Thermoacoustic instability is caused by interactions between acoustic waves, flames and flow. It leads to damaging oscillations in the combustors of aero-engines, rocket engines, gas turbines and boilers. Carbon-free fuels like hydrogen and ammonia show increased propensity to thermoacoustic instability, and the design of futuristic aerospace engines is dependent on being able to avoid it. Because of the range of length scales involved – from the tiny flame front wrinkling to the long acoustic wavelengths - computational prediction is a real challenge.
This talk will explore the acoustic, flame and flow interactions which underpin thermoacoustic instability. We will consider the response of the flame to acoustic waves, the damping of acoustic waves at area expansions with flow separation, and the importance of “entropy noise” – the noise generated when temperature fluctuations undergo a flow acceleration. The implications for efficient computational prediction will be discussed.