Complex gravity-acoustic impact on V-flame structure

Development of efficient and safe energy systems for space objects includes ensuring fire safety. This problem requires a deep understanding of influence of gravitational forces on combustion processes, which explains the importance of studying this issue. The paper analyzes the dynamics of inverted conical methane-air flame under conditions of normal and reverse gravitational force with external acoustic excitation. Applied frequencies of acoustic excitation could be parasitic or be produced during proper work of different technical systems of aircraft. High speed recording of flame chemiluminescence and PIV analysis were conducted. Decomposition of flow vector pictures into the modes was calculated using POD method. Energy contribution into the flow was analyzed for its separate elements at the different frequencies of excitation. At the high excitation frequencies vortex generation intensity in the shear layer with reverse gravity is about the same as it was observed in the experiments with normal gravity direction, that could indicate dominance of acoustic mechanism of the vortexes stimulation over the mechanism of shear instability. At external excitation frequency equals 240 Hz significant growth of shear vortex diameters and increasing of perpendicular oscillations amplitude of flame branches were obtained. Thereby in such experiment with 240 Hz external acoustic excitation the most intensive large scale instability of flow was observed.

Automated summary

Fire safety is crucial for the development of efficient and safe energy systems for space objects. This paper focuses on studying the influence of gravity on combustion processes and analyzes the dynamics of inverted conical methane-air flame under external acoustic excitation. The results show that at high excitation frequencies, the intensity of vortex generation is similar to that observed in experiments with normal gravity, indicating the dominance of acoustic mechanism. Additionally, at an external excitation frequency of 240 Hz, significant growth in shear vortex diameters and increased amplitude of perpendicular oscillations of flame branches were observed, indicating the most intensive large scale instability of flow.