Structure of transitionally rough and fully rough turbulent boundary layers

Abstract

Structural characteristics of transitionally rough and fully rough turbulent boundary layers are presented. These were measured in flows at different roughness Reynolds numbers developing over uniform spheres roughness. Inner regions of the longitudinal component of normal Reynolds stress profiles and log regions of mean profiles continuously change in the transitionally rough regime, as the roughness Reynolds number, Rek, varies. These properties asymptotically approach fully rough behaviour as Rek increases, and smooth behaviour at low Rek Profiles of other Reynolds-stress tensor components, turbulence kinetic energy, turbulence-kinetic-energy production, and the turbulence-kinetic-energy dissipation are also given, along with appropriate scaling variables. Fully rough, one-dimensional spectra of longitudinal velocity fluctuations from boundary-layer inner regions are similar to smooth-wall results for k1 y > 0.2 when non-dimensionalized using distance from the wall y as the lengthscale, and (τ/ρ)½ as the velocity scale, where τ is local shear stress, ρ is static density, and k1 is one-dimensional wavenumber in the flow direction.