This paper describes the flow dynamics inside a supersonic ejector using CFD modelling. Suitable ejector geometry is proposed for the high compression ratios encountered in real-world applications. Post-processing and physical analysis of the CFD results are presented to better understand the entrainment mechanism and the mixing between the primary and the secondary fluids. The effect of the primary pressure on the flow dynamics and the entrainment ratio is discussed for the two compression ratios of 1.67 and 3.4. It is found that the proposed ejector can operate at compression ratio as high as 3.4. It is also found that the strength of the shock waves, the supersonic jet expansion and the mixing between the primary and secondary fluid flows inside the ejector are strongly affected by the primary pressure. A significant increase in both the shear forces amplitude and the wall friction losses is observed when the boundary layer separates from the ejector wall.