Bubble-bearing fluid flows on an inclined plane

The effect of bubble-bearing state on fluid flows on an inclined plane is clarified. The deceleration or acceleration compared to the single-phase state is determined by a non-dimensional parameter Π, a ratio of the gravity-induced shear stress to the restoring force originated by the surface tension. At Π<O(1), the spherical bubbles contribute to increasing the viscosity and decelerating the flow. At Π>O(1), the deformed bubbles decrease the viscosity and accelerate the flow. The result is validated in experiments under the former condition, and this framework is applied to predict the arrival time of the bubble-bearing fluid flows. Through this work, it is shown that extending the application of the rheology model beyond just materials science to fluid mechanics offers new avenues for elucidating the underlying physics of bubble-bearing fluid flows across diverse disciplines.