Fluid friction between rotating cylinders II—distribution of velocity between concentric cylinders when outer one is rotating and inner one is at rest

Abstract

Measurements of the distribution of velocity between two cylinders when the outer one is at rest have been made by means of small Pitot tubes. The Pitot was traversed in from the outer wall towards the inner cylinder and the difference in pressure P between the Pitot tube and a hole in the outer cylinder was measured. The connexion between the velocity U and P is 2/ρ∫ p 0 r 2 d P = U 2 r , (1) where U is the velocity at radius r . A similar method can be used to determine the velocity between rotating cylinders when the inner cylinder is fixed and the outer one rotates. The small Pitot tube must now be fixed projecting from the inner cylinder. The formula (1) still applies for determining U. It may be conveniently expressed in the form 2/ρ∫ p 0 d P/N2 = U 2 r 2 /N 2 , (2) where N is the number of revolutions of the outer cylinder per second.