Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 11, 2020 - November 13, 2020
To understand turbulent flows over permeable roughness, PIV measurements are performed for turbulent channel flows over rib-roughened porous media. The porous ribs are mounted on the porous media with the same spacing w as the rib height k, w/k=1. Flows over impermeable roughness cases are also measured for comparison. It is confirmed that flow patterns below the ribs are changed by the permeability. Between the impermeable roughness elements, the recirculation bubbles are observed being isolated from the core flow. They move downstream and downward as the permeability increases and those in the highest permeability case disappear. This tendency is qualitatively the same as that for the previously reported permeable k-type roughness case, w/k=9. The magnitude of turbulent kinetic energy for d-type roughness becomes small as the permeability increases, while the opposite tendency is observed in k-type roughness cases. Further discussions on turbulence generated by the roughness are carried out by the two-point correlation analysis of the wall-normal fluctuating velocity. Although turbulence above the impermeable d-type roughness is isolated from the recirculation region below the ribs, it penetrates strongly into the square cavity between the ribs in the permeable roughness case. It is also seen that turbulence generated by permeable ribs tends to expand isotropically regardless of the roughness geometry.
