DOI: 10.1615/ICHMT.2009.TurbulHeatMassTransf
ISBN Print: 978-1-56700-262-1
ISSN: 2377-2816
Analysis of vortex breakdown from conical burners using a stream function formulation and Large Eddy Simulation
要約
Vortex breakdown of the flow through a conical swirler is studied here with an inviscid stream function method and Computational Fluid Dynamics. Both Reynolds Averaged Navier-Stokes (RANS) k - ε and Large Eddy Simulation (LES) models are considered. The stream function study is based on the analytical solution of the Long-Squire equation with an upstream generating vortex of the Rankine type. This transforms through a contraction to a vortex with characteristics similar to the one discharging from conical swirlers. Quasi-1D solutions of the Long-Squire equation are obtained across an expanding duct in terms of the in flow swirl number and the downstream duct maximum cross sectional area. It is shown that the sensitivity of the mean axial position and shape of the Central Recirculation Zone (CRZ, due to vortex breakdown) to variations in the in flow swirl number increases close to the conditions where vortex breakdown takes place at the maximum cross section. Such sensitivity is seen also in experiments and Computational Fluid Dynamics results. The standard RANS k - ε approach however largely overestimates the size of the rotational part of the vortex produced by the swirler and is totally unable to capture the changes in shape and position of the CRZ. Large Eddy Simulation captures instead the correct behavior of the vortex breakdown phenomenon.