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 Ruth August 22, 2007 12:21

Porosity of Trees

I am doing some wind modelling around a building which is overshadowed by a number of large trees. I plan to model the tree canopy as a porous subdomain, but the question is how porous are trees.

Having done a literature search, it appears that either the figure 50% porosity is plucked out of thin air, or detailed analysis is undertaken resulting in very specific and complex models.

Does anyone have a reference for the 50% figure, or a more accurate figure with some sort of validation? There are also seasonal, and species variation in porosity so any guidelines taking this into account would also be welcome.

Thank you, Ruth

 JWilliams August 22, 2007 14:34

Re: Porosity of Trees

Ruth,

50% is way too low a value for porosity of trees. Porosity should be closer to 0.99 for dense foliage, 0.999 for intermediately dense foliage, and 0.9999 light foliage.

One way to determine the porosity of a type of foliage is to look up its Leaf Area Index (LAI)

porosity = 1-[t/2*(LAI/h)]

where t=leaf thickness

h= height of the canopy

For coniferous trees,

porosity = 1-Dc/4*(LAI/h)

where Dc=needle diameter.

You should be able to find plenty of data on LAI in literature.

A few authors you should look into are:

R.M. Cionco J.J. Finnigan G. Gross M.J. Judd M.R. Raupach R.S. Kinerson L.J. Fritschen A.S. Thom R.H. Shaw U. Schumann T. Yamada

 charltonjames June 30, 2010 11:26

Hi JWilliams,

Im having the same problem, but thanks for the equation. Do you have a reference for it?

@Ruth - how did you progress with your model?

 ukduka September 2, 2010 08:21

air flow through trees

Hello,

I try to model a 2D air flow through a tree (conifer tree) and I wonder whether anyone knows any typical values of the following input settings required in the fluid panel for the porous media (the tree):

1) Viscous resistance
2) Inertial resistance

If you have a reference as well it will be also very useful.

Many thanks,
K.

 charltonjames September 3, 2010 04:38

Hi Ukduka! I have exactly the same problem. And need to know the same values. Please update any findings on this forum and ill do the same. Hopefully we'll be able to resolve it.

I've read several research papers relating to wind through tree modelling using CFD, but i havent found any useful information.

 sampournazeri October 6, 2010 14:51

Porosity of Crown

Hi guys,

I also have the same problem in Fluent modeling the flow through the forest, I really don't know what to put as the Viscous Resistance and Inertial Resistance there. As I was doing some literature survey ,the porosity numbers are significantly scattered. as a reference I have found the following article :

Pekin, B.; Macfarlane, C. Measurement of Crown Cover and Leaf Area Index Using Digital Cover Photography and Its Application to Remote Sensing. Remote Sens. 2009, 1, 1298-1320.doi:10.3390/rs1041298

and they are reporting values between 0.11 - 0.39 for the crowns.

however , JWilliams was reporting the numbers in the order ro 0.99 for densly packed canopy.

I was wondering , if you guys have found anything new.

Thanks

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