Response of a Turbulent Pipe Flow to a Change in Roughness

Measurements of mean longitudinal velocities, static pressure, turbulence quantities and Reynolds shear stress were made in the region between fully-developed smooth wall and rough wall flows in a circular tube. The rough tube was formed by placing rectangular cross-sectioned rings inside a smooth pipe. A phenomenological model was developed to describe the flow in the region of change. The longitudinal pressure gradient responds very rapidly (within a couple of diameters) to the new wall roughness. The effect on the mean and fluctuating velocity parameters was found to grow with the half-power of the longitudinal distance from the start of the roughened tube for the case when the initial roughness element is upstanding.