Abstract

This study investigates by Particle Image Velocimetry (PIV) the wavy Taylor vortex flow that develops in the gap between concentric rotating cylinders of low aspect ratio and low radius ratio, which is a configuration relevant to oil bearing chambers in turbomachinery. The configuration is characterised by a larger annular gap width than the one typically used in journal bearings and by a Taylor number ( ) of 2.47 x 10 6 , which is 1000 times higher than the first critical Taylor number. It is found that the non-uniform axial spacing of the vortex cores induces an asymmetric radial velocity profile and an inflected axial velocity profile close to the cylindrical walls. The outflow at the centre of each pair of Taylor vortices that make up a vortex cell is strong and it is characterised by a sharp radial velocity peak. The inflow between pairs of Taylor vortex cells is unconventional in that it is characterised by pairs of confluent streams from the outer cylinder that merge towards the inner cylinder. These results form a body of experimental evidence on the flow features that may occur in engineering practice in oil bearing chamber flows, with relevance to lubrication and wear.

A numerical investigation is conducted for the flow between two concentric cylinders with a wide gap, relevant to bearing chamber applications. This wide gap configuration has received comparatively less attention than narrow gap journal bearing type geometries. The flow in the gap between an inner rotating cylinder and an outer stationary cylinder has been modelled as an incompressible flow using an implicit finite volume RANS scheme with the realisablek-εmodel. The model flow is above the critical Taylor number at which axisymmetric counterrotating Taylor vortices are formed. The tangential velocity profiles at all axial locations are different from typical journal bearing applications, where the velocity profiles are quasilinear. The predicted results led to two significant findings of impact in rotating machinery operations. Firstly, the axial variation of the tangential velocity gradient induces an axially varying shear stress, resulting in local bands of enhanced work input to the working fluid. This is likely to cause unwanted heat transfer on the surface in high torque turbomachinery applications. Secondly, the radial inflow at the axial end-wall boundaries is likely to promote the transport of debris to the junction between the end-collar and the rotating cylinder, causing the build-up of fouling in the seal.

The three-dimensional flow separation over the Rood wing-body junction is an exemplar application of separation affecting many important flows in turbomachinery and aerodynamics. Conventional Reynolds Averaged Navier Stokes (RANS) methods struggle to reproduce the complexity of this flow. In this paper, an unconventional use is made of a hybrid Reynolds Averaged Navier Stokes (RANS) model to tackle this challenge. The hybridization technique combines the Menter − − model with the one equation sub-grid-scale (SGS) model by Yoshizawa through a blending function, based on the wall-normal distance. The hybrid RANS turbulence closure captured most of the flow features reported in past experiments with reasonable accuracy. The model captured also the small secondary vortex at the corner ahead of the wing nose and at the trailing edge. This feature is scarcely documented in the literature. The study highlights the importance of the spatial resolution near the wing leading edge, where this localised secondary recirculation was observed by the hybrid RANS model. It also provides evidence on the applicability of the hybrid Menter and Yoshizawa turbulence closure to the wing-body junction flows in aircraft and turbomachines, where the flows are characterised by a substantially time-invariant three-dimensional separation.

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