<I had put my message in the wrong category, hope it is better here!>

I am a still looking for a consistent method to derive the f parameter values for a tree (d=0, seems consistent).

Reading the report: https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=928986

how does formula (7) translated into the d and f parameters of Darcy-Forchheimer?

Formula (7) is: dP=rho/2*Cdryan*kappa*u^2*L

<Cdryan is the Cd in above artcile ~ 2.8>

Looking here:

How to Predict Darcy and Forchheimer Coefficients :

dP = rho/2*f*u^2*L (formula below formula (4))

Thus fryan looks to be Cdryan*kappa.

So with a tree (say Robin Red Holly):

fryan = 2.8*4.3 = 12.0

Looking here:

Surface Roughness & Porosity | Advanced Modelling PWC | SimScale

This document details multiple ways of modeling porous media and surface roughness under advanced modelling in PWC analysis using SimScale.

Est. reading time: 8 minutes

dp/dx=-rho*LAI/h*Cdsim*|u|*u

From this formula f would be

fsim = 2*LAI/H*Cdsim

<Cdsim is SIMSCALE’s Cd ~ 0.2; H is height of tree; LAI Leaf Area Index>

So for an oak tree of 15.5m height and LAI is 5.2:

fsim=2*5.2/15.5*0.2=0.134

<I also see this when using: Readyuse-Perforated Plate.xlsx - Google Sheets )

So this is a factor of 100 between the two.

Possible explanation of difference:

a) The Cdsim is around 0.2 (table 4 in Surface Roughness & Porosity | Advanced Modelling PWC | SimScale)

While Cdryan is around 2.8 (chapter 5).

b) In SIMSCALE’s formula there is H of the object (H)!

c) LAI (around 3 to 5.2) is quite close to kappa (around 2 to 4.3)

d) I must be doing/understand something wrong.

e) When using the low values of fsim (=0.134) in simulation, I get IMHO quite (too?) porous objects. I did not yet try the fryan=12 (and compare that with the results of the tree: trees by rtir | SimScale , as that tree matches quite well with a real tree: Atmosphere | Free Full-Text | The Influence of Wind-Induced Response in Urban Trees on the Surrounding Flow Field )

Any help to get a better understanding on my side, is welcome. Thanks.