Browsing by Subject "Fluid Mechanics"

Now showing 1 - 4 of 4
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    Experiments on Film Cooling of Gas Turbine Vane Passage Surfaces: The Effects of Various Distributions of Combustor Coolant and Endwall Injection Coolant
    (2019-08) Nawathe, Kedar Prasad
    The efficiency of gas turbines is known to increase with the exit temperature of the combustor gases. However, this temperature is limited by the melting point of various equipment downstream of the combustor. To increase this limit, coolants injected at different locations form low-temperature films on the surfaces of these regions to avoid melting and thermal stress damage. This injection significantly changes the flow field in the vane passage. Therefore, there is a need to study the aerodynamic and thermal effects of combustor, transition duct and passage coolant injection, which can assist the designers of gas turbines to employ better cooling schemes with minimal use of coolant, thus increasing the efficiency and durability of turbines. The study presented in this thesis discusses experimental tests performed to understand the coolant effectiveness for cooling the endwall and vane surfaces of a nozzle guide vane cascade. The test section contains an engine representative combustor-turbine interface along with a contoured endwall. High turbulence intensity as well as high Reynolds numbers are achieved in the facility to closely simulate engine conditions. In addition to recording the surface effectiveness values, in-field thermal and aerodynamic measurements were taken. It has been previously discovered that the effusion and louver coolants, used to cool the combustor section, can also be credited in cooling the endwall and the vane surfaces. Therefore, this study is helpful to understand the effects of changing the mass flow ratios of different coolants injected upstream of the passage. Especially, louver coolant injection in the combustor transition duct region, due to its location and injection angle, is suspected to provide significant passage endwall cooling. In-field measurements provide insight to the coolant transport through the passage and its interaction with the mainstream. As the net combustor coolant momentum is higher than the film coolant momentum, the changes in the flow field due to its injection are more significant and are sustained to the end of the passage, giving more streamwise coverage than with a conventional film cooling setup. The film coolant mass flow ratio is varied in this study to see how the interaction of different coolants changes with changes of their injected momentum. The measurements reveal that the upstream coolant flow helps in keeping the film coolant attached to the endwall for most of the passage and also keeping the film thickness fairly uniform in the pitchwise direction. An increase in louver coolant mass flow rate shows higher endwall cooling effectiveness. The velocity contours show that a dominant vortex is present due to combustor coolant injection and that the passage vortex was, although present, diminished due to this other vortex. While changing the louver coolant mass flow rate did not change the intensity of these vortices, changes in the film coolant mass flow rate increased the intensity of the dominant vortex near the pressure surface. Also, the presence of this new vortex helps in film cooling the pressure surface, a region where, conventionally, the least amount of coolant coverage is recorded.
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    Local and Non-local Geomorphic Effects of Hydrokinetic Turbines: Bridging Renewable Energy and River Morphodynamics
    (2019-06) Musa, Mirko
    Marine and Hydrokinetic (MHK) energy is an emerging renewable and sustainable technology which harnesses kinetic energy of natural water flows such as tides, rivers and ocean currents. In particular, rivers are currently an overlooked source of local and continuous kinetic energy that can be exploited using the available in-stream converters technology. The uncertainties regarding the interaction between these devices and the surrounding environment complicate the regulatory permitting processes, slowing down the expansion of MHK industry. A crucial issue that needs further attention is the interaction between these devices and the physical fluvial environment such as the bathymetry, sediment transport, and the associated morphodynamic processes. Analytical and experimental research conducted at Saint Anthony Falls Laboratory (SAFL) addressed this topic, unveiling the local and non-local (far from the device location) effects of hydrokinetic turbines on channel bathymetry and morphology. A theoretical model framework based on the phenomenology of turbulence was derived to predict the scour at the base of MHK device. Asymmetric installations of turbine array models within multi-scale laboratory channels were observed to trigger river instabilities known as forced-bars. Results suggest that the amplitude of these instabilities might be reduced by limiting the power plant lateral obstruction within the channel cross-section. A 12-turbine staggered array also proved to be resilient to intense flooding conditions, encouraging the expansion of this technology to large sandy rivers. Current research is investigating how hydrokinetic technology can be synergistically integrated in rivers, not only minimizing the environmental costs but also providing a positive feedback on the channel. Experiments suggest that turbines strategically installed in the river (i.e. at the side bank in yawed condition or in a vane-shaped array) could be used as stream bank protection systems and, eventually, be integrated in stream restoration projects.
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    Net Flow Through Soft Porous Media Generated by a Periodic Mean-Zero Pressure Gradient
    (2023-04) Stein, Jacob
    In this thesis, a soft porous media experiment is developed to investigate the effect of applying periodic mean-zero pressure gradients to a soft porous medium. These periodic mean-zero pressure gradients are composed of square waves, with a high magnitude positive pressure drop applied for 1/3 of the period and a negative pressure drop with half the magnitude applied for 2/3 of the period. We investigate the effect of varying the pressure magnitude and period. This setup uses a novel tracking method to quantify the porous media and fluid velocities simultaneously, and operates with high levels of accuracy and repeatability. The periodic mean-zero pressure gradients we investigate are shown to generate substantial net flow, in the direction associated with the smaller pressure magnitude portion of the period. The system is also shown to demonstrate hysteretic behavior, where complex packing features form and persist in the solid phase, influencing the results of the system for subsequent experiments. Results from this experiment have important implications for fluid flow in biological tissues, such as interstitial transport in the brain and body, as it demonstrates that small scale, periodic mean-zero pressure gradients can drive significant amounts of net transport through a deformable porous medium.
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    On the Effects of a Vortex Breaker on the Wake Meandering Characteristics of a Miniature Wind Turbine
    (2017-12-14) Storm, Noah J.
    This investigation sought to understand how the addition of a vortex breaker to the nacelle of a miniature wind turbine might disrupt, enhance, mitigate, or otherwise alter the meandering characteristics of the wake flow. Velocity measurements were taken in the wake of the turbine in a wind tunnel experiment, and analyzed with MATLAB and Microsoft Excel. Three vortex breakers were designed, and each of these cases was compared to the wind turbine with no nacelle additions. A decrease in mean streamwise wake velocity and appreciable shifts in the peak meandering frequency and intensity were observed. Peak spanwise frequencies were normalized by the mean wake velocity to compensate for effects due to increased drag on the turbine when the vortex breakers were added. This normalization is appropriate, as previous experiments have shown that wake meandering scales with the Strouhal Number (St = fD/U) for utility and small-scale turbines [1]. Meandering frequency variations between vortex breaker cases and the bare nacelle case were partially attenuated when analyzing Strouhal percent differences. This suggests that the alterations in the meandering characteristics were a combinatorial result of both increased nacelle drag and vortex interactions between the nacelle vortex and blade tip vortices.