UNSTEADY EXACT SOLUTION FOR FLOWS OF FLUIDS WITH PRESSURE-DEPENDENT VISCOSITIES

There are many applications, elasto-hydrodynamics being one, where the fluid can be modelled as an incompressible fluid with a viscosity that depends on the pressure (see [15]). The justification for such an assumption stems from the fact that while the density changes by merely a few percent, the pressure can change significantly and the viscosity can change by several orders of magnitude. Of course, there is the possibility that the dependence of viscosity on density is such that even a small change in density causes this change. Experiments clearly suggest that viscosity varies exponentially with pressure and that it is the relationship between the viscosity and the pressure that causes the tremendous change that occurs in the viscosity. That the viscosity of liquids could depend upon the pressure was known to the pioneers of the field. Stokes [14] is in fact very careful to delineate the special class of flows, those in channels and pipes at moderate pressures, when viscosity could be assumed a constant. There is also a considerable amount of literature even prior to 1930 concerning the variation of viscosity with pressure (see Bridgman [4] on the physics of high pressures for a detailed discussion of the same). Bridgman [4] makes it abundantly clear that he devoted a great deal of attention to determining the variation