Homotopy perturbation method for thin film flow of a fourth grade fluid down a vertical cylinder

The present Letter applies the homotopy perturbation method and the traditional perturbation method to obtain analytic approximations of the non-linear equations modeling thin film flow of a fourth grade fluid falling on the outer surface of an infinitely long vertical cylinder. Expressions for the velocity, volume flux and average velocity are obtained. Comparison of the results obtained by the two methods reveal that homotopy perturbation method is more effective and easy to use.