Chapter 7 - Passive control of combustion instabilities

Abstract

In engine combustion systems, such as rockets, aeroengines, and gas turbines, pressure fluctuations are always present, even during normal operation. One of the design prerequisites for the engine combustors is stable operation since large-amplitude self-sustained pressure fluctuations (also known as combustion instability) have the potential to cause serious structural damage and catastrophic engine failure. To dampen pressure fluctuations and to reduce noise, acoustic dampers are widely applied as a passive control means to stabilize combustion/engine systems; however, they cannot respond to the dynamic changes of operating conditions and tend to be effective in a certain narrow range of frequencies. To maintain their optimum damping performance over a broad frequency range, extensive researches have been conducted during the past four decades. The present work is to summarize the status, challenges and progress of implementing such acoustic dampers on engine systems. The damping effect and mechanism of various acoustic dampers, such as Helmholtz resonators, perforated liners, baffles, half- and quarter-wave tubes, are introduced first. A summary of numerical, experimental and theoretical studies is then presented to review the progress made so far. Finally, as an alternative means, “tunable acoustic dampers” are discussed. Potential challenges and issues associated with the damper’s practical implementation are highlighted.