Effects of Integral Scale on Darrieus–Landau Instability in Turbulent Premixed Flames
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Previous studies have revealed the existence of distinct regimes of DL-stable and unstable turbulent flames, depending on whether the DL instability could be minimized or not. The mechanism of how mixture composition, flame macroscale and turbulence intensity, etc. act on DL instability has been extensively studied. Even though, the role played by turbulent length scale on DL instability is still unclear. The present study has been experimentally focused on the effect of turbulent integral scale on DL instability of premixed turbulent Bunsen flames. Flame fronts of C3H8/air mixture (ϕ = 0.8) under different turbulence conditions are captured by OH-PLIF technique. It is observed that the DL-unstable flames, obtained at relatively large integral scale and with cusps observed on the flame fronts, transform to be DL-stable flames with planar or disorderly wrinkled flame fronts as the integral scale decreases, indicating the indispensable role of integral scale on DL instability. These cusps on DL-unstable flame fronts decrease flame surface density while enlarge flame volume. Turbulent burning velocities of DL-unstable flames are augmented compared to DL-stable flames, leading to a similar dual-propagation model as observed in literatures. The threshold where turbulence shadows DL instability is analyzed by upgrading a previous model of [Phys. Rev. E 84 (2011) 026322]. The modified model is more reliable to demonstrate the DL-stable and unstable regimes in the Peters-Borghi’s diagram.
KeywordsTurbulent premixed flames Bunsen flames Darrieus–Landau instability Integral scale Turbulent flame diagram
This study is supported by National Natural Science Foundation of China (No. 51776164, 91441203). The support from The State Key Laboratory of Engines, Tianjin University (K2017-03) and the State Key Laboratory of Laser Interaction with Matter (SKLLIM1508) are also appreciated.
This study was funded by National Natural Science Foundation of China (No. 51776164, 91,441,203).
Compliance with Ethical Standards
Conflict of Interests
The authors declare that they have no conflict of interest.
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