On the sign of the instantaneous spanwise vorticity component in the near-wall region of turbulent boundary layers

Abstract

A geometric feature of the vorticity field in the near-wall region is educed from an analysis of time-resolved spanwise vorticity measurements. The results of this analysis indicate the existence of a region near the wall in which the instantaneous z component of the vorticity vector is virtually always in the direction indicated by the mean shear. In accordance with the solenoidal condition of the vorticity field, this observed physical feature represents a limitation on the spatial structure of the vorticity field in the near-wall region. The present results also reinforce the conclusion of Klewicki (Ph.D. dissertation, Michigan State University, 1989) that, for the momentum deficit thickn..