Stopping thermoacoustic oscillations with double-tube coupling

Gas-turbine design needs to take into account large-amplitude thermoacoustic oscillations, which potentially causes severe structural damage to the combustors. Hyodo et al. explore a method called double-tube coupling for passively controlling self-sustained periodic oscillation in combustion systems.

Previous research has demonstrated that a time-delay coupling of two oscillators can lead to amplitude death, where the non-oscillating equilibrium state is stabilized by reducing the oscillation amplitude. To explore amplitude death via delay coupling in a thermoacoustic system, the researchers designed an experiment using a prototypical combustion system known as a Rijke tube oscillator that consists of a burning flame inside a resonance tube.

Delay coupling was achieved by connecting two Rijke tube oscillators with cylindrical tubes whose length and cross-section corresponds to the delay time and coupling strength. They also tested the effects of using one versus two connecting tubes to introduce the mutual interaction between the oscillators. Both led to the suppression of oscillations, but compared to single-tube coupling, double-tube coupling reduced the tube diameter necessary for stopping the oscillations from 25 mm to 8 mm.

Hyodo et al. found that the method was universal in that it also effectively stopped oscillations in a different thermoacoustic system without a burning flame. The results have important implications for the applicability of tube coupling in the combustors of gas turbine engines, with an expected increase in operation safety and lifetime. In terms of future work, the researchers would like to find a way to accurately predict the frequency and intensity of the oscillations before they happen.

Source: “Suppression of Rijke tube oscillations by delay coupling,” by H. Hyodo, M. Iwasaki, and T. Biwa, Journal of Applied Physics (2020). The article can be accessed at http://doi.org/10.1063/5.0012105 .