Journal of Fluid Mechanics



The effects of a favourable pressure gradient and of the Reynolds number on an incompressible axisymmetric turbulent boundary layer. Part 2. The boundary layer with relaminarization


D. WARNACK a1 and H. H. FERNHOLZ a1
a1 Hermann-Föttinger-Institut für Strömungsmechanik, Technische Universität Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany

Abstract

This is an experimental investigation of two turbulent boundary layers (cases 2 and 4) where the streamwise negative pressure gradient changes mean properties of the flow, e.g. mean velocity profiles and skin friction, so that they display laminar-like behaviour. The maximum acceleration parameter K[less-than-or-eq, slant]4×10−6 and the starting value of the Reynolds number is 862 or 2564. Relaminarization occurs in both boundary layers as a gradual change of the turbulence properties and is not catastrophic. Retransition, however, is a fast process due to the remaining turbulence structure and may be compared with bypass transition. Together with an extensive investigation of the turbulence structure as in the companion paper, Part 1, which describes two cases (1 and 3) of boundary layers which remain turbulent, spectra and integral length scales for all four boundary layers are discussed.

(Received June 21 1996)
(Revised November 4 1997)



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