IGM Colloquium: Flame and thermoacoustic dynamics in gas turbine combustors

Reacting flow instabilities in gas turbine and aeroengine combustion chambers must be understood and controlled in order to ensure safe and reliable operation and to increase the systems performances. The research presented in this talk is based on experiments (e.g. planar laser induced fluorescence, particle image velocimetry, acoustic piezosensors), large eddy simulations and low order modelling. In the first part, the problem of transition from autoignition to flame-propagation, which has a direct impact on ignition failure and on flashback risk, will be discussed. This phenomenon is highly relevant for the sequential combustors in the latest generation of heavy duty gas turbines, which enable fast balance of the intermittent production from renewable sources.
In the second part of the talk, recent progress on the understanding and control of thermoacoustic instabilities in combustion chambers will be presented. In real systems, it is very challenging to predict thermoacoustic instabilities. They must be avoided at all cost because they strongly impact the lifetime of the combustor parts. Several approaches like acoustic networks, linearised Euler or Navier-Stokes equations, compressible large eddy simulations can be used to attack the problem. In this presentation, one focuses on low order modelling in the form of coupled delayed differential equations with stochastic forcing in order to unravel nonlinear phenomena like avoided-bifurcations or synchronisation of eigenmodes. The statistics of the thermoacoustic transient obtained by solving the associated Fokker-Planck equations closely match the experimental observations. It will also be shown that the suppression of the limit-cycles using acoustic dampers is best achieved when the latter are tuned to the exceptional points of the thermoacoustic system.

Bio:
Nicolas Noiray is Assistant Professor at ETH Zürich, where he leads the laboratory of “Combustion and Acoustics for Power and Propulsion Systems” since August 2014. He obtained his Ph.D. from the Ecole Centrale Paris in 2007, and subsequently joined the Combustion Department of the Gas Turbine Research Division of Alstom. His research at ETH focuses on the modeling and control of reacting and non-reacting flows in practical systems like gas turbines for power generation, aero-engines or cryogenic rocket engines.The unifying theme of the experimental, theoretical and numerical research performed by his group is the study of flow instabilities at various time and length scales.