On the dynamics and kinetic energy of axisymmetric and wavy Taylor-Couette flows.

摘要

An experimental study of axisymmetric and wavy Taylor-Couette flows is presented in this research. The study is conducted to investigate the flow characteristics under steady state conditions in axisymmetric and wavy Taylor flows. Additionally, the time-dependent formation of axisymmetric vortices is also experimentally investigated. The radii and aspect ratios of the experimental facility utilized in this research are 0.672 and 20, respectively. The working fluid used during the experiments is water. The experiments were performed within the Taylor numbers range comprised by TC T 105 TC. A numerical scheme based on finite differences technique has been developed to validate the apparatus utilized to conduct the experiments. A time-dependent perturbation is introduced into the axisymmetric form of the Navier-Stokes equations and the result is linearized and then discretized in finite differences. The numerical scheme which is general in the sense that can be applied to any combination of radii and rate of rotation ratios, predicts the onset of axisymmetric Taylor vortex flow.; The entire velocity flow field in steady axisymmetric Taylor flow is determined by capturing the flow fields at planes perpendicular to the circumferential and axial directions using Particle Image Velocimetry (PIV). Flow fields perpendicular to the circumferential direction provide the radial and axial components of the velocity while planes perpendicular to the axial direction provide the circumferential component. Comparisons of the mass-normalized kinetic energy of axisymmetric Taylor flow systems with different wavelengths at the same Taylor number are presented. Through this comparison it has been determined that the wave number and kinetic energy of the flow are not related.; Laser Doppler Velocimetry (LDV) is used to continuously measure the axial component of the velocity at a fixed location. The power spectrum of the axial component of the velocity determined by LDV allows the determination of the range at which wavy Taylor flow exists. It also provides the number of circumferential waves in the flow and the tangential velocity of these waves. PIV realizations perpendicular to the circumferential direction have been studied to understand the interaction between vortices at different Taylor numbers within the wavy Taylor flow range.; Finally, the process of the formation of the secondary vortices under Taylor numbers corresponding to axisymmetric Taylor flow is studied. The secondary flows are generated under sudden starts of the inner cylinder. PIV realizations start being recorded simultaneously to the initiation of inner cylinder's rotation. Different experiments have shown that there are three time-dependent stages before the flow reaches steadiness. PIV realizations have also shown that the secondary vortices are formed from the end plates of the apparatus towards the center of the column of fluid.