Mathematical analysis of the discharge of a laminar hot gas in a colder atmosphere

Abstract

We study the boundary layer approximation of the, already classical, mathematical model which describes the discharge of a laminar hot gas in a stagnant colder atmosphere of the same gas. We start by proving the existence and uniqueness of solutions of the nondegenerate problem under assumptions implying that the temperature T and the horizontal velocity u of the gas are strictly positive: T >= delta > 0 and u > epsilon > 0 (here delta and epsilon are given as boundary conditions in the external atmosphere). We also study the limit cases delta = 0 or epsilon = 0 in which the governing system of equations become degenerate. We show that in those cases it appear some interfaces separating the zones where T and U are positive from those where they vanish.