FLOW VISUALIZATION OF THE EVOLUTION OF TAYLOR INSTABILITIES AND COMPARISON WITH NUMERICAL SIMULATIONS

摘要

The authors are presenting in this paper combined experimental and numerical results that bring up some less explored aspects the Taylor fluid instability. In fact the paper will concentrate on issues that explore flow formations on the road to the fully developed Taylor instability (500-1800 rpm). The experimental investigation uses the Full Flow Field Tracking{FFFT) method, developed at the University of Akron, to visualize the flow in longitudinal cross sections and at the same time correlate flow pattern observations to torque measurements. The experimental results indicate that incipient flow instabilities appear at lower speeds than the ones predicted by the critical Taylor number, and include formation of incipient Taylor cells that occupy only a part of the gap. The cells are separated by axially flowing narrow rope-like flowing streams that twist in a corkscrew fashion around the circumference, while separating the incipient cells. As the rotational velocities increase the Taylor cells keep growing until they occupy the entire gap. Three-dimensional CFD studies were also performed for the matching set of conditions and for the higher rotational velocities (above <1500 rpm), where experimental studies were not possible. The torque computed by the numerical model was compared with the experimentally obtained torque and the two results compare very favorably. Numerical simulation studies allowed an in-depth study of the flow mechanisms and trajectories inside the fully formed vortical Taylor instabilities. Computational studies were performed using CFD-ACE+ software package.