Experimental and Numerical Investigation into Buoyancy Induced Instabilities in Laminar Methane Diffusion Flame

Tamboli, Nikhil Kumar and Balusamy, Saravanan (2019) Experimental and Numerical Investigation into Buoyancy Induced Instabilities in Laminar Methane Diffusion Flame. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

The soul objective is to study flow structure and flow instability caused by buoyancy called as Kelvin Helmholtz instability in the upstream region of methane jet flame. A low density methane flame jet at low Reynolds number introduced into a high density air is known to display self-excited pulsations which is escorted by vortical structures across the flame. Oscillations at identical frequency are detected. Global oscillation frequency observed varies from 10 to 15 Hz. The generation and progression of eddies and scalar structures are examined for methane fuel which is discharged from a 4 mm diameter vertical tube into the ambient. Oscillations near the jet exit region are originated and are found to spread in the downstream direction. The characteristics of the flow and vortex formation at Re=500 are investigated and discussed. Quantitative schlieren visualization technique and Computational fluid dynamics analysis are performed to evaluate this buoyancy induced K-H instability. Experimentally, schlieren visualization setup is adopted to capture the density gradient profile of the methane flame jet. Numerically, large eddy simulations (LES) is carried out to capture methane jet diffusion flame instabilities and its interaction with the surrounding. The unsteady and laminar methane fuel jet introduced into quiescent air is simulated using general purpose CFD solver, FLUENT. Numerically, LES effectively anticipated the key characteristics of this oscillating buoyancy driven methane flame. Buoyancy effects and instability are evaluated by schlieren visualization techniques which captured density gradient profiles. The computed frequency and experimentally measured frequency are found to be identical.

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