Modelling of Circumferential Modal Coupling Due to Helmholtz Resonators

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. Acoustic waves produce fluctuations in heat release, for instance by perturbing the fuel-air ratio or flame shape. These heat fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. A linear model for thermoacoustic oscillations in LPP combustors is described. A thin annular geometry is assumed and so circumferential modes are included but radial dependence is ignored. The formulation is in terms of a network of modules such as straight ducts and area changes. At certain operating conditions, the flow is predicted to be unstable, with linear waves growing in amplitude. Helmholtz resonators can be used to absorb acoustic energy and, when carefully designed and installed at appropriate locations, can stabilise the flow. Helmholtz resonators are included in the model. Connecting a Helmholtz resonator to an annular duct destroys the axisymmetry of the geometry. This results in coupling of the circumferential modes which must be calculated. The model is used to investigate the best arrangement of resonators around the circumference of an annular duct to achieve maximum damping of a circumferential oscillation.Copyright © 2003 by ASME

[1]  Tom Hynes,et al.  Reflection of circumferential modes in a choked nozzle , 2002, Journal of Fluid Mechanics.

[2]  Christian Oliver Paschereit,et al.  On the Use of Helmholtz Resonators for Damping Acoustic Pulsations in Industrial Gas Turbines , 2001 .

[3]  Hukam Chand Mongia,et al.  Investigation of combustion dynamics in dry-low-emission (DLE) gas turbine engines , 1998 .

[4]  J. R. Tilston,et al.  Measurement and analysis of flame transfer function in a sector combustor under high pressure conditions , 2003 .

[5]  Ann P. Dowling,et al.  The Use of Helmholtz Resonators in a Practical Combustor , 2003 .

[6]  Dieter Bohn,et al.  Prediction of Thermoacoustic Instabilities With Focus on the Dynamic Flame Behavior for the 3A-Series Gas Turbine of Siemens KWU , 1999 .

[7]  K. N. C. Bray,et al.  Study of Flame Transfer Function With Three Dimensional Calculations , 2003 .

[8]  Anuradha M. Annaswamy,et al.  Adaptive Closed-Loop Control on an Atmospheric Gaseous Lean-Premixed Combustor , 2003 .

[9]  Dieter Bohn,et al.  Prediction and Measurement of Thermoacoustic Improvements in Gas Turbines With Annular Combustion Systems , 2000 .

[10]  Ann P. Dowling,et al.  Three Dimensional Thermoacoustic Oscillation in a Premix Combustor , 2001 .

[11]  Tom Hynes,et al.  Linearised Theory for LPP Combustion Dynamics , 2003 .

[12]  Hukam Chand Mongia,et al.  Combustion dynamic modeling for gas turbine engines , 1998 .

[13]  Ann P. Dowling,et al.  Sound and Sources of Sound , 1983 .

[14]  M. S. Howe,et al.  On the theory of unsteady high Reynolds number flow through a circular aperture , 1979, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[15]  Anuradha M. Annaswamy,et al.  Advanced Closed-Loop Control on an Atmospheric Gaseous Lean-Premixed Combustor , 2004 .

[16]  Wolfgang Polifke,et al.  Low-Order Acoustic Modelling for Annular Combustors: Validation and Inclusion of Modal Coupling , 2002 .

[17]  A. Dowling,et al.  Thermoacoustic Oscillations in an Annular Combustor , 2001 .