Free convection near a stagnation point in a porous medium resulting from an oscillatory wall temperature

A detailed theoretical study of unsteady free convection boundary-layer flo w near the stagnation point of a two-dimensional cylindrical surface embedd ed in a fluid-saturated porous medium is presented when the surface tempera ture oscillates about a mean value above ambient. Both numerical and asympt otic solutions are employed to solve the governing equations for general va lues of the frequency omega and amplitude A of the surface temperature osci llations. Results for the heat transfer rate, boundary-layer thickness and temperature profiles are obtained for both small and large Values of A and also for slow and fast oscillations. It is found that outside the thin boun dary layer on the surface, a steady flow is induced for large times and fas t oscillations. This steady boundary-layer flow is studied in detail for la rge values of the amplitude A. (C) 1999 Elsevier Science Ltd. All rights re served.