Impact of vibrating combustion chamber wall on flame thermoacoustic dynamics

Combustion instability is a critical challenge in rocket engines, aero-engines, and gas turbines. It can induce acoustic–structure coupling that imposes substantial mechanical loads on combustion chamber walls, leading to strong vibrations, which, in turn, influence flame dynamics. Prior research works have deepened the understanding of the interactions between solid boundaries and fluid flows, yet their consequent effects on flame dynamics remain insufficiently explored. The distance between the flame and the wall (δ) is expected to play a key role in modulating the flame's thermoacoustic dynamic response, which forms the focus of this study. An experimental system was developed to investigate the influence of a vibrating wall on flame dynamics, with δ conveniently adjustable. Results show that decreasing δ leads to stronger flame–wall interactions, causing the flame to become increasingly asymmetric, promoting cyclic blow-off and reattachment, and inducing strongly nonlinear heat release fluctuations with pronounced harmonic distortions, particularly under low-frequency excitation. In addition, it shifts the energy distribution toward longitudinal vibrational modes with enhanced coherence in lower-order modes. By contrast, increasing δ weakens flame–wall interactions, resulting in more symmetric flame dynamics, a linear global response, and energy preferentially distributed in transverse vibrational modes. High-frequency vibrations consistently excite small-scale flame wrinkling and forced oscillations, while steady flame deflection near the vibrating wall introduces noticeable asymmetry in wrinkle propagation. These findings provide important experimental evidence for understanding the coupled thermal–flow response induced by combustion chamber wall vibrations.