壁面せん断乱流の対数層に対する粗さの影響

Abstract

The roughness sublayer beneath a turbulent boundary layer has been investigated analytically and experimentally, and its effect has been discussed on the logarithmic velocity profile. The rough surface consists of two-dimensional square roughness elements. The roughness height is proportional to streamwise distance. It is one of conditions of an equilibrium boundary layer. The roughness pitch ratio is 4. The free stream velocity is about 9m/s. The experiments were made in zero pressure gradient. The velocity measurement within/outside the roughness sublayer was made using LDV and CTA, respectively. The momentum thickness and roughness Reynolds numbers are 6000 and 149, respectively. From the analytical solutions of streamwise mean velocity and Reynolds shear stress profiles in the cavity region between roughness elements and experimental results , the center height of drag moment and the constant of the roughness function can be represented as a function of the roughness pitch ratio. These functions are well consistent with the experimental and DNS results.