Precise Predictions on Turbulent Combustion in Rocket Combustion Chambers
Author: Professor Dr. rer. nat. Michael Pfitzner
One of the top research priorities at the Institute of Thermodynamics, Heat and Mass Transfer (LRT-10) is the modeling of turbulent high-pressure combustion in technical systems. Typical applications are car engines, (jet) gas turbines and rocket propulsion systems.
The propulsion systems of large space rockets use hydrogen or methane as fuel and cryogenic oxygen as oxidizer. Due to the low temperature and high pressure in combustion chambers, the fields of thermodynamics and aerodynamics must be combined. By the end of the 20th century, little research had been conducted particularly on the numeric calculation of high-pressure turbulent flow and combustion.
On account of work we had previously carried out, we became involved in the planning of the collaborative research center Transregio TR40 (SFB-TR40) of the German Research Foundation in 2003. SFB-TR40 was launched in 2007. It is one of the largest collaborative research centers that the German Research Foundation has ever funded. SFB-TR40 includes 27 projects at four universities (Munich, Stuttgart, Aachen, and Braunschweig) and two institutes of the German Aerospace Center (Lampoldshausen and Cologne). ASTRIUM (now ARIANE Group) funded PhD projects themselves and gave technological advice on rocket combustion chambers.
The objective was to conduct research on combustion in the combustion chambers of large space rockets, such as ARIANE 5, and tail air flow and its interaction with the propelling nozzle structure. The following projects were conducted at four universities:
- Modeling of combustion processes in rocket combustion chambers (Technical University of Munich (TUM) / UniBw M)
- Cooling of combustion chambers (Stuttgart)
- Tail air flow and fluid-structure interactions with the propelling nozzle (RWTH Aachen University, Technische Universität Braunschweig, German Aerospace Center Cologne)
Together with the Chair of Aerodynamics and Fluid Mechanics at TUM, LRT-10 carried out two joint SFB-TR40 projects with a total of three positions for PhD students. The projects focused on the development of a method to simulate real gas flow in high-pressure environments, the further development of the modeling of turbulent combustion, and the prediction of wall heat flow, which is crucial for the design of rocket combustion chambers. We were able to significantly advance the state of research in all three areas.
Experiments in sub-scale combustion chambers were conducted in close cooperation with Professor Haidn (TUM). Close cooperation was also established with the German Aerospace Center in Lampoldshausen, which provided data from larger combustion chamber experiments. Multicomponent, high-pressure turbulent flow was examined together with the University of Stuttgart (experiment by Stuttgart, calculations by UniBw M).
We have made substantial progress with respect to the calculation of real gas flow in high-pressure environments. We were able to show that sufficiently precise results can only be delivered through the close and consistent coupling of thermodynamics and numeric fluid mechanics. This allowed us to reproduce the high-pressure combustion experiments of ONERA, the German Aerospace Center in Lampoldshausen, and TUM (Professor Haidn) with a high degree of accuracy.
Left: Numeric simulation of a LOX / methane flame (recalculation of ONERA experiment) | Right: Simulation of turbulent combustion in a sub-scale combustion chamber (LOX / methane flame)
Experts of the German Research Foundation have repeatedly stated that our SFB-TR40 projects are important for the SFB as a whole. The models developed by LRT-10 to describe thermodynamics, flow, and combustion in rocket combustion chambers have been adopted by several other research groups of SFB-TR40. With the methods we developed, we have also successfully predicted combustion and wall heat flow in combustion chamber configurations developed by ASTRIUM. This demonstrates the applicability of the calculation methods. In addition, ASTRIUM / ARIANE Space gained valuable insights into the development of future combustion chambers.
Funding for SFB-TR40 was granted for three periods of four years each, which was the maximum possible. The project ended on June 30, 2020 (it was extended by three months due to the Covid-19 pandemic). As part of SFB-TR40 projects, six doctorates were awarded at LRT-10, three of them with distinction. Three further doctoral degree projects are almost completed.
Our research findings have been published internationally in 24 peer-reviewed articles and more than 30 conference papers. Some of the publications (particularly about the numeric simulation of high-pressure flow and simulation in sub-scale combustion chambers) are frequently cited. We have thus contributed to the excellent reputation of UniBw M in the research community.