Investigation of Flame Stretch in Turbulent Lifted Jet Flame

Abstract

DNS data of a laboratory-scale turbulent lifted hydrogen jet flame has been analysed to show that this flame has mixed mode combustion not only at the flame base but also in downstream locations. The mixed mode combustion is observed in instantaneous structures as in earlier studies and in averaged structure, in which the predominant mode is found to be premixed combustion with varying equivalence ratio. The nonpremixed combustion in the averaged structure is observed only in a narrow region at the edge of the jet shear layer. The analyses of flame stretch show large probability for negative flame stretch leading to negative surface averaged flame stretch. The displacement speed-curvature correlation is observed to be negative contributing to the negative flame stretch and partial premixing resulting from jet entrainment acts to reduce the negative correlation. The contribution of turbulent straining to the flame stretch is observed to be negative when the scalar gradient aligns with the most extensive principal strain rate. The physics behind the negative flame stretch resulting from turbulent straining is discussed and elucidated through a simple analysis of the flame surface density transport equation.

Modelling flame turbulence interaction in RANS simulation of premixed turbulent combustion

“…Furthermore for models relying on Σ transport equation (SDR2 and FSD) a higher reaction rate can be predicted in these regions due to an infinite growth of term a in eq. (23) as it always produces Σ, which is not always the case as the flame induced turbulence scalar interaction can desroy the flame due to local changes in the alignment of the strain rate with respect to the flame gradients [53]. Both the FTI (algebraic) and FTI (transport equation) predict similar reaction rates in the immediate wake of the back ward facing step at x/h = 1 and x/h = 3 as shown in figures 8a and 8b.…”

Simulation of turbulent lifted methane jet flames: Effects of air-dilution and transient flame propagation

“…Turbulent lifted flames are quite common in many practical devices such as aero engines, gas flares, etc. These flames have been investigated in the past using analytical methods [1,2], experiments [3][4][5][6][7][8][9][10][11] and numerical simulations [12][13][14][15][16][17][18][19].…”

Simulation of Premixed Combustion with Varying Equivalence Ratio in Gas Turbine Combustor

“…The assumption of statistical independence for ξ and ζ is not always justified [9] and their strong coupling in PPC is well established [9][10][11].…”