Effect of increasing channel width on the structure of rotating detonation wave

Abstract Higher fuel-burn rate and, hence, thrust from a rotating detonation engine (RDE) may be achieved through the use of larger channel widths for the annular tubes in which combustion occurs. However, while it is known that presence of solid walls influences the propagation of a detonation wave in a planar geometry, it is not clear how an increase in channel width would affect the characteristics of a rotating detonation wave in an annular tube. An experimental and numerical study is performed to understand how a rotating detonation wave evolves when the channel width is increased. Three annular tubes with identical inner-wall diameters but with channel widths of 7.8, 16.2, and 22.8 mm are considered. Reacting flowfields in the annular tubes are simulated using a three-dimensional CFD code that solves unsteady Navier–Stokes equations. Hydrogen–air mixture is used as fuel and is modeled with a two-step chemical-kinetics mechanism. Simulations have resolved the detailed structures of the rotating detonation waves including the Kelvin–Helmholtz instabilities associated with the fuel-products interfaces. Comparison of simulations obtained for different annular tubes suggest that as the channel width increases 1) the detonation front on the inner wall moves ahead of that on the outer wall and causes an inclination to the detonation wave between the walls, 2) the detonation front on the outer wall gets stronger, and 3) an oblique shock system establishes between the inner and outer walls. An experimental campaign has been conducted for verifying these predictions. The structure of the rotating detonation wave is recorded using OH* chemiluminescence. Measurements have qualitatively confirmed the predictions. Simulation data are then analyzed for understanding the physics behind the observed changes to the rotating-detonation-wave structure. The compression and expansion occurring at the outer and inner walls, respectively, are found to influence the rotating detonation wave.