Thesis (Ph. D.)--University of Wisconsin--Madison, 1964. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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Experiments have shown that the addition of small amounts of long-chained polymer additives to a Newtonian fluid produces desirable lubricants. Additives added to oil make the fluid viscoelastic. The effect of viscoelasticity on lubrication characteristics has recently taken on added significance with the move to yet lower-viscosity lubricants for improved energy efficiency. Any factor influencing load-bearing capacity and wear is clearly of renewed importance. The general trend towards the usage of high performance lubricants and environmentally friendly products also support the design of new lubricants. This thesis is aimed at investigating viscoelastic flows within eccentric rotating cylinders (practical application - journal bearings) using a commercial finite element software POLYFLOW. Numerous validations are performed and excellent agreements are achieved. Steady shear and small-amplitude oscillatory shear (SAOS) experiments are performed for specific lubricants including mineral-based and bio-based lubricants to characterize their rheological behavior. Experimental data are fitted by a viscoelastic constitutive model used for numerical simulations. The effects of fluid viscoelasticity between eccentric rotating cylinders on the flow field and on the lubrication performances are revealed in 2D and 3D respectively. From 2D investigation, an increased load capacity on the inner cylinder is found to be achieved by increasing the viscoelasticity of flow. For the first time, to our knowledge, 3D results for an UCM (Upper-Convected Maxwell) fluid at steady state are presented and the flow patterns along the axial direction within the eccentric rotating cylinders are investigated. The viscoelastic effects of those lubricants on the journal bearing performances are revealed and compared at various temperatures. The modeling and numerical simulations used to predict the flow of lubricant in a journal bearing can generate important economic benefits. This research will lead to advanced predictive tools that can be used to improve the design of journal bearing and to propose new economically viable and environmentally friendly lubricants. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The wind-induced vibration of bridge stay cables has been a long studied and documented topic including a vast literature presenting experimental and numerical investigation results. There are several aerodynamic phenomena which can be associated with the wind-induced vibrations of bridge stay cables, such as vortex-induced vibration, rain-wind induced vibrations, buffeting phenomenon, dry cable galloping, and high-speed vortex excitation, to name a few. One of the most critical types of vibrations for slender structures exposed to wind is the galloping instability. This is typically not encountered for round structures, like circular cylinders or cables, due to their symmetrical nature, and therefore a lack of negative slope in the lift coefficient. However, vibrations of inclined cables of cable-stayed bridges have been noticed for several bridges, and were associated with partial damage of the cable stays, and damaged noted to cable anchors. It is still unclear if these cable vibrations are caused by dry inclined cable galloping, or by high speed vortex excitation. For this reason, stay cables construction guidelines (FHWA, 2005) have not been able to clearly identify the aerodynamic instability resulting in the recommended use of high structural damping, and high Scruton numbers used to limit bridge stay cable vibrations. The current research addresses these issues by performing numerical CFD (computational fluid dynamics) simulations of wind flow around inclined and yawed cables in order to identify the flow behaviour around the circumference and downstream of the cable. Such numerical models provide a new understanding regarding the flow conditions around an inclined cable and the beginning of dry galloping instability. The simulation was performed for full scale cables in the form of cylinder models with high aspect ratios. The arrangement for the cable was considered as a combination of the inclination and yaw angles, in such a way that it should match the experimental setting considered by Cheng et al (2003), based on which a validating comparison of results was performed. A LES (Large Eddy Simulation) model was developed with a constant Smagorinsky model for simulating the turbulent flow around the cylinders. Reynolds numbers (Re) ranging from 1.1 × 105 to 6.7 × 105 were investigated for various combinations of the inclination angles of 0° to 60° and yaw angles of 0° to 40°. The diameter of the circular cylinder was set to D = 0.089 m and the length of the cable was 2.67 m (30D). Pressure on the surface of the cylinder was monitored on 5 rings arranged along the circular cylinder at equal intervals and velocities were recorded for intervals of 0.1 – 0.5D downstream the cylinder. Also pressure, vorticity and streamlines distributions were recorded for several plans along and across the cylinder. The flow pattern visualisations were clearly established and wind speed profiles were presented. An axial flow along the leeward side of the cylinder was identified for inclined circular cylinders. The predominant axial flows were noted at intervals of 0.1D to 0.3D downstream of the cylinder. As the distance from the leeward side of the cylinder increased, the effect of the far field flow increased as well, for the flow around the leeward side of the cylinder. The drag crisis encountered as a sudden drop in the drag coefficient CD, with the increase of Re number, was confirmed. The preliminary results for inclined cylinders showed good agreement with the experimental results available in the literature. Slight discrepancies for the upper and lower branches of the drag crisis were found between the published data and results obtained in the current study. A new flow classification for inclined and/or yawed circular cylinders was proposed based on the velocity profiles, eddy viscosity, and swirl threads formations, as a combination of the TrSL and TrBL regimes similar with the ones defined by Zdravkovich (1997), for flow perpendicular to cylinders. Four cases showed a potential aerodynamic instability when results of the current study were employed into the theoretical aerodynamic damping equation derived by MacDonald and Larose (2006). Three of these cases demonstrated a similar flow phenomenon to the TrSL-Short flow phenomenon defined in this study, which occurs when the major axis of the ellipse is close to the direction of flow, and the turbulent shear layers detach almost on the leeward side of the cylinder. The coherence, cross-coherence and cross-bicoherence were calculated for the frequency components of the coefficient of lift, the pressure coefficient along the leeward side of the cylinder, and the total velocity along the leeward side of the cylinder, and it was found that three cases of low non-linear interaction, intermediate non-linear interaction, and high non-linear interaction could be identified. Also it was concluded that the interaction between the lift and pressure coefficients monitored for the cylinder and the variation of the total velocity component, did not have a significant influence on the flow regimes, or on the transition between the flow regimes. The high-nonlinear interactions relate more to the potential coupling between the frequencies of the parameters mentioned above, especially for the critical case of 60° relative angle.

Experiments were performed in a wind tunnel on 3-inch diameter circular and D-section cylinders. A detailed investigation of the vortex shedding frequency, displacement amplitude, and the phase angle between the fluctuating pressure and the displacement signals of both circular and D-section cylinders was made in the "capture" region. These phenomena were investigated under various damping levels using magnetic dampers. Fluctuating surface pressures on a circular cylinder were measured along one half of the circumference at 11 sections selected along the span. The resulting sectional fluctuating lift coefficients as well as the total lift coefficients were obtained by integration for several wind speeds for both stationary and oscillating cylinders. Interesting to note are the vortex line inclination angles obtained from fluctuating surface pressure correlation. Using linearized hot wire anemometers, spanwise wake velocity correlation functions were measured and correlation lengths computed. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

This thesis investigates different examples of action at a distance, namely the interaction of two circular cylinders of different diameters and the interaction of a cylinder with a wall in various arrangements. Action at a distance modifies both the lift and drag of each one of the objects. The fluid flow interaction between a circular cylinder (of diameter D) with a wall, and a circular cylinder with a smaller (¼D) circular cylinder at Reynolds numbers of ≈ 10,000 were of interest. Manifestations of the interactions include mutual changes in the lift and drag forces, phase, onset and frequency of vortex shedding on the circular cylinders/wall. A novel force measurement device for lift and drag of circular cylinders and a data acqusition system was built to realize the above experiments in a water towing tank. The system was capable of simultaneously measuring lift and drag on two circular cylinders with time resolution and correlating these measurements with flow field pictures. Measurements of the lift and drag and phase, onset and frequency of vortex shedding were taken on the large and small cylinder simultaneously as a function of the relative position between itself and the smaller cylinder as the two are towed. These measurements make it possible to map out the areas within the cylinders' sphere of influence and measure the intensity of this influence as a function of the distance between the two cylinders. Every quantity that was mutually altered by the presence of another cylinder is used as measurements of the area of influence for a circular cylinder. It was found in general that the forces act up to a distance of about 3 diameters in the lateral direction. It was also noted that pressure fluctuations at the vortex shedding frequency penetrate into the laminar flow region up to about 3D in the lateral direction. The results agree with existing results for wall/cylinder proximity experiments and flow interference between identical circular cylinders. A novel method to trigger the onset of vortex shedding for towing tanks was also discovered. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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