Mitigating self-excited flame pulsating and thermoacoustic oscillations using perforated liners

Area of Science:

• Combustion dynamics
• Acoustics
• Control engineering

Background:

• Self-excited flame pulsations and thermo-acoustic instability pose significant challenges in combustion systems.
• Controlling these phenomena is crucial for operational stability and efficiency.
• Rijke-type combustors are common testbeds for studying combustion instabilities.

Purpose of the Study:

• To investigate an open-loop control strategy for self-excited flame pulsating oscillations and thermo-acoustic instability.
• To numerically and experimentally evaluate the performance of active cooling flow control through a perforated pipe.
• To understand the mechanisms, including vorticity-induced damping and acoustic losses, contributing to instability attenuation.

Main Methods:

• Numerical simulations of a 2D Rijke-type combustor with a perforated pipe.
• Experimental validation on a custom-designed Rijke-type combustor with active cooling flow.
• Analysis of sound pressure level (SPL) reduction and oscillation modes.
• Investigation of acoustic losses introduced by the perforated pipe.

Main Results:

• Numerical simulations showed approximately 38 dB SPL reduction by tuning cooling flow.
• Experimental results confirmed SPL reduction of approximately 35 dB at 245 Hz, with complete attenuation of harmonic modes.
• Vorticity-induced damping and increased acoustic losses from the perforated pipe were identified as key mechanisms.
• The control strategy successfully stabilized the combustor and attenuated both high- and low-frequency oscillations.

Conclusions:

• Open-loop control of cooling flow through a perforated pipe is an applicable method for attenuating thermo-acoustic instability and flame pulsations.
• The perforated pipe enhances stability by increasing acoustic losses and enabling vorticity-induced damping.
• This approach offers a practical solution for stabilizing combustion systems with self-excited oscillations.