Research

Research of the TFD group focuses on thermoacoustic combustion instabilities. These impair the security and reliability of gas turbines and rocket motors as well as domestic or industrial burners. In order to analyse and control these instabilities, fluid mechanics, acoustics and combustion science are combined in an interdisciplinary approach with methods of system identification and control theory. Intensive exchange with colleagues from research institutes in- and outside Europe furthers our efforts.

The BBC Documentary Space Race discusses in  Episode Four  briefly the severe difficulties with combustion instability of the Saturn V rocket's  F-1 engine. Start watching at about 5:00 minutes into the movie! These difficulties were ultimately overcome by a brute force effort at great expense. A short video clip on Acoustic instability in a combustion chamber by Prof. Thierry Poinsot from IMFT in Toulouse demonstrates the phenomenon, introduces the basic interaction mechanisms between combustion and acoustics and also mentions the challenges that designers in industry have to face.

Current fields of research

The ongoing projects in the TFD group contribute to several topics, as listed below. For several projects updates in video format are presented on our YouTube channel.

• Flame Dynamics 
  In the context of thermoacoustic instabilities, it is essential to predict and analyse the dynamic response of a flame to flow perturbations. Various types of flow perturbations are relevant, e.g. modulation of velocity, swirl or equivalence ratio. Analytical models for laminar flame dynamics provide important insight into flow-flame interaction mechanisms and allow to identify relevant time scales. For turbulent flames, a combination of Large Eddy Simulation of reactive flow with system identification provides quantitative information for configurations of applied interest. Recent interest focuses on spray flames.

• Combustion Noise 
  We strive to predict the generation of noise by enclosed turbulent flames and understand the relevant flow-flame-acoustic interactions. Ultimately, we want to devise and assess the effectiveness of approaches to reduce combustion noise.

• Uncertainty Quantification in Combustion Dynamics
  Thermoacoustic combustion instabilities can respond in a very sensitive manner to slight changes in operating or boundary conditions. It is thus very important to quantify the uncertainties in thermoacoustic stability analysis and/or determination of flame dynamics.

• Intrinsic thermoacoustic feedback and its implications for combustion dynamics
  We have identified in recent work the intrinsic thermoacoustic (ITA) feedback mechanism, a flow-flame-acoustic interaction mechanism that has been overlooked by the research community until now. It is now important to check and re-evaluate the established understanding and procedures of thermoacoustic analysis and design. We plan to study interactions of ITA and cavity modes, the relation between flame dynamics and ITA feedback, as well as the consequences of ITA resonances for combustor stability, control of thermoacoustic instabilities and combustion noise.

• Linearized Reactive Flow
  The goal is to develop numerical tools to solve linearized governing equations for reactive flows. We aim for using the tools to analyze the dynamics and stability of reacting flows, in particular premixed flames.

• taX - State-Space Interconnect Models for (Thermo-) Acoustics
  The TFD group is developing a state-space-based modelling framework for aero- and thermoacoustics. This approach allows to integrate a wide range of modelling approaches for thermoacoustic analysis; to compute shape, frequency and growth rate of eigenmodes; to determine acoustic scattering matrices and transfer functions; and to compute nonlinear triggering and/or limit cycles. All this in an open-source, user-friendly, extensible software environment! That is why several video tutorials can be found on our YouTube channel.