Turbulent flow structures and Reynolds stress anisotropy in an asymmetric sinuous mobile channel

Abstract

In the current experimental study, turbulent flow structures and Reynolds stress anisotropy in an asymmetric sinuous mobile channel are investigated. Experiments were conducted in a laboratory on an asymmetric plane-shaped sinuous model of a riverway with a sinuosity of 1.23. Three-dimensional instantaneous velocity data were measured using an acoustic Doppler vectrino profiler and processed to compute turbulent flow structures and Reynolds stress anisotropy. Spectral analysis of the streamwise fluctuating component of velocity shows the presence of “−1” and “−5/3” slope regions. Analysis of bursting events in the near-bed region reveals that the contribution of sweep and ejection events is more dominant than outward and inward interactions. The intermixing of events with depth shows the presence of helical flow. The probability of occurrence of bursting events indicated that the ejections are higher than other events. The Reynolds stress anisotropy tensor showed higher contribution in the streamwise followed by transverse and vertical directions, respectively, at all locations. The anisotropic invariant map indicated two-component turbulence in the near-bed region and one-component turbulence toward the surface at upstream and apex locations. At the bend downstream, the two-component turbulence diminished near the bed, and one-component turbulence increased with vertical depth. The eigenvalues of the non-dimensional anisotropy tensor indicated that the principal component was higher than the other two components in the near-bed region and started decreasing with increasing depth. The anisotropic invariant function showed that the near-bed region tended to approach an isotropic limit but departed from it in the outer flow region with increasing vertical depth.