Rotation of rigid elliptical cylinders in viscous simple shear flow: analogue experiments

We used experiments to investigate the behaviour of rigid elliptical cylind ers embedded in a viscous fluid of finite thickness, and for very small rat ios (S) between shear zone width (z) and the shortest principal axis (e(2)) of the ellipse that constitutes the base of the elliptical cylinder (3.5 g reater than or equal to S = z/e(2) greater than or equal to 1.2). Former th eoretical and experimental work on the rotation of rigid inclusions immerse d in a viscous matrix considered infinite shear zone thickness and/or a ver y large ratio between shear zone thickness and inclusion size (S >> 1), and concluded that inclusions rotate continuously and synthetically with the a pplied bulk simple shear flow (except for inclusions with infinite axial ra tio). Our results depart greatly from the analytical predictions. Experimen ts were carried out at constant shear zone thickness, but variable S and de gree of coupling at the inclusion/matrix interface. The results show that: (1) confined inclusion rotation always deviates from theoretical prediction s for infinite shear zone thickness, even for synthetic rotation; (2) the d eviation in the angular velocity and/or in the sense of rotation increases as S approaches 1, and antithetic rotation is possible from a position with ellipse longest axis parallel to the shear plane; and (3) a slipping inclu sion/matrix interface greatly enhances deviation from theoretical predictio ns, with antithetic rotations to as much as 20 degrees. (C) 2001 Elsevier S cience Ltd. All rights reserved.