For architects, engineers, urban planners, and other AEC professionals working in sustainability, porous media for LBM and Pedestrian Wind Comfort analysis can offer an insight into innovative wind effect mitigation solutions. This presentation demonstrates how to use SimScale's advanced features, like porous media, for urban flow simulation and, more specifically, to evaluate the effect of trees as windbreaks. Watch the webinar recording here: https://www.youtube.com/watch?v=r9c4t0tsvpA

1. With Arnaud Girin
CFD webinar
How to Model Trees with Porous
Media — Pedestrian Wind Comfort
CFD webinar
How to Model Trees with Porous
Media — Pedestrian Wind Comfort

2. About SimScale
Who we are
● Founded in 2012
● Offices in Munich, Boston, and New York
● 80+ employees across 6+ time zones
● 150,000 users worldwide
● More than 300k simulation projects
● Knowledge base and tutorials

3. We created the world’s first cloud-based
engineering simulation platform.
● Fluid dynamics (CFD)
● Solid mechanics (FEA)
● Thermodynamics
All accessible via a web browser.
About SimScale
What we do

4. What are the effects produced by trees and
other porous urban furnitures and buildings
on the comfort of pedestrian?
Today’s application
Porous media and
pedestrian wind
comfort

5. Setup and run a
simulation
Lawson Criteria
Assess directional
results
1
3 part workflow
1. Run 2 simulations of the same model
○ With trees modeled
○ Without trees modeled
2. Wind comfort criteria
○ At which location did the trees help
with the comfort?
3. Wind speed results in the predominant
direction
○ How did the trees impact on the flow
pattern?
How do we assess trees impact on pedestrian
comfort?
2
3

6. Overview
Reports [2] show the different outcomes in regards to
pedestrian wind comfort :
● Shops untenanted
● Parks under utilized
● Personal injury
● Venturi effect in passages
● Wind-blocking
What is wind comfort?
Today’s application
Example for mechanical wind comfort criteria [1]
[1] Adamek, Kimberley.,Vasan, Neetha., Elshaer, Ahmed., English, Elizabeth.,& Bitsuamlak,Girma.,Pedestrian Level Wind Assessment through City Development:A Study of the Financial Districtin Toronto.
[2] http://www.urbanphysics.net/windcomfort.htm

7. How can we combat
the undesired effects
of the wind?
Today’s application
Case scenario 1: New construction
General shape and layout
Canopies & Panels
Placement of entrances
Case scenario 2: Existing buildings
Implement trees
Implement urban furnitures or art pieces
https://www.sciencedirect.com/science/article/pii/S0167610516307644?via%3Dihub
https://www.sciencedirect.com/science/article/abs/pii/S0360132317300884?via%3Dihub
https://sci-hub.tw/https://www.tandfonline.com/doi/abs/10.1080/00038628.2018.1492899
https://www.sciencedirect.com/science/article/pii/S0360132319305037

8. Why are trees
important for cities?
Today’s application
http://www.fao.org/zhc/detail-events/en/c/454543/
https://www.smartcitiesdive.com/ex/sustainablecitiescollective/why-we-need-trees-our-cities/1100050/
https://www.theguardian.com/cities/2016/oct/12/importance-urban-forests-money-grow-trees
1. Increase property value
2. Reduce carbon emissions
3. Regulate water flow
4. Improve physical and mental health
5. Filters for urban pollutants
6. Climate change mitigation
7. Increasing urban biodiversity
8. Food and nutrition security

9. What is a porous media?
Today’s application
A porous medium is a solid with interconnected
voids distributed more or less uniformly through
the bulk of the body.
For trees, porosity is defined:

10. Why is it useful? How does
it affect the flow pattern?
Today’s application
In CFD, trees are defined as porous materials because:
● The physical structure is complex (we cannot
model each leaf)
● The value of porosity and inertial resistance are
essential for accurate results
The windbreak trees affect:
● The trajectory of the flow
● The wind speed
● The pressure drop windward/leeward

11. How is the porosity of
trees modeled on
SimScale?
Today’s application
There are different ways to define a tree zone in SimScale:
A Global Database of Field-observed Leaf Area Index in Woody Plant Species
GFDL and Creative Commons CC-BY 2.5
Option 1: Pick a predefined tree from the library
Option 2: Create a custom tree definition with
1. Leaf Area Index
2. Drag Coefficient
Leaf Area Index = Total Leaf Area/Total Ground Area
The dimensionless drag coefficient can be understood as
the ratio of the pressure difference of windward and
leeward and the dynamic force.

12. How trees should be modeled on SimScale?
Today’s application
The standard tree representative in Revit
NON ACCEPTABLE
An ideal representative of a tree for PWC
Solid representation of the foliage

13. Assessing the level of comfort
with and without trees
Porous Media and Wind Comfort
Example 1

14. ● Assessing the level of pedestrian comfort in front of
the Grace building and Bryant Park
● Identify areas that are uncomfortable for the main
activities involved
● Investigate the causes of uncomfortable zones,
taking into account wind effects generated by the
surrounding buildings
● Evaluating the impact of the presence of trees in the
urban layout
What is the goal of this
simulation?
Example 1

15. Today’s example
1. This model represents the vicinity of
Bryant park and the main buildings
around it, including’
a. The Grace building
b. NYC library
c. The Bank of America tower
CAD upload
Google (n.d.).[Google Maps of Bryant Park and its surrounding.. Retrieved April 18, 2020.

16. Define region of Interest
Define wind rose
Define pedestrian zones
1
3
2 minute setup
It’s that simple.
2
4 Define porous regions

17. What effect do the tree have on the pedestrian wind
comfort?
Example 1

18. What effect do trees have on the flow pattern?
Example 1

19. Assessing the level of comfort
with and without trees
Porous Media and Wind Comfort
Example 2: A bustling city center

20. ● Assessing the level of pedestrian comfort in a
specific urban area
○ Using year-round meteorological data
○ With multiple directions of wind
● Identify areas that are uncomfortable for the
designated activity
● Investigate the causes of uncomfortable zones,
taking into account wind effects generated by the
surrounding buildings
● Evaluating the impact of the presence of trees in the
urban layout
What is the goal of this
simulation?
Example 2

21. Today’s example
1. The model used represent a bustling
city center with trees along pavements
and squares
CAD upload

22. What effect do the trees have on the pedestrian
wind comfort?
Example 2

23. ● In some locations and directions, the differences, in
both transient and average are significant
What effect do the tree
have on the flow pattern?
Example 2

24. ● In some locations and directions, the differences, in
both transient and average are significant
What effect do the tree
have on the flow pattern?
Example 2

25. ● We simulate trees with porous media simplification
● For our first example :
○ The park is a lot more comfortable with tree
since they alleviate the downdraft effect of
the wind coming against the facade
● For our second example:
○ Implementing trees along pavement,
especially at street corners mitigate the
cornering and channeling effects
Trees make great
windbreakers!
Summary

26. Want to Learn more? Check out the articles below.
Additional Resources
● A wind tunnel study on aerodynamic porosity and windbreak drag
● Computational Fluid Dynamics Simulation of Tree Effects on Pedestrian
Wind Comfort in an Urban Area
● Including trees in the numerical simulations of the wind flow in urban areas:
Should we care?
● A Global Database of Field-observed Leaf Area Index in Woody Plant Species
● How to Upload an STL File With Separate Layers