Cerfacs Enter the world of high performance ...

LES of Rotating Detonation Engines: Sensitivity and Physics

To increase the efficiency of thermal engines, new pressure-gain combustion systems are the subject of extensive studies over the last years. Rotating Detonation Engines (RDE) constitute an example of such systems, where a self-sustained detonation continuously consumes fuel in a typically annular combustion chamber. Experimental investigation of these engines is ex- tremely difficult, hence numerical methods are used to further explore the processes governing these types of engines. A powerful tool to analyse the flow in Rotating Detonation Engines are Large Eddy Simulations (LES), but literature has shown that their implementation is not straightforward. Various groups use simplifications (e.g. perfect premixing, geometrical 2D representations of the chamber) and numerical high-fidelity analysis comparing mixing assumptions, numerical schemes or chemical schemes in full scale configurations are not commonly found in literature. This thesis investigates strategies for 3D LES of a full RDE tested at TU Berlin and the influence of various modelling parameters on the simulation results. This is done by first deriving a reliable 1-step chemical scheme for the correct prediction of detonation and deflagration properties. Second a reliable initialization procedure is developed and two postprocessing indices for evaluating the mixture quality (Imix) and the detonation efficiency (Idet) are introduced to further quantify the results of the simulations. Results confirm that mixing plays a significant role in the performance of RDEs and must be accurately repro- duced in LES the capture the essential features of RDEs. The manuscript also highlights the impact that the chemical and numerical schemes can have on the detonation dynamics inside RDEs. Finally, the simulations show the importance of deflagration in the overall RDE combustor, implying that chemistry models need to account for deflagration properties as well as for detonation to capture the efficiency of RDEs and reveal that all cases lose a high amount of fuel to non-detonative combustion.

Based on the sensitivity study, a numerical master setup is designed and simulations are performed. The results are validated by comparing the experimental detonation wave speed and estimated pressure gain. The LES overpredicts the experimental detonation wave speed by 21%. The LES also confirms the absence of pressure gain in the TUB configuration.

This thesis shows that LES can be used to understand the dynamics and stabilization mechanisms as well as overall performance of RDE systems. However, it also highlights the current limitations of the method and the many areas where the LES community has to shift the focus on for predictive LES of RDEs.

Jury

Prof. Dr. Antonio Andreini	Università degli Studi di Firenze	President of the Jury
Prof. Dr. Marc Bellenoue	ISAE-ENSMA – Institute Pprime	Member of the Jury
Prof. Dr. Myles D. Bohon	Technische Universität Berlin	Member of the Jury
Dr. Ratiba Zitoun	ISAE-ENSMA – Institute Pprime	Member of the Jury
Prof. Dr. Thierry Poinsot	IMF Toulouse	Director
Dr. Omar Dounia	CERFACS	Co-Director