Flow Past a Permeable Manipulator Ring Placed in a Turbulent Pipe Flow

Turbulent pipe flow past a ring-type permeable manipulator was investigated by measuring the mean flow and turbulent flow fields. The permeable manipulator ring had a rectangular cross section and a height 0.14 times the pipe radius. The experiments were performed under four conditions of the open area ratio β of the permeable ring (β = 0.1, 0.2, 0.3 and 0.4) for Reynolds number of 6.2×10⁴. The results indicate that as the open-area ratio increased, the separated shear layer arising from the permeable ring top became weaker and the pressure loss was reduced by increasing fluid flow through the permeable ring. When β was less than 0.2, the velocity gradient was steeper over the permeable ring and in the shear layer near the reattachment region. When β was greater than 0.3, the width of the shear layer showed a relatively large augmentation and the back pressure in the separating region increases. Further, the response of the turbulent flow field to the permeable ring was delayed compared with that of the mean velocity field, and these differences increased with β. The turbulence intensities and Reynolds shear stress profiles near the reattachment point increased near the wall region as β increased, while those peak values that were taken at the locus of the manipulator ring height decreased as β increased.