The main objectives of this study were to aerodynamically design and optimize a winglet for a wind turbine blade by using computational fluid dynamics (CFD) and to investigate its effect on the power production. For validation and as a baseline rotor, the National Renewable Energy Laboratory Phase VI wind turbine rotor blade is used. The Reynolds-averaged Navier-Stokes equations are solved, and k-e Launder-Sharma turbulence model was used. The numerical results have shown a considerable agreement with the experimental data. The genetic algorithm was used as the optimization technique with the help of artificial neural network to reduce the computational cost. In the winglet design, the variable parameters are the cant and twist angles of the winglet and the objective function the torque. Multipoint optimization is carried out for three different operating wind speeds, and a total of 24 CFD cases are run in the design. The final optimized winglet showed around 9% increase in the power production.

This paper presents the results of three-dimensional and time-accurate Computational Fluid Dynamics (CFD) simulations of the flow field around the National Renewable Energy Laboratory (NREL) Phase VI horizontal axis wind turbine rotor. The 3-D, unsteady, parallel, finite volume flow solver, PUMA2, is used for the simulations. The solutions are obtained using unstructured moving grids rotating with the turbine blades. Three different flow cases with different wind speeds and wind yaw angles are investigated: 7 m/s with 0 • yaw (pre-stall case I), 7 m/s with 30 • yaw (prestall, yawed case II), and 15 m/s with 0 • yaw (post-stall case III). Results from the inviscid simulations for these three cases and comparisons with the experimental data are presented. Some information on the current work in progress towards Large Eddy Simulations (LES), including details about the viscous grid and the implementation of wall-functions, are also discussed. The inviscid results show that the flow is attached for cases I and II, with the latter having an asymmetrical wake structure, whereas there is massive separation over the entire blade span in case III. There are considerable spanwise pressure variations in addition to the chordwise variations, in all three cases. Comparisons of sectional pressure coefficient distributions with experimental data show good agreement. These threedimensional and time-accurate CFD results can be used for the far-field noise predictions based on the Ffowcs Williams -Hawkings method (FW-H), which can provide a first-principles prediction of both the noise and the underlying turbulent flow that generates the noise, in the context of the wind turbine application.

A simulation of the helicopter/ship dynamic interface has been developed and applied to simulate a UH-60A operating from an LHA class ship. Time accurate CFD solutions of the LHA airwake are interfaced with a flight dynamics simulation based on the GENHEL model. The flight dynamics model was updated to include improved inflow modeling and gust penetration effects of the ship airwake. A maneuver controller was used to simulate pilot control inputs for specified approach and departure trajectories. The CFD solutions show significant time varying flow effects in the airwake. Time histories of the aircraft angular rate and pilot control activity indicate that the time varying nature of the airwake has significant effect on aircraft response and pilot workload.

This paper presents an investigation of the effect of steady and transient free-stream wind shear on the wake structure and performance characteristics of a horizontal axis wind turbine rotor. A new three-dimensional unsteady vortex-panel method potential flow solver based on a free-vortex wake methodology, AeroSIM+, is used for this purpose. The code is validated using the experimental data from the National Renewable Energy Laboratory Unsteady Aerodynamics Experiments. The effects of vortex core model, core size, expansion, and filament stretching on torque and thrust predictions are investigated. Three-different wind shear cases, i.e., uniform inflow (no wind shear), steady vertical wind shear that uses a power law velocity profile (Normal Wind Profile, NWP) and transient Extreme Wind Shear (EWS), are investigated. The results show that the existence of wind shear can create a very complex wake structure with substantial asymmetries, streamwise vorticity generation, and non-periodicities downstream of the turbine rotor. In addition, the blades are subjected to asymmetrical surface pressure variations that in turn result in high amplitude fluctuations in power and thrust levels generated by the turbine.

A simulation of the helicopter/ship dynamic interface has been developed and applied to simulate a UH-60A operating from an LHA class ship. Time accurate CFD solutions of the LHA airwake are interfaced with a flight dynamics simulation based on the GENHEL model. The flight dynamics model was updated to include improved inflow modeling and gust penetration effects of the ship airwake. An optimal control model of a human pilot was used to simulate pilot control activity for a specified approach trajectory. The pilot model was designed so that the tracking performance could be tuned based on a desired crossover frequency in each control axis. The model was used to predict pilot workload for shipboard approaches in two different wind-over-deck conditions. Although further validation is needed, preliminary results show that the simulation results in similar workload trends as recent flight test studies.

A computational study of unsteady, separated, low and high Reynolds number flows is made using a second-order accurate, cell-centered finite volume method on unstructured grids. The simulations include large-eddy simulation turbulence modeling based on a classical Smagorinsky subgrid-scale model. For the high Reynolds number simulations, wall shear stress is modeled by using the instantaneous logarithmic law of the wall. All the cases simulated are assumed to be fully turbulent, since the turbulence model is active over the entire surface of the sphere. The main objective of this work is to study the flow about a sphere at a Reynolds number of 1.14 × 10 6 which is in the supercritical range. Comparisons are made with experimental results by Achenbach and flow visualizations by Taneda. Predictions of the drag, mean pressure and mean skin-friction distributions along the sphere are in good agreement with experiments. The wake structure of the supercritical case is substantially changed compared to the subcritical flows with the wake in the supercritical case dominated by shedding of hairpin-like vortices. Three dimensional stereographic movies are also made using Ensight 7.6 to gain a deeper insight into wake-flow structure.

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Computational fluid dynamics (CFD) simulations of ship airwakes are discussed in this article. CFD is used to simulate the airwakes of landing helicopter assault (LHA) and landing platform dock-17 (LPD-17) classes of ships. The focus is on capturing the massively separated flow from sharp edges of blunt bodies, while ignoring the viscous effects. A parallel, finite-volume flow solver is used with unstructured grids on full-scale ship models for the CFD calculations. Both steady-state and time-accurate results are presented for a wind speed of 15.43 m/s (30 knot) and for six different wind-over-deck angles. The article also reviews other computational and experimental ship airwake research.