The Effect of a Single Roughness Element on a Flat Plate Boundary Layer Transition

Abstract

A turbulence wedge that develops downstream from a single roughness element placed in a laminar boundary layer on a flat plate is experimentally investigated in the chapter. Mean and fluctuating velocities and the Reynolds stress components are measured. Mean streamwise vorticity is estimated and velocity vectors are plotted. Many streamwise vortices appeared within the turbulence wedge just behind the roughness. On the other hand, many of these streamwise vortices disappeared, and a pair of streamwise vortices are found on both interfaces between the wedge and the outer laminar region. The wedge is expanded outwardly because the turbulent fluid within the wedge overflowed it. At both sections, just behind the roughness and farther downstream, the fluctuating velocities and the Reynolds stresses are larger than the values in the fully developed turbulent boundary layer over the whole height. The mixing length is also obtained.