TRANSIENT COUETTE FLOWS OF OLDROYD FLUIDS UNDER IMPOSED TORQUES

We study the transient Couette flow of an Oldroyd fluid that fills the gap between two circular cylinders when a constant torque is suddenly applied to the inner cylinder, the outer one being kept motionless. C ontrarily to most former studies, the inertia of the moving boundary i s not neglected. We give the exact solutions of this problem for a wid e class of initial conditions and we present a rigorous asymptotic ana lysis for small gap devices when the initial state is stationary. The case of Grade 2 fluids is also considered and treated. We also show in some experimental tests, that the knowledge of the relaxation curve o f the angular velocity of the rotor can be used to identify the parame ters of the model. (C) 1998 Elsevier Science B.V. All rights reserved.