Turbulent Flows Over Rough Forward Facing Steps

This paper reports an investigation of the effects of rough forward facing steps on turbulent flows. The surfaces of the rough steps were covered with sandpapers. A particle image velocimetry technique was used to conduct measurements at the mid-plane of the test section and at several locations downstream to 68 step heights. A Reynolds number of Re_h = 4800 and δ/h = 4.7 were employed, where h is the mean step height and δ is the incoming boundary layer thickness. The results indicate that mean reattachment length decreases with increasing roughness. In addition, the effect of the step roughness decreases with downstream distance. The proper orthogonal decomposition results showed that the step roughness affects even the large scale structures. Furthermore, the reconstructed turbulence quantities suggest that the step roughness suppresses the large scale turbulence.