The unsteady flow of a fourth-grade fluid past a porous plate

The unsteady flow of a hydrodynamic fluid past a porous plate is examined. The constitutive equations of the fluid are modelled by those for a fourth-grade fluid. They give rise to a boundary value problem consisting of a fifth-order differential equation but there are only two boundary conditions. With the augmentation of boundary conditions at infinity, it is possible to obtain a solution by implementation of the Lie group method.