Abstract: Pulse Detonation Engine (PDE) tests in the PDE tubeH_2-O_2-N_2 have beenperformed with central ignition in the tube end. The tube has 1000mm longwith the inner diameterof 30mm, filled with the H_2-O_2-N_2 mixture.Moreover, numerical simulationsof pulse detonation process induced by flame in the tube withH_2-O_2-N_2 mixture andthe distribution of the internal and external flow field were performed. Adetailed chemical mechanism of H_2-O_2-N_2 system was investigatedwith 19 element reactions and9 species. The generation and development of the vortex ring and suspendedshock were exhibited with the sequential shadowgraphs of the external flowfield both in test and simulation. The numerical results were in goodagreement with the measured results. The experimental and numerical resultsshow that the vortex ring was induced by baroclinic effect and Helmholtzinstability in the vicinity of the thruster exit after the donation waveexhausted the tube. The intensity, shape and location of the suspended shockvaried when the shape of the vortex ring changed.