Stability of Gravitationally Unstable Double Diffusive Transient Boundary Layers with Variable Viscosity in Porous Media Nasser Sabet, Hassan Hassanzadeh † , and Jalal Abedi Dept. of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4 Abstract We study the double diffusive convection (DDC) in porous media through linear stability analysis (LSA) and direct numerical simulations (DNS). Unlike the previous studies that assume static solutal or thermal fields, the developed model is able to capture the transient behavior of both fields. We show that under the assumption of static field, the role of Lewis number cannot be distinguished. Under transient fields, we conclude that higher Lewis numbers result in earlier instability of the boundary layers. Moreover, the effect of viscosity contrast is explained in terms of the mobility of the boundary layer. The DNS results confirm the validity of LSA predictions. We also obtain the critical Rayleigh number and show that in the presence of viscosity contrast, it can be much smaller than the conventional limit of 4π 2 . This study provides a better understanding of the transient nature of DDC in the presence of viscosity variations. Keywords: Double diffusive convection (DDC), linear stability analysis (LSA), direct numerical simulation (DNS) † Tel.: +1 403 210 6645; Fax: +1 403 284 4852; Electronic mail: hhassanz@ucalgary.ca Transport Phenomena and Fluid Mechanics AIChE Journal DOI 10.1002/aic.15626 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/aic.15626 © 2016 American Institute of Chemical Engineers (AIChE) Received: Oct 18, 2016; Revised: Dec 07, 2016; Accepted: Dec 27, 2016 This article is protected by copyright. All rights reserved.