Session: 04-27 Combustion Dynamics - Modeling

Paper Number: 152879

Linear Stability Analysis of Transversal Thermoacoustic Modes in Reheat Combustors 

Gas turbines featuring sequential combustion architectures are ideally suited to deliver carbon emissions free, fuel flexible and on-demand power to the grid. A sequential combustor is comprised of two axially staged combustion chambers with the first stage typically being a swirl-stabilised propagating flame. Post first stage combustion, the exhaust stream is diluted with air and later enriched with additional fuel in the second stage resulting in a vitiated product mixture at high temperatures leading to auto-ignition in the second combustor. Thereby, the sequential combustion architecture can be leveraged to vary the fuel split between the combustion chambers to account for different reactivities of gas turbine fuels. Thermoacoustically stable combustion stages are critical to ensure low emissions, high reliability, and mechanical integrity. Under specific conditions the second stage, which is firing under auto-ignition conditions, can be subject to transversal instabilities. This article presents a finite element-coupled method, which has shown to work for a lab-scale reheat combustor, to model the thermoacoustic behaviour of the Ansaldo Energia H-class GT36 reheat combustion stage in a two-dimensional efficient and cost-effective approach. To do so, flame modelling theory from planar wave thermoacoustics is leveraged to quantify the auto-ignition flame's heat release response. Subsequently, transverse eigenmode stability predictions are made and validated against experiments performed under engine conditions. We show that the framework can correctly predict the stability of high-frequency combustor modes. Consequently, it can be leveraged to get reliable and time-efficient stability estimates of high-frequency thermoacoustic modes in industrial reheat combustion chambers.

The work is part of the EU and Swiss funded FLEX4H2 project.

Presenting Author: Simon Manuel Heinzmann ZHAW Winterthur

Presenting Author Biography: Studied Mechanical Engineering in the Bachelor and Master studies at ETH Zürich.
Currently performing research on thermoacoustics of auto-ignition flames at ZHAW Winterthur as part of my Doctoral studies at ETH Zürich.

Authors:

Simon Manuel Heinzmann ZHAW Winterthur
Harish Subramanian Gopalakrishnan ZHAW Winterthur
Birute Wood Ansaldo Energia Switzerland AG
Mirko Ruben Bothien ZHAW Winterthur