LES study of bluff-body stabilized hydrogen turbulent flame subjected to axial and tangential excitations

  • Caban, Lena (Czestochowa University of Technology)
  • Wawrzak, Agnieszka (Czestochowa University of Technology)
  • Tyliszczak, Artur (Czestochowa University of Technology )

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In this paper, we perform numerical analysis of a turbulent flame in a model combustion chamber. The flame is stabilised by a conical bluff-body, which role is to create recirculation zone (RZ) that enables efficient mixing of fuel injected from a centre of the bluff-body and oxidizer supplied from its surrounding. In real configurations the mass flow of the fuel and/or oxidizer streams can undergo oscillations resulting from a supplier system, thermo-acoustic instabilities or due to nature of turbulent flow. These oscillations can have positive or negative impact on flame dynamics (position, size, temperature), they can intensify the mixing process and thus facilitates the combustion, or lead to local high strain regions causing flame extinctions. To mimic the oscillations, we assume varying amplitude and varying frequency harmonic excitation of the bulk mass flow rate. We analyse the impact of the excitation parameters on a size and position of the recirculation zone, flame localisation and combustion process parameters. The research is performed with the help of large eddy simulation (LES) method [1] to model a turbulent flow and Eulerian PDF approach for combustion modelling [2]. The simulations are carried out applying ANSYS-CFD software and an in-house high-order code SAILOR. The basic configuration reflects an experimental stand known as Sydney bluff-body burner [3]. The results obtained in [3] allows us to validate the simulation results and tune parameters of the numerical model, e.g., a mesh density, simulation and time-averaging time, LES and combustion model settings. Preliminary results show good agreement between the simulation and experimental data. The applied excitation leads to both qualitative and quantitative alteration of the flame dynamics. Changes of the excitation strength and frequency cause significant alteration of the axial and radial extend of RZ. This impacts on the amount of the oxidiser transported to the RZ center and its mixing with the fuel. In effect, the shape of the flame, localization of temperature maximum, species mass fractions and amplitudes of their variations are dependent on the excitation. REFERENCES [1] B.G. Geurts, Elements of Direct and Large-eddy Simulation, R.T. Edwards, (2004). [2] L. Valino, Flow Turbul. Combust., 60, 157–172 (1998). [3]