Sedimentation of rectangular particle in Oldroyd-B fluid

The sedimentation of a rectangular particle in a two-dimensional channel filled with an Oldroyd-B fluid was simulated by using distributed Lagrange multiplier/fictitious domain method in order to investigate the settling characteristics of rectangular particle in a viscoelastic fluid. The sedimenting trajectory, velocity and orientation of particles with different aspect ratio were obtained, and the effect of particle's shape on the sedimenting velocity was also discussed. Results show that the stable orientation of a settling rectangular particle in an Oldroyd-B fluid is that the longest line of the body parallels to gravity, and the final equilibrium position is at the center of the channel. The aspect ratio of rectangular particle has significant influence on its settling behavior. Both the lateral drifting distance and the sedimenting velocity increase with increasing aspect ratio. For different particles with same hydraulic diameter, the circular particle has the largest final sedimenting velocity while the square particle has the least one.