Journal of Heat Island Institute International Vol. 9-2 (2014)

Academic Article

An Experimental Study on Exploring the Possibility of Applying
Artificial Light as Radiation in Wind Tunnel
1 2

1 2

3

Ye Lin* *Toshiaki Ichinose* *Rudder T. Wu*
2
4
3
Yukio Yamao*
Hideaki Mouri*
Raymond V Rivera-Virtudazo**1 Department of Environmental Engineering and Architecture, Nagoya University, Nagoya, Japan*2 National Institute for Environmental Studies (NIES), Tsukuba, Japan*3 National Institute for Materials Science (NIMS), Tsukuba, Japan*4 Meteorological Research Institute (MRI), Tsukuba, Japan
Corresponding author: Ye LIN, lin.ye@nies.go.jp
ABSTRACT
Solar radiation heats the wall and surface of canopy, generates a strong buoyancy flow. The impact of thisbuoyancy is more obvious at the condition of low wind velocity. In a wind tunnel, heating elements were generally
used to generate buoyancy. We conducted experiments to explore the possibility of applying artificial light as solar
radiation using a scale building model made by real construction materials. Upon heating the roof top, the windvelocity increased while turbulent intensity decreased. We also changed the roof surface properties by applying
insulated coating (composed of micro-size hollow silica particles), and found out the influence of radiation can beobserved.
Key Words : wind tunnel, artificial light, heating, insulated coating, rooftop

study, we conducted experiments to explore the possibility of

1. Introduction

using artificial light as radiation in wind tunnel. Using radiation
In recent years, the Urban Heat Islands (UHI) phenomenon has

appropriately in wind tunnel can help better representing the

become a widespread problem and has attracted extensive

different solar angle and shading effects, and understanding theattention all over the world. Many research activities focusing on

UHI phenomenon.

different factors have been conducted to clarify how to mitigate
UHI with both experimental and numerical methods.

2. Methodology

For the experimental method, scale modeling is a very effective
and economical way, which can be carried out both indoor and

The experiment was conducted in the wind tunnel ofoutdoor[1]. The advantage of outdoor scale modeling is theMeteorological Research Institute (MRI), Japan. The size of the[2]

reality of the meteorological conditions . But fewer outdoor

test section is 3 m wide, 2 m high and 18 m long. The range ofexperiments were conducted because it is difficult to control thewind speed is 0.3 m/s-20 m/s. The probe volume is dx 0.033mm,

needed conditions. Indoor experiments were mainly applied indy 0.033mm, dz 0.411mm. As shown in Fig 1, a model housethe wind tunnel. Variables can be easily controlled. The main

made of real construction materials was used. Geometry scale is[3]

concerns include the investigation of flow regime , pollutant

1/15. Roof is made of asphalt shingle, wood model base, anddispersion[4], transfer coefficients[5], and radiation and energy

with extruded polystyrene foam as thermal insulated materials[6]balances .

under the roof. Albedo of used asphalt shingle is 2 % which was

Because of the difficulty to control the radiation and thermal

measured using CNR1 Net Radiometer, Kipp and Zonen Co.

conditions, and scale thermal admittance, few experiments wereLtd.

focusing on the radiation and energy balances. Most of theprevious studies used heating elements to generate buoyancy
flow and investigate the heating influence of canopy wall. In this- 108 -

H=380mm
Fig. 2 Configuration of halogen lamps
Wind velocity is calculated as below,
Fig. 1 Experimental setup
eqn. 1In this experiment, we chose four layers above rooftop to detect

Turbulent intensity is defined as,

the wind velocity, which are 1 cm, 2 cm, 3 cm and 5 cm. 8

Ipoints were selected along the centerline in each layer, as shown

eqn. 2

u is the mean velocity, u’is the root-mean-square of turbulent

in Fig 1. Table 1 shows the coordinate of all the testing points.

velocity fluctuations
Table 1 Coordination of testing points (unit: mm)

No roughness was set at the upwind area. It is considered to be
neutral condition, which the wind profile power lar isLayerapproximately 1/7. But the height of the model house is 380mm,

distance
Point 1 Point 2 Point 3 Point 4 Point 5 Point 6 Point 7 Point 8
above thewhich has exceeded the thickness of boundary layer in neutral
condition. Therefore, the wind speed of inlet flow was

rooftopconsidered to be vertically constant around the roof. The

50 mm

650,119 600,113.7 500,103.1 400,92.5 325,84.5 200,71.2 100,60.6

0,50

30 mm

650,990,30

blockage effect is 5 %.

20 mm

650,89600,83.7 500,73.1 400,62.5 325,54.5 200,41.2 100,30.6

0,20

10 mm

650,79600,73.7 500,63.1 400,52.5 325,44.5 200,31.2 100,20.6

0,10Solar spectral Irradiance [W/m2/m]

1400

600,93.7 500,83.1 400,72.5 325,64.5 200,51.2 100,40.6

Solar

(a)
1200
1000
800
600
400
200
0

The inflow wind velocity of 0.5 m/s and 1 m/s were studied.

200

400

600

800

1000

1200

1400

1600

1800

2000

Wavelength [nm]Wind speed was measured using Laser Doppler Velocimeter(LDV) continuously for five minutes to get the average windspeed. Roof surface temperature, indoor temperature and1400

background temperature were measured by thermo couples. For

Halogen(b)
1200

Irradiance [W/m2/m]heating the roof, we used four halogen lamps of 500 W each,
which were fixed 60 cm above from the roof (Fig 2). Air
temperature of inlet flow was 25.13 ºC. At this condition, thesurface temperature of asphalt could reach 65 ºC when windvelocity was 0.5 m/s, which is similar to the real condition.

1000
800
600
400
200

When we increased the velocity to 1 m/s, the surface

0

temperature of asphalt decreased to 57 ºC.

200

400

600

800

1000

1200

Wavelength [nm]Fig. 3 Comparison of irradiance between (a) solar[7] and (b)halogen radiation- 109 -

Due to the limitation of equipment, the spectral irradiance can

In addition, a vortex was formed near the windward edge,

only be measured to around 1050 nm wavelength (Fig 3). It canmainly because of the slightly inclined roof. The energy

be seen that the halogen lamp cannot fully reproduce the solar

maintaining the vortex came from the turbulent kinetic energy of2

radiation. Downward radiation of halogen lamp is 734W/m andwindward edge. The turbulent intensity decreased after heating,

513W/m2, which was measured at the center of the roof top

which is clearly shown in Fig 5, especially at the vortex area,

using CNR1 Net Radiometer, Kipp and Zonen Co. Ltd.

which inhibited the pollutant mixing. This decrease by heating isbecause of the effect of upward buoyancy flow generate for roof
surface, which reduced viscosity, weakened the vortex and3. Results and Discussion

speeded up the wind (Fig 6).
3.1 Applying artificial light with different inflow velocities
As shown in Fig 4, the wind velocity of each layer generally
increased upon heating the roof, which enhanced the transport ofpollutants. At a velocity of 0.5 m/s, the velocity increase was
Position (mm)more significant than that of 1 m/s. The difference of velocity
between heating and neutral condition could hardly be observedat the 5 cm level when inflow was 1 m/s. After heating the roof,
the wind velocity under 0.5 m/s and 1 m/s inflow increased by
12 % and 4 % respectively. It was thus concluded that, under
low velocity condition, the impact of buoyancy is more sensitive.
At the condition of relatively high velocity, the wind flow

(0,50)(100,60.6)(200,71.2)(325,84.5)(400,92.5)(500,103.1)(600,113.7)(650,119)-(0,30)(100,40.6)(200,51.2)(325,64.5)(400,72.5)(500,83.1)(600,93.7)(650,99)-(0,20)(100,30.6)(200,41.2)(325,54.5)(400,62.5)(500,73.1)(600,83.7)(650,89)-(0,10)(100,20.6)(200,31.2)(325,44.5)(400,52.5)(500,63.1)(600,73.7)(650,79)

through the roof before getting influenced by the buoyancy

1m/s
0.5m/s
-40

-20

0

20

40

60

Turbulent intensity increase (%)

generated by the heated roof.

Fig. 5 Turbulent intensity increase at each layer after heating therooftop
0.5m/s0.5m/s heating
1m/s
1m/s heating

50

(a)

z (mm)

40

30

20

Fig. 6 Turbulence difference above the rooftop between heating
10

and no heating conditions.
0.0

0.2

0.4

0.6

0.8

1.0

1.2

Position (mm)u/u

3.2 Applying insulated coating on roof top
Insulated coating[8] (composed of micro-size hollow silica(0,50)(100,60.6)(200,71.2)(325,84.5)(400,92.5)(500,103.1)(600,113.7)(650,119)-(0,30)(100,40.6)(200,51.2)(325,64.5)(400,72.5)(500,83.1)(600,93.7)(650,99)-(0,20)(100,30.6)(200,41.2)(325,54.5)(400,62.5)(500,73.1)(600,83.7)(650,89)-(0,10)(100,20.6)(200,31.2)(325,44.5)(400,52.5)(500,63.1)(600,73.7)(650,79)

1m/s
0.5m/s(b)particles with mesoporous shell wall) was applied on the roof
top. In this part of the experiment, the air temperature of inlet
flow was 23.16 ºC. After applying the insulated coating,although the roof surface temperature did not show significant
change, the indoor temperature decreased by nearly 1 ºC, as
shown in Table 2. This is because the insulating coating iscomposed of hollow microsphere with mesoporous shell wall
which can delay/lower the heat conduction. These micro-size
particles generate more surface reflectance, and maintain more

0

10

20

30

40

50

heat in the hollow part. The increased reflection and decreased

60

Velocity increase (%)

conduction nearly kept balance, and the heat storage in theFig. 4 Velocity (a) and velcocity increase (b) at each layer after

hollow particle increased, which maked the surface temperature

heating the rooftop

slightly higher.

- 110 -

Table 2 Surface temperature increase with and without insulated
coating
No coating

coating

Roof

44.47

44.48

Indoor6.38

5.63

Position (mm)Temperature increase (ºC)

With insulated coating, although the surface temperatures were
the same, the wind velocities under the heating and coatedcondition were generally 3% lower than that under only the(0,50)(100,60.6)(200,71.2)(325,84.5)(400,92.5)(500,103.1)(600,113.7)(650,119)-(0,30)(100,40.6)(200,51.2)(325,64.5)(400,72.5)(500,83.1)(600,93.7)(650,99)-(0,20)(100,30.6)(200,41.2)(325,54.5)(400,62.5)(500,73.1)(600,83.7)(650,89)-(0,10)(100,20.6)(200,31.2)(325,44.5)(400,52.5)(500,63.1)(600,73.7)(650,79)

heating condition, and 5% higher than the neutral condition, asWith insulation coating
Without insulation coating

-40

-20

0

20

40

60

80

100

Turbulent intensity increase (%)

shown in Fig 7. At the down wind part of the roof, this influence
was particularly more significant. As shown in Fig 8, turbulent

Fig. 8 Turbulent intensity increase at each layer after heating theintensity increased compared with the velocity under the heating

rooftop, with and without insulation coating

and non-insulated condition. This might be caused by thechanges in the surface properties generated by the insulating

4. Conclusion

coating. This change influenced the absorption and reflectanceof radiation, which means the impact of radiation on wind flow

A wind tunnel experiment using a scaled model made of real

might be observed when applying artificial light as radiation.

construction materials was conducted to explore the possibilityof applying artificial light as solar radiation. Under the low
inflow condition, the wind velocity was easily influenced by the

(a)

50

shape of building and buoyancy flow. After heating the roof top,

NeutralHeating without insulation coating
Heating with insulation coating

the velocity increased while turbulent intensity decreased. Thismight make pollutant transporting faster but inhibited pollutants

40

z (mm)

from mixing. After applying the insulated coatings on the roof
30

top, the velocity decreased while turbulent intensity increased.
We assume this might indicate the influence of radiation on wind

20

flow, and thus feasible to introduce radiation in wind tunnel.
Using radiation appropriately in wind tunnel can help better10

representing the different solar angle and shading effects, and
0.0

0.2

0.4

0.6

0.8

1.0

1.2

understanding the UHI phenomenon.

u/uHowever there are still many difficulties to overcome. For

Position (mm)example, it’s difficult to measure the air temperature precisely,
due to the effect of radiation on thermocouple. Also we should(0,50)(100,60.6)(200,71.2)(325,84.5)(400,92.5)(500,103.1)(600,113.7)(650,119)-(0,30)(100,40.6)(200,51.2)(325,64.5)(400,72.5)(500,83.1)(600,93.7)(650,99)-(0,20)(100,30.6)(200,41.2)(325,54.5)(400,62.5)(500,73.1)(600,83.7)(650,89)-(0,10)(100,20.6)(200,31.2)(325,44.5)(400,52.5)(500,63.1)(600,73.7)(650,79)-60

With insulation coating
Without insulation coating(b)take consideration on the effect of the lamp body, and conduct a
better simulation technique for solar radiation study.
Acknowledgement
We thank Shigeru Onogi, Toshimasa Yagi, and Akihiro Hori forassisting with the wind tunnel experiment.
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(Received Nov. 30, 2014, Accepted Dec. 27, 2014)- 112 -