Fine-scale activity and coherent structures in a turbulent plane wake

Abstract

In the first part of this paper the behaviour of the random stresses obtained from triple decomposition are contrasted with a fine-scale turbulence indicating function (FSTIF) derived from velocity signals which have been low-pass filtered with several cut-off frequencies. Results show that most of the contribution to the incoherent stresses computed from the triple decomposition is mainly due to differences between individual events rather than to true fine scale activity. In the second part of this paper the streamwise evolution of the Karman vortices and the associated footprints of FSTIF and incoherent normal stresses are analysed and compared at x/D = 16, 30, 60 and 90. The results obtained support the hypothesis that the so-called double-roller eddies of the far wake can be interpreted as the evolution of the Karman vortices shed by the cylinder. On the other hand, the differences between FSTIF and normal stresses already detected in the near wake are enhanced as the flow evolves downstream. At x/D = 60 and 90 the fine-scale activity is observed to concentrate in the lateral flow ejection which is connected with the centre of the double roller.

This article was chosen from selected Proceedings of the Second International Symposium on Turbulence and Shear Flow Phenomena (KTH-Stockholm, 27-29 June 2001) ed E Lindborg, A Johansson, J Eaton, J Humphrey, N Kasagi, M Leschziner and M Sommerfeld.