Long-wave instability of a regularized Bingham flow down an incline

We investigate the linear stability of a flow down an incline when the fluid is modeled as a regularized Bingham-like fluid, i.e., a material whose constitutive equation is smoothed out. We perform a theoretical analysis by using the long-wave approximation method. The results show the existence of a critical condition for the onset of instability, which arises when the Reynolds number is above a critical threshold that depends on the tilt angle and on rheological parameters. The comparison of our findings with experimental studies is rather satisfactory