Propagation of detonation waves influenced by radial expansion on inner side in curved channels

In the disk-shaped rotating detonation chamber with injection from the outer side, the detonation wave propagates in a curved channel without the constraint of the inner wall. Actually, both the channel curvature and the radial expansion have a great influence on the propagation of detonation waves. To clarify the propagation characteristics in curved channels under the radial expansion on the inner side, this study has been carried out utilizing a mixture of ethylene, oxygen, and nitrogen. First, the effects of the equivalence ratio on the propagation characteristics in both confined and semi-confined curved channels are focused on in this study. Then, the formation mechanism of the inflection structure in the radial expansion region is revealed by numerical simulations. The results show that the curvature of the detonation wave front decreases under the influence of radial expansion, and the wave velocity along the wave front is reduced when introducing the radial expansion near the inner wall which is below 0.7 times theoretical C-J velocity. However, the circumferential wave velocity increases near the outer wall. Under the fuel-lean and fuel-rich conditions, the intensity of detonation waves in the expansion region decreases, and the expansion angle increases rapidly. Three propagation modes are observed after the stable detonation waves enter the curved channels, i.e., a stable mode, a critical mode, and an unstable mode. Finally, the critical conditions for the stable mode are clarified with the influence of the radial expansion on the inner side. The critical inner radius is 19.01 times the average cell width, and meanwhile, the minimum mixture height is equivalent to 8.77 times the average cell width.