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FRACTAL GRID TURBULENCE AND ACOUSTIC PREDICTIONS

Sylvain Laizet
Turbulence, Mixing and Flow Control Group, Department of Aeronautics Imperial College London, London, SW7 2BY, United Kingdom

V. Fortune
Department of Fluid Flow, Heat Transfer and Combustion, Institute PPRIME CNRS - Universite de Poitiers - ENSMA Teleport 2, Boulevard Marie et Pierre Curie, BP 30179 86962 Futuroscope Chasseneuil Cedex, France

Eric Lamballais
Institute PPRIME, Department of Fluid Flow, Heat Transfer and Combustion, Université de Poitiers, CNRS, ENSMA, Téléport 2 – Bd. Marie et Pierre Curie B.P. 30179, 86962 Futuroscope Chasseneuil Cedex, France

John Christos Vassilicos
Turbulence, Mixing and Flow Control Group, Department of Aeronautics Imperial College London, London SW7 2AZ, United Kingdom

Аннотация

In this numerical work, we compare the acoustic properties of a fractal square grid with those of a regular grid by means of a hybrid approach based on Lighthill's analogy and Direct Numerical Simulation (DNS). It has been shown that the turbulence generated by fractal objects can have different properties than those generated by a regular object: whereas a regular object effectively introduces a single length-scale into the flow, a fractal object can introduce a wide range of length-scales into the flow. These distinct turbulent states depending on the grid are found to lead to different acoustic radiations both in terms of sound pressure levels and frequencies.