Computational analysis for air fuel mixing and transport in a combustor used for co fired burner has been done by RANS (Reynolds-Averaged Navier?Stokes) model comparing with 3D (Three Dimensional) LES (Large Eddy Simulation). To investigate the better turbulence level and mixing within co fired combustor using the solid fuel biomass with coal is main purpose of this research work. The results show the difference in flow predicted by the two models, LES give better results than the RANS. For compressible flow the LES results show more swirling effect, The velocity decays along axial and radial distance for both swirling and non-swirling jet. Because of no slip condition near boundary the near the wall velocity is about zero.