The experimental study of the comparison between propagation frequency of rotating detonation waves and combustion chamber tangential acoustic frequency

To verify the relationship between rotating detonation waves and the intrinsic high-frequency tangential instability of the combustor, this experimental study has been conducted in an annular combustor with the width of 11 mm and a hollow combustor. Oxygen-enriched air, with the volume fractions of 33%, 50% and 100%, and ethylene have been used as propellants. In the annular combustor, three propagation modes have been observed as the different volume fractions of the oxygen-enriched air have been used. The dual-wave collision mode has been obtained as the oxidizer of 33% O₂ has been utilized. In this propagation mode, the velocity deficit is around 37%–63% and the values of the dual-wave propagation frequency are lower than the intrinsic second order tangential frequency. As the volume fraction of the oxidizer increasing from 50% to 100%, the single detonation mode and two detonation waves mode have been obtained. The velocity deficit is around 14%–40% for the unidirectional propagation detonations. The propagation frequency values of the single detonation mode and two detonation waves mode are obviously higher than the value of the intrinsic first order and second order tangential frequency, respectively. In the hollow combustor, the single detonation mode has been obtained when the oxidizer of 50% O₂ has been adopted. It is observed that the propagation velocities are higher than the theoretical C−J velocity and the propagation frequency values are higher than the intrinsic first order tangential frequency in most cases. In summary, the propagation frequency values calculated from different propagation modes of rotating detonation waves are obviously different from the intrinsic tangential frequency of the combustor and this result indicates that the discrepancy between rotating detonation waves and high-frequency tangential instabilities is evident.