On the mechanism of bounded turbulent shear flows

Abstract

To model bounded turbulent shear flows, one would like to have an accurate mechanistic picture of the coherent motions in the wall region; unfortunately, this picture is still far from completely clear. The present effort is to combine several techniques we have developed in the past in an attempt to further clarify the correct mechanism.

Streamwise vorticity measurements were made at Göttingen (Kastrinakis [1]) with a four-sensor vorticity probe of non-dimensional viscous length of five. Previously reported results indicated that the streamwise vorticity is indeed important, for at a y⁺ of 30, the rms value is about 20% of the mean velocity gradient at the wall (the mean vorticity). Other measurements indicated that the streamwise vorticity is very intermittent as is the Reynolds stress.

To help establish the best possible picture of the flow in the wall region, flow visualization films designed to enhance the lateral (spanwise) (y-z) plane view of the flow, i.e., looking into the flow, have been obtained and analyzed. The view is one moving with the flow (x-direction). In addition, a reevaluation of the films of Corino [2] was made. Finally, the ensembled averaged streamwise vorticity pattern during the passage of the structure sequence as determined by pattern recognization applied to the u-signal was obtained. The present paper reports on progress in these researches.