Experimental Study of Wall Temperature Effect on Thermoacoustic Instabilities in Annular Combustor

Based on an integrated annular combustor-turbine experimental platform，the effects of wall temperature on thermoacoustic instability were experimentally studied in a fixed case with an equivalence ratio Φ=0.82 and a combustion power P=15.5kW. Compared with the typical independent annular combustor test，the outlet with the component of the turbine guide vane in this paper provided a more similar matching to an actual engine with a more consistent thermoacoustic environment and heat capacity. In the experiment，mode switching between different thermoacoustic modes was captured，and the corresponding modal frequencies and amplitudes greatly changed with the increasing wall temperature. Six typical state points were selected to analyze the flame dynamics and acoustic characteristics. The dynamic modal decomposition results based on the flame high-speed image sequences were compared with the photomultiplier tube signals and the acoustic pressure signals at different azimuth angles for each state point. The experimental results showed that even under the condition of a fixed combustion power and equivalent ratio，the dominated mode was changing due to the wall temperature effect：from a Helmholtz mode to a 1/4 wave longitudinal mode，to an azimuthal standing wave mode，and finally to an azimuthal spinning wave mode. The azimuthal modes acted as the standing-spinning mixed mode with fat-tailed distributions of the spin ratio in the beginning and then transformed into a counterclockwise spinning mode with relatively concentrated distributions of the spin ratio. © 2022 Journal of Propulsion Technology. All rights reserved.