Indirect combustion noise

An analysis is made of the noise generated during the passage of quiescent temperature/entropy inhomogeneities through regions of rapidly accelerated mean flow. This is an important source of jet engine core noise. Bake et al. (J. Sound Vib., vol. 326, 2009, pp. 574–598) have used an ‘entropy wave generator’ coupled with a converging–diverging nozzle to perform a series of canonical measurements of the sound produced when the inhomogeneity consists of a nominally uniform slug of hot gas. When flow separation and jet formation occur in the diffuser section of the nozzle, it is shown in this paper that the vortex sound generated by the jet is strongly correlated with the entropy noise produced by the slug and that the overall noise level is significantly reduced. Streamwise ‘stretching’ of the hot slug during high subsonic acceleration into the nozzle and the consequent attenuation of the entropy gradient in the nozzle are shown to significantly decrease the effective rate at which indirect combustion noise increases with the Mach number. Numerical predictions indicate that this is responsible for the peak observed by Bake et al. in the entropy-generated sound pressure at a nozzle Mach number near 0.6.

[1]  M. S. Bohn,et al.  Response of a subsonic nozzle to acoustic and entropy disturbances , 1977 .

[2]  T. N. Stevenson,et al.  Fluid Mechanics , 2021, Nature.

[3]  M. S. Howe.  Acoustics of Fluid–Structure Interactions: Index , 1998 .

[4]  M. S. Howe.  Theory of Vortex Sound: Index , 2002 .

[5]  Masanobu Iida,et al.  Rapid calculation of the compression wave generated by a train entering a tunnel with a vented hood , 2006 .

[6]  S. Candel,et al.  ANALYTICAL STUDIES OF SOME ACOUSTIC PROBLEMS OF JET ENGINES , 1972 .

[7]  N.,et al.  The interaction of entropy fluctuations with turbine blade rows; a mechanism of turbojet engine noise , 2022 .

[8]  M. Lighthill.  On sound generated aerodynamically I. General theory , 1952, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[9]  Matthieu Leyko,et al.  Comparison of Direct and Indirect Combustion Noise Mechanisms in a Model Combustor , 2009 .

[10]  H. Lu.  An Analytical Model for Entropy Noise of Subsonic Nozzle Flow , 1978 .

[11]  Warren C. Strahle,et al.  Separation of Hydrodynamic, Entropy, and Combustion Noise in a Gas Turbine Combustor , 1978 .

[12]  G. Batchelor,et al.  An Introduction to Fluid Dynamics , 1968 .

[13]  E. Sparrow,et al.  Flow separation in a diverging conical duct: Effect of Reynolds number and divergence angle , 2009 .

[14]  Raymond Brun,et al.  Elements of Gas Dynamics , 2009 .

[15]  Frank E. Marble,et al.  Core noise from gas turbine exhausts , 1977 .

[16]  T. Poinsot,et al.  Theoretical and numerical combustion , 2001 .

[17]  L. Rayleigh,et al.  The theory of sound , 1894 .

[18]  Friedrich Bake,et al.  Investigation of Entropy Noise in Aero-Engine Combustors , 2007 .

[19]  Friedrich Bake,et al.  The Entropy Wave Generator (EWG): A Reference Case on Entropy Noise , 2009 .

[20]  Willi Moehring,et al.  Modelling low Mach number noise , 1979 .

[21]  N. A. Cumpsty,et al.  Jet engine combustion noise: Pressure, entropy and vorticity perturbations produced by unsteady combustion or heat addition , 1979 .

[22]  E. Müller,et al.  Mechanics of Sound Generation in Flows , 1979 .

[23]  E. E. Zukoski,et al.  Experiments Concerning the Response of Supersonic Nozzles to Fluctuating Inlet Conditions , 1976 .

[24]  S. Kotake,et al.  Combustion Noise , 2015 .

[25]  W. Strahle.  On combustion generated noise , 1971 .

[26]  C. Morfey.  Amplification of aerodynamic noise by convected flow inhomogeneities , 1973 .

[27]  Michael S. Howe,et al.  The generation of sound by density inhomogeneities in low Mach number nozzle flows , 1975, Journal of Fluid Mechanics.

[28]  I. Röhle,et al.  Experimental Investigation of the Entropy Noise Mechanism in Aero-Engines , 2009 .

[29]  M. S. Howe.  Contributions to the theory of aerodynamic sound, with application to excess jet noise and the theory of the flute , 1975, Journal of Fluid Mechanics.

[30]  A. W. Bloy.  The pressure waves produced by the convection of temperature disturbances in high subsonic nozzle flows , 1979 .

[31]  E. T. Copson,et al.  The mathematical theory of Huygens' principle , 1939 .

[32]  F. E. Marble,et al.  Acoustic disturbance from gas non-uniformities convected through a nozzle , 1977 .

[33]  P. Morse,et al.  Methods of theoretical physics , 1955 .

[34]  F. G. Leppington,et al.  Modern Methods in Analytical Acoustics , 1992 .

[35]  Luciano Castillo,et al.  Separation criterion for turbulent boundary layers via similarity analysis , 2004 .

[36]  Manfred Aigner,et al.  Numerical Investigation of the Fundamental Mechanism for Entropy Noise Generation in Aero-Engines , 2009 .

[37]  Stéphane Moreau,et al.  Numerical and analytical investigation of the indirect combustion noise in a nozzle , 2009 .

[38]  M. S. Howe,et al.  Sound generated by aerodynamic sources near a deformable body, with application to voiced speech , 2007, Journal of Fluid Mechanics.

[39]  Friedrich Bake,et al.  Investigation of Entropy Noise in Aero-Engine Combustors , 2007 .

[40]  M. S. Howe.  Acoustics of fluid-structure interactions , 1998 .

[41]  Ann P. Dowling,et al.  Modern Methods in Analytical Acoustics: Lecture Notes , 1992 .