Effects of Clearances and Grooves on Fluid Friction of Rotating Discs

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Experiments on a rotating grooved disc in a closed grooved vessel were carried out with various clearances, especially very small axial clearances, and over a wider range of Reynold's numbers. From these results the effects of axial clearance S, pitch p and depth T of grooves on the moment coefficient are determined as follows : (1) When the axial clearances are very small and the surfaces are smooth, the moment coefficient C_f is proportional to R^<-5/6> in laminar flow region, and to R^<-1/4>_e in turbulent flow region, and independent of R_e in transitional region. (2) C_f takes a minimum value at S/d≒0.0066,where d is the disc diameter, irrespective of the existence of grooves. In general, grooves have little influences on S/d. (3) C_f of a smooth or grooved disc in a grooved vessel takes a minimum value, when p/d=0.088,T/d=0.0066. The combination of a smooth disc and a grooved vessel is desirable in order to decrease C_f in laminar flow region. on the other hand, in turbulent flow region, the combination of a grooved disc and a grooved vessel is preferred.
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