Three dimensional flow structures in journal bearings

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.In general, the fluid flow in journal bearings can be described by the Navier-Stokes Equations and the conservation of mass. The application of the small gap criterion allows a simplification of these equations yielding the Reynolds Equation, which links the local gap size with the pressure gradient resulting in a powerful tool for the designing process of journal bearings. Typically, the Reynolds Equation is used in EHD-design software based on FE-methods, which is used to compute pressure distributions, forces, deformations and many more parameters needed for the selection of the right bearing geometry. However, there are regions in the journal bearing where the Reynolds Equation must fail, because either the small gap criterion or the Couette flow assumption is violated. There are pockets, grooves and holes, which are necessary to distribute the oil supply across the gap. Moreover, the oil feed represents a cross flow perpendicular to the circumferential main flow. In these regions three dimensional flow structures replace the undisturbed Couette flow, which are strongly affected by vortices, but are non-turbulent due to the Re-scale. This work presents experimental data obtained from a cylinder apparatus with moderate gap sizes, which features independently rotating cylinders and a cross flow through a hole in the sidewall. LDV-measurements of velocity profiles and visualization methods to animate the three dimensional nature of the flow are presented. The experimental data are used to validate 3D-CFD calculations, which are expanded towards smaller gap sizes in the range of typical journal bearings in automotive applications

Scale Model Equations and Optimization for Annular Flow of Non-Newtonian Fluids Between Eccentric and Rotating Cylinders

A broad range of engineering applications involves helical flow of non-Newtonian fluids between two eccentric cylinders. These applications often require estimation of the frictional pressure losses along the axes of the cylinders. Laboratory flow loops are commonly used to study the flow characteristics at smaller scales of investigation. This study uses the laws of similarity and dimensional analysis to obtain a set of scaling equations between the laboratory and prototype scales of the described annular flow. These equations are derived for four types of fluid rheology including Newtonian, power-law, Bingham-plastic, and yield power-law. Results are expressed through a set of closed-form formulae that would determine the flow rate and rotational speed of the inner pipe in the laboratory model in terms of the flow rate and pipe rotation speed, as well as other flow parameters of the prototype. The specific forms of these scaling equations are developed in such a way that the dimensionless friction factors of the annular flows at the laboratory model and prototype scales become identical. In the case of the yield power-law fluid, a complete similitude between the two scales requires using a fluid in the laboratory model that is different from the prototype fluid. As such, application of the obtained equations in minimizing the laboratory flow loop size is demonstrated. It is shown that proper selection of the rheological parameters of the fluid in the flow loop model would enable substantial reduction in the geometric scale of the similitude

The Twente turbulent Taylor-Couette (T3C) facility: Strongly turbulent (multiphase) flow between two independently rotating cylinders

A new turbulent Taylor-Couette system consisting of two independently rotating cylinders has been constructed. The gap between the cylinders has a height of 0.927 m, an inner radius of 0.200 m, and a variable outer radius (from 0.279 to 0.220 m). The maximum angular rotation rates of the inner and outer cylinder are 20 and 10 Hz, respectively, resulting in Reynolds numbers up to 3.4 x 10^6 with water as working fluid. With this Taylor-Couette system, the parameter space (Re_i, Re_o, {\eta}) extends to (2.0 x 10^6, {\pm}1.4 x 10^6, 0.716-0.909). The system is equipped with bubble injectors, temperature control, skin-friction drag sensors, and several local sensors for studying turbulent single-phase and two-phase flows. Inner cylinder load cells detect skin-friction drag via torque measurements. The clear acrylic outer cylinder allows the dynamics of the liquid flow and the dispersed phase (bubbles, particles, fibers, etc.) inside the gap to be investigated with specialized local sensors and nonintrusive optical imaging techniques. The system allows study of both Taylor-Couette flow in a high-Reynolds-number regime, and the mechanisms behind skin-friction drag alterations due to bubble injection, polymer injection, and surface hydrophobicity and roughness.Comment: 13 pages, 14 figure

COMPARISON OF VARIOUS NUMERICAL DIFFERENCING SCHEMES IN PREDICTING NON-NEWTONIAN TRANSITION FLOW THROUGH AN ECCENTRIC ANNULUS WITH INNER CYLINDER IN ROTATION

Flow through annulus is a widely solved problem in fluid mechanics because of its practical applicability in many areas. In oil well drilling, cuttings generated are of non-Newtonian nature which flows through an eccentric annulus with inner cylinder in rotation, considering the real drilling situations. In the present work, a comparison have been done amongst three differencing schemes, the second order upwind, the Power law scheme and QUICK scheme used in computational fluid dynamics solution algorithms, so as to find the best amongst them to solve transition flow for this case as well as in general. A three dimensional orthogonal hexahedral mesh with suitable boundary conditions & input parameters was taken as computational domain for eccentric annulus. This was solved with standard k-ω turbulence model and SIMPLE algorithm. Results were validated against the published experimental work of J. M. Nouri, et. al [1]. Radial velocity, axial velocity and tangential velocity of fluid were plotted along chosen planes and contours of molecular viscosity as well as turbulence kinetic energy were observed for comparison amongst the solutions obtained by three differencing schemes. Although in most of the cases close agreement have been observed between computational data, but as far as prediction of radial velocity is concerned there was surprising difference amongst the three schemes

Stuck pipe prediction in deviated wellbores: a numerical and statistical analysis.

Due to the significant non-productive times and recovery costs associated with stuck pipe events in oil and gas drilling operations, there is value in being able to predict an impending stuck pipe event. To achieve this, the use of numerical cuttings transport (hole cleaning) models and statistical analysis of real-time drilling data is proposed by this research. Current cuttings transport models are based on unhindered, free settling in the wellbore and do not adequately account for the effect of vortices created as the drill string rotates about its axis. This thesis addresses both shortcomings, and presents improved cutting transport models that consider hindered centrifugal settling of drilled cuttings, effect of Taylor vortices and Van der Waals forces. The implication is that the resulting cuttings settling velocity used to estimate critical transport velocities and flow rates are more representative. The transport ratio, a measure of the hole cleaning efficiency, is consequently more realistically predicted. Although several proprietary automated stuck pipe prediction tools exist in the industry, this research found that they broadly fall into five main groups. It is also apparent that current capabilities do not simultaneously and continuously combine real-time data, offset wells data and well design analytical models in a single approach. On that basis, this thesis presents an integrated stuck pipe prediction concept that utilizes all three data streams, called the "ROW" approach. The concept presented in this thesis was then coded into a tool called the stuck pipe index (SPI). The SPI tool risk assessment is determined in real-time and is referenced by a traffic light alert system (green – amber – red), to warn the user of an impending potential stuck pipe situation. The numerical models developed in this research estimate critical velocities to within 10 – 15% and show strong agreement with published empirical data. Combined with the cuttings transport numerical models developed in this research and other publicly available well design models (such as hydraulics, and torque and drag), the SPI tool has been tested with several case histories and proven to detect stuck pipe events with warning alerts significantly ahead of the event. The tool has equally been deployed in real-time with >90% success rate and without spurious alerts recorded. The results thus confirm that the developed numerical models and the "ROW" approach are robust, and offer an improvement to current industry capabilities in terms of accuracy and sensitivity to changing downhole wellbore conditions

Annular flow of viscoelastic fluids: Analytical and numerical solutions

This work provides analytical and numerical solutions for the linear, quadratic and exponential Phan–Thien–Tanner (PTT) viscoelastic models, for axial and helical annular fully-developed flows under no slip and slip boundary conditions, the latter given by the linear and nonlinear Navier slip laws. The rheology of the three PTT model functions is discussed together with the influence of the slip velocity upon the flow velocity and stress fields. For the linear PTT model, full analytical solutions for the inverse problem (unknown velocity) are devised for the linear Navier slip law and two different slip exponents. For the linear PTT model with other values of the slip exponent and for the quadratic PTT model, the polynomial equation for the radial location (β) of the null shear stress must be solved numerically. For both models, the solution of the direct problem is given by an iterative procedure involving three nonlinear equations, one for β, other for the pressure gradient and another for the torque per unit length. For the exponential PTT model we devise a numerical procedure that can easily compute the numerical solution of the pure axial flow problemCOMPETE, FEDER and Fundação para a Ciência e a Tecnologia (FCT) through projects PEst-C/CTM/LA0025/2013 (Strategic Project – LA 25 – 2013-2014), PTDC/EQU-FTT/113811/2009 and PTDC/EME-MFE/113988/2009. LLF and AMA would also like to thank FCT for financial support through the scholarships SFRH/BD/37586/2007 and SFRH/BPD/75436/2010, respectively

Improving Hole Cleaning on High Angle Wells

Poor hole cleaning becomes a serious issue specially when drilling high angle (deviated) wells because, drilled cuttings tend to settle on the lower side of the well bore which may lead to other drilling problems such as suck pipe. By increasing hole cleaning efficiency we will speed up the drilling operations, and therefore, reduce the total cost to drill one well

ANALYSIS OF FLOW IN A CONCENTRIC ANNULUS USING FINITE ELEMENT METHOD

This work presents the computational modelling of the velocity distribution of an incompressible fluid flowing in a cylindrical annulus pipe, using the finite element method. The result shows that the velocity distribution increases from the boundaries until midway between the boundaries where it was maximum. Also, the velocity increases as the viscosity decreases. The results obtained were compared with exact second order differential equation solution. The results obtained were highly accurate and converges fast to the exact solution as the number of elements increases. http://dx.doi.org/10.4314/njt.v35i2.1

Tunneling and Drilling for OTEC Cold Water Pipes

This report summarizes the results of a study to determine the feasibility of using a tunnel or large-diameter drilled shaft as a conduit for transporting cold water from an ocean depth of 2000 ft to an ocean thermal energy conversion (OTEC) plant located on shore. The report identifies five possible cold water pipe (CWP) approaches that are dependent on the geologic formation and hydrology of the site. For this survey, the site under consideration is Keahole Point on the west coast of the big island of Hawaii. The site was chosen because of the easy access to deep cold water provided by the steep offshore slope, the proximity to air and sea transportation, and the availability of land. The survey concludes that although many site-specific factors must be considered, tunneling or drilling is in general a viable option for meeting the long-term OTEC cost goals. This study was carried out for the United States Department of Energy (DOE) by the Energy Technology Engineering Center (ETEC) as part of the OTEC Cold Water Pipe Technology program.Prepared for the United States Department of Energy, Ocean Engineering Technology Division, under Contract Number DE-AC03-76-SF00700, Task 43532-6530