Meteorological observatories use measuring boards on even ground in open areas to measure the amount of snowfall. In order to measure the amount of snowfall, areas unaffected by wind should be found. This study tried to determine the internal wind flow inside a windbreak fence, identifying an area unaffected by wind in order to measure the snowfall. We performed a computational fluid dynamics analysis and wind tunnel test, conducted field measurements of the type and height of the windbreak fence, and analyzed the wind flow inside the fence. The results showed that a double windbreak fence was better than a single windbreak fence for decreasing wind velocity. The double fence (width 4 m, height 60 cm, and fixed on the bottom) has the greatest wind velocity decrease rate at the central part of octagonal windbreak.

Fresh snowfall is defined as new snow covering an even plane. The depth of snowfall is defined as the increment of the snow layer cover during the time of measurement. The snow depth is generally measured each day and the snowfall is reported in centimeters per day. The depth of fresh snowfall on open ground can be measured directly using scaled rulers or a snow ruler. The depth of snow covering the ground, or accumulated onthe ground, is measured by inserting a scaled rod vertically into the ground. However, snow covering the ground may come into the measurement plate by wind. Another limitation is that the snow ruler might meet an ice layer, rather than the ground. Thus, it is difficult to obtain a representative height measurement in an open area. We need to make sure that the total depth, including the ice layer, is measured and we need to average multiple measurements from each observation. The amount of snowfall measured in open areas is greatly affected by wind. Piles of snow formed by frequently blowing wind are scattered, resulting in some difficulty in evaluating the exact amount of snowfall. Current studies have focused on diverse equipment to measure the exact amount of snowfall. In addition, snowfall equipment is installed in areas where snowfall is not particularly influenced by wind. However, there is no research on wind control at the point where the amount of snowfall is measured. There has been much research undertaken on windbreak fences. In 1971, Plate [

In order to determine the height of a windbreak fence and experimental wind velocity, the amount of snowfall and wind velocity was analyzed using data on weather conditions over five recent years (2008–2012). Data from weather stations located in western and eastern coastal areas (where heavy snowfalls occur) was the primary source. In the western coastal area, data from weather stations in Gochang (35°20′N, 126°35′E), Gunsan (36°00′N, 126°76′E), and Mokpo (34°81′N, 126°38′E) were used, while in the eastern coastal area, weather stations in northern Gangneung (37°80′N, 128°85′E) and Daegwallyeong (37°67′N, 128°71′E) were analyzed. Figure

Location of weather station.

Snowfall frequency of occurrence and wind velocity frequency of occurrence.

Snowfall frequency of occurrence of the western coastal area

Snowfall frequency of occurrence of the eastern coastal area

Wind velocity frequency of occurrence of the western coastal area

Wind velocity frequency of occurrence of the eastern coastal area

The geometric model of the windbreak fences exhibits suburban conditions. The dimensions of the linear windbreaks and the windbreak fences according to the analysis model were

The analyzed domains of CFD.

The turbulence kinetic energy,

Figure

Dimension of the CFD Model for linear windbreak fences.

Analysis distances (1H–20H) and heights (LEVEL1–LEVEL4) of the linear windbreak fences.

Analysis distances

Analysis height

This study has analyzed the downwind and vertical velocity distributions scaled by the height of the fence (H). It has interpreted the distance-based wind velocity distribution up to the range of 1H–20H. The vertical wind velocity distribution on the downwind side of the fences has been interpreted at the central point of the fence. Figures

Wind velocity distribution of the linear windbreak fence by distance (GAP 0 cm, reference velocity = 3 m/s).

TYPE1 (height of fence: 40 cm)

TYPE2 (height of fence: 40 cm)

TYPE1 (height of fence: 60 cm)

TYPE2 (height of fence: 60 cm)

TYPE1 (height of fence: 80 cm)

TYPE2 (height of fence: 80 cm)

Wind velocity distribution of the linear windbreak fence by distance (Gap 0 cm, reference velocity = 6 m/s).

TYPE1 (height of fence: 40 cm)

TYPE2 (height of fence: 40 cm)

TYPE1 (height of fence: 60 cm)

TYPE2 (height of fence: 60 cm)

TYPE1 (height of fence: 80 cm)

TYPE2 (height of fence: 80 cm)

Wind velocity distribution of the linear windbreak fence by distance (Gap 15 cm, reference velocity = 3 m/s, 6 m/s).

TYPE1: height 60 cm, velocity 3 m/s

TYPE2: height 60 cm, velocity 3 m/s

TYPE1: height 60 cm, velocity 6 m/s

TYPE2: height 60 cm, velocity 6 m/s

Wind velocity flow the double windbreak fence by height (velocity 3 m/s).

Height of fence: 40 cm

Height of fence: 40 cm

Height of fence: 80 cm

Based on a wind flow analysis of the linear windbreak fence, we found a double fence with a 6 m length that was fixed to the ground to be the most effective. The wind direction will vary in a natural environment, so we analyzed the internal wind flow characteristics by installing an octagonal type windbreak, while considering the direction of the wind. After the octagonal windbreak fence was installed, we determined the width of the fence. Two fence widths (4 m and 6 m) were tested, based on the simulation of the linear fence. Figure

Specifications of the octagonal windbreak fence.

CASE 1 (width: 4 m)

CASE 2 (width: 6 m)

Figures

Internal wind velocity flow at a measurement height of 10 cm according to the windbreak fence width.

Width of windbreak fence: 4 m (velocity 3 m/s)

Width of windbreak fence: 4 m (velocity 6 m/s)

Width of windbreak fence: 6 m (velocity 3 m/s)

Width of windbreak fence: 6 m (velocity 6 m/s)

Internal wind velocity flow at a measurement height of 20 cm according to the windbreak fence width.

Width of windbreak fence: 4 m (velocity 3 m/s)

Width of windbreak fence: 4 m (velocity 6 m/s)

Width of windbreak fence: 6 m (velocity 3 m/s)

Width of windbreak fence: 6 m (velocity 6 m/s)

Wind velocity flow inside the fence by height.

Width of windbreak fence: 4 m, velocity: 3 m/s

Width of windbreak fence: 4 m, velocity: 6 m/s

Width of windbreak fence: 6 m, velocity: 3 m/s

Width of windbreak fence: 6 m, velocity: 6 m/s

A wind tunnel test was performed to analyze the wind flow inside the windbreak fence. Wind tunnel tests were conducted in an open-type wind tunnel located at the Department of Architectural Engineering, Chonbuk National University, which has a test section of 1.5 m (width) × 1.7 m (height) and 20 m (length). The boundary layer flow condition, representing natural wind flow over suburban terrain, indicated that the power law exponent of the mean longitudinal wind velocity profile was 0.15 and that the longitudinal turbulence intensity was about 16% at the top of the building model. Terrain category C, as described in the Standard Design Loads for Building, 2010, Architectural Institute of Korea, was simulated over the test section using spires and wooden blocks [

Specifications of the windbreak fence used in the wind tunnel test (unit = m).

Width | Height | |||
---|---|---|---|---|

Full-scale | Model | Full-scale | Model | |

Case A | 4 | 0.8 | 0.6 | 0.12 |

Case B | 6 | 1.2 | 0.6 | 0.12 |

Vertical distribution of the mean longitudinal wind velocities and turbulence intensities.

Wind velocity measurement locations and CASE 1 model installed in the wind tunnel.

Velocity measurement location

Model

Wind velocity measurement locations and CASE 2 model installed in the wind tunnel.

Velocity measurement location

Model

The average wind velocity and turbulence intensity changed according to the location analyzed. The nondimensional average velocity used in the experimental analysis was calculated using (

Figures

Distribution of wind velocity within the windbreak (CASE 1).

Height of measurement: 2 cm, velocity: 1.38 m/s

Height of measurement: 2 cm, velocity: 2.68 m/s

Height of measurement: 4 cm, velocity: 1.38 m/s

Height of measurement: 4 cm, velocity: 2.68 m/s

Distribution of wind velocity within the windbreak (CASE 2).

Height of measurement: 2 cm, velocity: 1.38 m/s

Height of measurement: 2 cm, velocity: 2.68 m/s

Height of measurement: 4 cm, velocity: 1.38 m/s

Height of measurement: 4 cm, velocity: 2.68 m/s

Distribution of the turbulence intensity inside the windbreak fence. (CASE 1).

Height of measurement: 2 cm, velocity: 1.38 m/s

Height of measurement: 2 cm, velocity: 2.68 m/s

Height of measurement: 4 cm, velocity: 1.38 m/s

Height of measurement: 4 cm, velocity: 2.68 m/s

Distribution of the turbulence intensity inside the windbreak fence (CASE 2).

Height of measurement: 2 cm, velocity: 1.38 m/s

Height of measurement: 2 cm, velocity: 2.68 m/s

Height of measurement: 4 cm, velocity: 1.38 m/s

Height of measurement: 4 cm, velocity: 2.68 m/s

We compared the wind tunnel test results and the CFD results. The CFD simulation was performed using the same size of model and the same wind velocity as the wind tunnel test. The CFD simulation and wind tunnel test results were compared with CASE 1 (fence width 4 m). We used 1.38 m/s and 2.68 m/s as the wind velocities in the wind tunnel test. The wind velocity distribution heights inside the windbreak fence were 2 cm and 4 cm. Figure

Wind velocity distribution and correlation coefficients for wind tunnel test and CFD.

Width: 4 m, velocity: 3 m/s, height: 2 cm

Width: 4 m, velocity: 3 m/s, height: 4 cm

Width: 4 m, velocity: 6 m/s, height: 2 cm

Width: 4 m, velocity: 6 m/s, height: 4 cm

The windbreak fences for field measurement included two fences, one with a width of 6 m and one with a width of 4 m. The height of the windbreak fences was constant at 60 cm. The windbreak’s vertical bars were fixed on the bottom. Table

Specifications of the windbreaks installed in the weather station (unit = m).

Width | Height | The distance from the windbreak wings to the ground | |
---|---|---|---|

Model A | 6 | 0.6 | 0 |

Model B | 4 | 0.6 | 0 |

Model C | 6 | 0.6 | 0.15 |

Average and maximum wind velocities by the type of models (unit: m/s).

Model A | Model B | Model C | Outside | |
---|---|---|---|---|

Average | 0.40 | 0.26 | 0.43 | 0.75 |

Maximum | 1.49 | 0.99 | 1.48 | 1.93 |

Arrangement plan and measurement process of anemometers.

Average and maximum wind velocities during each time.

Average wind velocity

1 hour maximum wind velocity

Weather stations plates are set up on the flat ground in meteorological observatories, in order to measure the amount of snowfall. However, accurately measuring the amount of snowfall covering the ground is hard due to the influence of the wind. The results of the CFD analysis, wind tunnel test, and field measurement (aimed at examining changes in wind velocities within the fences, according to varying fence widths and heights) are as follows.

According to the result of the CFD analysis of the linear windbreak fences, a double fence whose vertical bars were fixed on the bottom is more effective in decreasing wind velocity. The distance where wind velocity decreased to a maximal extent varied according to the height of fences. The results of the CFD analysis, wind tunnel test, and field measurement of the octagonal windbreak fences showed that the wind velocity decrease rate was greatest at the center of the ooctagonal windbreak, when the fence width was 4 m and its height was 60 cm.

The authors declare that there is no conflict of interests regarding the publication of this paper.

This work was supported by the National Research Foundation of Korea (NRF) and was grant funded by the Korea government (MEST) (no. 2011-0028567).