Intense structures of different momentum fluxes in turbulent channels

Abstract

The effect of different definitions of the momentum flux on the properties of the coherent structures of the logarithmic region of wall-bounded turbulence is investigated by comparing the structures of intense tangential Reynolds stress with those of the alternative flux proposed in [Jimenez (2016) J. Fluid Mech. 809:585]. Despite the fairly different statistical properties of the two flux definitions, it is found that their intense structures show many similarities, such as the dominance of 'wall-attached' objects, and geometric self-similarity. However, the new structures are wider, although not taller, than the classical ones, and include both high-A nd low-momentum regions within the same object. It is concluded that they represent the same phenomenon as the classical group of a sweep, an ejection, and a roller, which should thus be considered as the fundamental coherent structure of the momentum flux. The present results suggest that the properties of these momentum structures are robust with respect to the definition of the fluxes.