Year

1993

Degree Name

Doctor of Philosophy

Department

Department of Mechanical Engineering

Abstract

This thesis contains a superlaminar* lubrication theory which is applicable in both transition and fully developed turbulent regimes. A theory which covers the superlaminar regime is necessary, as nowadays bearings operate beyond the laminar regime, and especially in the transition regime with the Reynolds number between 1000- 3000. The existing theories have adequately predicted the bearing performance in the fully turbulent regime, but they are not accurate for the transition regime analysis.

The theory described in this thesis has been derived from the study of boundary layer flow in channels which employs mixing length concept. In the experimental work, law of wall profiles of flows in channels with gaps ranging from 5mm to 1mm were obtained. The measurements were made possible by means of an LDA system which was constructed especially for flow measurement in thin channel gaps. Initially the experimental work involved the testing of the LDA system for fluid velocity measurements in the laminar regime. From the analysis of the experimental data, it was found that the flow in the boundary layer of transition flow is affected by (equation: ac+/ay+). The law of wall profile can be modelled by a mixing length formula with the Van Driest constant (λ) modified by (equation: ac+/ay+ .

The theory is tested in two different ways. Firstly, it was used in turbulent lubrication analysis (in Chapters 4 and 6) and compared with existing theories. Secondly, it was used to construct velocity profiles (in Chapter 5) and the results were compared with the existing experimental data as well as those obtained in hydrodynamic journal bearings with minimum gap of 0.49mm.

Further in the thesis, the theory was used to carry out analysis of hydrodynamics bearings namely, slider bearing and journal bearing. From these analysis, performance charts for designing hydrodynamic bearings were established. A specially shaped diaphragm sector-shaped thrust bearing operating in the superlaminar regime was also investigated. The analysis also included the misalignment effect. The finding shows that this type of bearing gives improved load carrying capacity and can act as a good vibration damper in misaligned operation.

* In this thesis superlaminar flow is defined as flow beyond laminar regime from transition to fully developed turbulent regime.

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