Unsteady flame-wall interactions in a reacting jet injected into a vitiated cross-flow

This paper describes measurements and analysis of the unsteady characteristics of a turbulent reacting fuel jet in a vitiated cross-flow. This problem involves coupling between the hydrodynamic stability of the jet-wall system, combustion induced gas expansion and interactions of the autoigniting jet with the wake flow. Analysis of the unsteady jet motions shows that the reacting jet flaps in a sinuous manner with an amplitude that increases with downstream distance but is relatively independent of jet-to-cross-flow momentum flux ratio, J. This study particularly focuses on unsteady flame-wall interactions in these systems, showing that even though the time averaged flame trajectory may be well removed from wall regions, its instantaneous trajectory may be very near or even attached to the wall. Specifically, for lower J jets (J < similar to 20), the flame intermittently attaches to the wall for some fraction of time that decreases with downstream distance and increasing J. From a practical point of view, intermittent flame-wall interactions cause an increase in the time averaged wall temperature, raising durability concerns. We suggest that this unsteady jet-wall attraction can be understood from analogies to the dynamics of co-flowing jet or wake pairs, as low J jets deflect into the cross-flow direction quickly. Side-by-side jets or wakes are "attracted" toward each other and exhibit global instabilities that are not present when they are isolated. In support of this argument, we show that data taken over the 1.7 < J < 7.2 range and a range of axial locations can be collapsed using the time averaged distance of the reacting jet from the wall. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.