Vortical dynamics and acoustic response in gas-turbine swirl-stabilized injectors

The vortical flow dynamics and acoustic response of a gas-turbine swirl-stabilized injector are investigated by means of a large-eddy-simulation (LES) technique. The flow passes the injector through three radial swirlers, which are counter-rotated with each other. The formulation includes Favre-averaged mass, momentum, and energy conservation equations in three dimensions. Several instability modes with well-defined frequencies, such as vortex breakdown and Kelvin-Helmholtz instabilities as well as their interactions, are observed in the flowflelds. The method of proper orthogonal decomposition (POD) and spectral analysis is employed to identify the complex flow structures and several dominant frequencies in various regions. The acoustic response of the injector to imposed oscillations at the inlet is also studied over a wide range of frequency. Results show that external forcing has minor effects on the mean flow properties due to the broadband characteristic of turbulence. However, the instantaneous mass flux distribution at the injector outlet depends on the frequency of external excitation although the vortex breakdown is not sensitive to the imposed excitation in the current study. The radius of the central toroidal recirculation zone (CTRZ) varies during externally excitation and is out of phase with the overall mass flow rate at the injector outlet.