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Prediction of combustion noise for an aeroengine combustor
Combustion noise may become an important noise source for
lean-burn gas turbine engines, and this noise is usually associated with
highly unsteady flames. This work aims to compute the broadband
combustion noise spectrum for a realistic aeroengine combustor, and
to compare with available measured noise data on a demonstrator
aeroengine. A low-order linear network model is applied to a
demonstrator engine combustor to obtain the transfer function that
relates to unsteadiness in the rate of heat release, acoustic, entropic
and vortical fluctuations. A spectral model is used for the heat release
rate fluctuation, which is the source of the noise. The mean flow
of the aeroengine combustor required as input data to this spectral
model is obtained from RANS simulations. The computed acoustic
field for a low-medium power setting indicates that the models used in
this study capture the main characteristics of the broadband spectral
shape of combustion noise. Reasonable agreement with the measured
spectral level is achieved.The current research has been conducted under UK Technology Strategy Board contract
TP11/HVM/6/I/AB201K.This is the accepted manuscript. The final published version is available from ARC at http://arc.aiaa.org/doi/abs/10.2514/1.B34857. Copyright © 2013 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission
Deconstructing Conformal Blocks in 4D CFT
We show how conformal partial waves (or conformal blocks) of spinor/tensor correlators can be related to each other by means of differential operators in four dimensional conformal field theories. We explicitly construct such differential operators for all possible conformal partial waves associated to four-point functions of arbitrary traceless symmetric operators. Our method allows any conformal partial wave to be extracted from a few \u201cseed\u201d correlators, simplifying dramatically the computation needed to bootstrap tensor correlators. \ua9 2015, The Author(s)