Proceedings in Fluid Design

Abstract

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.

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

“…Moreover, the fluid must have an appropriate viscosity and refractive index, which is compatible with the housing material of the model experiment, enabling the application of optical measurement of fluid velocity, bubble size and visualization. A detailed description of the fluid design can be found in [21] and the thermodynamic properties of the cavitating fluid are listed in Table 4. The value of the bulk modulus is adopted from data given by Watter [22] for mineral oil, because the cavitating fluid uses alkenes as basic liquid.…”