Numerische Untersuchung der Lärmentstehung und der Lärmabstrahlung turbulenter Flammen
Final Report Abstract
The acoustic field of generic lean premixed flames was analyzed by a hybrid approach. First, the effect of the numerical flame front description on the acoustic field by a turbulent flame was analyzed. The thickening of the combustion model showed an overall minor effect on the sound pressure level (SPL) spectrum. Only at a subfilter-variance σ/∆ = 4, the sound pressure level in the dominating region 10 < St < 25 decreases compared to the thinner flame’s sound emission. The investigation of the shear-layer effect showed that the shear-layer turbulence generates initial flame front perturbations that grow at a rate that depends on the hydrodynamic instability, which is mainly determined by the temperature ratio. For the more unstable flames, i.e., for higher temperature ratios the sound is generated mainly at the flame tip due to an increased growth of the flame front perturbations leading to large flame front deflections and flame pocket generation. For lower temperature ratios, the sound generated due to the interaction of the shear layer and the flame front near the flame base is more pronounced. Changing the burner from a slot to a round geometry has a similar effect. That is, the hydrodynamic instability of the flame decreases and the noise generation by the shear layer interaction with the flame front near the flame base becomes significant. This underlines the importance of an accurate description of the turbulent flow field for the prediction of the acoustic field of a round jet burner. In agreement with this, it was found that for the investigated experimental burner configuration the turbulent flow field has a significant impact on the acoustic spectrum. Discrepancies were found between the acoustic spectra of the measurements and numerical data when a reduced domain with synthetic inflow turbulence was used. Therefore, to accurately reproduce the experimental turbulent flow field and hence, the acoustic field, the full burner plenum was included into the LES domain. For this full burner-plenum computation, several peaks were observed in the pressure inside the burner plenum as well as in the far field. The peak frequencies correspond to the quarter-wave resonances of the burner plenum. It was found that the plenum acoustics influences the flow field and causes the flow to contain higher turbulent kinetic energy which reduces the length of the potential core compared to the computations without the burner plenum such that it quantitatively matches the experimental findings. The far-field acoustic pressure spectrum from the CAA simulation based on the sources determined by the full burner-plenum LES subsequently showed a very good agreement with the acoustic measurements. The validated numerical data was further used for a detailed source analysis. The analysis of the flame’s sound generation determined by the single thermoacoustic source terms of the acoustic perturbation equations revealed that not only the effect of heat release fluctuations but also the interaction of velocity fluctuations and entropy gradients at the flame front must be considered to accurately predict phase and magnitude of the pressure signal. The findings of the source analysis were further supported by the DNS data and the analysis of a set of forced laminar flames. It is concluded that the Rayleigh criterion, which considers only sound generation by heat release fluctuations, will fail for the investigated flames and has to be reformulated. The additional relevant acoustic source is connected to the local changes of the entropy gradient ∼ v ∆s' and to the change in the flow velocity at the flame front ∼ v' ∆s. These terms will vary with the operating conditions and geometry of the combustion device. Their impact has to be taken into account in an extended form of the Rayleigh criterion.
Publications
- (2020) Impact of burner plenum acoustics on the sound emission of a turbulent lean premixed open flame. International Journal of Spray and Combustion Dynamics 12 175682772095690
Herff, S.; Pausch, K.; Nawroth, H.; Schlimpert, S.; Paschereit, C. O.; Schröder, W.
(See online at https://doi.org/10.1177/1756827720956906) - „The effect of flame thickening on the acoustic emission in turbulent combustion“, AIAA Paper, no. 2016–2745, 2016
K. Pausch, S. Schlimpert, S. R. Koh, J. Grimmen, and W. Schröder
(See online at https://doi.org/10.2514/6.2016-2745) - „Acoustic flame response of a round and a slot burner“, AIAA Paper, no. 2017–3360, 2017
K. Pausch, S. Herff, S. Schlimpert, M. Meinke, and W. Schröder
(See online at https://doi.org/10.2514/6.2017-3360) - „Analysis of combustion noise of a turbulent premixed slot jet flame“, Combust. Flame, vol. 175(1), pp. 292–306, 2017
S. Schlimpert, S. R.Koh, K. Pausch, M. Meinke, and W. Schröder
(See online at https://doi.org/10.1016/j.combustflame.2016.08.001) - „Impact of turbulent inflow distributions on combustion noise of lean-premixed flames“, AIAA Paper, no. 2017–3219, 2017
S. Herff, K. Pausch, H. Nawroth, S. Schlimpert, C. O. Paschereit, and W. Schröder
(See online at https://doi.org/10.2514/6.2017-3219) - „Investigation of the acoustic flame response in turbulent combustion“, Proceedings of the ICTCA, p. 168., 2017
K. Pausch, S. Herff, S. Schlimpert, and W. Schröder
- „Numerical prediction of combustion noise for leanpremixed turbulent flames“, Proceedings of the Symposium for Combustion Control, pp. 231–240, 2017
S. Herff, K. Pausch, and W. Schröder
- „A Hybrid Level-Set LES / CAA Method for Thermoacoustic Analyses“, Proceedings of the DAGA, pp. 505–508, 2018
K. Pausch, S. Herff, W. Schröder
- „Noise sources of a lean-premixed jet flame“, AIAA Paper, no. 2018–4088, 2018
K. Pausch, S. Herff, H. Nawroth, C. O. Paschereit, and W. Schröder
(See online at https://doi.org/10.2514/6.2018-4088) - „Numerical and experimental investigation of the noise generation of a turbulent flame“, Proceedings of the Joint Meeting of the German and Italian Sections of the Combustion Institute, pp. 52–57 2018
K. Pausch, S. Herff, H. Nawroth, C. O. Paschereit. and W. Schröder
- „Numerical investigation of turbulent combustion noise using a hybrid LES/CAA approach“, Proceedings of NIC Symposium, pp. 413– 420, 2018
S. Herff, K. Pausch, M. Meinke, and W. Schröder
- „Noise sources of lean premixed flames“, Flow. Turbul. Combust., vol. 103(3), pp. 773–796, 2019
K. Pausch, S. Herff, F. Zhang, H. Bockhorn, and W. Schröder
(See online at https://doi.org/10.1007/s10494-019-00032-0) - „Sound sources of generic laminar and turbulent flames“, Proceedings of the 17th International Conference on Numerical Combustion, p. 50, 2019
K. Pausch, S. Herff, and W. Schröder
