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Oil flow in the oilwell tube annulus of vertical bearing assemblies

University of British Columbia

Oil leakage from the oilwell tube annulus of self-contained vertical bearing assemblies has been of practical industrial concern for many years. Earlier observations of bearing behavior indicated that this leakage was associated with the complicated physical processes that describe the flow of oil in the bearing's reservoir. In this latest study, we seek to obtain a better understanding of this oil flow, particularly in the annular clearance space surrounding the oilwell tube. This will be done by means of numerical simulation and experimental flow visualization. A test rig was designed and built for the purpose of simulating the bearing's oilwell tube annulus. A major feature of this rig was to provide visual access to the annular clearance space, and also to the region beneath the rotating runner where strong secondary flow effects are known to exist. A light sheet visualization technique, using micro air bubbles as the tracer, was the primary method for tracing the secondary flow pathlines. In particular, the effect of runner speed on these pathlines was investigated. Appearances of the air bubbles in the light sheet (radial-axial plane) were timed and analyzed in order to quantitatively examine the velocity of the oil flow, and to compare the experimental results with numerical data. The oilwell tube has an axisymmetric geometry. Accordingly, a three dimensional CFD code for laminar, axisymmetric flow with a free surface (A3D-CFD code) was developed for the purpose of analyzing the flows in the oilwell tube. This code was verified using results from the experimental study, and also using data obtained from classical analytical studies of free surface shapes, velocity distributions and flow patterns. The experimental and analytical data were in good agreement with the computational results. Using the A3D-CFD code, oil flow patterns in the oilwell tube annulus of the test rig were computed. This study showed that the primary (circumferential) swirling flow was well stratified inside the oilwell tube annulus, while a strong secondary flow beneath the runner was in the form of a vortex. The strength of this secondary vortex (in terms of the local secondary flow vorticity ω[sub θϲ] at the core of the secondary vortex) was also studied. The non-dimensional vorticity (ω[sub θϲ]/ω[sub R]) was correlated with the Reynolds number (ReR). A numerical technique was developed for the purpose of tracing micro air bubbles in the oil flow field computed from the A3D-CFD code. By considering buoyancy effects due to the gravitational and centrifugal forces, the pathline of an air bubble was determined. Various parameters that affect the path of the air bubble, such as bubble size, oil viscosity and runner speed, were included in this study. The computed pathlines of the air bubble were in reasonably good agreement with the experimental results.

Thesis/Dissertation

application/pdf

2009-04-02

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http://hdl.handle.net/2429/6750

Mechanical Engineering

University of British Columbia

UBCV

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