Development of 1-D model for swirl decay rate inside annular swirl injectors*

Many gas turbine combustors use swirls to generate a central toroid recirculation zone (CTRZ) for flame stabilization. The characteristics of CTRZ can be predicted using the swirl number at the nozzle. We propose a new ODE-based model to predict the axially varying swirl number inside an annular swirl injector with varying cross-sectional area. Wall shear stress and turbulent viscosity are modeled by applying empirical correlations to include viscous diffusion and turbulent dispersion effects. An approach to apply the proposed model to a flat-vane axial vortex generator was developed for practical applications. The proposed model was verified by 3-D simulations for various vortex injectors. The results of the proposed model show good agreement with the simulation results. For a swirl-stabilized burner, the predicted swirl number and CTRZ are validated, which confirms the importance of the swirl number and accuracy of the proposed model. A comparison is made with an inviscid model to identify conditions where the proposed model is relativey more useful.