No abstract

No abstract

The wakes of two different porous disks have been evaluated experimentally. Such disks are commonly used as physical actuator disk analogs for wind turbines. One disk is made of a uniform wire mesh, while the other has a nonuniform design with radial spars connected by rings. The disks have the same solidity and produce approximately the same drag. The wakes have also been compared to the wake of a model wind turbine and a solid disk. In contrast to earlier studies, the far wake, up to 30 diameters downstream, is included in the comparison. In the near wake, the velocity deficit and turbulence intensity profiles of the disk wakes differ significantly. High levels of turbulence intensity in the wake of the nonuniform disk increase the transverse transport in the wake, which leads to faster spreading and lower velocity deficits in the far wake, compared to the uniform disk and the wind turbine. High velocity gradients in the wake of the uniform disk give rise to turbulence production farther downstream, maintaining higher turbulence levels in the far wake. In addition, coherent vortex shedding is only identified in the wake of the nonuniform disk. None of the disks were able to replicate the asymmetric features of the wind turbine wake. Nonetheless, the results highlight important flow physics that should be considered in the design process of a porous disk used as a wind turbine surrogate.

The flow over the leading edge of an NREL S826 reference airfoil with three different icing-inspired leading-edge contamination geometries has been assessed experimentally. Particle image velocimetry was performed on the leading edge of the airfoil for a range of angles-of-attack between −4 and 16 . This work primarily focuses on the flow physics at Reynolds numbers (Re c = 455 000) within the Reynolds number independent regime of the airfoil. The present work illuminates our understanding of the flow phenomena as well as provides a validation dataset for future numerical work. From the acquired data, the mean velocity, turbulent kinetic energy and mean vorticity have been estimated. The results show how the different contamination geometries affect the point of separation. It is also shown that the intermittency of the flow behind horn-shaped contamination is dependent on the angle-of-attack, even at angles above stall. Proper orthogonal decomposition was performed on the velocity fields to identify whether reduced order modelling is an appropriate tool for rapid estimation of these flows. It was found that a limited number of modes carried a large fraction of the fluctuating energy, demonstrating that reduced order modelling is feasible.

With the increasing demand for wind energy, it is important to be able to understand and predict the available wind resources. To that end, the present wind tunnel study addresses the flow in the induction and entrance region of wind farms through particle image velocimetry, with focus on differences between actuator disks and two‐bladed rotating wind turbine models. Both staggered and aligned farm layouts are examined for three different incoming wind directions. For each layout, 69 disks or turbines are used, and the field of view ranges from 12 rotor diameters upstream of the farms to 8 diameters downstream of the first row. The results show that the induction, or blockage effect, is higher for the disks, even though the thrust (or drag) coefficient is the same. In contrast, the wake is stronger downstream of the turbines. The orientation and layout of the farm do not have a major impact on the results. Modal decomposition of the flow shows that the flow structure similarity between the disk and turbines improves downstream of the second row of wake generating objects, indicating that the substitution of wind turbines by actuator disks is more appropriate for wind farms than for the investigation of single wakes.