Large eddy simulation of turbulent unconfined swirling flows

Swirl stabilized flames are common in many engineering applications and modeling of such flames is particularly difficult due to their recirculation and vortex characteristics. Most standard approaches such as k-e and Reynolds Stress models based Reynolds averaged Navier-Stokes (RANS) equations which work very well in other situations fail to perform well in high swirl recirculating flows. In this study a recently developed large eddy simulation (LES) code has been applied for the prediction of non reacting swirling flows experimentally tested by Al-Abdeli and Masri [1]. For the sub-grid scale closure, the localized dynamic Smagorinsky eddy viscosity model is used. Predicted results are compared with experimentally measured mean velocities, rms fluctuations and Reynolds shear stresses. The agreement between predictions and experiments are very good at most axial and radial locations, although some discrepancies exist at certain locations downstream from the burner exit plane. It is observed that great care has to be taken over the boundary conditions specification for the LES simulation of high swirl intensity recirculation flows.