Control of mixing via entropy tracking

We study mixing of isothermal fluids by controlling the global hydrodynamic entropy ...s. In particular, based on the statistical coupling between the evolution of ... and the global viscous dissipation ..., we analyze stirring protocols such that ..., with

Control of mixing via entropy tracking

We study mixing of isothermal fluids by controlling the global hydrodynamic entropy ...s. In particular, based on the statistical coupling between the evolution of ... and the global viscous dissipation ..., we analyze stirring protocols such that ..., with

Intrinsic instability of flame–acoustic coupling

This paper shows that a flame can be an intrinsically unstable acoustic element. The finding is clarified in the framework of an acoustic network model, where the flame is described by an acoustic scattering matrix. The instability of the flame acoustic coupling is shown to become dominating in the limit of no acoustic reflections. This is in contrast to classical standing-wave thermoacoustic modes, which originate from the positive feedback loop between system acoustics and the flame. These findings imply that the effectiveness of passive thermoacoustic damping devices is limited by the intrinsic stability properties of the flame

Flames in context of thermo-acoustic stability bounds

Bounds are derived for the acoustic losses such that a thermoacoustic system with a given flame can be guaranteed to be stable. The analysis is based on the flame’s acoustic input-to-output properties represented by its scattering matrix. The developed analytical and numerical techniques allow estimating the maximum reflection coefficients (equivalently – acoustic losses) which are sufficient to ensure stable operation of a given burner. It is shown that the calculated numerical upper-bound is less conservative than the analytical one. The frequency dependence of the required acoustic losses provides (i) a thermo-acoustic signature of the flame and (ii) guidelines for the proper design of the up- and downstream acoustics from the flame. The method is illustrated on two burners/flames of premixed multiple Bunsen type. The frequency dependence of the upper bounds allows to identify those frequency ranges where the flame is more likely to cause instability of the complete system

Effect of burner partitioning on system thermo-acoustics

In this paper the thermo-acoustic properties of a system equipped with a segmented burner are investigated. Such segmentation can for example be realized by combining two different burners on the same deck. The study is conducted using finite element and network modelling techniques. It is found that even a small spatial separation of the burner's sections can lead to significant alteration of the global acoustic behavior of the system. In particular, the location of the eigenmodes and hence the stability of the system can be affected. It is shown that the local modification of the acoustic field in the vicinity of the partitioned burner is the physical reason for this phenomena. This finding poses some limitations on to use of the lumped transfer function decomposition approach to estimate the global burner response of a composite flame/burner

Intrinsic instability of flame–acoustic coupling

This paper shows that a flame can be an intrinsically unstable acoustic element. The finding is clarified in the framework of an acoustic network model, where the flame is described by an acoustic scattering matrix. The instability of the flame acoustic coupling is shown to become dominating in the limit of no acoustic reflections. This is in contrast to classical standing-wave thermoacoustic modes, which originate from the positive feedback loop between system acoustics and the flame. These findings imply that the effectiveness of passive thermoacoustic damping devices is limited by the intrinsic stability properties of the flame