Development of Biomimicry Wind Louver Surface Design

Transcription

1 International Proceedings of Chemical, Biological and Environmental Engineering, V0l. 93 (2016) DOI: /IPCBEE V93. 6 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 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.: ; fax: address: gunsong@gmail.com 39

2 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. 40

3 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] 41

4 Fig. 3: A silent and high efficient air conditioner fan which the form of imitated the form of humpback whales and shells (Seoul News, ) 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 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

5 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 avg. Velocity of air flow between louvers avg. Velocity of interior

6 Table 4: Result of simulation Velocity _ section Model Flat type Patterned type Wing type (width: mm) Velocity _ plan

7 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 45

8 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-C ) 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, [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 [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, [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, ,