The paper studies turbulent separation flows in the intermediate turbine diffusers and their control via synthetic jets using a combined high-resolution RANS/ILES method (Reynolds Averaged Navier-Stokes - RANS, Implicit Large Eddy Simulation - ILES). Calculations were performed for two variants of S-shaped diffusers geometry: standard and "aggressive" (20% shorter than standard) on the grids containing 0.88×106 cells. The paper also considers flow modes in diffusers for several values of pressure difference. The effect of diffusers geometry on their flow parameters in them was defined. The effect of synthetic jets on the flow separation and characteristics of flow and turbulence was considered. A parametric study was conducted to define the influence of synthetic jet amplitude and frequency on the flow. Synthetic jets are generated by periodic gas blowing and suction through the slots of the cavity with a movable diaphragm - a generator of synthetic jets. They do not require special working gas and means for its supply are compact and efficient. For studied modes, the levels of total pressure losses and turbulent fluctuations at the diffusers output, as well as distribution of the averaged flow parameters were shown. The flow parameters in the standard and the "aggressive" diffusers both with jets and with no jets in the same mode were compared. It was found that using the synthetic jets in considered diffusers allows us to improve their characteristics and in case of "aggressive" diffuser approximate them closer to the level of the standard.