Experimental study of sharp noise caused by rotating detonation waves

Previous studies of rotating detonation engines (RDEs) focused on combustion, heat transfer, and propulsion, but not noise, which is considered here. High-frequency pressure sensors, such as dynamic sensors, are often used as contact measurements to determine the detonation pressure and rotating detonation cycle time, but they obtain data for only a few seconds. Here, a simple and inexpensive acoustic measurement method is used to obtain the high-frequency sound pressure of the detonation and cycle time over more than a few hours and is not affected by high-temperature products. The results show that data of non-contact acoustic measurements, which can reflect the rotating detonation characteristics, agree well with those of picocoulomb pressure sensors and high-speed imaging. The production mechanism of sharp noise caused by rotating detonation waves is analyzed theoretically and compared with experimental results. Kinematic equations for vibrations are derived, and disturbance trajectories caused by oblique shock waves are found to be Archimedes spirals. This constitutes the first study on noise from RDEs. The study also promotes acoustic measurements, which have rarely been used to study RDEs.