A “swallowtail” cavity for the supersonic com-bustor was proposed to serve as an efficient flame holderfor scramjets by enhancing the mass exchange between thecavity and the main flow.A numerical study on the “swallow-tail” cavity was conducted by solving the three-dimensionalReynolds-averaged Navier-Stokes equations implementedwith a k-e turbulence model in a multi-block mesh.Turbu-lence model and numerical algorithms were validated first,and then test cases were calculated to investigate into themechanism of cavity flows.Numerical results demonstratedthat the certain mass in the supersonic main flow was suckedinto the cavity and moved spirally toward the combustorwalls.After that,the flow went out of the cavity at its lateralend,and finally was efficiently mixed with the main flow.The comparison between the “swallowtail” cavity and theconventional one showed that the mass exchanged betweenthe cavity and the main flow was enhanced by the lateralflow that was induced due to the pressure gradient inside thecavity and was driven by the three-dimensional vortex ringgenerated from the “swallowtail” cavity structure. A “swallowtail” cavity for the supersonic com-bustor was proposed to serve as an efficient flame holder for scramjets by enhancing the mass exchange between the cavity and the main flow. A numerical study on the “swallow-tail” cavity was conducted by solving the three-dimensional Reynolds-averaged Navier-Stokes equations implemented with a ke turbulence model in a multi-block mesh. Turbu-lence model and numerical algorithms were validated first, and then test cases were investigated to investigate into the themechanism of cavity flows.Numerical results demonstratedthat the certain mass in the supersonic main flow was suckedinto the cavity and moved spirally toward the combustorwalls.After that, the flow went out of the cavity at its lateralend, and finally wasaly mixed with the main flow.The comparison between the “swallowtail” cavity and theconventional one showed that the mass is betweenthe cavity and the main flow was enhanced by the lateralflow that was induced due to the p ressure gradient inside thecavity and was driven by the three-dimensional vortex ringgenerated from the “swallowtail” cavity structure.