For decades, researchers have recognized the potential of rotating detonation engines (RDEs) in powering the next generation of hypersonic air-breathing engines, rocket engines and stationary power generation gas turbine systems. Rotating detonation engine (RDE) concepts have been studied since the early 1960s, largely focused on gaseous mixtures as fuel. (Earlier post.) But realizing the potential has been fraught with challenges.

Still in the experimental stage, RDEs are an innovative power generation and propulsion technology that utilize supersonic detonation waves to combust fuel. By extracting energy with remarkable efficiency, RDEs have potential advantages over traditional gas turbine engines, including increased effectiveness and reduced emissions. While mechanically simple, the unsteady combustion process is highly complex, making the technology extremely difficult to study and develop with traditional methods. 

Computer modeling and simulations can play a critical role in helping scientists and engineers better understand the key physics behind the inner workings of RDEs and develop strategies to improve their design. Specifically, RDEs have the potential to be an ultra-high-efficiency alternative to conventional gas turbine engines.

In a new collaboration, the US Department of Energy’s (DOE) Argonne National Laboratory and DOE’s National Energy Technology Laboratory (NETL) are leveraging their expertise in RDEs to develop advanced computational fluid dynamics (CFD) tools that can give scientists a deeper understanding of the combustion process to unlock more of the engine’s potential. They are also looking to make the modeling process faster and more affordable without sacrificing predictive accuracy.

As part of this effort, Argonne is exploring and analyzing RDEs using advanced combustion modeling and unique high-fidelity CFD simulation tools. Scientists are also leveraging Argonne’s world-class supercomputing and artificial intelligence capabilities to enable computationally efficient simulations of full-scale RDEs. 

NETL is contributing experimental test data from its state-of-the art high-pressure RDE facilities to help verify and validate Argonne’s novel CFD simulation tools. NETL leads the RDE experimental research program focused on transitioning this promising technology to the power generation industry.

High-fidelity large-eddy simulation capturing combustion dynamics in a full-scale hydrogen-air rotating detonation engine. (Video by Argonne National Laboratory.)

Among its advantages, RDEs are highly compatible with natural gas and blends with alternative fuels such as hydrogen, which is critical to the future of stationary power generation. Stationary power generation systems, such as gas and steam turbines, are used in power plants to generate electricity. 

In addition, aerospace companies and governments around the world are actively pursuing RDEs which could revolutionize space exploration through benefits such as greater effectiveness and reduced weight compared to traditional rocket engines.

While significant advances have been made in high-speed experimental diagnostics, the unsteady and chaotic nature of the RDE combustion process can make it difficult to adequately characterize the important chemical and physical processes.

As CFD tools become increasingly sophisticated, they enable better simulations and deeper understanding of RDE phenomena that can’t be easily measured, such as injector mixing and backflow, flame anchoring, manifold dynamics and startup transients. Computer simulations also help to provide additional information that is critical for optimizing RDE designs and can help down-select promising configurations for further experimental study.

—NETL research engineer and collaborator Peter Strakey

But computer simulation of RDEs isn’t without hurdles. These engines have complicated unsteady physics involving flow turbulence, shockwaves, chemical kinetics and wall heat transfer. Because the interaction among these phenomena is not well understood, they are not incorporated into current CFD modeling approaches. RDE performance is also tied heavily to the design of the combustion chamber and fuel/air feed systems.

CFD models need to account for the full-scale geometry and complex physics so that simulations of RDEs can be predictive. But on the flip side, this leads to high computational expense. The gap between predictive accuracy and computational efficiency of RDE simulations is what we hope to bridge through this research effort.

—Pinaki Pal, a senior research scientist at Argonne and principal investigator of the project

To accomplish project goals, researchers are leveraging Argonne’s unique high-fidelity CFD and reduced-order, or simplified, combustion modeling tools. Scientists are using Argonne’s Nek5000 flow solver that can solve CFD problems with remarkable speed and precision. The code is designed to run efficiently on massive supercomputers and combines cutting-edge mathematical techniques with flexible modeling of complex shapes and systems.

Detailed high-order simulation of a premixed detonation performed using Argonne’s compressible Nek5000 CFD solver. (Video by Argonne National Laboratory.)

Recent upgrades have expanded Nek5000’s capabilities to modeling of high-speed compressible reacting flows. High-fidelity datasets from these Nek5000 simulations will be used to develop turbulent combustion and wall heat transfer models to enhance understanding of RDE physics. These models will then be used in faster, full-scale engine simulations, which will be tested against experimental data from NETL.

Lastly, researchers will work to minimize the high computational cost related to detailed chemical kinetics. Researchers will leverage in-house, physics-based and data-driven techniques for reduced-order representation of fuel chemistry. This will involve a unique modeling framework for turbulent combustion, called dynamic adaptive combustion model.

This modeling will be extended to RDEs for the first time, coupled with a previously developed CFD approach at Argonne. The goal is to speed up simulations by at least tenfold compared to the state-of-the-art CFD models.

Argonne is leading the three-year RDE modeling and simulation focused project funded by DOE’s Advanced Turbines Program.