Duran, I

Han, XS

Morgans, AS

Xia, Y

English

Spiral - Imperial College Digital Repository

Dispersion of entropy waves advecting throughcombustion chambersI. Duran, Y. Xia, A. S. Morgans and X. HanImperial College LondonMarch 4th 2016Unsteady combustion in modern gas turbines generates large entropy waves,also known as hot spots. When these are accelerated through the stator vanes,they generate acoustic waves via a mechanism known as indirect combustion noise[1]. The upstream-propagating acoustic waves interact with the the flame andcan contribute to the thermoacoustic feedback loop [2], while the downstream-propagating waves contribute to the global noise [3]. The strength of each acousticwave is directly proportional to the amplitude of the entropy wave reaching theinlet of the first stator blade.Low-order models can be used to predict the noise generated by an entropywave with reasonable accuracy, and at a fraction of the cost of numerical methods[4, 5]. These analytical models neglect the advection of the entropy wave throughthe turbulent combustion chamber, assuming the entropy wave arrives at the tur-bine inlet in the same form as that in which it was generated by the flame. Thefirst computational analysis of the advection of entropy waves through a turbulentflow was performed by Morgans et al. [6]. For a fully resolved turbulent channelflow, they found that the entropy wave was strongly deformed by the shear dis-persion of the flow, but all of the entropy was eventually convected downstreamof the flow without loss in time-integrated amplitude.The aim of this work is to extend the study of entropy wave advection tothe case of a real gas turbine combustor geometry, whose flow includes far morecomplex features, such as recirculation zones and swirl. The particular combus-tor considered is the SGT-100 combustor [8, 9] shown in Fig. 1. Simulations areperformed using the ReactingFOAM solver of OpenFOAM [7]. For entropy waveadvection, a similar approach to that in [6] is used; the entropy wave is assumed tooriginate in the areas where mean heat release occurs. It is then advected as a pas-sive scalar with the flow, using either the mean flow velocity or the instantaneousvelocity at each point.Example results, showing the effect of advection by the mean flow, are shown infigure 2. The outlet entropy wave strength indicates that a large amount of entropyis still able to reach the outlet. The flow features typical of industrial combustionchambers do have a significant effect on the entropy waves; in particular therecirculation zone results in an effective loss of entropy wave amplitude. Thisstudy will prove useful in deriving entropy wave advection models that pertain toreal combustor flows.104Figure 1: The SGT-100 combustorsimulated for the study [8, 9].Time0 0.02 0.04 0.06 0.08 0.1Amplitude050100150200250300350400SourceOutletFigure 2: Source term of entropy(black) and entropy at the outlet of thecombustor chamber (red).References[1] F. E. Marble and S. M. Candel. Acoustic disturbance from gas non-uniformitiesconvected through a nozzle. J. of Sound and Vib., 55:225–243, 1977.[2] C. S. Goh and A. S. Morgans. The influence of entropy waves on the thermoa-coustic stability of a model combustor. Combustion Science and Technology,185(2):249–268, 2013.[3] N. A. Cumpsty and F. E. Marble. The interaction of entropy fluctuations withturbine blade rows; a mechanism of turbojet engine noise. Proc. R. Soc. Lond.A, 357:323–344, 1977.[4] I. Duran and S. Moreau. Solution of the quasi one-dimensional linearized Eulerequations using flow invariants and the Magnus expansion. Journal of FluidMechanics, 723:190–231, 2013.[5] I. Duran and A. S. Morgans. On the reflection and transmission of circum-ferential waves through nozzles. journal of fluid mechanics. Journal of FluidMechanics, 773:137–153, May 2015.[6] A. S. Morgans, C. S. Goh, and J. A. Dahan. The dissipation and shear dis-persion of entropy waves in combustor thermoacoustics. Journal of Fluid Me-chanics, 733 R2:1–11, 2013.[7] http://www.openfoam.com/.[8] G. Bulat. Large Eddy Simulations of Reacting Swirling Flows in an IndustrialBurner. PhD thesis, Imperial College London, 2012.[9] U. Stopper, W. Meier, R. Sadanandan, M. Stöhr, M. Aigner, and G. Bulat.Experimental study of industrial gas turbine flames including quantification ofpressure influence on flow field, fuel/air premixing and flame shape. Combus-tion and Flame, 160(10):2103–2118, 2013.105View publication stats

Dispersion of entropy waves advecting through combustion chambers

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Dispersion of entropy waves advecting through combustion chambers

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