Description

Project Description of Darrieus VAWT:

A vertical-axis wind turbine (VAWT) is a type of wind turbine where the main rotor shaft is set transverse to the wind and perpendicular to the ground. This arrangement provides VAWTs to capture wind energy in every azimuth angles. There are three types of VAWTs: Savonius which is a drag-based wind turbine, Darrieus wind turbine that works based on lift generation and H-type wind turbine.

The H-type wind turbine is actually like Darrieus but with different blades. In this project, we aim to validate a related paper entitled “ The Darrieus wind turbine: Proposal for a new performance prediction model based on CFD “.

According to the paper 2D simulation, the turbine has three NACA0021 blades and the diameter is 1010mm shown in figure below.

For better understanding, a three-dimensional view of the experimental setup is illustrated below. Note that, the geometry is designed in ANSYS Design Modeler software.

Moreover, ANSYS Meshing software is used to generate mesh grids. It should be considered that a coarse boundary layer or any size jump in cells will be caused errors. Therefore, the problem is highly grid-sensitive.

In the figures below, generated cells in the rotating domain, stationary zone and the vicinity of the blades are depicted. All in all, 904018 quad/tri cells were used.

Methodology of Darrieus turbine simulation:

The pressure-based solver type is used due to incompressibility of the air. Also, the simulation is performed in Transient mode. Most importantly, mesh motion (sliding mesh) is hired to rotate the rotor to investigate wind turbine performance.

Results:(Darrieus  turbine numerical validation)

The wind turbine needs to rotate several rounds to get to its steady condition. Normally, it happens in the fifth or sixth round. Therefore, we need to monitor a crucial value like the moment coefficient of the wind turbine. As the difference in two consecutive rounds becomes less than 2%, we can be assured of the convergence.

The power coefficient of the wind turbine is achieved by multiplying TSR by the moment coefficient. The Tip Speed Ratio is defined as: (R: turbine radius, w: rotational velocity, V: uniform wind speed)

TSR= (w*R)/V_in

Note that, the moment coefficient can be reported by ANSYS Fluent. So with a simple calculation, the power coefficient is accessible. Thus, the power coefficient in 4 TSRs is calculated including 2, 2.5, 2.68 & 2.8 and then compared with the article.

The figure below indicates the article and simulation data in a plot. The plot proves that the simulation results have a good agreement with the paper results. Finally, 2d contours of the velocity field, pressure distribution and turbulence intensity are exported.