Technical Analysis of Combustion Dynamics in Single Annular Combustor (SAC) Sectors

1. Introduction to Thermo-Acoustic Instabilities

Thermo-acoustic instabilities represent a significant obstacle in the advancement of lean-premixed gas turbine technology. These phenomena are governed by the constructive coupling between unsteady heat release (q') and acoustic pressure oscillations (p'), as described by the Rayleigh Criterion.

When these fluctuations occur in phase, the acoustic field extracts energy from the combustion process, leading to high-amplitude pressure pulsations.

In modern swirl-stabilized systems, these instabilities are driven by:

• Feed-coupling mechanisms: Equivalence ratio oscillations at the burner inlet.
• Hydrodynamic instabilities: Vortex shedding and swirling flow periodicity.