Mixing-effective motions are both numerically and experimentally studied fo
r a very viscous fluid around a rotating elliptic cylinder installed in a c
ylindrical vessel. A two-dimensional direct numerical simulation was conduc
ted in an elliptic boundary-fitted curvilinear coordinate system rotating a
t the same angular velocity as the elliptic cylinder. Time-dependent stream
lines and streaklines were observed with the aid of visualization technique
. It is found that a mixing-effective (folding) motion actually occurs in t
he vicinity of the edges of the elliptic cylinder, and that such a motion m
ay result from the unstableness of hyperbolic fixed points on an integrable
two-dimensional heteroclinic orbit due to experimentally unavoidable three
-dimensional disturbances.