Coupling of vibro-acoustic waves with premixed flame

We investigate the coupling between a premixed flame freely propagating inside a Hele-Shaw burner and the mechanical vibrations of the burner structure. The combustion chamber deformations are not only able to damp the classical thermo-acoustic instabilities but they can also trigger a new oscillating combustion instability. We demonstrate that the flow oscillations induced by the burner vibrations can be used to control the shape of the flame surface, by damping the Darrieus-Landau dynamics, or by triggering Faraday-like waves.

Figure 1

Left: Hele-Shaw burner consisting of two plates (one is a 19-mm-thick glass plate) separated by a 5-mm gap. Accelerometer probes can be placed on the plates and electret microphones are inserted in the cell side. A shaker can force the plates in Secs. 4 and 5. Center: Evolution of the pressure fluctuations during propane-air flame (equivalence ratio 1.2) propagation when the second plate is a PMMA plate of 8 mm thickness. Right: associated periodogram exhibiting an 11 Hz frequency.

Figure 2

Plate vibrations induced by a propane-air flame $\left(\phi =1.4\right)$ propagating downward with the 5-mm glass plate configuration. The strong oscillations that emerge when the flame is in the bottom part of the burner are recorded by two accelerometers at two different positions. (a) Signal recorded by the microphone at the bottom of the cell. (b) Detail in the black rectangle. The signals recorded by the two accelerometers are in phase opposition. (c) Fourier transform of the signal recorded by the upper accelerometer. The dominant mode emerges at $f=63$ Hz.

Figure 3

Left: Vibrating accelerations measured on the two plates. The first four resonant frequencies of the thin plate are highlighted by red arrows. Comparison of the theoretical plate mode shapes and frequencies (right) with the experimentally measured ones along the vertical with accelerometers (center).

Figure 4

Flow speed oscillations experienced by the flame when the plate is forced for the first and third resonant frequencies and corresponding front wrinkling that undergoes periodic restabilization and destabilization during its propagation. The restabilization (respectively, destabilization) zone corresponds to the antinodes (respectively, nodes) of the plate modes.

Figure 5

Flame propagation speed in the cell when forcing at 156 Hz. The velocity increases in the zones where Darrieus-Landau wrinkling is at play and decreases where the wrinkles are flattened by the parametric restabilization.