Vortex-driven acoustically coupled combustion instabilities

TLDR

The study investigates combustion instability in a multiple‑inlet combustor with dump, verifies the global Rayleigh criterion, and proposes a mechanism for low‑frequency vortex‑driven instabilities. Using spark‑schlieren and phase‑average C₂‑radical imaging, the authors map non‑steady heat release, describe vortex shedding, growth, interaction, and burning, and determine the phase relationships between pressure, velocity, and heat‑release fluctuations to elucidate the vortex‑driven instability mechanism. Low‑frequency instabilities are acoustically coupled and occur at the system’s eigenfrequencies, confirming the global Rayleigh criterion and supporting the proposed vortex‑driven mechanism.

Abstract

Combustion instability is investigated in the case of a multiple inlet combustor with dump. It is shown that low-frequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system. Using spark-schlieren and a special phase-average imaging of the C 2 -radical emission, the fluid-mechanical processes involved in a vortex-driven mode of instability are investigated. The phase-average images provide maps of the local non-steady heat release. From the data collected on the combustor the processes of vortex shedding, growth, interactions and burning are described. The phases between the pressure, velocity and heat-release fluctuations are determined. The implications of the global Rayleigh criterion are verified and a mechanism for low-frequency vortex-driven instabilities is proposed.