Combustion Noise and Combustion Dynamics
Institute of Aerodynamics, RWTH Aachen University (Germany)
Local Project ID:
HPC Platform used:
JUQUEEN of JSC
Research in combustion noise is increasingly gaining interest for mainly two reasons. First, combustion noise can lead to thermoacoustic instabilities. Especially the lean-premixed regime, which is favorable for a highly efficient combustion process with low emissions, is prone to an unstable feedback loop between the flame's unsteady heat release and its resulting acoustic emission that can lead to hazardous loads within the combustion chamber. Second, combustion noise is expected to become an important contributor to the overall sound emission of future jet aero engines, since the sound emission of the other components, such as jet noise, fan noise, etc., is being reduced through recent technological progress.
The goal of this project is to gain a deeper understanding of the acoustic source mechanisms, which is necessary for the prediction and the control of thermoacoustic instabilities in future combustor systems at lean premixed conditions. This is achieved by a hybrid simulation approach. First, the combustion process is predicted with a large-eddy simulation. The resulting flow field determines the noise sources, which are used in the second step to compute the generation and propagation of the acoustic waves. With this approach, the acoustic emission can be analyzed for various setups, i.e., depending on flow parameters, flame parameters and the burner geometry. The numerical data is used to further analyze the interaction between the turbulent flow field, the flame, and the acoustic field.
Figure 1 shows a juxtaposition of the flame shape of an experimental image (left) with LES results and a snapshot from the LES computation (right). The good agreement with the experiment is achieved with a highly resolved flow field and a level-set approach for the flame front which is especially suitable for the analysis of lean-premixed flames due to their thin reaction zones.
Figure 2 shows the mean velocity magnitude with the mean flame front contour and the streamlines of the flow (left). Furthermore, a video of the vorticity field is shown on the right side together with the flame front contour. At the bottom of the flame vortices evolve periodically due to the hydrodynamic instability of the shear layer. These interact with the flame especially at the base of the flame. It is mandatory to correctly capture this flame-vortex interaction to accurately predict the sound emission of the flame.
The highly-resolved simulations performed in this project require the extensive usage of HPC systems. The LES simulations are performed on JUQUEEN of JSV on 16384 cores. For the computational aeroacoustics simulation (CAA) 6000 snapshots from the LES computation are required. The results of the CAA simulations gave new insights to fundamental sound-generation mechanisms and their phase-relationship.
Project Team and Scientific Contact
M.Sc. Sohel Herff, Dr.-Ing. Matthias Meinke, M.Sc. Konrad Pausch, Prof. Dr.-Ing. Wolfgang Schröder (PI)
Institute of Aerodynamics
RWTH Aachen University
Wüllnerstraße 5a, D-52062 Aachen (Germany)
e-mail: office [@] aia.rwth-aachen.de
JSC project ID: PRA094