Experimental investigation of flow fields in a square channel roughened with various ribs on one wall

The present work studies the separated flow in a square channel with ribs on one wall by using the PIV method. In this study, the spacing between ribs is kept constant and the heights of rib are varied in order to investigate the influence of the pitch-to-height ratio, P/e on the flow structures. Depending on the various pitch ratios, the enclosure between ribs can be regarded as closed or open cavity. Results are included for mean velocity, streamlines, skin-friction coefficient, anisotropy parameter, turbulent kinetic energy production and two-point correlation. It is found that the separated shear layer in the closed cavity has strong momentum exchange with the mainstream. By contrast, the fluid contained in the open cavity is self-sustained and the outside streamlines are almost parallel to the bottom wall. Moreover, for the open cavity, the velocity fluctuations become vigorous as the flow reattaches directly on the trailing edge