Browsing by Subject "fluid mechanics"

Now showing 1 - 4 of 4
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    Data for The colloidal nature of complex fluids enhances bacterial motility
    (2022) Kamdar, Shashank; Shin, Seunghwan; Leishangthem, Premkumar; Francis, Lorraine F; Xu, XinLiang; Cheng, Xiang; xcheng@umn.edu; Cheng, Xiang
    The archived data are the post-processed final data corresponding to figures in the manuscript as well as codes used for generating key plots.
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    Improvement of the Mellor-Yamada Type Planetary Boundary Layer Scheme for Use in Mesoscale Models
    (2020-08) Keester, Adam
    Atmospheric mesoscale models are highly complex and their performance varies widely depending on the models used. Turbulent transport within the boundary layer is especially difficult to analyze, but has a significant impact on mesoscale model applications. In this study, the Mellor-Yamada-Nakanishi-Niino planetary boundary layer model is improved. A new length scale and turbulent closure constants are calculated from two large eddy simulations. The modified MYNN model maintains the original’s accurate eddy coefficients and drastically improves the prediction of the momentum dissipation rate, length scale and stability functions. A 12-member WRF ensemble is used to validate the new model outside of the database on which it is based. The WRF results show that the new model improves the bias and mean absolute error of temperature and relative humidity. There is a significant change in the TKE and length scale predictions that motivates further study of the modified boundary layer scheme.
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    Multi-resolution Modeling and Simulation of Marine Hydrokinetic Turbine Arrays at Site Scale
    (2017-04) Chawdhary, Saurabh
    Marine and hydro-kinetic (MHK) energy hold promise to become significant contributor towards sustainable energy generation. Despite the promise, commercialization of MHK energy technologies is still in the development stage. While many simplified models for MHK site resource-assessment exist, more research is needed to enable efficient energy extraction from identified MHK sites. A marine energy company named Verdant Power Inc. was granted first federal license to install up to 30 axial hydrokinetic turbines in the East River in New York City under what came to be known as Roosevelt Island Tidal Energy (RITE) project. Therefore, in this study we investigate issues of relevance to post-site-identification stage for a real-life tidal energy project, the RITE project, using high-fidelity numerical simulations. An effective way to develop arrays of hydrokinetic turbines in river and tidal channels is to arrange them in TriFrame configurations where three turbines are mounted together at the apexes of a triangular frame. The TriFrames serve as the building block for rapidly deploying multi-turbine arrays. The wake structure of a TriFrame of three model turbines is investigated. We employ large-eddy simulation (LES) with the curvilinear immersed boundary method (CURVIB) for fully resolving the turbine geometry details to simulate turbine-turbine wake interactions in the TriFrame configuration. First, the computed results are compared with experiments in terms of mean flow and turbulence characteristics with overall good agreement with bed-flume experiments. The flow-fields are then analyzed to elucidate the mechanisms of turbine interactions and wake evolution in the TriFrame configuration. We found that the wake of the upstream TriFrame turbine exhibits unique characteristics indicating presence of the Venturi effect as the wake encounters the two downstream turbines. We finally compare the wakes of the TriFrame turbines with that of an isolated single turbine wake to further illustrate how the TriFrame configuration affects the wake characteristics and power production in an array of TriFrames. Lastly, we propose a large eddy simulation (LES)-based framework to investigate the site-specific flow dynamics past MHK arrays in a real-life marine environment. To this end, the new generation unstructured Cartesian flow solver, coupled with a sharp interface immersed boundary method for 3D incompressible flows, is used. Optimized data-structures and efficient algorithms were developed to enable faster simulation on high-resolution grids. Multi-resolution simulations on locally refined grids are then employed to model the flow in a section of the East River with detailed river bathymetry and inset turbines at field scale. The results are analyzed in terms of the wake recovery and overall wake dynamics in the array. Comparison with the baseline flow in the East River reveal the effects of tidal array installation.
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    Particle image velocimetry measurements of smooth- and rough-wall turbulence from the SAFL Atmospheric Boundary Layer wind tunnel
    (2020-01-10) Heisel, Michael; Guala, Michele; mguala@umn.edu; Guala, Michele; St. Anthony Falls Laboratory, University of Minnesota
    Wall-bounded turbulent flows under smooth- and rough-wall surface conditions were measured using particle image velocimetry (PIV) in the Atmospheric Boundary Layer Wind Tunnel at St. Anthony Falls Laboratory (SAFL), University of Minnesota. In the rough-wall case, the tunnel surface was covered with woven wire mesh. The smooth- and rough-wall conditions were each measured for two free-stream velocities (7 m/s and 10 m/s), totaling four flow cases. The friction Reynolds number in the four cases ranges from 3,800 to 14,000. In each case, the PIV imaging field was oriented in the streamwise–wall-normal plane. To enhance the spatial resolution, the measurement field was positioned in the lowest 10 cm of the boundary layer, capturing the roughness sublayer and logarithmic region in the rough-wall cases. Separate high-frequency hotwire anemometer measurements of the full boundary layer profile were used to estimate the scaling parameters such as the boundary layer thickness. This dataset includes the processed velocity vector fields from the PIV measurements and the key scaling parameters.