer to the design systems.