Browsing by Subject "Computational Fluid Dynamics (CFD)"

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    Advanced modeling of nanoparticle nucleation: towards the simulation of particle synthesis
    (2012-11) Liu, Jun
    Nanotechnology holds a lot of promise for the discovery of new phenomena, and many of the envisioned processes involve nanoparticles. These particles are found in chemical sensors, drug targeting and delivery, and one important application is motivated by the need of clean renewable energy sources. Gas-to-particle conversion in the form of homogeneous nucleation within flow systems plays a significant role in a variety of natural and industrial processes of nanoparticle synthesis. In this work, nucleation processes of several metal materials and dibutyl phthalate (DBP) nanoparticles in laminar and turbulent flows are investigated via direct numerical simulations (DNS). The flows consist of condensing vapor diluted in argon or nitrogen issuing into a cooler particle-free stream. DNS facilitates probing the interactive effects of fluid dynamics and nucleation in an accurate manner. The fluid, thermal and chemical fields are obtained by solving the Navier-Stokes, enthalpy, and mass transport equations. Nucleation is simulated via calibrated classical homogeneous nucleation models. Recently developed size dependent surface tension model offers increased accuracy in predicting metal particle nucleation. This approach is attractive in that it promises to be more accurate than the classical nucleation theory while maintaining much of its simplicity when coupling with fluid dynamics. The effects of turbulence on metal nucleation are also studied using fully resolved DNS to elucidate the effects of different stages of fluid mixing on metal particle nucleation. The effects of nucleation on fluid dynamics are investigated via DNS of DBP nucleation within both laminar and turbulent jet flows. The simulations provide a demonstration of how heat release affects the interactions of fluid dynamics and nucleation at different Reynolds numbers and particle formation rates. The results provide insights into the interaction of fluid, thermal transport and nanoparticle nucleation in various flows, which stimulate development of models that will allow engineers to optimize the fluid and thermal environments for industrial nanoparticle production. For brevity, specific conclusions are provided in each chapter.
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    Tidal Turbine Rotor Spacing Influence On Power Performance: Simulating A Scaled Dual-Rotor Axial Flow Turbine
    (2023) Guzman de la Rosa, Javier
    Power performance and turbulent wake characteristics of a scaled current-driven marine turbine were simulated using unsteady 3D RANS with the k-ω SST turbulence model and sliding mesh technique. The turbine is an axial flow, dual rotor tidal turbine with counter-rotating rotors, each with two blades and a diameter of d_T = 0.5 m, representing an approximately 1:40 scale system based on the U.S. Department of Energy’s Reference Model 1 (RM1) tidal turbine. Validation of numerical results for three tip speed ratios was performed by comparison with experimental data. The influence of rotor cross-stream spacing on power production was also studied by modeling three distinct lateral rotor separations, equal to 1.2d_T, 1.4d_T, and 1.6d_T. Numerical results showed a good correlation ranging within ±3.8% of turbine performance to experimental measurements for all tip-speed ratios studied, validating the numerical results for power estimation and demonstrating the advantages of this model when dealing with high-flow detachment. Inflow dynamics were captured well, exhibiting a difference of less than 5% compared to experimental data. However, wake dynamics showed a significant difference between numerical results and experimental data, ranging from 16% error at approximately 〖X/d〗_T=4, up to 170% error at 〖X/d〗_T=8. Finally, numerical results indicated a tendency for higher power production as the rotors are spaced farther apart, with the resulting power coefficient values of C_p = 0.449, 0.461, and 0483 for lateral rotor spacings of 1.2d_T, 1.4d_T, and 1.6d_T, respectively. This behavior was accredited to the reduction of the flow through the swept area of the rotors, causing what is known as 'choking effect’.