Lift force in size and density segregation

We computationally study the forces experienced by a large intruder in a sheared particle bed. The intruder is attached to a virtual spring, which allows measurement of segregation forces when the intruder reaches an equilibrium position. By subtracting a buoyancy-like contribution from the overall segregation force, the lift force on the intruder is measured for a variety of size and density ratios, and local shear rates. We find that lift force depends only on size ratio and shear rate, but not on density ratio. At a given shear rate, the lift force scales with the square of the size ratio. We propose a lift force model that successfully predicts the combination of size and density ratios at which the intruder rises or sinks. In the future, the lift force model will be used to predict segregation velocity in size and density disperse mixtures.