Self-excited oscillation may arise when the inlet of ramjet is under a certain condition.This phenomenon for a supersonic inlet was numerically studied

and changes in fluid flow fields were analyzed.The results demonstrate that

in the occurrence of oscillation

the fluid flow in inlet generates large amplitude

resulting in violent periodic aerodynamic loads on ramjet wall structures.The frequency spectrum of oscillation comprises some characteristic frequencies similar with acoustic modal frequencies

implying a close relationship between acoustic modes and self-excited oscillation.