Effects of wall heat loss on the flame shape and preheat layer dynamics in a premixed swirling flame under varying turbulence intensities

Wall heat loss in gas turbine combustors can significantly modify the near-wall temperature field, thereby influencing flame shape, flame stability, and pollutant formation. However, the effects of such heat loss remain incompletely understood. In this work, laser diagnostic and large eddy simulation (LES) coupled with the dynamic thickened flame model are used to investigate the shape and structure of the flame at two inlet flow rates, 50 L/min and 140 L/min, corresponding to the Karlovitz numbers, 6 and 30, with a focus on assessing how the loss of wall heat influences the flame structures under varying operation conditions. The results of the LES show reasonable agreement with the experimental data in terms of the spatial distributions of CH₂O and OH. Increasing turbulence intensity leads to a transition from a corrugated flamelet zone to a thin reaction zone, characterized by pronounced flame front corrugations, widening of the CH₂O (preheat) layer, and localized flame extinction caused by elevated strain rates. Additionally, with a higher inlet flow rate, the outer recirculation zone (ORZ) accumulates more high temperature combustion products, forming an additional outer preheat layer, which helps stabilize the flame. The peak wall heat loss values computed in the LES reach approximately 17000 J/m²/s at 140 L/min and 9000 J/m²/s at 50 L/min. By employing adiabatic walls, the wall heat loss is eliminated, and the temperature in the ORZ region increases to the adiabatic flame temperature. As a result, the flame shape evolves from a V shape to an M shape with adiabatic walls accompanied by a reduction in the flame front area of more than 50% at both operation conditions. This work provides fundamental insights into the flame structures with/without wall heat loss in an ideal gas turbine combustor.