Abstract <p>When a ramjet engine inlet operates under off-design conditions, the large-scale separation zone formed by the shock wave/boundary layer interaction significantly degrades engine performance, making separation control critically important. Based on a five-stage mixed-compression inlet designed for shock-on-lip condition under inviscid assumptions, six secondary flow circulation configurations with different locations for suction and blowing ports were designed. For comparison, two boundary layer suction configurations were also developed as baseline models. The numerical results demonstrate that under sub-rated conditions (M = 4), the suction port should be located away from the shoulder, while the blowing port should be positioned within the isolator. Comparing with the boundary layer suction method, the secondary flow circulation method increased the total pressure recovery coefficient by 11.00%, reduced the total pressure distortion index by 14.80%, and improved the mass flow coefficient by 1.75%. Under super-rated conditions (M = 8), the suction port should also be away from the shoulder, but the blowing port should be located on the first wedge. Compared with the boundary layer suction, the secondary flow circulation method resulted in a 6.59% decrease in the total pressure recovery coefficient. However, it reduced the total pressure distortion index by 4.24% and increased the mass flow coefficient by 0.98%. Furthermore, a feasible wide-speed-range flow control method with the use of the secondary flow circulation is proposed, offering a potential flow control strategy for enhancing the performance of ramjet inlets across a broad operational envelope.</p>