Three-dimensional absolute and convective instabilities in mixed convection of a viscoelastic fluid through a porous medium.

Dra. Silvia Hirata - Laboratoire de Mécanique de Lille, Université Lille 1, Lille - França

Dia: 23/07/2010, 6ª feira.
Hora: 14 horas
Local: Bloco G, sala 205, Centro de Tecnologia - UFRH

By using the mathematical formalism of absolute and convective instabilities we study the nature of unstable three-dimensional disturbances of viscoelastic flow convection in a porous medium with horizontal through-flow and vertical temperature gradient. Temporal stability analysis reveals that among three-dimensional (3D) modes the pure down-stream transverse rolls are favored for the onset of convection. In addition, by considering a spatiotemporal stability approach we found that all unstable 3D modes are convectively unstable except the transverse rolls which may experience a transition to absolute instability. The combined influence of through-flow and elastic parameters on the absolute instability threshold, wave number and frequency is then determined, and results are compared to those of a Newtonian fluid.