Modeling Swirl Decay Rate of Turbulent Flows in Annular Swirl Injectors

초록

Gas turbine combustors often use swirling flows to generate central-toroidal recirculation zones for flame stabilization. The characteristics of a central-toroidal recirculation zone can be predicted using the swirl number from a nozzle. We aim at developing a new ordinary-differential-equation-based model of the swirl number for annular swirl injectors with a variable cross-sectional area. A one-dimensional model for mean azimuthal velocity is derived using a simplified momentum conservation law. To include the effects of viscous diffusion and turbulent dispersion, the wall shear stress and turbulent viscosity are modeled by adapting empirical correlations. An approach to couple the proposed model to a flat-vane axial swirl generator is developed for practical application. The proposed model is validated with computational fluid dynamics simulations for various swirl injectors. The results from the proposed model show overall good agreement with simulation results. For a swirl-stabilized burner, the predicted swirl number and formation of a central-toroidal recirculation zone are compared using flow residence time and flammability limits, which confirms importance of the swirl number and accuracy of the proposed model. Effects of primary nondimensional parameters are investigated. Also, a comparison with an inviscid model is performed to identify the conditions in which the viscous effect is important.

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