Numerical Investigation of a Bias-Flow Perforated Liner for Damping of Thermoacoustic Instabilities

Abstract

Lean premixed prevaporized (LPP) gas turbine generators are naturally prone to thermoacoustic instabilities. Strategic placement of passive damping devices can provide simple, effective fixes for such unstable behavior. In this work, the thermoacoustic damping characteristics of a perforated liner with mean bias flow are examined. A recently-developed theoretical model, along with accompanying experimental investigation, has demonstrated that a bias-flow liner can very effectively absorb incident acoustic waves. Here, a modular simulation tool is utilized to examine the capability of the liner for stabilizing an unstable ducted flame. The simulation tool represents the acoustic interactions between duct elements in the form of transfer matrices, which can be modularly arranged for exploring a variety of configurations. An unstable thermoacoustic system is produced with a gain-delay flame model in a duct. The frequencies and growth rates of the linear model are examined. It is shown that, by tailoring the liner porosity and the bias flow, unstable modes of the thermoacoustic system can be stabilized. Furthermore, it is found that, for a double liner system, there is an optimal liner porosity for a given choice of bias flow, at which the modal decay rate is maximized.