Effect of viscosity changes on the motion of debris flow by considering entrainment

Debris flows are typical two-phase flows that commonly occur with entrainment. By involving sediment materials, the fluid viscosity of debris flow may change significantly along with the variety of solid volume fraction, which further influences debris flow routing. To address this issue, a two-phase model is incorporated with a correlation for the apparent viscosity of the mixture and an entrainment formula, which is applied for studying how the changing fluid viscosity affects the interaction force between the solid and fluid phases during flow propagation. A second-order accuracy numerical scheme based on the finite volume method is applied to solve model equations. The numerical results correlate well with the available experimental data, and indicate the importance of viscosity changes in debris flow routing.