ROTATION OF RIGID ELLIPTICAL CYLINDERS IN VISCOUS SIMPLE SHEAR FLOW: ANALOGUE EXPERIMENTS

Abstract

We used experiments to investigate the behaviour of rigid elliptical cylinders embedded in a viscous fluid of finite thickness, and for very small ratios (S) between shear zone width (z) and the shortest principal axis (e2) of the ellipse that constitutes the base of the elliptical cylinder (3.5=< S = z/e2 =<1.2). Former theoretical and experimental work on the rotation of rigid inclusions immersed in a viscous matrix considered infinite shear zone thickness and/or a very large ratio between shear zone thickness and inclusion size (S >> 1), and concluded that inclusions rotate continuously and synthetically with the applied bulk simple shear flow (except for inclusions with infinite axial ratio). Our results depart greatly from the analytical predictions. Experiments were carried out at constant shear zone thickness, but variable S and degree of coupling at the inclusion/matrix interface. The results show that: (1) confined inclusion rotation always deviates from theoretical predictions for infinite shear zone thickness, even for synthetic rotation; (2) the deviation 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 inclusion/matrix interface greatly enhances deviation from theoretical predictions, with antithetic rotations to as much as 20°.