Oscillatory behaviour in statically stressed viscoelastic inflation flow

The influence of fluid elasticity is investigated by examining the biaxial inflation of a spherical shell of a viscoelastic fluid subject to a constan t and a linearly ramped change of pressure. In contrast to the monotonic gr owth of a Newtonian fluid, that of a viscoelastic fluid is found to be osci llatory under conditions of large Deborah number, for a thick shell, and fo r sudden inception. Although this type of non-monotonic behaviour has been predicted in other similar flow configurations of viscoelastic fluids, ther e is no evidence of it occurring experimentally. The current calculations, in the case of a bubble growing in an infinite viscoelastic medium, show th at, if a ramped rather than a sudden pressure is applied initially, the amp litude of the oscillations decreases as the rate of pressure decreases. Thi s may explain why oscillations have not been observed in experiment, since a sudden initial driving pressure is difficult to realize.