High-fidelity Simulations for Rotating Detonation Engines

Abstract

RDEs have drawn increased attention throughout the world as a viable technique for pressure gain combustion. An annular cylindrical combustor is used to drive a detonation wave azimuthally, which provides a continuous detonation process. RDEs provide a promising route to substantially increasing cycle efficiency compared to traditional cycles because of their ability to use shock-based compression to increase the pressure of the fluid in the combustor. Due to these characteristics, it is expected to bring revolutionary advancements to aviation and aerospace propulsion systems such as rocket engines, ramjet engines, and turbojet engines.

The goal of this dissertation is to provide the RDE community with a comprehensive database of full-scale RDE calculations for a variety of injector designs and operating conditions which enables design teams to make rapid progress for the realization. The main design challenge emerges from a non-premixed feed system where the fuel and oxidizer are injected separately into the combustion chamber. A non-premixed injection scheme is employed not only for safety and controllability, but also for an air-breathing RDE where the air stream will not come from a plenum, but rather through an intake. The main design challenge at this stage is developing a non-premixed fuel feed system that achieves adequate mixing and minimizes pressure losses while ensuring a reliable and safe detonation process. In order to rapidly accelerate such engineering design, comprehensive RDEs physics including chemistry, effects of complex geometry on detonation structures, and the complexity of the injection scheme need to be understood. With this mind, my dissertation will focus on the detailed detonation structure affected by the mixing process with a variety of injection geometries.

To perform large scale simulations of realistic RDEs geometry, a finite volume method (FVM)-based solver, named as UMdetFOAM, with following three key features is developed in this work: (1) implementation of schemes to reduce dispersive/dissipative errors at the detonation front where a spatial discontinuity exists, (2) the capability of dealing with complex geometries, and (3) the ability to incorporate user-specified chemical kinetics by coupling the FVM solver with a chemistry solver. These large-scale simulations using thousands of cores, validated in conjunction with the experimental group at U of M, provide detailed understanding into the performance of such detonation processes.

One of the main outcomes of this work is the development of a solver that enables the simulation of RDEs with the practical geometry. Furthermore, this dissertation demonstrated the effect of mixing-limited detonations on engine performance by identifying key sources of spurious losses. In particular, it was shown that turbulent mixing of fuel and air control the detonation processes. But, additional mixing with products of detonation can lead to premature ignition and parasitic losses. It was identified that the differential recovery of the injectors is the prime reason for the mixing-induced losses. These features were also found in other experimental studies, which validates the hypothesized flame processes.