Torque Around Axial Direction on Rotating Detonation Engines

Abstract

A rotating detonation engine (RDE) generates a continuous thrust with one or more rotating detonation waves. Because of the velocity on the order of kilometers/second, the reaction zone is relatively small. Therefore, the RDE realizes a short combustion chamber length. However, the detonation waves induce an azimuthal motion of propellant, resulting in torque around the thrust axis. Because the motion does not contribute to the thrust, the torque is important in terms of performance loss. Herein, we conducted combustion tests with a six-axis force sensor to simultaneously measure $0.149\pm 0.009\mathrm{Nm}$ torque and $48.1\pm 0.9\mathrm{N}$ thrust. A comparison of detonation waves captured by high-speed camera revealed that the torque followed the direction and was offset when the waves existed in both of two directions simultaneously, which indicates the possibility of controlling the torque. Under a mass flow rate at $87\pm 9\mathrm{g}/\mathrm{s}$ and an equivalence ratio at $1.43\pm 0.28$ , when the azimuthal component of shear force was $8.8\pm 0.6\%$ of the thrust, $0.77\pm 0.10\%$ of the total kinetic energy of the exit flow was distributed to the azimuthal component of velocity and did not contribute to the thrust. We therefore concluded that the effect of the azimuthal motion on the RDE’s performance was small.