The tonal sound production during thermoacoustic instability is detrimental to the components of gas turbine and rocket engines. Identifying the root cause and controlling this oscillatory instability would save manufacturers from investing in maintenance and power outages costs. An optimal method is to identify the regions that are critical to tonal sound production and perform control measures onto that region. Passive control experiments were performed on a bluff-body stabilized combustor by injecting a secondary jet of air. Simultaneous measurements such as unsteady pressure, velocity, local and global heat release rate fluctuations are acquired during the regime of thermoacoustic instability and also in the optimized controlled regime of thermoacoustic instability. Secondary jet is injected into the critical region identified to be in the region between the dump plane and the leading edge of the bluff-body. To understand the saddle point dynamics that dictate the flame dynamics, strain lines are obtained from the saddle point that is present in the upstream of the bluff-body during thermoacoustic instability. Upon implementing the passive control measures during the thermoacoustic instability regime, nearly 89% of suppression in terms of r.m.s (root mean square) of pressure fluctuations is observed. Using the wavelet transform, we see that the coherence in the dominant frequency during thermoacoustic instability becomes incoherent during the suppressed stage. This incoherence of dominant frequency in time is seen as a loss of periodicity in the Lagrangian coherent structures (LCS) extracted from the flow-field during the suppressed stage of thermoacoustic instability.


Smart Passive Control of Thermoacoustic Instability in a Bluff-Body Stabilized Combustor: A Lagrangian Analysis of Critical Structures

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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