Study On Urban Ventilation Network Mordel Based On The Flow Characteristics Of The Roads In Shenzhen

With the development of the city and the people’s living standards improve, thewind environment has become an important factor that affects the quality of humansettlements. On the one hand, the continuous development of the urban construction, thepopulation is increasing along with a series of production and living activities,significantly enhances the urban heat island effect; On the other hand, industrialdevelopment, automobile exhaust emissions, raw biomass burning due to the largenumber of air pollutants, which directly influence the city’s climate and the health ofresidents. Urban wind environment is directly related to the ability to reduce the heatisland effect, diluting and removing air pollutants. In contrast, the the city internalairflow become complex, the original urban ventilation airflow physical model has beennot fit. Therefore, it’s important to built a new urban ventilation model.This paper carry out the study from the following aspects:First, it analysis the wind environment of Shenzhen, and the results show thatShenzhen has strong potential for ventilation. Urban road network like fluid network, itwalks the entire city.It not only connects city’s transportation, but also the main path ofnatural wind gets into each block of each building, so the urban road network and urbanventilation are related closely. By the road network analysising, Shenzhen is a typicalcheckerboard road network.Second, it measures the wind environment of the checkerboarded road network onthe horizontal direction and vertical direction. The crossroads of main road and branchroad, adjacent crossroads of branch road, tri-crossroads are selected to measure in thehorizontal direction; ground point, the flyover point and ten meters height point aremeasured on the vertical direction to study its wind speed and direction variation, inaddition to larger vehicles traveling factors which affect the air flow on the road. Byanalysising the measured data using MATLAB software, it shows the characteristicvariation of average wind (average wind speed and direction) and fluctuating wind(including turbulence intensity and integral scale).Third, because the field test of the road network is influenced by weatherconditions which are difficult to control, and it’s not conducive to a wide range ofobservations. It selects the method of numerical simulation to study the road networkwind environment. Porous medium theory is used to simplify the physical model. Then the road network wind environment is simulated by using RNG k-ε model and standardk-ε model. The results show that the RNG k-ε model is superior to the standard k-εmodel; By comparising with the measured value, numerical simulation is highlyconsistent with actual the flow; Furthermore, it analysis the air flow characteristics ofeach layer of the road network on the vertical height.Lastly, the the city ventilation network model is built. It vertically divides to thelower building dense layer, mid buildings roof layer, super structure sporadic layer.According to the architecture distribution characteristics of each layer, it proposes theventilation model of each layer on horizontal direction. At the building dense layer, theair flow can be described as a submerged network flow model, air flow through theroad mesh. Due to the flow path is not closed, the flowing can upward develop into thebuilding roofing layer, the upper air can import this network, and also air flow into thehigh-density areas. The air pressure of the flow of the street network decide the air flowdirection. At the building roof layer, most of the building roofs are distributed in thislayer, the roof are relatively separaed, not continuous, the vertical surface is stillbuilding facade. At this layer, the surface distribution density is smaller up to the height.the constructions are only distributed in the living areas between the street network, thevoid over the street are still a free flow. At the construction sporadic layer, only theupper part of the supper building are existed. Due to the small number of high-risebuildings, their spacing sparse are large, and there is almost non-existent interactionbetween each single building. And the flow around various buildings are independent ofeach other. It can be treated as the monomer flow around the single building. Thereasonable planning guidance are recommended to the important factors which affectthe ventilation network model (including urban ventilation corridors, the direction of theroad, and branch roads aspect ratio, the road network density).