Calculation of Gas Self-Oscillations in Low-Emission Combustors of Gas Turbine Power units Operating on Gaseous Fuel

A cost-effective calculation method for self-excitation of gas oscillations in low-emission combustors of gas turbine units is developed. The method is based on the shear stress transport scale-adaptive simulation (SAS SST) turbulence model and the turbulent combustion model with a modified equation for a variable combustion completeness. A multiplier associated with gas pressure oscillations is introduced into the source term of this equation. The tendency of the combustor to excite gas oscillations is estimated by two parameters: the exponent of this multiplier (interaction index) and the logarithmic decrement of oscillation damping. Within the framework of the solution to a problem of self-excitation of oscillations in the case of a specified homogeneous methane-air mixture at the combustor inlet, there is the first radial oscillation mode with a frequency of 2700 Hz. In the case of separate air and fuel supply to the combustor, there is the first longitudinal oscillation mode with a frequency of 300 Hz. The use of resonant absorbers (small anti-oscillation screens) makes it possible to completely suppress radial oscillations.