RANGA-DINESH, K.K.J....et al., 2010. Modelling of instabilities in turbulent swirling flames. Fuel, 89(1), pp. 10-18.
A large eddy simulation based data analysis procedure is used to explore the
instabilities in turbulent non-premixed swirling flames. The selected flames known as
SM flames are based on the Sydney swirl burner experimental database. The
governing equations for continuity, momentum and mixture fraction are solved on a
structured Cartesian grid and the Smagorinsky eddy viscosity model with dynamic
procedure is used as the subgrid scale turbulence model. The thermo-chemical
variables are described using the steady laminar flamelet model. The results show that
the LES successfully predicts the upstream first recirculation zone generated by the
bluff body and the downstream second recirculation zone induced by swirl. Overall,
LES comparisons with measurements are in good agreement. Generated power
spectra and snapshots demonstrate oscillations of the centre jet and the recirculation
zone. Snapshots of flame SM1 showed irregular precession of the centre jet and the
power spectrum at a downstream axial location situated between the two recirculation
zones showed distinct precession frequency. Mode II instability defined as cyclic
expansion and collapse of the recirculation zone is also identified for the flame SM2.
The coupling of swirl, chemical reactions and heat release exhibits Mode II
instability. The presented simulations demonstrate the efficiency and applicability of
the LES technique to swirl flames.