Analysis of apparent temperature in cold area of building layout based on computational fluid dynamics

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JLJU

PNU

Analysis of apparent temperature in cold area of building layout based on computational fluid dynamics

Fang Yikun

Kim A.A.

Changchun

Khabarovsk

Abstract

This article uses CFD (Computer Fluid Dynamics) to calculate the wind speed of a building site, selects the wind speed of the route that people walk, and then calculates the temperature using the wind chill formula, and analyzes how to improve the comfort of the site.

Keywords: CFD (Computer Fluid Dynamics), wind speed, wind chill index, apparent temperature, airflow, turbulence.

Аннотация

Анализ кажущейся температуры зимнего периода с помощью вычислительной гидродинамики в зависимости от градостроительной ситуации

ЩУС, Чаньчунь, Китай ²ТОГУ, Хабаровск, Россия

В статье с помощью вычислительной гидродинамики рассчитывается скорость ветра на территории застройки, анализируются ветровые потоки на пешеходных маршрутах, вычисляется кажущаяся температура в зависимости от силы ветра и предлагаются решения для повышения комфортности среды.

Keywords: вычислительная гидродинамика, скорость ветра, ветрохолодовый индекс, кажущаяся температура, воздушные потоки, турбулентность.

Main part

In many cities where the outdoor temperature is below zero degrees Celsius, people rarely go out. This is bad for human physical and mental health. The main factor affecting this behavior is apparent temperature.

Apparent temperature refers to the equivalent temperature perceived by humans. It is caused by the combined effects of air temperature, relative humidity and wind speed [1]. People's comfort in the cold outdoors is related to many factors, such as clothing, moving speed, wind speed, temperature, humidity, and metabolic efficiency. From an architectural perspective, if the temperature and humidity of an area are available, the main factors affecting apparent temperature are wind speed, which is related to the building layout.

Wind chill index is a physical quantity that characterizes the relationship between wind speed and cooling. Experiments show that when the air temperature is -1.1°С, if the wind speed is 11.1 m/s, people will feel the degree of cold is equivalent to a temperature of -17.2°С when there is no wind; if the wind speed is 15.6 m/s, it is equivalent to the temperature when there is no wind It is cold at -20°С. It can be seen that people feel colder than the actual temperature in the cold wind (pic. 1) [2].

1 Mathematical model analysis

The fundamental basis of almost all CFD problems is the Navier-Stokes equations, which define many single-phase (gas or liquid, but not both) fluid flows. These equations can be simplified by removing terms describing viscous actions to yield the Euler equations [3]. Navier-Stokes equations have limitations and are difficult to solve in complex three-dimensional flows, so we idealize the model as incompressible flows and make corrections to the natural environment, p is the dynamic viscosity of the fluid creases.

Pic. 1. Wind chill index

In Cartesian coordinates, it can be written as:

Large turbulence will become small turbulence, from kinetic energy to internal energy. Molecular thermal motion (pic. 2).

We conducted two experiments on this phenomenon. In the first type, we carried out the building layout on a flat ground to analyze the influence of the building on the wind speed. In the second type, we carried out the building layout on the ground with a slope to analyze the influence of the slope on the wind speed.

2 Research data development

Experimental environment

This article chooses Khabarovsk Pacific National University (48.65°N, 135.05°E). Parkland, bushes, numerous obstacles give a ratio 0.5.

Time is Khabarovsk is the coldest five days with average temperature -29.5°С, average wind speed 3.8 m/s, and average wind direction SW [4].

Experimental models and sizing

Pacific National University on 1:1 scale. Six models made using Rhino CFD.

Environment Canada's standard air cooling formula is [5]:

where T_wc-the wind chill index, based on the Celsius temperature scale;

T_a - the air temperature in degrees Celsius;

v-the wind speed at 10 m (33 ft) standard anemometer height, in km per hour.

3 Research results and analysis

The upper part is north, average temperature -29.5°С, average wind speed 3.8 m/s, and average wind direction SW.

Pic. 2. Left-laminar flow; right-turbulence

Solved according to Environment Canada's standard air cooling formula (table 1).

Table 1. Values of wind chill index

Flat ground

Floor plan

Data height is 1.8 m.

Blank comparison group added plant correction data (pic. 3, left), status added Pacific National University and plant correction data (pic. 3, right, pic. 4). Comparing the graphs, it can be concluded that the effect of plants on the wind speed is large, and the enclosed building layout has a greater effect on the reduction of wind speed than the distributed building layout.

By comparing (pic. 3, right, pic. 4), it can be concluded that the wind volume is projected onto the building along the direction of the wind speed. The larger the projection surface, the wind speed behind the building decreases significantly.

Section

The section selects (pic. 5) the road from the campus to the urban road. These roads are also places with a lot of people.

The main entrance (pic. 6, left) of the main campus building is in a low wind speed area. Analysis of charts (pic. 6-7). The area near the ground and far away from the building have the plants, and the wind speed is low relative to the 50 m height area.

Slope site

Comparison (pic. 8) found that the wind speed on the leeward slope was small, in line with the turbulence and laminar flow models previously analyzed.

Comparison (pic. 9) found that the wind speed on the leeward slope was small, but the effect was not obvious.

4 Strategies to improve comfort

Optimize the road

No matter how the building is laid out, the wind cannot be avoided. At this time, it is important to set up walking paths in areas with low wind speed.

Reasonable building design

The building's functional division is reasonable, and the main entrance should avoid facing the cold wind in winter.

Planting

In physics and fluid mechanics, a boundary layer is the layer of fluid in the immediate vicinity of a bounding surface where the effects of viscosity are significant. In the Earth's atmosphere, the atmospheric boundary layer is the air layer near the ground affected by diurnal heat, moisture or momentum transfer to or from the surface [6]. Increasing viscosity is a very effective deceleration measure.

Pic. 3. Left-blank comparison group; right-status 1

Ріс. 8. Left - leeward slope; right-windward slope

Pic. 9. Left - leeward slope building; right-windward slope building

hydrodynamics wind pedestrian

Building layout

When considering the layout of a building, not only the impact of sunlight on the building, but also the shelter from the wind.

Terrain

For different terrain areas, use different design methods. Consider the impact of windward or leeward slopes on the site.

CFD can be used to design building layouts, but for real environments in three dimensions, it is difficult for computers to get accurate answers. Because the environment is complicated.

Even so, this experiment provides a new perspective for wind environment assessment. CFD and wind tunnel experiments can be used in our future designs to provide more accurate results.

Bibliographic references

1. ' (ФіШтІЇ [Apparent Temperature; electronic resource] // Baidu. URL: https://baike. baidu.com/item/#^M® (date of the application 20.12.2019).

2. [Wind-Chill Index; electronic resource] // Baidu. URL: https://baike. baidu.com/item/Jx((date of the application 20.12.2019).

3. Hunter J.K. An Introduction to the Incompressible Euler Equations [Electronic resource] // University of California, Davis. URL:

https://www.math.ucdavis.edu/~hunter/notes/euler.pdf (date of the application 20.12.2019).

4. SP 131.13330.2018 «SNiP 23-01-99* Building climatology». M.: Standardinform, 2019.107 p.

5. Calculation of the 1971 to 2000 Climate Normals for Canada [Electronic resource] // National Climate Data and Information Archive. URL: http://climate.weatheroffice.gc.ca/prods_servs/normals_documentation_e.html (date of the application 27.06.2013).

6. Young A.D. Boundary layers. Washington, DC: American Institute of Aeronautics and Astronautics, 1989. 269 p.

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