Blade-Resolved CFD Simulations of a Periodic Array of NREL 5 MW Rotors with and without Towers

A fully resolved (FR) NREL 5 MW turbine model is employed in two unsteady Reynolds-averaged Navier–Stokes (URANS) simulations (one with and one without the turbine tower) of a periodic atmospheric boundary layer (ABL) to study the performance of an infinitely large wind farm. The results show that the power reduction due to the tower drag is about 5% under the assumption that the driving force of the ABL is unchanged. Two additional simulations using an actuator disc (AD) model are also conducted. The AD and FR results show nearly identical tower-induced reductions of the wind speed above the wind farm, supporting the argument that the AD model is sufficient to predict the wind farm blockage effect. We also investigate the feasibility of performing delayed-detached-eddy simulations (DDES) using the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within the farm, such as the interaction of large-scale hairpin-like vortices with smaller-scale blade-tip vortices. The computational cost of the DDES required for a given number of rotor revolutions is found to be similar to the corresponding URANS simulation, but the sampling period required to obtain meaningful time-averaged results seems much longer due to the existence of long-timescale fluctuations.

CFD analysis of operational flow nature of a wind turbine model using environmental wind data from Nigerian Defence Academy (NDA)

A wind turbine is a machine which converts the power in the wind into electricity. It operates under varying wind speeds depending on the environmental wind conditions. In this paper, we have presented the operational flow analysis of a proposed wind turbine model in Nigerian Defence Academy (NDA) Kaduna. The case study is for 5.6m/s, 7.5m/s and 9.5m/s wind speed. The model design and assembly of the components were done with the help of SolidWorks 2018 and the operational flow analysis done with ANSYS 15.0. The result showed that the flow nature of the turbine model grew from laminar flow to turbulent flow increasingly with the environmental wind speed. The flow nature remained laminar from 0.0356 to 1780 Reynolds at 5.6m/s. At 7.5m/s wind speed, from laminar 0.403 Reynolds to turbulent 4290 Reynolds and at 9.5m/s, from laminar 0.381 Reynolds to turbulent 4900 Reynolds. High turbulent flow and mass imbalance nature depicts that phenomenon like wake and vibration of the system occurred.

FAST.Farm load validation for single wake situations at alpha ventus

The main objective of the presented work is the validation of the simulation tool FAST.Farm for the calculation of power and structural loads in single wake situations; the basis for the validation is the measurement database of the operating offshore wind farm alpha ventus. The approach is described in detail and covers the calibration of the aeroelastic turbine model, transfer of environmental conditions to simulations, and comparison between simulations and adequately filtered measurements. It is shown that FAST.Farm accurately predicts power and structural load distributions over wind direction with discrepancies of less than 10 % for most of the cases compared to the measurements. Additionally, the frequency response of the structure is investigated, and it is calculated by FAST.Farm in good agreement with the measurements. In general, the calculation of fatigue loads is improved with a wake-added turbulence model added to FAST.Farm in the course of this study.