Study on Nonlinear Dynamics Using the State Space of Combustion Oscillation in a Rocket Combustor

Abstract

Combustion oscillation in a rocket combustor was analyzed using a Variational Auto-Encoder (VAE). Dimension reductions were conducted on various physical quantities (p′, ˙q′, etc.) in the combustor. Orthogonal modes were obtained using proper orthogonal decomposition for the output of VAE. Pumping and damping regions in the combustor were identified using the distribution of the Rayleigh Index for each mode. Three characteristic modes were identified that supply energy to the oscillation. A phase plane was spanned by the latent variables obtained by the reductions. Activation of each of the characteristic six modes was mapped on the plane. The three characteristic modes were found to be activated at different phases. From the trajectory of the oscillation on the plane, the plane was confirmed to satisfy the requirements to be a state space. In the high-pressure amplitude phase, the pumping regions near the combustor wall were clarified.