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FAR AXISYMMETRIC WAKES IN TURBULENT STREAMS

Elad Rind
School of Engineering Sciences University of Southampton Southampton, SO17 1BJ, UK

John A. Redford
School of Engineering Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

Ian P. Castro
School of Engineering Sciences, University of Southampton, Southampton, SO17 1BJ, U.K.

Résumé

A time developing far axisymmetric wake at moderate Reynolds numbers (Re = O(104)) has been simulated without a generating body. When the wake achieved its self-similar state it was artificially combined with three different isotropic turbulent backgrounds with different intensities (u'bg = √u2). It was found that the presence of the background enhances the wake's decay rate to one which depends on the initial ratio of the free-stream turbulence intensity to the wake centre-line deficit velocity, u'bg/Ud. Moreover, the time required for enhancing the decay rate of the wake was also found to decrease with an increase in u'bg/Ud. In no case (with ubg > 0) did the wake achieve a self-similar state. Finally, rms turbulence levels inside the wake were clearly influenced and eventually dominated by the free stream levels. A tendency to isotropy in the rms normal stresses (i.e. u' ~ ν' ~ w') was noticed within the wakes, whilst the turbulence shear stress seemed to be largely maintained.