An axisymmetric supersonic inlet is computationally studied at a freestream Mach number of 2.0. The Reynolds-Averaged Navier-Stokes (RANS) equations are solved in an unsteady state and the SST k-ωturbulence model is used in this study. Several throttling ratios have been set to study the inlet flow field from supercritical to subcritical conditions, including little buzz and big buzz. Recently, studies have been about the new reasons for the buzz initiation beyond the accepted buzz criteria. The primary purpose of the current research is to discover the source of the buzz phenomenon in a supersonic inlet by examining the Ferri and Dailey criteria, which are the main criteria for predicting the buzz onset. The results showed that the low-speed flow above the vortex sheet, generated due to the intersection of the conical shock with normal shock, and the flow separation near the cowl lip are the main reasons for the buzz onset in the current inlet. To further study the source of buzz instability, the boundary layer suction was used on the cowl surface to investigate its effects on the buzz onset. According to the results, the bleed can remarkably postpone the buzz phenomenon and increase the last stable throttling ratio of the inlet from 65.0% to 77.5%. Furthermore, the big buzz at the throttling ratio of 80.0% is converted to the little buzz and the inlet performance is significantly improved after applying the bleed.

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