The current research focuses on the use of synthetic jets with a rectangular orifice of high aspect ratio as means of separation suppression. Large Eddy Simulations of a synthetic jet in a quiescent domain and a the flow over a two-dimensional hill with a synthetic jet in the vicinity of separation were undertaken. Experimental results presented during the NASA workshop titledI "CFD Validation a of Synthetic Jets and Turbulent Separation Control" were used for validation purposes. In the case of the flow of a synthetic jet in a quiescent domain, agreement between LES and experimental results is only qualitative. The The jet spread is under-predicted and the centre-line velocity is over-predicted downstream of the jet orifice. Also the primary vortex pair is shown to travel slower than that in the experiment. In the case of the flow over a two-dimensional hill, the flow without any kind of separation control as well as the tlow with a synthetic jet in the vicinity of separation were simulated. The agreement in long-time-averaged velocity and Reynolds stresses between LES and experimental resuhs was good in both baseline and synthetic-jet cases.