Turbulent nonpremixed H2/N2 and H2/CO syngas flames were simulated using 3D large eddy simulations coupled with a laminar flamelet combustion model. Four different syngas fuel mixtures varying from H2-rich to CO-rich including N2 have been modelled. The computations solved the Large Eddy Simulation governing equations on a structured non-uniform Cartesian grid using the finite volume method, where the Smagorinsky eddy viscosity model with the localised dynamic procedure is used to model the sub-grid scale turbulence. Non-premixed combustion has been incorporated using the steady laminar flamelet model. Both instantaneous and time-averaged quantities are analysed and data were also compared to experimental data for one of the four H2-rich flames. Results show significant differences in both unsteady and steady flame temperature and major combustion products depending on the ratio of H2/N2 and H2/CO in syngas fuel mixture.