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.

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The research of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, is a challenging task due to spatial restrictions combined with a high time-resolution. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for bubble generation and collapse is less than a few milliseconds. The authors have developed a journal bearing model experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. This work presents the high-speed photography of bubble evolution and transportation in a Stokes-type flow under the influence of shear and a strong pressure gradient which are typical for lubricant films. A paramount feature of the experiment is the dynamic variation (increase/decrease) of the minimum film thickness which triggers the onset of cavitation in narrow gap flows. Results presented in the work on hand include the time-resolved data of the gas release rate and the transient expansion of gas bubbles. Both parameters are necessary to set up numerical models for the computation of two-phase flows.

This work presents the process of designing a cavitating fluid for the lubricant flow in journal bearings. Hydrodynamic journal bearings are used in a wide range of technical and industrial applications because they provide low friction and minimal wear. The principal operational feature of these bearings is an eccentrically rotating shaft inside the bushing resulting in a convergent and divergent lubricating film of just a few micrometers in thickness between the shaft and the bushing. For the particular case of internal combustion engines the displacement of the shaft is transient with strong variations in eccentricity and displacement velocity. Hence, the flow inside the lubricating film is transient and three‐dimensional. Investigations of the flow inside journal bearings are technically challenging. The following geometrical and physical conditions have to be tackled: small lubricating film thickness, optical accessibility, Reynolds and cavitation similarity. The combination of these conditions requires a scaled journal bearing experiment with a special fluid that fulfills the cavitation condition. The most important component of the experimental setup is the fluid in order to create the desired flow conditions. The authors of this work have proven that a cavitating fluid can be designed to specification by applying the new approach to the cavitating Taylor‐Couette flow. The proper fluid design has to fulfill three criteria: physical compatibility, Reynolds analogy and cavitation number at the operating point. Physical compatibility stems from material specifications of the apparatus and the need to provide optical accessibility by providing identical refractive indices of fluid and housing. The fluid must be chemically compatible with acrylic glass of the apparatus preventing unwanted reactions. Laser‐optical measurements are the most suitable means to obtain significant data of the flow field inside the lubricating film. The relation of dynamic pressure at the operating point and mechanical dimensions of the apparatus defines the viscosity necessary to fulfill the Reynolds analogy. Finally, the cavitation number in relation to the combination of dynamic and static pressure provides the target vapor pressure of the special fluid. Thus, the present work describes the development of a special fluid applicable for journal bearings in model scale, which not only fulfills pressure and cavitation analogy but also features a favorable refractive index and a chemical suitability for the task. Furthermore, the work shows results of a cavitating flow in a small gap arrangement by means of the designed fluid.

The volume-of-flow method combined with the Rayleigh–Plesset equation is well established for the computation of cavitation, i.e., the generation and transportation of vapor bubbles inside a liquid flow resulting in cloud, sheet or streamline cavitation. There are, however, limitations, if this method is applied to a restricted flow between two adjacent walls and the bubbles’ size is of the same magnitude as that of the clearance between the walls. This work presents experimental and numerical results of the bubble generation and its transportation in a Couette-type flow under the influence of shear and a strong pressure gradient which are typical for journal bearings or hydraulic seals. Under the impact of variations of the film thickness, the VoF method produces reliable results if bubble diameters are less than half the clearance between the walls. For larger bubbles, the wall contact becomes significant and the bubbles adopt an elliptical shape forced by the shear flow and under the influence of a strong pressure gradient. Moreover, transient changes in the pressure result in transient cavitation, which is captured by high-speed imaging providing material to evaluate transient, three-dimensional computations of a two-phase flow.