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

K e y w o r d s F o u r t h g r a d e fluid, Unsteady flow, Lie symmetries. 1. I N T R O D U C T I O N In recent years, considerable efforts have been usefully devoted to the s tudy of flow of nonNewton ian fluids. This is ma in ly due to their m a n y appl icat ions in pe t ro leum drilling, manufactu r ing of food and paper, and other similar activities. A vast a m o u n t of l i te ra ture is now available for various kinds of geometries and a variety of non -Newton ian fluids. Very few studies which *Author to whom all correspondence should be addressed. E. M. acknowledges funding from the National Research Foundation, South Africa under Grant Number 2053745. 0895-7177/05/$ see front matter (~) 2005 Elsevier Ltd. All rights reserved. doi: l O. l O16 /j.mcm.2004.01.010 Typeset by AJ/18-TEX