The windbreak concept is widely used primarily in agriculture and rural areas, protecting fields from the wind but after the increase of building density in urban areas and the change of environmental conditions, it has started to gain increasing interest in urban outdoor spaces in recent years.
All recent studies on usage of windbreaks in such spaces are based on the assumption that the space is completely open with no other obstacles, but referring to a built environment the presence of buildings affect the effectiveness of a windbreak and it is not proved yet in what extend. This thesis tries to exploit work done on basic characteristics of windbreaks and how they fit into solving the phenomenon under question.
The most important factors that are affecting windbreaks effectiveness during the design process are the height and the aerodynamic porosity of the windbreak. (Heisler and Dewalle, 1988, Forman, 1995). The height of a windbreak is referred to the distance form the ground to the top and it determines the extent of the protected zone. According to Heisler and Dewalle (1988) there is an analogy between the height (H) of the windbreak and the distance of the protection area expressing the later in the horizontal axis as height units (xH) (Fig_17, Fig_18).
On the other hand, the aerodynamic porosity of the windbreak determines the ratio between airflow that passes through the barrier pores (‘‘through-flow’’) and airflow that diverges over the barrier (‘‘diverged-flow’’) (Vigiak, Sterk, Warren, and Hagen, 2003). As it is clear from the diagram below (Fig_19) the relation between the porosity and reduction of wind flow that is directly correlated with the effectiveness of the windbreak is that as less the porosity as much the reduction of wind.
The windbreaks can be categorized into three different clusters according to their porosity. (Abel et al., 1997) to wind porous, wind medium porous and non- porous. According to Forman (1995) the best solution that can mitigate the wind are medium porous windbreaks showing same speed reduction properties with a lower porous (non-porous) windbreak avoiding the problems of turbulence and size distance protection that the latter creates. There is a constant trade off between porosity percentage and windbreak effectiveness and there is no optimal choice but it is strongly correlated with the wind behavior and the general in situ characteristics. Examples from various numerical investigations show that a windbreak with 30% porosity can decrease wind speed up to 70% (Fig_20).
Except from height and porosity, there are some other characteristics of wind flow and windbreak that can affect this relation. Concerning wind flow the parameters are wind speed, wind direction, turbulence intensity, and atmospheric stability and taking into account windbreak the properties are the orientation, length, shape, width, uniformity and continuity. (Heisler and Dewalle, 1988)
All recent studies on usage of windbreaks in such spaces are based on the assumption that the space is completely open with no other obstacles, but referring to a built environment the presence of buildings affect the effectiveness of a windbreak and it is not proved yet in what extend. This thesis tries to exploit work done on basic characteristics of windbreaks and how they fit into solving the phenomenon under question.
The most important factors that are affecting windbreaks effectiveness during the design process are the height and the aerodynamic porosity of the windbreak. (Heisler and Dewalle, 1988, Forman, 1995). The height of a windbreak is referred to the distance form the ground to the top and it determines the extent of the protected zone. According to Heisler and Dewalle (1988) there is an analogy between the height (H) of the windbreak and the distance of the protection area expressing the later in the horizontal axis as height units (xH) (Fig_17, Fig_18).
On the other hand, the aerodynamic porosity of the windbreak determines the ratio between airflow that passes through the barrier pores (‘‘through-flow’’) and airflow that diverges over the barrier (‘‘diverged-flow’’) (Vigiak, Sterk, Warren, and Hagen, 2003). As it is clear from the diagram below (Fig_19) the relation between the porosity and reduction of wind flow that is directly correlated with the effectiveness of the windbreak is that as less the porosity as much the reduction of wind.
The windbreaks can be categorized into three different clusters according to their porosity. (Abel et al., 1997) to wind porous, wind medium porous and non- porous. According to Forman (1995) the best solution that can mitigate the wind are medium porous windbreaks showing same speed reduction properties with a lower porous (non-porous) windbreak avoiding the problems of turbulence and size distance protection that the latter creates. There is a constant trade off between porosity percentage and windbreak effectiveness and there is no optimal choice but it is strongly correlated with the wind behavior and the general in situ characteristics. Examples from various numerical investigations show that a windbreak with 30% porosity can decrease wind speed up to 70% (Fig_20).
Except from height and porosity, there are some other characteristics of wind flow and windbreak that can affect this relation. Concerning wind flow the parameters are wind speed, wind direction, turbulence intensity, and atmospheric stability and taking into account windbreak the properties are the orientation, length, shape, width, uniformity and continuity. (Heisler and Dewalle, 1988)
Fig_17
Analogy between the height (H) of the windbreak and the distance of the protection area D=xH
Analogy between the height (H) of the windbreak and the distance of the protection area D=xH
Fig_18
Protection Area and reduction of wind
Protection Area and reduction of wind
Fig_19
Porosity of windbreak velocity of wind and distance from the protection area
Porosity of windbreak velocity of wind and distance from the protection area
Fig_20
Solid windbreak
Porous windbreak
Solid windbreak
Porous windbreak