Memory effects of local flame dynamics in turbulent premixed flames |
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| Affiliation: | 1. Steinbuch Centre for Computing, Karlsruhe Institute of Technology Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany;2. Engler-Bunte-Institute, Division of Combustion Technology, Karlsruhe Institute of Technology, Engler-Bunte-Ring 1, 76131 Karlsruhe, Germany;3. Department of Mechanical Engineering, Stanford University, Stanford CA 94305, USA;1. State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China;2. School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, China;3. Department of Mechanical Engineering and Science, Kyoto University, Kyoto 615–8540, Japan;4. College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310023, China;1. Simulation of Reactive Thermo-Fluid Systems, TU Darmstadt, Otto-Berndt-Straße 2, Darmstadt 64287, Germany;2. Institut für Technische Verbrennung (ITV), Universität Stuttgart, Pfaffenwaldring 31, Stuttgart 70569, Germany;3. Institute for Combustion and Gasdynamics (IVG), Chair for Fluid Dynamics, University of Duisburg-Essen, Carl-Benz Straße 199, 47057 Duisburg, Germany;1. SKLTCS, CAPT, BIC-ESAT, College of Engineering, Peking University, Beijing 100871, China;2. Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, 117575, Singapore;3. Steinbuch Centre for Computing, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany;4. Engler-Bunte Institute/Division of Combustion Technology, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany |
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| Abstract: | A premixed and thermo-diffusively unstable turbulent hydrogen-air flame-in-a-box case is simulated in conjunction with the flame particle tracking (FPT) method. The flame is located in the flamelet regime. The focus lies on the assessment of memory effects in local flame dynamics. By tracking flame particles on an iso-surface of the flame during flame-turbulence interaction, the time history of flame speed and flame stretch can be recorded for each point on the flame iso-surface in a Lagrangian reference frame. The results reveal a time delay between the local flame speed and flame stretch signal, showing that previous values of flame stretch affect currently observed values of flame speed. Furthermore, by choosing flame particles whose trajectories are dominated by single frequencies, the time delay can be quantified. While plotting instantaneous values of flame speed and flame stretch results in a large scattering for turbulent flames, a quasi-linear correlation can be achieved by shifting the time signal of flame stretch according to the time delay. The time delay itself depends on the local flow time scale, which is expressed as a local Damköhler number. There is, however, an important difference between consumption and displacement speed. While most analyses in the literature are limited to the flame displacement speed, the flame consumption speed is evaluated for each flame particle in this work as well, which shows a strong correlation with the local equivalence ratio even at unsteady conditions. As the flame particles move toward regions with more negative flame stretch, the consumption speed decreases as the flame locally extinguishes. At the same time, the diffusive component of the displacement speed increases, as the tangential component of the diffusive flux increases in regions with strong negative flame curvature. |
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