Engineering topics
Publications and source records attributed to Brown, Kenneth.
A robust, simple-to-use workflow is developed in this study which allows mesoscale information from the NOW-23 database to be easily incorporated into microscale wind farm simulations. This process will enable many different wind farm configurations to be simulated under realistic inflow conditions spanning a variety of atmospheric phenomena.
ABSTRACT In this work, we develop a new analytical turbine induction model that can incorporate complex inflow conditions including cases where the wind velocity and temperature profiles can vary as functions of height. This induction model is derived from the linearized Navier–Stokes and leads to a second‐order ODE that can be solved using a Green's function formulation. The corresponding Green's function for several configurations are found including the infinite domain, semi‐infinite domain with ground plane, and a power law velocity inflow profile. The results of this approach are then compared with simulations of the turbine induction field using the AMR‐Wind CFD solver with a uniformly loaded actuator disk model. These comparisons show that the Green's function approach captures the centerline blockage, three‐dimensional blockage flow field, and streamwise velocity slow down, with very good agreement for lower thrust conditions and at larger distances away from rotor disk. The effects of shear on the turbine blockage were also compared using a power law inflow profile, and we show that this approach matches the CFD predictions for the cases considered.
This work demonstrates that classical shear-flow stability theory can be successfully applied to modify wind turbine wakes and also explains the success of several emerging, empirically-arrived control methods (i.e., dynamic induction and helix control). Linear stability theory predictions are extended to include the effects of non-axisymmetric inflow profiles, such as wind shear, which is shown to not strongly affect the primary forcing frequency. The predictions, as well as idealized large-eddy simulations using actuator-line representation of the turbine blades, agree that the n = 0 and ±1 modes have faster initial growth rates than higher-order modes, suggesting the lower-order modes are more appropriate for wake control. Exciting the lower-order modes with periodic pitching of the blades produces higher entrainment into the wake and consequently faster wake recovery.
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A large-scale numerical computation of five wind farms was performed as a part of the American Wake Experiment (AWAKEN). This high-fidelity computation used the ExaWind/AMR-Wind LES solver to simulate a 100km × 100km domain containing 541 turbines under unstable atmospheric conditions matching previous measurements. The turbines were represented by Joukowski and OpenFAST coupled actuator disk models. Results of this qualitative comparison illustrate the interactions with wind farms with large scale ABL structures in the flow, as well as the extent of downstream wake penetration in the flow and blockage effects around wind farms.
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A series of numerical simulations of wind farms, using different model fidelities and for different atmospheric stability conditions, were performed as a part of the American WAKE ExperimeNt. The simulations included using FLORIS wake models, a number of microscale AMR-Wind and Nalu-Wind runs, as well as idealized and complex terrain WRF runs. The largest computations used the AMR-Wind LES solver to simulate a 100 km x 100 km domain containing 541 turbines under unstable atmospheric conditions matching previous measurements, while other LES computations focused on sections of the King Plains wind farm. Results of this qualitative comparison illustrate the interactions with wind farms with large-scale ABL structures in the flow, as well as the extent of downstream wake penetration in the flow and blockage effects around wind farms.
Mesophase pitch and linear low-density polyethylene (LLDPE) were blended by shear mixing and extruded producing precursor fibers which were then converted to carbon fibers (CFs). LLDPE additives agglomerate within the isotropic spheres rather than uniformly dispersing throughout the entire matrix. The blends possess different thermal properties and precursor tensile properties evident by two-phase tensile stress nature not present in precursor fibers produced from pure pitch. The resultant CFs were oxidized at 280 °C for 4 h and carbonized at 1000 °C for 15 min. This process created pitch CFs with a tensile strength of 1.23 GPa and a Young’s modulus of 99 GPa. All CFs produced from blends of pitch and LLDPE possessed a tensile strength of 0.63 GPa and less. These CFs showed a microstructure slightly different from the pure pitch CFs with fractured CF cross sections revealing voids present in all blended CFs due to burnt off LLDPE stemming from carbonization. Further study into compatibilizers and new conversion processes is required to successfully blend LLDPE with mesophase pitch for the purpose of producing a new low-cost CF.
Abstract not provided.
Abstract not provided.