Simulation of Aerodynamics and Combustion in Open Swirl Flow

Flame stabilization by swirl is a common feature of many combustors. While most of the swirl combustors are enclosed, there have been relatively few studies of open swirl-stabilized flames. In the current study, an open swirl-stabilized turbulent premixed flame is studied numerically. The purpose of this work is to obtain a better understanding of the flame properties by simulating the flow field, combustion and heat transfer. Spalding’s stretch-cut-slide model is extended to determine the mixing controlled fuel burning rate per unit volume, Sfu,T , which is defined by           + ∂ ∂ + ∂ ∂ − = o L o fu fu,T /l S x v y u 5 . 0 i M , M min ñ S 2 . The results are comparable to previous studies. Intense combustion occurs in a narrow region. A stationary planar flame is maintained above the burner exit, where the turbulent flame speed is equal to local flow velocity. Although the flame is stabilized by swirl, the flame zone is in fact free of swirl. Predictions reveal that flame stabilization does not rely on recirculation, but on flow divergence, though a recirculation zone is located downstream of the flame. It is noted that the recirculation zone becomes wider and longer under combustion than in cold swirling jets. Apart from an increase of adverse pressure gradient, the decrease in turbulent diffusion tends to increase recirculation in the open system. The strong impingement between swirling jet and reverse flow makes the flame planar. Introduction The necessity to ensure stability and high combustion efficiency and to localize the flame in a given part of the combustion space requires the use of special methods of flow organization. The main principle of combustion stabilization is to create a region where the local velocity is equal to the flame propagation velocity. This is achieved either using a stabilizer in the form of a bluff body, or by means of swirl. Flame stabilization by the latter is a common feature of many combustors and many fundamental aspects of the complex interaction between swirl and flames have been studied experimentally and theoretically. However, most of the swirl combustors are enclosed, and there has been relatively few studies of open turbulent swirl stabilized flames.