The effect of g-jitter on vertical free convection boundary-layer flow in porous media

We consider how the boundary-layer flow induced by a constant temperature vertical surface embedded in a porous medium is modified by time-periodic variations in the gravitational acceleration. The amplitude of these variations is assumed to be small compared with the mean acceleration. An amplitude expansion is used to determine the detailed effect of such g-jitter, and the expansion is carried through to fourth order. It is found that the mathematical problem has no free parameters when Darcy-flow is assumed; the resulting nonsimilar boundary-layer equations are solved using the Keller-box technique. The numerical and asymptotic solutions show that the g-jitter effect is eventually confined to a thin layer embedded within the main boundary-layer, but it becomes weak at increasing distances from the leading edge. (C) 2000 Elsevier Science Ltd.