Zhaohua Sheng

With the rotating detonation engine's (RDE) development to engineering applications, the selection and optimization of nozzle is garnering great concerns, with the aim to maximize the performance benefits of this pressure gain propulsion system. The present study represents the first effort to explore the distinct impacts of two commonly used nozzles in RDE, namely, the plug nozzle and the Laval nozzle, on the internal flow and performance within the combustion chamber. Three-dimensional numerical simulations are conducted on non-premixed annular RDEs with plug nozzles and Laval nozzles. It is found that the Laval nozzle induces a forward-leaning wavefront structure in the combustion chamber. Furthermore, the overall pressure gain of the RDE is divided into the injection pressure loss, the average pressure gain at the chamber bottom, and the flow losses downstream, by combining the wavefront coordinate averaged flow field, which is proposed and applied in this study, and laboratory coordinate averaged flow field. The results show that, for the performance of the combustion chamber, while Laval nozzles enhance pressure gains at the chamber bottom and reduce exit flow non-uniformity, they also increase downstream losses. By comparing the RDE performance with the ideal performance of deflagration-based combustors, it is found that the premixed control group exceeded the deflagration ideal performance by 30%. Despite lower combustion efficiency, non-premixed configurations nearly match the ideal deflagration performance, underscoring the inherent advantages of RDEs.

A rotating detonation engine (RDE) is a highly promising detonation-based propulsion system and has been widely researched in recent decades. In this study, BYCFoam, the latest gaseous version of the BYRFoam family, is developed specifically for RDE simulations. It is based on the standard compressible flow solver rhoCentralFoam in OpenFOAM and incorporates several enhancements: improved reconstruction variables and flux schemes; detailed chemistry and transport properties; the utilization of an adaptive mesh refinement (AMR) and dynamic load balancing (DLB). A series of comprehensive numerical tests are conducted, including the shock-tube problem, shock-wave diffraction, homogeneous ignition delay, premixed flame, planar detonation, detonation cellular structure and rotating detonation combustor (RDC). The results demonstrate that BYCFoam can accurately and efficiently simulate the deflagration and detonation processes. This solver enhances the capability of the BYRFoam family for the in-depth exploration of RDE in future research.

Film cooling is a promising thermal management solution for rotating detonation combustors (RDCs) maturing toward long-duration engineering implementation. Aimed at elucidating the interaction between air coolant and rotating detonation waves (RDWs) and assessing the cooling performance, three-dimensional numerical simulations are conducted on an RDC utilizing four different film cooling injection inclination angles and compared to a case without coolant injection. Increasing injection angles from 30° to 90° results in a broader detachment region and deeper penetration, negatively influencing the cooling performance. A time-averaged method is adopted to evaluate the overall cooling performance, including axial temperature profiles, film protection coverage, RDC film effectiveness, and pattern factor. The results show that the cylindrical cooling hole with a 30° injection angle outperforms others due to enhanced wall attachment of the coolant and reduced interaction with the mainstream hot gas. Consequently, a low injection angle within the manufacturing limits is recommended for practical applications. Furthermore, this study uncovers several phenomena unique to RDCs when introducing film cooling, absent in conventional gas turbines, such as temperature discrepancy between the inner and outer walls, elevated upstream temperature caused by coolant injection, and non-uniform cooling effectiveness between the two sides of the cooling holes. Finally, the interplay between film cooling and RDW is illustrated through temperature and pressure gradient contours.

Numerical simulations were conducted to investigate the flow field characteristics and performance of a carbon–hydrogen/oxygen-rich air rotating detonation engine (RDE). Three distinct flow field structures were observed in the gas–solid two-phase RDE. The results show that reducing the hydrogen equivalence ratio and particle diameter contribute to the transition from gas-phase single-front detonation to gas–solid two-phase double-front detonation and further to gas–solid two-phase single-front detonation. The effects of the solid fuel particle diameter and hydrogen equivalence ratio on the flow field characteristics and performance are revealed. The results show that reducing the particle diameter enhances the speed of the two-phase detonation wave, improves the pressure gain in the combustion chamber, and increases the specific impulse. Decreasing the hydrogen equivalence ratio reduces the detonation wave speed, enhances the stability of the detonation flow field, increases the pressure gain in the detonation wave and combustion chamber, and boosts the thrust. Furthermore, the selection of operational conditions to ensure stable operation and optimal performance of the RDE is discussed. In order to take into account the requirements of stability, pressure gain performance, and propulsion performance, two-phase single-front detonation should be realized in gas–solid two-phase RDE, and smaller hydrogen equivalent ratio and appropriate particle diameter should be selected. According to the conclusion of this study, the particle diameter should be 0.5–1 μm. Under such conditions, the detonation flow field demonstrates good stability, allowing the RDE to achieve higher pressure gain and specific impulse while maintaining stable operation.

In the present study, an experimental performance analysis of hollow rotating detonation engines (RDEs) with Laval nozzles is carried out for the first time. Experiments of a hollow rotating detonation engine with a Laval nozzle were performed with a modular RDE at a backpressure condition of 1 atm. Two configurations with area ratios of the outlet throat to the inlet of [ ] and 2.7 have been tested with gaseous methane/oxygen as propellants. Three normalized metrics, usually used for evaluating the performance of conventional rocket engines, are introduced to analyze the performance deficit between the measured value of an RDE and the ideal value of an isobaric-combustion-based engine. These metrics allow for assessing the entire engine and each component separately. The metric analysis suggests a small outlet-to-inlet area ratio ([ ]) is detrimental to the propulsive performance. To explain the mechanism, a gas-stratification flowfield model is further proposed. It is found that the unchoked region in the combustible gas layer, which is caused by unchoked injection on the injecting plate, is responsible for the performance deficit of the combustion chamber. This model is then validated by one-dimensional numerical simulations and experimental data. In addition, we also focus on the global performance, including the gross thrust, the specific impulse, and the utilization of the supplied stagnation pressure. The result implies a tradeoff space when choosing an appropriate [ ].

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.