Simulations - Results

 


Simulations

From this point, it is possible to run a simulation. First, initialize then run . After convergence (it might be necessary to use the first order : Continua $\rightarrow$ Physics 1 $\rightarrow$ right click on Models $\rightarrow$ Edit $\rightarrow$ Segregated Solver $\rightarrow$ first order) one wants to actually see the wake :

 


Visualization

To do so, the velocity is seen on a plane cutting the domain.

Right click on Derived part $\rightarrow$ Section $\rightarrow$ Plane.

Then, a scalar scene is created. Right click on Scene $\rightarrow$ New Scene $\rightarrow$ Scalar scene.

Now that the scalar scene is opened, click on Scene/Plot .

Displayers $\rightarrow$ Scalar 1 $\rightarrow$ Parts. Choose the threshold part created for every virtual disks and the Plane section. In Scalar Field, choose velocity magnitude.

Finally :

 

The visualization obtained is :

 


Quantify the results

The next step of the study is to compare the simulation results with experimental data.

Those experimental data are normalized power produced by each turbine(normalized by the power produced by the first turbine) in two cases :

  • every turbine working
  • the 4th turbine stopped

To quantify the simulation results it is necessary to get the velocity entering each wind turbines. To do so, the velocity is averaged on a disk just before the virtual disk :

The method will be quickly explained here :

first create a part :geometry $\rightarrow$ right click on parts $\rightarrow$ New Shape part $\rightarrow$ cylinder. Place it conveniently. As it was done for the domain, split the surface in 3 (right click on surface $\rightarrow$ split by angle). To be faster, copy and paste the cylinder then transform $\rightarrow$ translate to place it just in front the second disk.

However, now the created cylinders are independant from the region. So if the averaged velocity is taken at this point, it will be 0. That is why a derived part is used.

Right click on derived part $\rightarrow$ New part $\rightarrow$ Section $\rightarrow$ Arbitrary section. Use the following parameters :

Now, let us create a report : right click on report $\rightarrow$ New report $\rightarrow$ surface average :

To display the velocities : right click on report $\rightarrow$ Run all reports.

With these velocities, one can interpolate on the MM70 power curve (with the function interp1 of Matlab for example) and obtain the power produced by each turbine. After normalization :

The order of magnitude remains the same, however, the drop in term of power after the first turbine is bigger in the experimental data. Moreover, the simulations do not predict the stabilization of the loss after the second turbine.


Conclusion and possible improvements

In conclusion, this part of the project made it possible to simulate an existing wind farm and compare its production to experimental data. To improve the results, one can do again the simulations with some changes :

  • creating a bigger domain to make sure that the limit conditions do not have an impact on the solution
  • try to use the first order and then use the second order to improve precision.
  • improve the way of getting the velocities with StarCCM+ to be closer to reality.
  • use the V2F turbulence model which theorically predict better a mixing flow.