Statistical properties of a d-type rough wall turbulent boundary layer : low Reynolds number effect

Statistical properties of d-type rough wall boundary layer in a transitionally and a fully rough regime have been investigated experimentally. Probability density distributions and higher-order moments of the u-and v-fluctuating velocity components were measured in the momentum thickness Reynolds number range of R_θ=700-5140. Existence of the local energy equilibrium was recognized in the inner layer at the whole Reynolds number range. Difference of the turbulent structure among smooth, d-type rough and k-type rough wall flows can be found in the profiles of turbulent energy production and dissipation near the wall. It is seen that the difference of smooth wall flow and d-type rough wall flow and also the Reynolds number dependence in the wake component of the mean velocity profile can be fairly explained in terms of the triple velocity correlations involved in the turbulent diffusion terms for the Reynolds shear stress. The effective velocity of turbulent diffusion for the turbulent energy and Reynolds shear stress fluxes were evaluated.