Session: 04-38 Combustion dynamics - flame response I

Paper Number: 128680

128680 - Effect of Transverse Acoustic Excitation Over a Partially-Premixed Swirling Flame 

In this work, we investigate the effect of transverse acoustic excitation on non-premixed swirl stabilized flame. Gas turbine combustors face high amplitude self-sustained pressure oscillations called thermoacoustic instability. The instability occurs due to constructive interference between chamber acoustics and unsteady heat release rate in the combustion chamber. Due to longer circumferential length of annular combustion chamber in comparison to their streamwise length or height, these thermoacoustic instabilities are driven by azimuthal acoustic modes. Azimuthal instabilities in annular gas turbine combustors are one of the major challenges in aero-engines. This necessitates the study of response of a swirling flame to transverse acoustics under controlled conditions. We have designed and fabricated a multi nozzle (up to three nozzles) linear array combustor to simulate the flow conditions of an annular combustor. The nozzle features an axial swirler and a centre-body through which gaseous fuel is injected into the chamber. Two compression drivers (power 400 W each) placed on either side of the combustion chamber generate planar acoustic field in the direction transverse to the flow. In-phase and out-of-phase acoustic conditions can be realised based on the phase difference between the two acoustic drivers. Experimental diagnostics techniques - 2D-2C Particle Image Velocimetry (PIV), OH* chemiluminescence, OH-Planar Laser Induced Florescence (OH-PLIF) and high-frequency pressure measurements are conducted to measure the time-averaged velocity field, flame structure and chamber acoustics. The investigation is made for a range of flow Reynolds number (Re), flame power, and amplitude and frequency of acoustic excitation. The time-averaged flow field of the quiescent swirling jet shows a typical swirling flow feature with a central recirculation zone (CTRZ) surrounded by a high velocity annular jet. Once the swirling jet is exposed to transverse acoustic forcing it is observed that the jet instantaneously transitions to a wall-jet state. It is observed that at low flow Re under out-of-phase forcing condition, the flame oscillates in the streamwise direction at the forcing frequency. Spectral proper orthogonal decomposition (SPOD) is used to identify dominant structures in the flow field of the swirling flame.

Presenting Author: Ravi Gupta Indian Institute of Science, Bangalore

Presenting Author Biography: Ravi Gupta is a doctoral student in the Department of Aerospace Engineering, IISc Bangalore. His research includes flow-physics of swirling flows, thermo-acoustic instabilities relevant to gas turbine engines.

Authors:

Ravi Gupta Indian Institute of Science, Bangalore
Aayushi Bohrey Indian Institute of Science Bangalore
Pratikash Panda Indian Institute of Science