Analysis of weak secondary waves in a rotating detonation engine using large-eddy simulation and wavenumber-domain filtering

Abstract

Rotating detonation engines (RDEs) are pressure-gain combustion devices which allow for a compact and mechanically simple engine design with improved thermodynamic efficiency compared to traditional deflagration devices. However, achieving these gains in practical devices that are operated with non-premixed reactants requires overcoming non-idealities in the mixing and combustion process. We investigate these non-ideal effects in the Air Force Research Laboratory's rotating detonation rocket engine using large-eddy simulation. The simulation results are compared against experimental measurements, showing overall reasonable agreement for critical performance metrics of thrust, specific impulse, and chamber pressure. A wavenumber-domain filtering method is presented to separate the clockwise-rotating waves and counter-clockwise waves, which enables the unambiguous identification of secondary weak waves and their interaction with detonation waves. The analysis of the flow field and response of the injectors shows that these interactions lead to precessing regions of higher pressure, characterized by less parasitic combustion, higher heat release rate, and higher injector blockage. Furthermore, the thrust contributed by the pressure gain combustion process during these interactions is significantly increased, which leads to a modulation of the overall thrust output of the engine. Novelty and significance statement This study analyzes non-ideal effects inherent to rotating detonation rocket engines (RDRE), which prevent achieving theoretically higher thermodynamic efficiencies compared to traditional deflagration devices. This manuscript has three major novel contributions: First, we assess the predictive accuracy of our large-eddy simulation approach in predicting the combustion performance of an RDRE at high-mass flow conditions, which is a benchmark case of the Model Validation for Propulsion workshop. As such, it contributes to the literature in identifying capabilities and deficiencies of current simulation tools in predicting such complex combustor configurations. Second, we extend the method of Bennewitz et al. [AIAA Paper 2018-4688, 2018] and introduce a wavenumber domain filtering method as an efficient approach for separating clockwise and counter-clockwise rotating features in RDREs. This analysis tool is significantly simpler than other methods found in the literature, and enables a detailed analysis of detonation and secondary combustion modes. Third, this study contributes new knowledge about the role of secondary waves in RDREs. Specifically, the effects of these waves on the flow field and injector response are analyzed, showing that these effects are related to the overall thrust of the engine, which is the first time to the authors’ knowledge.