STRUCTURE OF LARGE-SCALE VORTICES AND UNSTEADY REVERSE FLOW IN THE REATTACHING ZONE OF A TURBULENT SEPARATION BUBBLE.

This paper describes experiments concerning the structure of large-scale vortices and the unsteady reverse-flow properties in the reattaching zone of a nominally two-dimensional separation bubble formed at the leading edge of a blunt flat plate with right-angled corners. An important feature of this study is a judicious use of surface-pressure fluctuations as a conditioning signal to educe the structure of the large-scale vortices. Distributions of fluctuating-velocity vectors and contour lines of high-frequency turbulent energy in a few space-time domains are presented and discussed. The most economical interpretation of these space-time distributins is that the large-scale vortices in the reattaching zone are hairpin vortices whose configuration is sketched in the text. The strength of the large-scale vortices in the reattaching zone seems to be dependent on the phase of the low-frequency unsteadiness. Refs.