A COMBINED METHOD FOR DETERMINING VELOCITY OF STARTING FLOW IN A LONG CIRCULAR TUBE

A combination of experimental and analytical methods is used to determine the velocity of fluid in a starting flow process in a circular tube. The developing pressure gradient, measured experimentally in the fully developed region, is expressed as a function of time and is used in the solution of Navier-Stockes equations for axial flow in a circular tube. Expressions for velocity in time and space and the average discharge are obtained by Laplace's transformation technique. The velocity profiles and discharge under time-dependent pressure gradient are compared with those under constant pressure gradient. Significant differences between the velocities are found during the flow establishment, and the assumption of constant pressure gradient in the period of flow establishment, as considered in a number of studies, appears to be unsatisfactory. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.