WAsP-CFD in forest sites

[Gil]

Dear Team,

i am doing resource assessments in forest site with multi-masts mainly based on WAsP.  Western and southern parts of the site have a steep slope > 16.7 degree, so that I ordered WAsP-CFD. i read most of forest issues in this forum and also from webpage: https://www.wasp.dk/software/wasp-cfd/flow-model to understand better of WAsP-CFD.

However I still did not fully understand. I have some questions below. 

(Question 1) Are there any benefit of WAsP-CFD focusing on forest area? based on webpage above, it seems to me that WAsP-CFD use/interpret roughness data differently.

(Question 2) if WAsP-CFD has zero benefit compared to WAsP in terms of forest, should I apply same displacement heights in WAsP-CFD that were applied to WAsP?

(Question 3) based on WAsP, three main inputs are oro + rou + obs. How are obstacles dealt with in WAsP-CFD if they are not a part of input before run?

My last WAsP course was long time ago and i have used 3rd party CFD tools to handle forest. i think that could be the reason why I am still confused to understand how WAsP-CFD works. Could you please advise/guide me with details?

Thanks

Gyeongil

[Gil]

still no answers? it seems like the forest has not considered at all but it would be great if expert(s) could explain this clearly because it could not find many information on the internet.

[Morten]

Answer 1 – The forest model in WAsP-IBZ uses the displacement height concept. It should also be possible to implement that method in WAsP-CFD, but we have not done that yet. I guess my colleagues involved in the development project were worried about the lack of data for model validation and maybe also felt that the combination of forest and complex terrain might be too difficult to handle correctly by the displacement height approach. Read more on this difficult topic at https://link.springer.com/article/10.1007/s10546-020-00564-3

Answer 2 - Obviously, the missing support for forest modelling in WAsP-CFD raises the question of the best procedure for forest on top of complex terrain? This is a difficult question and it probably has no universal answer. If the forest is uniform, you might correct measurement heights and turbine hub heights for the expected displacement height, but I cannot guarantee it will work. Try to test the method by cross-predictions between measurement masts.   

Answer 3 – The obstacle shelter model in WAsP is independent of the flow model. Thus, it works the same way with either IBZ or CFD.

[Gil]

Hi Morten,

Thanks for your three answers and information of internal progress.

I have already read the paper you have linked but maybe a good time to re-visit. 

The main reason to ask of this question was recently I learned that WAsP-CFD models of micro-terrain and roughness is not relevant.

This made me confused because roughness is not used for running of WAsP-CFD. i did not expect three parameters (wind data, contour, roughess) can be separated like this. However, now i understood better.

It would be great if WAsP team clarify more in details in WAsP.dk.

Regarding IBZ, it is still not clearly stated anywhere but quite often mixed with BZ model, IBZ model.

Therefore, I would like to ask the following.

To my understanding BZ = Bessel-expansion on a zooming grid , IBZ = Integrated BZ.

Can someone says BZ and IBZ are different? if yes, is it because BZ is based on Troen (1990) and then later many new features were implemented to BZ model?

i would be appreciate if you clarify this as I could not find anywhere at all.

Regards,

Gyeongil