Session: 04-09 Combustion Dynamics III

Submission Number: 178102

Stable Exceptional Point-Based Thermoacoustic Design of a Turbulent Can-Annular Combustor 

Thermoacoustic instabilities are a major bottleneck for the development of modern, low-emission energy systems such as rocket engines or gas turbines [1]. Such systems may be modeled and designed by means of thermoacoustic network analysis, and the resulting thermoacoustic eigenvalue spectrum. However, the complexity of these systems, e.g., industry-scaled annular and can-annular configurations, makes the design challenging: large systems involve multiple possible combinations of system parameters; the impact of one parameter variation on the resulting change of the system’s stability cannot be predicted a-priori, especially when multiple parameters are modified together. These problems persist also when the thermoacoustic eigenmodes are traced back to their respective acoustic or intrinsic thermoacoustic (ITA) nature.

To overcome these challenges, Casel and Ghani [2,3] focussed on exceptional points (EPs) that were only recently found in thermoacoustic spectra [4]: EPs constitute points in the spectrum where the acoustic and ITA mode branches interplay the strongest and therefore contain a relation between the respective mode origins that is of high relevance for stability of the entire thermoacoustic system. Based on this, Casel and Ghani [2] conzeptualized the EPTD (Exceptional Point-based Thermoacoustic Design) method: shift the EP towards smaller growth rates, and by this, shift the entire thermoacoustic spectrum while preserving the original relations between EP and mode origin.

While the EPTD method succesfully stabilized three different longitudinal thermoacoustic configurations that were originally unstable [3], its applicability for configurations featuring rotational symmetry, e.g., can-annular combustors, that are of relevance in gas turbine applications, remains an open question. Therefore, in this study, we extend the EPTD framework to an unstable laboratory-scale can-annular combustor that was experimentally studied [5] and demonstrate it's applicability for stabilizing the configuration.

We first validate our model by means of experimentally recorded unstable sound pressure level spectra. Subsequently, we identify multiple EPs for different azimuthal wave numbers, i.e., clusters of EPs, which we analyze with respect to system parameter variations not only seperately but also as a whole. Thereafter, we apply the extended method and demonstrate its applicability by shifting the EPs towards the stable half plane in the spectrum, which results in stabilized spectra.

References:
[1] T. Poinsot, Prediction and control of combustion instabilities in real engines, Proc. Combust. Inst. 36, 1 (2017).
[2] M. Casel and A. Ghani, A novel method for stable thermoacoustic system design based on exceptional points - Part I: Conceptualization, Combust. Flame 267, 113559 (2024).
[3] M. Casel and A. Ghani, A novel method for stable thermoacoustic system design based on exceptional points - Part II: Application to laminar and turbulent flame configurations, Combust. Flame 267, 113558 (2024).
[4] G. A. Mensah, L. Magri, C. F. Silva, P. E. Buschmann, and J. P. Moeck, Exceptional points in the thermoacoustic spectrum, J. Sound Vib. 433, 124 (2018).
[5] P. E. Buschmann, N. A. Worth, and J. P. Moeck, Thermoacoustic oscillations in a can-annular model combustor with asymmetries in the can-to-can coupling, Proc. Combust. Inst. 39, 5707 (2023).

 

 

Presenting Author: Mario Casel Chair of Reactive Flows

Presenting Author Biography: Mario obtained his MSc.-degree in Engineering Science. After this, he joined the DMF-group at TU Berlin. Now he is a research assistant at the Chair of Reactive Flows at the Leibniz Universität Hannover. Here, he investigates Exceptional Points (EPs) in thermoacoustics.

Authors:

Mario Casel Chair of Reactive Flows
Abdulla Ghani Chair of Reactive Flows