TY - JOUR
T1 - Suspension flow past a cylinder
T2 - Particle interactions with recirculating wakes
AU - Haddadi, Hamed
AU - Shojaei-Zadeh, Shahab
AU - Connington, Kevin
AU - Morris, Jeffrey F.
N1 - Publisher Copyright:
© 2014 Cambridge University Press.
PY - 2014/10/31
Y1 - 2014/10/31
N2 - Experimental observations of the flow of a suspension of solid fraction φ 0.084 over a circular cylindrical post in a shallow microchannel (depth smaller than the cylinder radius) find that the recirculating wake behind the obstacle at moderate Reynolds numbers is depleted or devoid of particles. Particles injected into the wake exit to regain the depleted state. By numerical simulation of the discrete particle motion, the basis for the depletion behind the cylinder is studied; rather than a shallow channel, the numerical simulations consider a periodic domain, mimicking the flow past an infinite cylinder. The Reynolds number is defined, using the average axial velocity U, diameter of the obstacle D and the kinematic viscosity of the suspension v, as Re=UD/v, and is studied for Re<30 in the simulation - conditions for which the pure fluid exhibits an extended steady closed-streamline (recirculating) wake behind the cylinder; unsteadiness is found to be suppressed by the channel walls in the experiments, allowing steady flow at a larger Re than expected for an infinite cylinder (up to at least Re=300). The simulations use the lattice-Boltzmann method to determine the motion of the fluid and neutrally buoyant particles. The trajectory of a single particle (small relative to the cylinder) shows migration to a limit cycle inside the wake. With an increase of the number of particles in the wake alone (no particles in the free stream), particles can escape the wake due to velocity fluctuations. Simulation of the flow of suspensions of φ=0.04,0.06 and 0.08 demonstrates that there is particle exchange between the wake and the free stream; the net flux of particles out of the wake leads to a particle-depleted wake, qualitatively very similar to the experimental observation.
AB - Experimental observations of the flow of a suspension of solid fraction φ 0.084 over a circular cylindrical post in a shallow microchannel (depth smaller than the cylinder radius) find that the recirculating wake behind the obstacle at moderate Reynolds numbers is depleted or devoid of particles. Particles injected into the wake exit to regain the depleted state. By numerical simulation of the discrete particle motion, the basis for the depletion behind the cylinder is studied; rather than a shallow channel, the numerical simulations consider a periodic domain, mimicking the flow past an infinite cylinder. The Reynolds number is defined, using the average axial velocity U, diameter of the obstacle D and the kinematic viscosity of the suspension v, as Re=UD/v, and is studied for Re<30 in the simulation - conditions for which the pure fluid exhibits an extended steady closed-streamline (recirculating) wake behind the cylinder; unsteadiness is found to be suppressed by the channel walls in the experiments, allowing steady flow at a larger Re than expected for an infinite cylinder (up to at least Re=300). The simulations use the lattice-Boltzmann method to determine the motion of the fluid and neutrally buoyant particles. The trajectory of a single particle (small relative to the cylinder) shows migration to a limit cycle inside the wake. With an increase of the number of particles in the wake alone (no particles in the free stream), particles can escape the wake due to velocity fluctuations. Simulation of the flow of suspensions of φ=0.04,0.06 and 0.08 demonstrates that there is particle exchange between the wake and the free stream; the net flux of particles out of the wake leads to a particle-depleted wake, qualitatively very similar to the experimental observation.
KW - multiphase and particle-laden flows
KW - suspensions
KW - wakes/jets
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U2 - 10.1017/jfm.2014.613
DO - 10.1017/jfm.2014.613
M3 - Article
AN - SCOPUS:84910628523
SN - 0022-1120
VL - 760
SP - R21-R12
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
IS - 6
ER -