Transient effects of orthogonal pipe oscillations on laminar developing incompressible flow

This paper presents a numerical study of the transient developing laminar f low of a Newtonian incompressible fluid in a straight horizontal pipe oscil lating around the vertical diameter at its entrance. The flow field is infl uenced by the tangential and Coriolis forces, which depend on the through-f low Reynolds number, the oscillation Reynolds number and the angular amplit ude of the pipe oscillation. The impulsive start of the latter generates a transient pulsating flow, whose duration increases with axial distance. In any cross-section, this flow consists of a pair of symmetrical counter-rota ting vortices, which are alternatively clockwise and anti-clockwise. The ci rcumferentially averaged friction factor and the axial pressure gradient fl uctuate with time and are always larger than the corresponding values for a stationary pipe. On the other hand, local axial velocities and local wall shear stress can be smaller than the corresponding stationary pipe values d uring some part of the pipe oscillation. The fluctuation amplitude of these local variables increases with axial distance and can be as high as 50% of the corresponding stationary pipe value, even at short distances from the pipe entrance. Eventually, the flow field reaches a periodic regime that de pends only on the axial position. The results show that the transient flow field depends on the pipe oscillation pattern (initial position and/or dire ction of initial movement). Copyright (C) 2000 John Wiley & Sons, Ltd.