An effective impedance for modelling the aeroacoustic coupling of ducts connected via apertures

Orchini, Alessandro

doi:10.1016/j.jsv.2021.116622

Cited by 5 publications

(2 citation statements)

References 17 publications

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“…The current analytical model follows the method proposed by von Saldern et al [4] and later extended by Orchini [7]. This section gives a derivation that includes the effect of a general downstream impedance without other complications.…”

Section: Connection Impedance Analytical Modelmentioning

confidence: 99%

Acoustic Boundary Conditions for Can-Annular Combustors

Brind

2023

IJTPP

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This paper derives and validates an analytical model for acoustic boundary conditions on a can-annular gas turbine combustion system composed of discrete cans connected to an open annulus upstream of a turbine. The analytical model takes one empirical parameter: a connection impedance between adjacent cans. This impedance is extracted from time-marching computations of two-can sectors of representative combustors. The computations show that reactance follows the Rayleigh conductivity, while resistance takes a value of order 0.1 as a weak function of geometry. With a calibrated value of acoustic resistance, the analytical model reproduces can-to-can transfer functions predicted by full-annulus computations to within 0.03 magnitude at compact frequencies. Varying the combustor–turbine gap length, both model and computations exhibit a minimum in reflected energy, which drops by 63% compared to the datum gap. A parametric study yields a design guideline for gap length at the minimum reflected energy, allowing the designer to maximise transmission from the combustion system and reduce damping requirements.

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Section: Connection Impedance Analytical Modelmentioning

confidence: 99%

Acoustic Boundary Conditions for Can-Annular Combustors

Brind

2023

IJTPP

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“…Von Saldern et al [36] derived an effective impedance model for non-compact connections and analyzed the role of liners in damping azimuthal thermoacoustic modes. Orchini [37] and Pedergnana and Noiray [38] explored the effect of mean flow and derived effective impedance models that show explicit dependence on the grazing flow Mach number. Orchini et al [39] then showed that such effect gives rise to new sets of clusters of modes of aeroacoustic origin due to the coupling with the response of the shear layer in the apertures.…”

Section: Introductionmentioning

confidence: 99%

Interplay of Clusters of Acoustic and Intrinsic Thermoacoustic Modes in Can-Annular Combustors

Fournier

Schaefer

Haeringer

et al. 2022

Journal of Engineering for Gas Turbines and Power

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Thermoacoustic systems can exhibit self-excited instabilities of two nature, namely cavity modes or intrinsic thermoacoustic (ITA) modes. In heavy-duty land-based gas turbines with can-annular combustors, the cross-talk between cans causes the cavity modes of various azimuthal order to create clusters, i.e. ensembles of modes with close frequencies. Similarly, in systems exhibiting rotational symmetry, ITA modes also have the peculiar behavior of forming clusters. In the present study, we investigate how such clusters interplay when they are located in the same frequency range. We first consider a simple Rijke tube configuration and derive a general analytical low-order network model using only dimensionless numbers. We investigate the trajectories of the eigenmodes when changing the downstream length and the flame position. In particular, we show that ITA and acoustic modes can switch nature and their trajectories are strongly influenced by the presence of exceptional points. We then study a generic can-annular combustor. We show that such configuration can be approximated by an equivalent Rijke tube. We demonstrate that, in the absence of mean flow, the eigenvalues of the system necessarily lie on specific trajectories imposed by the upstream conditions.

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