Modal decomposition of the unsteady flow field in compression-ignited combustion chambers

[EN] In this paper, the unsteady behaviour of a compression-ignited (CI) engine combustion chamber is studied by analysing the results of a Computational Fluid Dynamics (CFD) model through the application of different flow decomposition techniques, aiming to resolve the underlying modal structure of the process. Experimental validation for the combustion simulation is provided, and a methodology for extracting coherent pressure information is proposed in order to provide a suitable input for different analysis methods. These range from straightforward Fourier transform techniques to more sophisticated modal decomposition approaches. In particular Proper Orthogonal Decomposition (POD) is shown to provide valuable insight into the time-spatial structure of the combustion flow field, allowing the establishment of correlations between pressure modes and physical parameters of the combustion, such as the injection timing or the chamber geometry. Dynamic Mode Decomposition (DMD) on the other hand is proven to successfully highlight the link between the frequency of the unsteady energy components and their spatial distribution within the chamber. Advantage is then taken of the modal characterization of the unsteady behaviour in the chamber to showcase how physical parameters such as the spray angle can be modified to optimize the acoustic signature of the combustion process, helping CI internal combustion engines reduce their acoustic environmental impact (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.The equipment used in this work has been partially supported by FEDER project funds "Dotacidn de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT)" [grant number FEDER-ICTS-2012-06], framed in the operational program of unique scientific and technical infrastructure of the Spanish Government.Torregrosa, AJ.; Broatch, A.; Garcia Tiscar, J.; Gómez-Soriano, J. (2018). Modal decomposition of the unsteady flow field in compression-ignited combustion chambers. Combustion and Flame. 188:469-482. https://doi.org/10.1016/j.combustflame.2017.10.007S46948218

Thermo-acoustic Velocity Coupling in a Swirl-stabilized Gas Turbine Model Combustor

The research presented herein describes the coupling of acoustic and heat release fluctuations in a perfectly-premixed swirl-stabilized combustor by analysis of simultaneous high-repetition-rate laser diagnostics data. Nine cases are studied, varying the thermal power and the equivalence ratio. Proper orthogonal decomposition (POD) of the velocity data shows that cases with higher amplitude thermoacoustic oscillations have flow fields containing helical vortex cores (HVC); these cases are further analysed to determine the driving mechanisms of the oscillations. Flow and flame statistics are compiled as a function of both the phase in the thermoacoustic cycle and a phase representing the azimuthal position of the HVC relative to the measurement plane. These data are used to spatially map the thermoacoustic energy transfer field, as described by the Rayleigh integral. It is found that periodic deformations of the HVC cause large-scale flame motions, resulting in regions of positive and negative energy transfer.MAS