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A localized stationary dipole solution to the Euler equations with a relationship between the vorticity and streamfunction given as w=-++ @ is presented. By numerical integration of the Euler equations this dipole is shown to be unstable. However, the initially unstable dipole reorganizes itself into a new nonlinear -dipole, which is found to be stable. This new structure has a functional relationship given as o=c$+~@-y@. Such dipoles are stable to head-on collisions and they are capable of creating tripolar structures when colliding off axis. The effects of increasing Newtonian viscosity on the nonlinear dipole is studied revealing that even though the nonlinearity is weakening, the dipole does not relax towards a Lamb dipole. 0 199.5 American Institute of Physics.

Abstract. The appearance of cavitation is still a problem in technical and industrial applications. Especially in automotive internal combustion engines, hydrodynamic journal bearings are used due to their favourable wearing quality and operating characteristics. Cavitation flows inside the bearings reduces the load capacity and leads to a risk of material damages. Therefore an understanding of the complex flow phenomena inside the bearing is necessary for the design development of hydrodynamic journal bearings. Experimental investigations in the fluid domain of the journal bearing are difficult to realize founded by the small dimensions of the bearing. In the recent years more and more the advantages of the computational fluid dynamics (CFD) are used to investigate the detail of the cavitation flows. The analysis in the paper is carried out in a two-step approach. At first an experimental investigation of journal bearing including cavitation is selected from the literature. The complex numerical model validated with the experimental measured data. In a second step, typically design parameters, such as a groove and feed hole, which are necessary to distribute the oil supply across the gap were added into the model. The paper reflects on the influence of the used design parameters and the variation of the additional supply flow rate through the feed hole regarding to cavitation effects in the bearing. Detailed pictures of the three-dimensional flow structures and the cavitation regions inside the flow film of the bearing are presented.

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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