Aerospace (Apr 2023)
The Impact of Temperature on the Surface Colour of Gas Turbine Blades Heated in the Presence of Kerosene
Abstract
The reliability and operational safety of an aircraft engine gas turbine are extremely important in terms of its operation. In the course of operation, these turbines undergo complex thermal, mechanical, aerodynamic, and chemical exhaust gas loads. Due to such a load, particularly acting upon the rotor blades, they undergo various damages. Therefore, the maintenance processes continuously strive for enhancing diagnostic methods in order to improve the sensitivity and reliability of damage identification. The basic diagnostic method is a visual one, supported by an optoelectronic device. It only enables determining the fact of a damage, e.g., mechanical, thermal, or chemical. The turbine blade material degradation degree is very difficult to assess in a nondestructive manner in the course of engine operation. No objective, and yet nondestructive, diagnostic method enabling the assessment of blade alloy structural changes has been developed so far. Therefore, a thesis was put forward that it was possible to apply the visual method and correlate its results with the results of gas turbine blade microstructural change tests, which would enable detecting early damage phases and assessing their fitnesses. The tests were conducted with the laboratory method. The authors received new blades of the SO-3 aircraft gas turbine engine made of the EI-867 WD alloy and then subjected them to heating in a laboratory furnace, over a temperature range of T = 1123–1523 K, in increments of 100 K. Cooling took place in the furnace. Prior to and after heating, the blades were subjected to visual testing. Blade surface colour is a diagnostic symptom which indicates a change in the blades’ technical condition. The images were analysed using software developed for the MATLAB environment. The extracted surface image features are presented in the form of brightness distribution histograms for individual colour components RGB(red, green, and blue) and grayscale Sz. Histogram parameters — average value, standard deviation, maximum value and its position — were calculated. In consequence of conducted studies, it was concluded that an increase in blade heating temperature entailed changes in individual RGB colours and the grayscale (Sz) of their surface images, which indicate the overheating intensity.
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