Turbulent Flow Over Undular Permeable Boundaries

Abstract

The effects of boundary permeability and undulation in turbulent pipe flow are observed in an air flow conduit lined with a granular permeable material. Boundary pressure, mean velocity distribution, and longitudinal turbulence intensity were measured at several sections along the sinusoidal boundary. The observed boundary pressure shows a phase shift relative to the boundary wave form and a magnitude similar to that found from a simple potential flow analysis. The mean velocity distributions differ drastically from those observed in impervious wavy pipes, implying an important effect of the aspiration from the porous boundary in the lee of the wave form. The observations of turbulence intensity show that boundary permeability dramatically alters the turbulence structure as compared to an impervious wavy pipe. In the permeable pipe, a zone of high intensity turbulence develops in the lee of the boundary wave form and expands to the central portion of the pipe. For impervious wavy pipes, the high turbulence intensity occurs only near the boundary as in the case of a straight pipe.