Assessing the Sliding Cylinder Approach to Determine Instantaneous Viscosity Under Unsteady Flow Conditions

Abstract

This preliminary numerical investigation is carried out in order to assess the usefulness of a new variant of the sliding cylinder approach to determine “instantaneous” viscosity under unsteady flow conditions. A fixed cylindrical reservoir is considered with a coaxial inner cylinder which is sliding into the liquid with different time dependent velocity profiles, i,e. a constant velocity, linear velocity and parabolic profile. For each velocity profile, three different blockage ratios (the ratio of the impactor’s diameter over the reservoir’s diameter) of 1/1.5, 1/3 and 1/6 are considered.

OpenFOAM 2.4.0 is used to simulate the fluid flows, and the multiphaseInterDyMFoam solver is employed to handle dynamic mesh for solving the Navier-Stokes equations of two phases flow consisting of air and the liquid. The simulations start with the sliding cylinder’s tip at the interface of the two phases (liquid-air), and it moves toward the liquid with the prescribed velocity profile. In order to assess the usefulness of this approach to perform rheological measurements at short acquisition times, we focus our attention on the fluid-structure interaction between the sliding cylinder and the liquid, mainly the contributions of drag and pressure force to the total force exerted by the fluid to the piston.