  We show that a micropolar fluid model successfully describes collisional
granular flows on a slope. A micropolar fluid is the fluid with internal
structures in which coupling between the spin of each particle and the
macroscopic velocity field is taken into account. It is a hydrodynamical
framework suitable for granular systems which consists of particles with
macroscopic size. We demonstrate that the model equations can quantitatively
reproduce the velocity and the angular velocity profiles obtained from the
numerical simulation of the collisional granular flow on a slope using a simple
estimate for the parameters in the theory.
