Abstract
This paper presents a new method for evaluating the virtual origin of the mean flow over the riblet-mounted surface. First, the standardized distribution of mixing length is estimated from meam velosity measured in the wall region. From this result, the position of outer edge of boundary sub-layer is decided. Then, virtual origin is decided by comparison of the measured mean velosity in wall region with the calculated velocity from the distribution of mixing length estimated above. It became clear that the virtual origin and the thickness of viscous sub-layer is almost decided by roughness Reynolds number.
