Characterization of the low-pressure filaments in a three-dimensional turbulent shear flow

Abstract

In this paper results on the low-pressure filaments that appear spontaneously in three-dimensional turbulent flows are presented. An individual characterization of the filaments is first obtained by studying the correlations between the flow visualization and local measurements of the pressure and the velocity. Then, a statistical study of the time recordings of the pressure that exhibits intermittent short and deep depressions is presented. It is shown that the pressure histograms depend only on the square of the injection velocity, and that the rate of production of strong depressions is independent of the Reynolds number. These results impose severe constraints on the possible mechanisms of formation of the filaments; they are consistent with a simple model, in which the formation of the filaments results primarily from the partial rollup of stretched shear layers. In this model there is a difference between the hierarchies of pressure and vorticity filaments: the filaments with the largest depression are the thickest (and the longest), while the filaments with the strongest vorticity are likely to be the thinnest (and shortest).