DOI: 10.1615/TSFP8
ROUGHNESS EFFECTS ON TURBULENT FLOW DOWNSTREAM OF A BACKWARD FACING STEP
ABSTRAKT
This study investigates the effects of surface roughness on turbulent shear flow downstream of a backward-facing step. Particle image velocimetry was used to conduct velocity measurements over two roughness elements and a reference smooth surface. In each test, the Reynolds number based on the step height and the centerline velocity was kept constant at 6750. The results show that roughness caused a marginal increase in the reattachment length. The distribution of the mean velocity, Reynolds stress, wall-normal transport of turbulent kinetic energy and spatial structures embodied in the two-point auto-correlation functions are independent of roughness in the recirculation region and immediately downstream of reattachment. Further downstream of reattachment, roughness reduced the streamwise mean velocity but increased the levels of the Reynolds stress, wall-normal transport of turbulent kinetic energy and the characteristic streamwise and wall-normal sizes of the spatial structures in the vicinity of the rough surface. Proper orthogonal decomposition is also used to reconstruct low-order representation of the flow field.