Laminar–turbulent transition in Poiseuille pipe flow subjected to periodic perturbation emanating from the wall

Abstract

Transition in fully developed circular pipe flow was investigated experimentally by the introduction of periodic perturbations. The simultaneous excitation of the azimuthal periodic modes m=+2 and m=−2 was chosen for detailed analysis. The experiments were carried out at three amplitudes. At the smallest amplitude the disturbances decayed in the direction of streaming. At intermediate input amplitude the disturbances amplified initially but then decayed with increasing distance downstream. Their growth was accompanied by the appearance of higher harmonics. At still higher amplitudes transition occurred. A mean velocity distortion corresponding to an azimuthal index of m=4 was observed at the intermediate and at the higher levels of forcing. When four stationary jets were introduced through the wall to emulate a similar mean velocity distortion, transition was observed at smaller amplitudes of forcing at modes ±2. Thus, weak longitudinal vortices provide an added instability needed to generate a secondary disturbance which, in turn, amplifies the steady vortical structures introduced by the jets. Such vortices may also be generated through the interaction of time-periodic helical modes.

Turbulence Transition in Pipe Flow

“…That is, for instance, the phase velocity of center modes approaches the laminar pipe centerline velocity in this limit. 30 5 Physics of pipe flow and verification of the new pipe code…”

Transition to Turbulence in Particulate Pipe Flow

“…For small perturbations, laminar motion is observed as far as Re ≈ 10 5 but the transition in pure fluid can be reached for Re ≈ 2100 provided that the perturbation is strong enough to allow the growth of turbulent "puffs" [2]. Recent studies have investigated with different kinds of perturbations the nature of the unstable modes, either in the inlet region or in the fully developed flow [4,5].The objective of the present work is to examine how transition to turbulence is affected by the presence of suspended particles in the simplest case of neutral buoyancy. More specifically, we focus upon determining the transition threshold between the laminar and the intermittent regime as a function of the particle volume fraction φ of the suspension.…”

“…For small perturbations, laminar motion is observed as far as Re ≈ 10 5 but the transition in pure fluid can be reached for Re ≈ 2100 provided that the perturbation is strong enough to allow the growth of turbulent "puffs" [2]. Recent studies have investigated with different kinds of perturbations the nature of the unstable modes, either in the inlet region or in the fully developed flow [4,5].…”

Stability of Thixotropic Fluids in Pipe Flow

“…Figures 3 and 4 show typical basic-ow velocity pro les using Eq. (11). As can be seen in Figure 3, by an increase in , the velocity pro les deviate more and more from the parabolic pro le of Newtonian uids.…”

“…To the best of our knowledge, the e ect of thixotropy on the stability of pipe ow has not been addressed in the past. The interest in the stability of pipe ow stems from the fact that this particular geometry is widely used for the transport of Newtonian and nonNewtonian uids [9][10][11][12][13][14][15]. In previous studies dealing with non-Newtonian uids, the e ect of shear-thinning and yield stress has already been investigated on the critical Reynolds number in pipe ow.…”