On Fluid Resistance of Enclosed Rotating Rough Discs

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In this paper, by using rough surfaces consisting of various grains or wire-netting, axial clearance taking minimum value of resistance was found out in the same way as the cases of smooth surface when the roughness of disc is equal to that of vessel and when not equal. And the experiments of partially roughened surface in which lathed only outside parts of disc having large effect on friction were carried out. The main results are summarized as follows : (1) When axial clearance is measured from the mean half value of protuberance height, moment coefficient C_f is not affected by roughness in laminar flow region. (2) C_f takes minimum value at S/d≒0.008 8 for rough vessel and S/d≒0.006 6 for disc only roughened, where S is clearance and d is disc diameter. (3) C_f of rough disc in smooth vessel and that of vice versa are identical at S/d ⪈ 0.006 6. (4) When the surface is partially roughened within a certain radius, C_f is nearly constant. (5) For netted surfaces equivalent roughness is considerably varied by pitch of netting and clearances.
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