The cavitating Taylor-Couette flow

Abstract

This work presents an investigation of a new phenomenon of the Taylor-Couette flow: the onset of Taylor vortices in a cavitating fluid. This particular form of the Taylor-Couette flow develops if the shear flow between a rotating inner and a fixed outer cylinder approaches the critical Taylor number and the vapor pressure of the fluid simultaneously. This process is achieved by increasing the rotational speed of the inner cylinder, which causes an increase of the radial pressure gradient inside the laminar flow. The fully developed Taylor vortex flow is characterized by a pressure distribution in the azimuthal plane showing a local minimum adjacent to the wall of the inner cylinder between a pair of vortices that form a radial flow towards the outer cylinder. Thence, cavitation occurs simultaneously if the local pressure minimum drops below the vapor pressure of the fluid. This transition from a two-dimensional (Couette) into a three-dimensional (Taylor) flow triggered the idea to apply a newly developed unsteady 2-phase 3D-computational fluid dynamics code by computing the generation of vapor that is coinciding with the formation of Taylor vortices at the critical Taylor number. Whereas the results of a numerical simulation prove the existence of toroidal vapor caused by cavitation, the experimental validation demands additionally the development of a special fluid. Thus, the present work describes this specifically tailored fluid, which not only fulfills Taylor and pressure analogy but also features a favorable refractive index and a chemical suitability for the task.

Proceedings in Fluid Design

“…The fluid is a mixture of two alkanes, a low boiling pentane, which enables cavitation, and a long chain alkane to reach viscosity and refractive index. The authors [5] have successfully demonstrated the process of designing a cavitating fluid in the case of the cavitating Taylor-Couette flow. The viscosity of the fluid defines the time scale and demands an adjustment of the rotational speed of the experiment.…”

Taylor‐Couette reactor: Principles, design, and applications

“…In general, it relates centrifugal to the viscous forces, meaning that growing values correspond to higher levels of turbulence. Different definitions for Ta exist in literature and an overview of common definitions is given in Table 1 12,14,29,[31][32][33][34][35][36][37][38] . For the sake of brevity, in this work the definition in equation 1is based on the definition given by Lueptow et al 35,39 and Richter et al 35 The flow regimes in the annular gap vary with ω and can be characterized in terms of turbulence and the type and shape of the forming vortices.…”

“…While the aforementioned flow patterns are the most common ones, a few additional flow regimes can be observed as explained in the following, namely: cavitating Taylor‐Couette, global heat convection flow, stable vortices, or the alternation of the latter two. It has been shown that the pressure gradient between rotor and shell is large enough to cause cavitation, given the use of a fluid with a sufficiently low vapor pressure 36 . For this to occur, the transition to the Taylor‐Couette flow and the undercutting of the vapor pressure have to be reached simultaneously.…”

Bubble Dynamics in a Narrow Gap Flow under the Influence of Pressure Gradient and Shear Flow

“…For this purpose, the authors [20] have developed a special cavitating fluid, which was already applied successfully to demonstrate that a cavitating Taylor-Couette flow shows a double transition: Taylor vortices and vaporization simultaneously at one operation point. The fluid in question is a mixture of a low boiling pentane, which triggers cavitation, and a long chain alkane (paraffin) to meet viscosity and refractive index.…”