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Dynamics of premixed hydrogen flames forced by harmonic velocity oscillations : scaling and prediction of transfer functions

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Bibliographic Details
Title: Dynamics of premixed hydrogen flames forced by harmonic velocity oscillations : scaling and prediction of transfer functions
Authors: Gopalakrishnan, Harish S., Gruber, Andrea, Bothien, Mirko R.
Publisher Information: ZHAW Zürcher Hochschule für Angewandte Wissenschaften, 2025.
Publication Year: 2025
Subject Terms: Sustainable combustion, Combustion instability, Computational fluid dynamics, 620: Ingenieurwesen
Description: Hydrogen and ammonia are crucial carbon-free fuels to ensure sustainable power production with minimal 𝐶𝑂2 emissions in gas turbines. These carbon-neutral fuels possess different combustion properties to that of natural gas: increased reactivity (laminar consumption speed) and non-unity Lewis numbers (propensity for thermo-diffusive instabilities). Therefore, the implications of a change in fuel on the flame dynamic characteristics must be better understood. This is important in the context of thermoacoustic instabilities, which is an important practical problem affecting the stable operation of aircraft gas turbine combustors. In this work, we examine the response of hydrogen-air premixed flames to acoustic perturbations. We consider a geometrically simple slit-flame configuration where the kinematic restoration is the primary mechanism driving the flame response to acoustic disturbances. We compute the flame transfer functions of hydrogen flames and elucidate the differences to natural gas flames using high-fidelity numerical computations. Further, the computational results are also compared to analytical models based on the flame front tracking equation (G-equation) to reveal useful insight on the scaling of the transfer functions. The key contribution of this paper is the proposition of a parameter based on the stretch-affected global consumption speed to scale the transfer functions of hydrogen flames across different conditions.
Document Type: Conference object
Language: English
DOI: 10.21256/zhaw-32147
Accession Number: edsair.doi...........922b547ffc6a021d5130d922d3589b4e
Database: OpenAIRE
Description
Abstract:Hydrogen and ammonia are crucial carbon-free fuels to ensure sustainable power production with minimal 𝐶𝑂2 emissions in gas turbines. These carbon-neutral fuels possess different combustion properties to that of natural gas: increased reactivity (laminar consumption speed) and non-unity Lewis numbers (propensity for thermo-diffusive instabilities). Therefore, the implications of a change in fuel on the flame dynamic characteristics must be better understood. This is important in the context of thermoacoustic instabilities, which is an important practical problem affecting the stable operation of aircraft gas turbine combustors. In this work, we examine the response of hydrogen-air premixed flames to acoustic perturbations. We consider a geometrically simple slit-flame configuration where the kinematic restoration is the primary mechanism driving the flame response to acoustic disturbances. We compute the flame transfer functions of hydrogen flames and elucidate the differences to natural gas flames using high-fidelity numerical computations. Further, the computational results are also compared to analytical models based on the flame front tracking equation (G-equation) to reveal useful insight on the scaling of the transfer functions. The key contribution of this paper is the proposition of a parameter based on the stretch-affected global consumption speed to scale the transfer functions of hydrogen flames across different conditions.
DOI:10.21256/zhaw-32147