This work focuses on the large eddy simulation and the study of turbulent dilute methanol spray flames in vitiated coflow using the secondary-oxidizer Flamelet Generated Model (FGM). The modified FGM model uses an additional secondary oxidizer parameter in addition to the three other parameters previously used for spray flames - progress variable, mixture fraction, and enthalpy. The results for gas phase and droplet properties are validated against the dilute methanol spray flame database for varying fuel injection amounts. The droplet statistics and the liftoff flame heights are accurately captured for all the cases. A proper orthogonal decomposition (POD) of the scalar fluctuating hydroxyl radical (OH) field and the velocity-temperature field captures the flame structures in the downstream region of ignition kernels. The detailed POD analysis reveals that the base frequency of the dominant OH field equals that of the dominant vortical structure of 67.3 Hz. The flame propagation happens around these dominant vortical structures because of the less-strained fluid mixing.

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A probability density function (PDF) based combustion modeling approach for RANS is used in the simulation of a jet issuing into a hot and diluted coflow. A tabulated chemistry based model, i.e. Flamelet Generated Manifold (FGM), is adopted in the PDF method. The manifolds are constructed using igniting counter-flow diffusion flamelets with different coflow composition. To handle the inhomogeneity of the coflow and the entrainment of the ambient air, a second mixture fraction is defined to quantify the mixing of a representative coflow composition with the ambient air. The chemistry is then parameterized as a function of two mixture fractions and a reaction progress variable. Two flames, namely HM1 and HM3, having different oxygen mass concentration in the hot coflow, 3% and 9% O2 respectively, have been simulated for Reynolds number (Re) =10000. The mean oxygen concentration and temperature profiles are well predicted showing the capability of the tabulated chemistry. Profiles of mean mixture fraction and major species are also accurately captured by the model.@en