Resistance of a Flow through an Annulus with an Inner Rotating Cylinder

In this paper, the resistance of a water flow through co-axial cylinders when the inner cylinder rotates, is studied experimentally. The resistances are measured for six gap sizes (s/r1=0.0136∼0.115, s : gap, r1 : radius of inner cylinder) and for various combinations of axial and rotational flows. Results obtained are as follows : 1. When the axial flow is laminar, the resistance of a flow is unaffected up to a certain rotating speed (Rωc : critical rotating Reynolds number), but beyond this speed the flow resistance increases as the Rω increases. 2. The value of critical Taylor number Rωc(s/r1)1/2 increases as the axial Reynolds number (Re=vms/ν) increases up to a certain value (Re=600), beyond this value Rωc(s/r1)1/2 decreases to zero with the increase of Re. When the axial flow is turbulent, such a critical rotating Reynolds number cannot be recognized. 3. When Rω>10 000, the resistance coefficient of a flow λ can be expressed by λ= 0.26 Re-0.24 ×{1+(7/8)2(Rω/2Re)2}0.38 even for small Re.