[vagge]

Hello to everyone!

I am very new to CFD and I ‘ve just my first experience with OpenFOAM.

I ‘ve been using version 3.0.

I ‘ve been trying to achieve a steady state solution for the flow around a 3-bladed horizontal axis Wind Turbine rotor.
To this end, I have been studying just 1/3 of the rotor by considering 120° periodicity.

As explained in the attached picture 1, my domain consists of a (1/3)-cylinder type domain with the following patches: “inlet”, “outlet”, “summetryUp” (cyclicAMI), “symmetryDown” (cyclicAMI), “symmetrySide” (outer wall), “blade” (spinner & blade as one body) and “rotor” (baffle so as to create a cell zone within snappyHexMeshDict).

Since the domain is very large compared to the blade, which is the main point of interest, I have preferred to apply the MRF approach by creating a rotational (MRF) zone under/inside the “rotor” baffle patch. I have tried different lengths, heights and even shapes of the MRF zone.

I have chosen to have an intense volume cell refinement close to the blade as well as 9 layers around it with the first one having a height of 0.75mm, so as to be able to “catch” the boundary layer on the blade’s surface. Till a distance of 1.5m away from the blade surface, the mesh refinement level is pretty high. After, that the mesh is super coarse with no refinement applied. The whole computational domain consists of ~12 M cells.

I have deactivated the residual controls.
Although my main focus is on studying the estimated torque and thrust, I have two problems:

1. My simulations crash after around 800 steps/iterations (although I achieve stable satisfactory torque/thrust values already from the first 500 iterations)

2. The wake behind the blade doesn’t seem realistic. It improves after many steps far from the blade, but not in a close distance after it. Especially close to the hub region is like I have no wake at all, while close to the tip I even get a flow acceleration right after the blade (please see pictures (2-4) attached). Plotting normal-to-blade-height planes (example pictures 5-6) shows that there is a wake right after the blade Moreover, right on the imaginary boundary of the MRF zone, I get a sudden change of the flow velocity (obvious line on picture 4).

Regarding the crashing, by following the steps before it happens on paraFoam, I have realized that something fishy happens on the blade (please, see start of the problem on pictures 7-8 attached), especially close to the tip where the layering is not that good. Please see the checkMesh results attached.

Regarding the wake, I have tried to refine a larger region around the blade (5m) or even refine the expected wake region, but I the outcome has been just a faster crash. Trying many different MRFZones’ sizes and shapes hasn’t helped at all. Trying longer or shorter domains (in the direction of freestream velocity) hasn’t helped either.

The freestream velocity is 10 m/s.

Please, find attached the boundary conditions’ p and U fields files and the fvSolution/fvSchemes files.

I would really appreciate any advice on which direction I should work on.

If anyone has done something similar and wants to share the differences, I would be glad to see them.

Thank you all in advance!