Accounting for Acoustic Damping in a Helmholtz Solver

Thermoacoustic Helmholtz solvers provide a cheap and efficient way of predicting combustion instabilities. However, because they rely on the inviscid Euler equations at zero Mach number, they cannot properly describe the regions where aerodynamics may interact with acoustic waves, in the vicinity of...

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Bibliographic Details
Published in:AIAA journal 2017-04, Vol.55 (4), p.1205-1220
Main Authors: Ni, F, Miguel-Brebion, M, Nicoud, F, Poinsot, T
Format: Article
Language:English
Subjects:
Acoustic waves
Acoustics
Aerodynamics
Boundary conditions
Combustion
Computer simulation
Damping
Dilution
Dissipation
Engineering Sciences
Euler-Lagrange equation
Fluids mechanics
Helmholtz equations
Injectors
Instability
Large eddy simulation
Mach number
Mathematical models
Mechanics
Methodology
Resonant frequencies
Simulation
Solvers
Thermoacoustics
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Summary:Thermoacoustic Helmholtz solvers provide a cheap and efficient way of predicting combustion instabilities. However, because they rely on the inviscid Euler equations at zero Mach number, they cannot properly describe the regions where aerodynamics may interact with acoustic waves, in the vicinity of dilution holes and injectors, for example. A methodology is presented to incorporate the effect of non-purely acoustic mechanisms into a three-dimensional thermoacoustic Helmholtz solver. The zones where these mechanisms are important are modeled as two-port acoustic elements, and the corresponding matrices, which notably contain the dissipative effects due to acoustic–hydrodynamic interactions, are used as internal boundary conditions in the Helmholtz solver. The rest of the flow domain, where dissipation is negligible, is solved by the classical Helmholtz equation. With this method, the changes in eigenfrequency and eigenmode structure introduced by the acoustic–hydrodynamic effects are captured, while keeping the simplicity and efficiency of the Helmholtz solver. The methodology is successfully applied on an academic configuration, first with a simple diaphragm, then with an industrial swirler, with matrices measured from experiments and large-eddy simulation.
ISSN:0001-1452
1533-385X
DOI:10.2514/1.J055248