Generation and Mitigation Mechanism Studies of Nonlinear Thermoacoustic Instability in a Modelled Swirling Combustor with a Heat Exchanger

In the present work, 3D Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are performed to investigate the generation and mitigation mechanism of combustion-sustained thermoacoustic instabilities in a modelled swirl combustor. The effects of (1) swirling number S-N, (2) inlet air flow rate V-a and (3) inlet temperature T-i on the amplitudes and frequencies of swirling combustion-excited limit cycle oscillations are examined. It is found that the amplitude of acoustic fluctuations is increased with increasing S-N and V-a and decreased with the increase of T-i. The dominant frequency of oscillations is also found to increases with the increase of S-N and V-a. However, increasing T-i leads to the dominant frequency being decreased first and then increased. An alternative passive control method of installing an adjustable temperature heat exchanger on the combustion chamber wall is then proposed. Numerical results show that thermoacoustic oscillations could be excited and mitigated by setting the heat exchanger temperature to T-H. Global and local Rayleigh indexes are applied to further reveal the excitation and attenuation effects on mechanisms. The present study is conducive to developing a simulation platform for thermoacoustic instabilities in swirling combustors. It also provides an alternative method to amplify or mitigate thermoacoustic oscillations.

Automated summary

In this study, 3D URANS simulations were used to investigate the combustion-sustained thermoacoustic instabilities in a swirl combustor. The effects of swirling number, inlet air flow rate, and inlet temperature on the amplitudes and frequencies of oscillations were examined. It was found that amplitude increases with swirling number and air flow rate, but decreases with inlet temperature; dominant frequency increases with swirling number and air flow rate, but has a complex relationship with inlet temperature.