Browsing by Author "Delafin, Pierre-Luc"
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Item Open Access Blade-resolved CFD simulations of a periodic array of NREL 5 MW rotors with and without towers(MDPI, 2022-01-14) Ma, Lun; Delafin, Pierre-Luc; Tsoutsanis, Panagiotis; Antoniadis, Antonis F.; Nishino, TakafumiA 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.Item Open Access Comparison of low-order aerodynamic models and RANS CFD for full scale 3D vertical axis wind turbines(Elsevier, 2017-03-21) Delafin, Pierre-Luc; Nishino, Takafumi; Athanasios, Kolios; Lin, WangA Double Multiple Streamtube model, a free-wake vortex model (both widely used for vertical axis wind turbine design) and RANS CFD simulations are used in this work to predict the performance of the 17 m Vertical Axis Wind Turbine, field tested by Sandia National Laboratories. The three-dimensional, full scale calculations are compared with the experiments in terms of power coefficient, power and instantaneous turbine torque to assess the validity of each model. Additionally, the two aerodynamic models and RANS CFD are compared to each other in terms of thrust and lateral force. The two models and CFD agree well with the experiments at the turbine optimal tip speed ratio. However, away from the optimal tip speed ratio, the streamtube model significantly deviates from the experimental data and from the other numerical models. RANS CFD gives a good agreement with the experiments, slightly underestimating the power coefficient at every tip speed ratio tested. The vortex model proves to be a useful tool with a better accuracy than the streamtube model and a much lower computational cost compared to RANS CFD.Item Open Access Effect of the number of blades and solidity on the performance of a vertical axis wind turbine(IOP Publishing: Conference Series / Institute of Physics (IoP), 2016-10-03) Delafin, Pierre-Luc; Nishino, Takafumi; Wang, Lin; Kolios, AthanasiosTwo, three and four bladed phgr-shape Vertical Axis Wind Turbines are simulated using a free-wake vortex model. Two versions of the three and four bladed turbines are considered, one having the same chord length as the two-bladed turbine and the other having the same solidity as the two-bladed turbine. Results of the two-bladed turbine are validated against published experimental data of power coefficient and instantaneous torque. The effect of solidity on the power coefficient is presented and the instantaneous torque, thrust and lateral force of the two-, three- and four-bladed turbines are compared for the same solidity. It is found that increasing the number of blades from two to three significantly reduces the torque, thrust and lateral force ripples. Adding a fourth blade further reduces the ripples except for the torque at low tip speed ratio. This work aims to help choosing the number of blades during the design phase of a vertical axis wind turbine.Item Open Access Momentum balance in a fully developed boundary layer over a staggered array of NREL 5MW rotors(IOP Publishing, 2017-06-13) Delafin, Pierre-Luc; Nishino, Takafumi3D Reynolds-averaged Navier-Stokes (RANS) simulations of a fully developed wind farm boundary layer over a staggered array of NREL 5MW turbines are presented. The turbine is modeled as an actuator disk and as a fully resolved rotor to compare the effect of the turbine model on the wind farm aerodynamics, in particular the streamwise momentum balance across the farm. Results show that the difference in the turbine model affects the average wind speed through the farm as well as the local flow pattern around each turbine; both contributing to the difference in the prediction of farm performance. Results are also compared with a simple theoretical model of very large wind farms proposed recently. The actuator disk simulations agree very well with the theoretical model, whereas the fully resolved rotor simulations show some consistent and expected differences from the model. Paper presented at the Wake Conference 2017 30 May to 1 June 2017, Visby, Sweden.Item Open Access Structural optimisation of vertical-axis wind turbine composite blades based on finite element analysis and genetic algorithm(Elsevier, 2016-06-02) Wang, Lin; Kolios, Athanasios; Nishino, Takafumi; Delafin, Pierre-Luc; Bird, TheodoreA wind turbine blade generally has complex structures including several layers of composite materials with shear webs, making its structure design very challenging. In this paper, a structural optimisation model for wind turbine composite blades has been developed based on a parametric FEA (finite element analysis) model and a GA (genetic algorithm) model. The optimisation model minimises the mass of composite blades with multi-criteria constraints. The number of unidirectional plies, the locations of the spar cap and the thicknesses of shear webs are taken as design variables. The optimisation model takes account of five constraints, i.e. stress constraint, deformation constraint, vibration constraint, buckling constraint, and manufacturing manoeuvrability and continuity of laminate layups constraint. The model has been applied to the blade structural optimisation of ELECTRA 30 kW wind turbine, which is a novel VAWT (vertical-axis wind turbine) combining sails and V-shape arm. The mass of the optimised blade is 228 kg, which is 17.4% lower than the initial design, indicating the blade mass can be significantly reduced by using the present optimisation model. It is demonstrated that the structural optimisation model presented in this paper is capable of effectively and accurately determining the optimal structural layups of composite blades.