Development of Biomimicry Wind Louver Surface Design

Jaepil Choi 1, Donghwa Shon

2, Gensong Piao

2 and Youngwoo Kim

3

1 Professor, Department of Architecture, Seoul National University, Korea

2 Researcher, Department of Architecture, Chungnam National University, Korea

3 Ph. D candidate, Department of Architecture, Seoul National University, Korea

Abstract. This study aims to determine the appropriate surface geometry of a wind louver system that

introduces the outside air into the interior of a building. In this study, we applied biological principles to

determine the geometry of a wind louver surface by observing the characteristics of organisms, and conduct

computational fluid dynamics (CFD) simulation to verify the effect. Simulation was conducted for three

different types of wind louver surfaces, flat, patterned, and wing types, and the effect was analyzed both

visually and quantitatively. Visual analysis was based on the observation of the change in direction of the air

flow into the indoor space, and the quantitative analysis was based on the examination of the influence of the

change in wind louver surface geometry on the overall change in wind velocity within the indoor surface. As

a result, it was found that installing a 100mm-wide wing-shaped plate on the wind louver surface leads to a

pleasant introduction of outside air into the indoor space.

Keywords: biomimicry, wind louver system, computational fluid dynamics (CFD), passive design

1. Introduction

1.1. Background

Numerous mechanical facilities have been developed to enhance the indoor amenity of buildings. For

example, this includes sanitary facilities, air-conditioning systems, and heating and cooling facilities. Since

such mechanical facilities utilize electrical energy, the energy consumption of buildings grew to comprise a

large proportion of the entire society. [1] Owing to the global attention toward green growth, it is believed

that the current energy consumption of the newly constructed buildings can be reduced by 80%. [2] To

achieve this objective, there is an increasing interest toward passive architecture. Given this trend, this study

focuses on the wind inlet devices that employ passive techniques in order to enhance the amenity of the

indoor air environment of buildings. The aim of this study is to determine the appropriate wind louver

geometry for the introduction of fresh outside air into an indoor space.

In this study, wind louver refers to a device installed on the surface of a building that aids the

appropriate introduction of fresh air outside a building into the indoor space. While external sunblind devices

can be said to be geometrically similar, the difference is that the role of wind louvers is to introduce wind,

unlike the role of the louvers in sunblind systems, which is to block sunlight. Similar to sunblind systems,

wind louver systems can be installed vertically and horizontally. However, external wind usually flows

horizontally upon contact with the building surface. Therefore, the direction of louvers in wind louver system

is selected to be vertical in this study.

1.2. Methods

This study focuses on which wind louver surface geometry leads to the appropriate introduction of

external wind into the indoor space. To achieve this objective, this study adopts the method of imitating the

Corresponding author. Tel.: + 8228808869; fax: +8208715518.

E-mail address: gunsong@gmail.com

International Proceedings of Chemical, Biological and Environmental Engineering, V0l. 93 (2016)

DOI: 10.7763/IPCBEE. 2016. V93. 6

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intrinsic principles of organisms. Such biomimicry is considered a form of research approach that have been

adopted not only in architecture, but also in various fields such as mechanical, material, and industrial

designs since a long time ago. In architecture, biological principles are also widely utilized in architectural

space, form, structure, and material. [3] This study also utilizes biomimetic techniques for the determination

of wind louver surface geometry for buildings.

Fig. 1: Horizontal, Vertical, Hybrid type louver

Fig. 2: Research flow

The specific objective of this study is to find the wind louver surface geometry that prevents the

entrance of strong wind due to the bias toward one side during the introduction of external wind into the

indoor space induced by the wind louver. Following research procedures are required to achieve this

objective.

Firstly, a basic geometry of the wind louver is configured. The specific objective of this stage is to

assume a louver plate with the most basic geometry of rectangular cross-section.

Secondly, biological information relevant to fluid flow is collected. The specific objective of this stage is

to find the biological geometry that affects the direction of air flow, while having small resistance to the flow.

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Thirdly, the principle of the biological information collected during the previous stage is analyzed. We

derive the geometric characteristics that are applicable to wind louver, by analyzing the characteristics of the

biological principle for the application to this study.

Fourthly, a surface geometry design for wind louver is established through biomimicry. The specific

objective of this stage is to determine the surface geometry by directly applying the principle of the organism

obtained from the biological information to the wind louver surface.

Fifthly, the final design is selected that is appropriate for the use in wind louver, through the

computational fluid dynamics (CFD) simulation of the biomimetic wind louver designs established during

the previous stage.

2. Biomimetic Wind Louver Surface Geometry

2.1. Geometrical Characteristics of Organisms Relating to Fluid Flow

Collecting the biological information pertinent to fluid flow as shown in Table 1, it was found that

biological characteristics such as the wing feather of an owl, the hump of a humpback whale, and the

grooves on the surface of the shell of a scallop have particular influences on the flow of air or water.

Table 1: Biological principles that induce air flow & bio performance for air flow

Name of organisms Biological principles Biological features

Owl

Flying silently during night

time due to wing feathers is

shaped to minimized air

resistance

Minimize air resistance

Humpback

whale

Form of pectoral helps to

move rapidly for hunting

Minimize air resistance &

Change air flow

Shell

Structure of shell surface

helps to move rapidly to

avoid from predators and to

hunt

Minimize air resistance &

Change air flow

There are also real-life applications where such biological characteristics are utilized. For example,

there was a case of the decrease in heating and cooling efficiency due to the increase in noise following

generation of complicated air flow from the rotation of the fan of the outdoor unit of an air-conditioning

system. To resolve this, an air-conditioning fan was developed that imitates biological characteristics. [4]

The organisms utilized in the development of the air-conditioning fan are humpback whales and scallops.

Humpback whales can rapidly move owing to the frontal hump, which maintain the buoyant force by

reducing the vorticity, which is the swirling flow during the change in direction. Moreover, it was discovered

that the groove structure of the surface of the shell of a scallop is based on a principle that aids agile

movements. Moreover, the longitudinal grooves at the two ends of the shell surface lead to the increase in

maximum buoyant force, and those in the middle lead to the decrease in buoyant force. [5]

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Fig. 3: A silent and high efficient air conditioner fan which the form of imitated the form of humpback whales and

shells (Seoul News, 2015.11.05)

Such longitudinal grooves on the shell surface directly affect the buoyant force in water. There is a need

to examine the effect of applying the longitudinal groove of shell surface to the surface of wind louver from

this perspective. This study aims to examine the change in air flow into indoor space and wind velocity with

varying surface geometry of wind louvers.

2.2. Determination of Wind Louver Surface Geometry

Patterned and wing type wind louver surface geometries are proposed, inspired by humpback whales and

the shell surface of scallops previously examined. Patterned-type geometry has grooves at constant intervals

on the surface of general louvers. This type is the direct application of the surface geometries of the two

organisms, and the motivation was to observe whether the surface grooves directly affect the wind velocity

and air flow. Wing type is an extension of the patterned type, wherein wings are installed in constant

intervals on the surface of general louvers.

3. CFD Simulation

3.1. Overview of the Simulation

In this study, CFD analysis was conducted to verify the effectiveness of the patterned and wing type

geometries. CFD analysis was based on the widely used Star CCM+, and standard k-ε model was adopted as

the turbulence model. This is to observe the effectiveness of each wind louver surface geometry, and the

samples were selected as general louver, which is the benchmark, and patterned and wing type louvers,

which are proposed in this study. Basic details of the analysis are as follow. First of all, a 3.6(m) × 3.6(m) ×

2.4(m) space was assumed, and wind louvers were placed at the front section. This was tilted 45°

horizontally. In order to observe whether the grooves and wings of the wind louvers affect the wind flow, the

direction of the groove and wing was set as 30° downward. Under this basic configuration, simulation was

conducted for each of general, patterned, and wing type wind louvers. The detailed geometries of each type

were set as the table below. Lastly, the external wind was set to flow from the front, and its velocity was set

as 1m/s.

Fig. 4: Modeling for simulation

In order to examine the change in indoor environment with wind louver surface geometry, the average

velocity through the louvers and the average wind velocity within the indoor space were computed for each

wind louver type. Moreover, the effects of each wind louver type were examined by comparing and

analyzing the wind flow within the indoor space. 42

3.2. Simulation Results

From the simulation results, it was observed that the wind louver surface geometry does not have a

significant influence on wind velocity. First of all, the average wind velocity from the external atmosphere

was the highest in general type, followed by patterned type, and the wing type being the lowest. While there

was such minute difference, the wind velocity was around 0.4m/s in all three types, showing no meaningful

difference. The average velocity in the indoor space was in the reverse order to that in between louvers, as it

was the highest in wing type, followed by patterned type and general type. However, the average velocity

was around 0.25m/s in all types, which is almost equivalent.

Table 2: Size of louver types (mm)

Flat type Patterned type Wing type

Fig. 5: Velocity of air flow between louvers

Table 3: Avg. Velocity of air flow between louvers & interior of each types

flat type

patterned

type

wing type

30 50 70 100

avg. Velocity of air flow

between louvers 0.448 0.447 0.444 0.431 0.420 0.414

avg. Velocity of interior 0.2452 0.2492 0.2561 0.2483 0.2472 0.2575

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Table 4: Result of simulation

Model Velocity _ section Velocity _ plan

Flat type

Patterned type

Wing type

(width: mm)

30

50

70

100

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Subsequently, the wind flow was examined. The flow within the plane appeared to flow toward the right

along with the louvers, then over the walls, and exit through the opening at the left-hand side edge. This was

consistent in all louver types (See Table 4). While the wind within the plane did not show a significant

difference, there was a difference in the cross-section view. Examining the wind flow from the cross-section

view, in general type louver, it was observed that the external wind flows directly to the middle of the indoor

space after the entrance, and changes direction to the horizontal along the rear wall. However, it flows

linearly without vertical changes. In contrast, in patterned type louver, it was observed that the vertical wind

flow propagates in a similar way to the general type until the 1/4 point after reaching the interior, but

separates vertically afterward, and merges again at the midpoint of the indoor space. In wing type louver, the

wind flow was observed to flow downward along the direction of the wings, unlike the previous two types. It

was found that the wind from the external atmosphere flows downward and that the exhaust wind flows

upward, exhibiting a vertically circulating current.

According to the simulation results herein, the grooved geometry similar to the surfaces of scallop shells

and the fin of humpback whales do not seem to have a direct influence on the velocity of the wind. While

there was a change in the air current, it was found that there is no significant influence on the overall flow.

Wing type geometry also did not have a direct influence on the change in wind velocity. However, there was

a noticeable change in air current, which indicates the possibility of adjusting the direction vertically.

It is believed that the effect of vertical adjustment of direction will be more significant with longer

wings. However, since the length of the wings cannot be increased indefinitely in realistic terms, there is a

need to select an appropriate length. For this purpose, we subsequently aimed to determine the length of the

wing where the change in air current starts to appear. The length of the wing was additionally varied to

30mm, 50mm, and 70mm, and the air current was compared and analyzed. From the analysis, it was

observed that the air current becomes similar to that of patterned type with decreasing length of the wings.

Conversely, it appeared that the air current at the top becomes weaker and the air current at the bottom

becomes stronger with increasing length of the wings. While there was at least a minimal amount of air flow

at the top until the length of the wing reaches 70mm, from 100mm, it was observed that the directions of the

top and bottom currents are clearly opposite to each other. It is thought that this relates to both the length of

the wing and the width of the empty space between the wings, rather than the length of the wings only.

While the wings appear to have almost no influence on the air current if the space between the wings is

larger than the length of the wings, in the contrary case, there seems to be an influence. Thus far, we

examined the influence of the surface geometry of wind louvers on wind velocity and air current. To

summarize, while both patterned and wing types do not directly affect the wind velocity, it can be deduced

that wing type significantly affects the air current when the length of the wing is larger than the width of the

space between each edge of the wings. It is expected that the results from this analysis will be useful to the

architectural designs where it is intended to achieve the ventilation of a building that contacts the external

atmosphere at one side only in a natural manner.

4. Conclusion

This study proposed patterned and wing type louvers to achieve the objective of combined-type louvers

that are efficient in various aspects, and aimed to verify the effectiveness of these louvers through simulation.

The two proposed louvers reflect the functional aspects of the surface geometries of scallops and the fin of

humpback whales. To analyze the effectiveness, we compared the average wind velocity in space between

louvers and the average velocity within the indoor space in each type, and comparatively analyzed the

horizontal and vertical indoor air current. From the analysis, it was observed that both of the two types do not

directly affect the wind velocity. In contrast, a meaningful change was observed in wing type during the

comparison of air current. Additionally, during the process of determining the appropriate length of the

wings, it was revealed that the air current is affected by the relationship between the length of the wings and

the space between each wing, rather than the length of the wing only. This study is a fundamental analysis

for the design of surface geometry of wind louvers, and the present analysis does not yet suffice to define the

appropriate surface geometry. However, we intend to sufficiently develop the analysis through various

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additional future researches on the surface material, louver geometry, and the optimization of the direction of

louver angle.

5. Acknowledgements

This research was supported by a grant (15CTAP-C077364-02) from Land Transport Technology

Promotion Program funded by Ministry of Land, Infrastructure and Transport Affairs of Korean government.

6. References

[1] Z. Yi, China Building Energy Status Analysis And Energy Saving Method, Woosong University Architecture,

master's thesis, 2012

[2] J. Lee, J. Kang, E. Kim, H. Byun, A Case Study on Biomimicry Methodology for Building and Architectural

Design, Journal of the Branch Association of Architectural Institute of Korea, Vol.17 No.2, 2015.04

[3] H. Koh, Study of evaluation model for thean analysis of the techniques of passive building, Department of

Architectural Engineering Graduate School of Konkuk University, doctor's thesis, doctor's thesis 2015.02

[4] Department of Engineering at Seoul National University – LG Electronics, remove the vortex during fan rotation

to decrease noise and increase efficiency, Seoul Newspaper, Society , 2015.11.05

[5] T. Kim, H. Choi, Effect of longitudinal grooves of the scallop surface on aerodynamic performance, The Korean

Society of Mechanical Engineers Spring and Autumn Conference , 2008.11, 2419-2422

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