Effects of wall roughness over forward facing step in open channel turbulent flow

Abstract

An experimental investigation was performed to evaluate the effects of wall roughness on the reattachment and recovery regions over a forward facing step in an open channel turbulent flow. Detailed velocity measurements were conducted using a particle image velocimetry (PIV) system over four wall conditions: a smooth upstream and downstream wall, an upstream rough wall produced from sandpaper 36 grit and a smooth downstream wall, an upstream rough wall produced from sand grain and a smooth downstream wall, and an upstream rough surface coated with sandpaper 36 grit and a rough downstream wall coated with sandpaper 36 grit. The streamwise and wall-normal mean velocities, Reynolds stresses, turbulent kinetic energy and integral parameters were obtained and compared with previous studies. The results show that wall roughness reduced the reattachment length by as much as 29%.