UNESCO-JASTIP Joint Symposium on Intra-Regional Water Security
and Disaster Management, Quezon City, the Philippines, November 16, 2017

Modeling of wind flow around tree for CFD
simulation
Ryuichi Inoue, Kyoto University
Kazuyoshi Nishijima, DPRI, Kyoto University (Speaker)

Bangladesh, courtesy of Prof. Ando

Background• Field surveys on vernacularconstructions in southeast Asia.
• Damage survey after typhoon
Yolanda with UP Diliman in2014, J-RAPID project.

Bangladesh• Damage survey after hurricane
Pam in Vanuatu in 2015
Samar, the Philippines

Observations• Damages on non-engineered
construction with industrial
materials.
• Sometimes, traditional
constructions behave wellunder extreme events.

Tanna, Vanuatu

17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

2

Motivation• Re-evaluate the performance of traditional construction
techniques by state-of-the-art technology engineering tools.
• Justify the advantages of the traditional techniques, where true.

Engineeringknowledge body

Feedback

ProgressEngineering
frontier

Non-engineeredsystems
JSPS project: 16H05905, Grant-in-Aid for Young Scientists (A), Re-evaluation of vernaculardisaster mitigation technologies by engineering manner – case of wind-induced disaster(2016-2019)17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

3

Some ongoing projects in our research team• JASTIP WP4 in corporation with the University of the Philippines,
Diliman, 2015-2020.
New tower
Telecommunication
tower

Kapit Bahay 1.0
developed by UPD

Wind

More anemometers

Incoming wind

Boundary layer

Physicalcomputing
AnemometerIntelligent anemometer

Anemometers

Full-scale testing• JICA grass-root project“Advancement of vernacularconstructions in Tanna island,
the Republic of Vanuatu”,
2016-2018.
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

4

Today’s talk is...Wind-breaking effect of tree

Contents• Objective of research• Wind tunnel experiment• CFD simulation• Optimized aerodynamic parameters in CFD
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

17/04/2008
Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

5

Objective
Challenge addressed in this research• Current canopy models do not consider mechanical characteristicsof tree behavior under various wind speed; hence, fail to simulate
wind field accurately.
Goal of the research• To develop a canopy model that can simulate wind flow affected bytree and other plants.

Wind tunnel (2m/s)

Wind tunnel (4m/s)
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

6

Wind tunnel experiment

17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around treeKazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

7Tree model••••Tree model consists of trunk, branches and leaves.
Made of timber, acryl and plastic film respectively.
Leaves are connected to branches with silicon tubes.
Leaves are painted white for image analysis.
Φ5mmacryl tube

20°

330mm

Leaf area density: 4.7

Top view

Leaf area density: 4.65

120mm

500mm

Leaf area density: 4.8(m2/m3)

plastic film
Side viewΦ24mm
Timber solid pole
17/04/2008

UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around treeKazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

8Inflow wind condition• Uniform flow
• Wind speed: 2, 4 and 8 m/s

U: Mean wind speed
Ur: Reference wind speed (at 510mm)
σu: Standard deviation of wind speed
z: height
Average time = 30 sec.

330
120
(Unit: mm)
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

9Measurement condition
Side view400x

wind500

zPitottubeo420 120

600

30mm×141000

MeasurementpointTop view
600

1000

500

windxo30mm×24y400Measurements• Wind speed
measured with Ishape hotwire probe.
Floor• Drag force acting on
the tree model withaerodynamic balance.
• Motion of the treemodel with videocamera.

（mm）
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

10

Result: horizontal wind profile behind tree modelwindU(z)

z

Pitot

-1000

o540

• Wind speed recovery
in furtherer points.

U0(z)
500

• Wind speed reduction
behind the tree modelx600

1000
(mm)

Horizontal wind speed profile at height of300 mm at x=600 mm and 1000mm.
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

11

Result: Drag force• (Projected) leaf area density, a• Drag coefficient, Cf
Measured drag force

TheoryCalculated Cf aA
D

u1
A’ObjectDrag force: D UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around treeBρ：Air densityu2

u：Wind speed
σ：AreaB’22udu 1 2 dAB

17/04/2008
Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU12

Result: Aerodynamic parameters• (Projected) leaf area density, a• Drag coefficient, Cf
Measured drag force

Calculated Cf aObservations• Aerodynamic parameters depend on wind speed• Drag force (hence, aerodynamic parameters) are interrelated tothe change of the wind speed profile
 “Optimal” aerodynamic parameters are identified by CFD
AB
simulation.
Theoryρ：Air density
Du2
u1
u：Wind speed
A’ObjectDrag force: D UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

σ：AreaB’22udu 1 2 dAB

17/04/2008
Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

13

CFD simulation

17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

14

Generation of inflow• Boundary condition– Ceil boundary: slip
– Side boundary: slip
– Floor boundary: canopy model
Generationof inflow

2.01m• Grid condition– X direction:20mm– Y direction:10mm– Z direction:10mm - 80mm
– Volume:18m×2.5m×2.01m

Analysis ofwind flow
around thetree modelzy Ox2.5m
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

15

Generated inflow*u is calculated based on 0.01-sec
averaged wind speed.
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

16

Analysis condition around the tree model• Boundary condition– Ceil boundary: slip
– Side boundary: slip
– Floor boundary: canopy model• Grid condition– X direction:20mm– Y direction:20mm– Z direction:20mm - 60mm
– Volume:3.5m×2.5m×2.01m

zyOx17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

17Re-parameterization of aerodynamic parameters• (Projected) leaf area density, a• Drag coefficient, Cf

Re-parameterization

a
aC f  a '  C f  a' Wind speed
dependentWind speed
dependent

Leaf area density
under no windx-direction wind speed
at z=280mm

17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

18

Result: simplistic modelling of tree

wind330

Three layered cuboids

wind330

Rotated three layered cuboids

 More precise modeling required.
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

19

Detailed tree modeling for CFD

Binary modeling• Image of tree silhouette at wind speed=0m/s• Binary analysis (black: no object,: object)– If an <50% area is occupied by objects,– Otherwise, black.
• Estimation of the location of objects– Based on the image analyses
from three directions• Assign a single leaf area density at thoselocations.
Assumptions• Solid modeled object• Aerodynamic parameters arefurther adjusted in terms of(a/a’Cf).
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

20

Optimized aerodynamic parameters

Comparison of CFD results and experiment results at x=600, z=300

Optimized aerodynamic parameters

a'a /a' *C fWind speed(m/s)
24
19.8
19.80.4
0.3

8
19.8
0.2

a’： Projected leaf area density
under no winda： Projected leaf area density
Cf： Drag parameter

Adjusted drag parameter
17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

21

Conclusion• A tree model for wind tunnel experiment is developed– It can show the wind-speed dependence characteristics ofaerodynamic parameters.
• Simplistic modeling approach for tree in terms of canopy model
fails to reproduce the wind speed profile behind the tree in CFD.
• An elaborated modeling approach shows a potential to be able toreproduce the wind speed profile.
• We will have a tool to evaluate the advantages of wind-breaking
forest on wind-resistant performance of buildings.

17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

22

“to measure is to know –if you cannot measure it,
you cannot improve it”
Lord Kelvin17/04/2008
UNESCO-JASTIP
会議名 発表タイトル
Symposium Modelling of wind field around tree

Kazuyoshi
西嶋一欽
Nishijima,
京都大学防災研究所
DPRI-KU

23