Experimental investigation of gravity-driven film flow inside an inclined corrugated pipe

Abstract

Gravity-driven film flow through an inclined corrugated pipe is experimentally investigated following field observations of unsteady, periodic flow patterns. Initial experiments confirmed surging flow at the pipe outlet as originally observed in the field. Fluorescence imaging of the film flow inside the pipe was then applied to examine the traveling wave behavior that leads to surging flow at the outlet. To our knowledge, this is the first investigation of traveling wave behavior in film flow in a corrugated pipe. The effect of flow rate and angle of inclination was studied in both experiments, with the characteristics of the traveling waves becoming the focus of the investigation. Similar to film flows over two-dimensional periodic topography, a statically deformed free surface with a wavelength approximately equivalent to the corrugations developed at all flow rates and angles examined with an amplitude that increased with angle of inclination. In contrast to film flows over two-dimensional periodic topography, the statically deformed free-surface amplitude was independent of the flow rate. Comparative to some two-dimensional studies, traveling waves developed from ambient noise through a strongly selective process. Traveling waves were observed to be approximately nondispersive and having nearly constant frequency and wavelength regardless of the flow rate or angle of inclination. The consistency in traveling wave character with changes in the angle and flow rate seems stronger than that seen for two-dimensional flows. Comparisons with large-scale flow applications, such as stepped spillways, indicate similarities in flow behavior that should be studied further.