The formation of shear layers in a fluid with temperature-dependent viscosity

The presence of viscosity normally has a stabilizing effect on the flow of a fluid. However, experiments show that the flow of a fluid in which viscosity decreases as temperature increases tends to form shear layers, narrow regions in which the velocity of the fluid changes sharply. In this paper, we present evidence that the formation of shear layers is due to an inherent instability in the fundamental conservation laws governing fluid flow when the viscosity decreases sufficiently quickly with temperature.