The counter-rotating shock wave and wave direction control of the hollow rotating detonation combustor with Laval nozzle are studied. The in-house solver BYRFoam, developed on the OpenFOAM platform, is used. The phenomenon and spatial distribution of the counter-rotating shock wave in the combustor are revealed. The result suggests that the closer the location is to the outer wall, the stronger the counter-rotating shock wave is. A method of controlling the wave direction is proposed. It's shown that the intensity of the counter-rotating shock wave is controlled by reducing the total pressure of inlet, and then the direction of the detonation wave is controlled. The process of detonation wave reversing is divided into four steps, namely, counter-rotating shock waves evolve into detonation waves, several detonation waves are extinguished, detonation waves form again, and detonation waves propagate stably. The mechanism of wave direction control is investigated. The result shows that the fluctuation of the total pressure of inlet stimulates the positive feedback interaction between the counter-rotating shock wave and the fresh gas, which causes initial detonation waves to be extinguished and the intensity of counter-rotating shock waves to become stronger and stronger, and eventually counter-rotating shock waves evolve into reverse detonation waves.

Recently, with the development of detonation-based propulsion systems, scholars have begun to study how to perform mode control on the rotating detonation combustor (RDC). It is important to figure out the influence of operation mode transition on the RDC. Actually, the essential of different modes is the different multi-wave structures. In this study, two-dimensional numerical simulations of the RDC are conducted to study the multi-wave effect on the stability and performance of the RDC. A uniform inlet condition is adopted in simulations to eliminate the impact of discrepancy mass flow rates, and a mode-locked ignition method is used to induce RDC flow fields with different detonation wave numbers. It is found that the flow field stability and outlet uniformity are improved with increasing detonation counts, and the energy proportion in the flow field is little affected by the multi-wave structure. However, the increase in detonation number will cause a reduction of the mass-averaged total pressure ratio at the exit. Underlying relationship between the unsteady flow field and the total pressure gain is discussed. The total pressure gain is directly linked with the non-uniformity of the circumferential flow field. Then, by utilizing particle trace, the envelope of the thermodynamic cycle is illustrated and the pseudo-thermal efficiency of each case is given. The result implies that the wave number has hardly effect on the thermal efficiency of the combustion chamber. By summarizing the perimeter, axial length, and wave number in the combustor, parameter ξ is carried out and its effects on the uniformity and total pressure ratio in the RDC are concluded.

A numerical study of the longitudinal pulsed detonation (LPD) is conducted in the present paper. The occurrence mechanism of the LPD, called shock wave amplification by coherent energy release (SWACER) is verified preliminarily in this study. To be specific, upstream propagating shock waves, which originate from the outlet, induce a specific gradient of reactant distribution and then detonation waves are ignited and evolve along the gradient in close succession. It is worth noting that the occurrence of LPD does not mean that the LPD will necessarily be sustained. The low injection pressure ratio PR (i.e. the ratio of inlet pressure to outlet pressure) = 1.3 is found to be conducive to the sustenance of the LPD instability in the baseline model. A lower PR (PR {less than or equal to} 1.2) or a slightly higher PR (1.4 {less than or equal to} PR {less than or equal to} 1.8) shall lead to an unstable detonation or a quenching of detonations, while a much higher PR (PR > 1.8) contributes to the formation of stable canonical rotating detonation waves. In addition, the combustion regimes of five combustors of different heights at different PR are explored. As the combustion chamber height increases, the PR of the sustainable LPD is nearly linearly increasing and its operating frequency decreases gradually. The calculation formula between the sustainable LPD propagating frequency and natural acoustic resonance frequency of the combustor is employed and discussed, but in consideration of its imperfection further investigation is required.

Solid-gas rotating detonation engines have been widely studied, but experimental limitations have prevented the full information of the flow field from being revealed. This paper describes a numerical investigation of the effect of the equivalence ratio on the two-phase flow field of a rotating detonation engine fueled by carbon and air. The discrete phase model and multiple surface reaction model are employed to determine the flow and combustion of carbon particles. The Reynolds-Averaged Navier-Stokes equations are solved for the gas flow. The results show that a low-temperature air gap appears in place of deflagration in the two-phase flow field, and the gap extends into the products. Before the detonation wave, this air gap is the difference between the air and fuel layers. At higher equivalence ratios, two rotating detonation waves are formed by the contact between the high-temperature products and the fuel-air mixture.

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