Pipe flow

About: Pipe flow is a research topic. Over the lifetime, 13826 publications have been published within this topic receiving 351605 citations.

Particle migration and single-line particle focusing in microscale pipe flow of viscoelastic fluids

Abstract: The elasto-migration of microparticles across a streamline induced by elasticity and inertia in microscale pipe flow of viscoelastic fluids was investigated using a holographic technique. The effects of blockage ratio (d/D), flow rate (Q), and entry length (L) on particle migration induced by fluid elasticity were evaluated. Single-line particle focusing was demonstrated for an elasticity-dominant fluid. Furthermore, shear-thinning effect on particle migration was evaluated. Finally, we propose the focusing number, a non-dimensional parameter, to estimate the focusing state of particles in elasticity-dominant fluids. This criterion can be used to accurately estimate the design parameters, such as rheological properties, channel length, and particle diameter, for microfluidic devices using elasto-migration.

Finite-amplitude thresholds for transition in pipe flow

Abstract: We report the results of an experimental study of the finite-amplitude thresholds for transition to turbulence in a constant mass flux pipe flow. The flow was perturbed using small impulsive jets and push–pull disturbances from holes in the pipe wall. The flux of the disturbance is used to define an amplitude for the perturbation and the critical value required to cause transition scales in proportion to Re−1 for jets. In this case, the transition is catastrophic and the scaling suggests a simple balance between inertia and viscosity. On the other hand, the threshold scales as Re−1.3 or Re−1.5 for push–pull disturbances with the precise value depending on the orientation of the perturbation. Further, the amplitudes required to cause transition are typically an order of magnitude smaller than for jets. When the push–pull perturbation was applied in the oblique direction, streaks and hairpin vortices appeared during the growth phase of the disturbance. The scaling of the threshold and the growth of structures are both consistent with ideas associated with temporary algebraic growth.

Steady entry flow in a curved pipe

Abstract: Laser-Doppler velocity measurements were performed on the entry flow in a 90° bend of circular cross-section with a curvature ratio a/R = 1/6. The steady entry velocity profile was parabolic, having a Reynolds number Re = 700, with a corresponding Dean number ? = 286. Both axial and secondary velocities were measured, enabling a detailed description of the complete flow field. The secondary flow at the entrance of the bend was measured to be directed completely towards the inner bend. Significant disturbance of the axial velocity field was not measured until a downstream distance (aR)½. Maximum secondary velocities were measured at 1.7 (aR)½ downstream from the inlet. The development of the axial flow field can be quite well explained from the secondary velocity field.