The flow field around a low pressure turbine blade is examined using smoke-wire flow visualization, static surface pressure measurements, and particle image velocimetry (PIV). The purpose of the experimental study is to investigate the transition and separation characteristics on low pressure turbine blades under low Reynolds number (Re) and varying freestream turbulence intensity (FSTI). A cascade model consisting of 6 Pratt andamp; Whitney PAK-B low pressure turbine blades was examined in a wind tunnel using PIV and flow visualization. Smoke-wire visualization was performed for test section exit angles of 93°, 95°, and 97°, in the range Re = 3 · 104 to 9 · 104 and three levels of FSTI varied with a passive grid. The locations of separation and transition were determined to be approximately 45% and 77% of the suction surface length, respectively, based upon the smoke stream lines observed in the images, and appear to be independent of Re, turning angle, and FSTI. The maximum size of the separation bubble was found to decrease with increasing Re, turning angle, and FSTI. PIV images from three camera views were processed for an exit angle of 95° and a Re range of 3:0 · 104 to 30:0 · 104 and three levels of FSTI. Velocity, vorticity, and reversed flow probability field plots were generated along with velocity, vorticity, and RMS velocity profiles. The point of separation point was determined to be from 63% SSL to 67% SSL. The area of reversed flow was computed for each image pair from camera views 1 and 3, as an approxiamtion of the relative size of the separation region. For low Re and FSTI cases the area was much larger than for higher FSTI cases at any Re. The raw PIV images include some of the rst clear pictures of the turbulent flow structures forming in the unsteady shear layer over the suction surface of low pressure turbine blades. Several movies are compiled that show how the geometry and location of the shear layer evolve in time for a given set of flow conditions.

An experimental research was performed to study the effects of surface roughness on the characteristics of separated and reattached turbulent flows in an open channel. A backward facing step was used to induce flow separation. The rough surfaces comprised wire mesh grit-80 and sand grains of average diameter 1.5 mm. In each experiment, the Reynolds number based on the step height and freestream velocity of approach flow was fixed at 3240 and the Reynolds number based on the approach flow depth and freestream velocity was kept constant at 25130. Particle image velocimetry (PIV) technique was used to measure the flow velocity. The results showed that roughness effects on the mean and turbulent quantities are evident only in the recovery region. Moreover, roughness effects on the flow dynamics are dependent on the specific roughness element.

The research focus of this thesis is on modelling techniques for river kinetic turbines, to develop predictive numerical tools to further the design of this emerging hydro technology. The performance benefits of enclosing the turbine in a shroud are quantified numerically and an optimized shroud design is developed. The optimum performing model is then used to study river kinetic turbines, including different anchoring systems to enhance performance. Two different turbine numerical models are studied to simulate the rotor. Four different computational fluid dynamics (CFD) turbulence models are compared against a series of particle image velocimetry (PIV) experiments involving highly-separated diffuser-flow and nozzle-flow conditions. The risk of cavitation is briefly discussed as well as riverbed boundary layer losses. This study is part of an effort to develop this emerging technology for distributed power generation in provinces like Manitoba that have a river system well adapted for this technology.

Turbulence is ubiquitous in naturally-occurring and man-made flows. Despite its importance in scientific and engineering applications, the transition from smooth laminar flow to disorganized turbulent flow is poorly understood. In some cases, the transition can be understood in the context of linear stability theory, which predicts when the underlying laminar solution will become unstable as a parameter is varied. For a large class of flows, however, this approach fails spectacularly, with theory predicting that the laminar flow is stable but experiments and simulations showing the emergence of spatiotemporal complexity. In this dissertation, the direct or subcritical transition to turbulence in Taylor-Couette flow (i.e., the flow between independently rotating co-axial cylinders) is studied experimentally. Chapter 1 discusses different scenarios for the transition to turbulence and recent advances in understanding the subcritical transition within the framework of dynamical systems theory. Chapter 2 presents a comprehensive review of earlier investigations of linearly stable Taylor-Couette flow. Chapter 3 presents the first systematic study of long-lived super-transients in Taylor-Couette flow with the aim of determining the correct dynamical model for turbulent dynamics in the transitional regime. Chapter 4 presents the results of experiments regarding the stability of Taylor-Couette flow to finite-amplitude perturbations in the form of injection/suction of fluid from the test section. Chapter 5 presents numerical investigations of axisymmetric laminar states with realistic boundary conditions. Chapter 6 discusses in detail the implementation of time-resolved tomographic particle image velocimetry (PIV) in the Taylor-Couette geometry and presents preliminary tomographic PIV measurements of the growth of turbulent spots from finite-amplitude perturbations. The main results are summarized in Chapter 7.

Digital particle image velocimetry is employed to investigate acoustically-coupled flow past a coaxial deep cavity (side branch) resonator mounted in a duct. The emphasis is on the effect of the separation between the coaxial side branches on the interaction between separated shear layers that form across the side branch openings. Various resonator geometries are characterized in terms of patterns of instantaneous and time-averaged flow velocity, vorticity. and streamline topology at several phases of the acoustic cycle. In addition. phase-averaged images of the flow in conjunction with unsteady pressure measurements are evaluated in order to provide insight into the mechanisms of acoustic power generation. Generally, the acoustic source undergoes a significant transformation as the distance between the coaxial side branches changes. When the side branches are located relatively far away from each other. each of them forms an independent acoustic source. As the distance between the side branches decreases. interaction between the associated oscillating shear layers results in formation of a single acoustic source of complex spatial structure.

Effervescent atomization has been a topic of considerable investigation in the literature due to its important advantages over other atomization mechanisms. This work contributes to the development of both effervescent atomizers and also laser-based techniques for spray investigation In order to develop non-intrusive measurement techniques for spray applications, a procedure is suggested to characterize the shape of droplets using image-based droplet analyzers. Image discretization which is a major source of error in droplet shape measurement is evaluated using a simulation. The accuracy of StereoPIV system in conducting droplet velocity measurement in a spray field is also investigated. To assist in the design of effervescent atomizers, bubble formation during gas injection from a micro-tube into liquid cross-flow is investigated using a Shadow-PIV/PTV system. The generated spray fields of two effervescent atomizers which operate using a porous and a typical multi-hole air injector are compared using qualitative images and Shadow-PTV measurement.

Concern for the nonphysiologic energy required to actuate medical devices utilizing “smart material” properties of shape memory polymer (SMP) compels a rigorous investigation into the flow and temperature fields surrounding a thermally activated catheter device. Multiple analyses include the theoretical approaches of exact analytical solutions and finite difference modeling combined with the experimental techniques of particle image velocimetry (PIV) and laser-induced fluorescence (LIF). The attained velocities and temperatures related to the convective heat transfer impact the potential for blood or tissue damage caused by intravascular heating. The clinical scenario involving a catheter device receiving heat within an artery is modeled in its simplest form as a cylindrical metal cap on the tip of a hollow glass rod placed inside of a long straight tube of constant cross-sectional area. Using a working fluid with properties comparable to blood, flow rates and energy input is then varied to determine their effects on velocity fields and temperature gradients. Analytical solutions for both the straight tube and concentric annulus demonstrate the two velocity distributions involved, as flow moves past the gap between the catheter and artery wall and then converges downstream to the Poiseuille solution for steady pipe flow of an incompressible fluid. To solve for the transition between the velocity profiles, computational fluid dynamics software simulates a finite volume model identical to the experimental setup used for intravascular heating experiments. PIV and LIF, both experimental techniques making use of similar hardware, determine velocity fields and temperature distributions, respectively, by imaging fluid seeding agents and their particular interaction with the light sheet. The velocity and temperature fields obtained experimentally are matched with the analytical and finite volume analysis through fluid properties, flow rates, and heating rates. Velocities determined during device heating show a small increase in local velocity, due to temperature dependent viscosity effects. When the device is centered in the model, flow patterns constrain the heat flow near the center axis and away from the channel walls. Increasing flow rate consequently decreases temperature rise, as the heat is carried more quickly downstream and away from the heat source. Using multiple analyses, fluid velocity and temperature distributions are first theorized with analytical and finite element methods and then validated through experimental imaging in a physical model.

Zugl.: Aachen, Techn. Hochsch., Diss., 2007.

Thesis (Ph.D.) - Carleton University, 2007. / Includes bibliographical references (p. 251-264). Also available in electronic format on the Internet.

Thesis (M.Oc.E.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaf 70). Also available on the World Wide Web.