This paper describes numerical predictions of the forced heat release responses of a lean premixed bluff-body stabilized ethylene/air flame, using the hybrid Stress-Blended Eddy Simulation (SBES) turbulence model and the Flamelet Generated Manifold (FGM) combustion model. The unforced flow field and flame structures are firstly simulated and validated against available experimental data. The forced heat release rate responses of the flame to upstream harmonic velocity fluctuations are then computed and accounted for using the weakly nonlinear Flame Describing Function (FDF), which again match well the experimental measurements. These findings indicate that the use of SBES and FGM models can accurately predict the forced flame responses and the resultant FDFs, which can be applied to predicting thermoacoustic instabilities in real gas turbine combustors.