Unwanted, uncontrolled oscillations in thermoacoustic systems like rocket and gas turbine engines can not only reduce the lifetimes of such systems, but can also even lead to structural damage and complete failure. These thermoacoustic instabilities, which arise when heat release rate fluctuations come into phase with pressure waves, can be suppressed or eliminated by inducing the phenomenon of amplitude death (AD). One way of inciting the behavior is to couple individual oscillators in differing ways.

A team of researchers reports in Chaos on the effects of symmetric and asymmetric coupling on a thermoacoustic system, demonstrating theoretically that AD can be achieved under both coupling modes. Their mathematical model consists of two horizontal Rijke tubes, which create high-amplitude acoustic pressure oscillations with the application of heat. With this, the team investigated the effects of time-delay and dissipative coupling applied both separately and simultaneously.

Most work on thermoacoustic oscillations to date has focused on passive suppression in isolated systems, and may have only limited applicability for practical thermoacoustic systems. This new work is the first systematic investigation of suppression in coupled systems.

The authors applied each form of coupling — time-delay and dissipative — to the two Rijke tubes separately and then simultaneously. AD was easiest to achieve with both forms applied simultaneously, but was also attainable under asymmetric coupling and when the coupled oscillators displayed dissimilar amplitudes. Even when the coupling is not strong enough to achieve AD, both oscillators displayed significantly reduced amplitudes.

The researchers note that if these results can be verified in an experimental thermoacoustic model, they may point the way toward new applications for the use of AD in the suppression and control of damaging oscillations in practical systems.

Source: “Effect of time-delay and dissipative coupling on amplitude death in coupled thermoacoustic oscillators,” by Nevin Thomas, Sirshendu Mondal, Samadhan A. Pawar, and R. I. Sujith, Chaos (2018). The article can be accessed at https://doi.org/10.1063/1.5009999.