Dynamics of Swirl and Jet Flames (SWJET)

• Applicants: Professor Dr.-Ing. Kilian Oberleithner; Professor Wolfgang Polifke, Ph.D.
• Subject Area: Hydraulic and Turbo Engines and Piston Engines ; Acoustics ; Fluid Mechanics ; Technical Thermodynamics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 441269395

The prediction and control of thermoacoustic combustion instabilities (TCIs) poses severe challenges to the development of efficient lean premixed combustion systems. A crucial input for current TCI models is the flame transfer function (FTF), which represents the response of the flame to acoustic forcing. It is currently deduced from extensive measurements, high-fidelity numerical simulations, or strongly simplified analytic models. In the SWJET project we propose to develop a holistic method to determine the FTF and the related flow and flame dynamics from the pertinent governing equations linearized around a base state, i.e. time-averaged distributions of flow variables of the unperturbed turbulent flame. This Linearized Reactive Flow (LRF) approach was recently explored by Avdonin et al., Proc. Comb. Inst. 2019. Promising result were obtained, but the study was limited to a laminar flame based on one-step chemistry. The central goal of the SWJET project is to extend the application range of LRF solvers to more complex reaction mechanisms and turbulent flames. The SWJET project is structured in three Work Areas (WA). WA 1 will focus on laminar flames. More advanced chemistry models will be integrated in the linearized solver. Flame dynamics obtained in the linear framework will be validated against nonlinear numerical simulations of forced and self-excited flames. WA 2, which constitutes the core of this project, will explore the applicability of the linearized methods to turbulent reacting flows and validate results against LES of a turbulent jet flame. The linear methods will be applied to predict the flow and flame response to acoustic harmonic forcing and to improve the understanding of the relevant physical mechanisms. In WA 3, the workflow of WA 2 is repeated for a turbulent swirl flame. Special focus will be on the generation and transportation of swirl waves, as well as their impact on flame dynamics. Both research groups contributed significantly to the state-of-the-art of analysis and modeling of flame dynamics. In particular, the expertise at TUB is on describing flow dynamics in highly turbulent reacting flows. The group at TUM, in contrast, has acquired significant complementary experience in treating reacting laminar flows in a linearized framework. The linearized solvers from both institutes will be merged in an early stage of the project. Due to their complementary specialties this will propel the research lined out in this proposal. The methods that are to be developed in SWJET constitute a leap forward in combustion science, as they open up new ways to analyze and control flame dynamics in general and TCIs in particular. The SWJET project will be co-funded by the FVV at a rate of 24%, which covers the personal costs of the third WA. The projects further benefits from another, experimental FVV project at TUB, providing empirical data for model validation of the turbulent jet and swirl flames.

• DFG Programme: Research Grants