WALL HEAT FLUX IN TURBULENT PREMIXED REACTING FLOW

ISSN： 0010-2202

Source： Combustion Science and Technology, Vol.174, Iss.1, 2002-01, pp. : 135-165

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Abstract

Direct numerical simulations (DNS) are used to study non constant density reacting turbulent Couette flow. The objectives are to understand the interaction of wall turbulence and premixed flames, to study wall heat flux from the flame, and to identify mechanisms and correlations that can help in model development for engineering calculations. A variety of turbulent mechanisms were found to increase the wall heat flux. It was found that turbulent boundary layer sweeps, which are normally the main mechanism in turbulent production, push the flame toward the wall and increase wall heat flux. At the same time, a quadrant analysis of the Reynolds stresses shows that they switch from their normal second and fourth quadrants to first and third quadrants. Since the flame is sensitive to stretch for nonadiabatic flow near a wall, low speed streaks decrease the stretch on the flame and increase the wall heat flux. High-speed streaks increase flame stretch and decrease wall heat flux. Stream-wise vortex structures convect the flame toward the wall increasing the wall heat flux. Studying the instantaneous wall heat flux shows peak values approximately 1.25 times the laminar value. These repeat on a time scale of ∼3.2 outer time units (based on mean velocity and channel half width). Larger peak values of ∼1.4 times the laminar value repeat on a time scale of 120 outer units that corresponds to major burst events in the approaching boundary layer.