Calculation of gas self-oscillations in low-emission combustion chambers of gas turbine power units operating on gaseous fuel

An economical calculation method for self-excitation of gas oscillations in low-emission combustion chambers of gas turbine units has been developed. The method is based on the SST SAS turbulence model and the turbulent combustion model with a modified equation for a variable degree of combustion completion. A multiplier associated with gas pressure oscillations is introduced into the source term of this equation. The tendency of the combustion chamber to excite gas oscillations is estimated by two parameters: the exponent of this multiplier (interaction index) and the logarithmic decrement of oscillation damping. When solving the problem of self-excitation of oscillations in the case of specifying a homogeneous methane-air mixture at the combustion chamber inlet, the first radial oscillation mode with a frequency of 2700 Hz appeared. In the case of separate air and fuel supply to the combustion chamber, the first longitudinal oscillation mode with a frequency of 300 Hz was excited. The use of resonant absorbers (small anti-vibration screens) made it possible to completely suppress radial oscillations.