DOI: 10.1615/ICHMT.2009.TurbulHeatMassTransf
ISBN Print: 978-1-56700-262-1
ISSN: 2377-2816
Robust outflow boundary conditions for strongly buoyant turbulent jet flames
SINOPSIS
Direct numerical simulations of turbulent jet flames tend to show large buoyancy-driven vortical structures as the distance from the nozzle exit increases. These vortices may lead to numerical instabilities at the outflow boundary when using standard outflow boundary conditions. Previously proposed approaches such as extending the computational domain or perfectly matching layers are mostly computationally expensive or laborious to implement. The present work proposes as an alternative a selective increase in viscosity close to the outflow boundary, based on a Smagorinsky type eddy-viscosity model. The approach is tested in a direct numerical simulation of a strongly buoyant, lifted jet flame. A uniform, steady-state flamelet solution is imposed to model the hydrodynamical effects of the flame. The present concept is proven to be computationally efficient approach, which impedes the growth of numerical instabilities by adding only insignificant amounts of viscosity, thus keeping upstream effects as small as possible.