Research On The Influence Of Pavement Parameters On The Near-surface Thermal Environment

In the process of urbanization, a lot of natural surface are replaced by manmade pavement, and it leads to the changes of near-surface atmospheric thermal environment, then the urban heat island effect is created. In order to analyze the influence law of pavement type and material properties on the near-surface thermal environment, the pavement and near-surface atmosphere were considered as an interactive system, and a three-dimensional numerical model was developed. The computational fluid dynamics(CFD) method was used to solve the unsteady governing equation. The influences of underlying surface of different types and the intensity of solar radiation on the near-surface thermal environment were analyzed by using measured data, and the results of numerical calculation was also validated. Finally, by using the pavement-air interactive model, the influence of solar radiation, pavement material properties on the near-surface thermal environment in the group of buildings was analyzed and the spatial distribution of air temperature above different pavement type was also summarized. The main conclusions are as follows:① The test method for pavement surface reflectivity by double table apparatus composed of positive and negative solar radiation tables was proposed. And the average reflectivity of 11:00~13:00 in the local solar time was as the pavement surface reflectivity.② Based on the computational fluid dynamics(CFD) method, considering the short wave solar radiation, heat conduction and effective long wave radiation between the pavement and atmosphere, a three-dimensional numerical model was developed. The 3D finite element results of pavement-air interaction were verified by the measured data, and it shown that the model has a good accuracy and applicability especially for the data simulation during the daytime, however, the precision for simulating the temperature during the night was needed to be further optimized.③ On a sunny day, above the grass paving within 0~60cm height range, the air temperature change is volatile. For the rigid impermeable pavement and cement pavement, the height range are 0~50cm, 0~100cm respectively. For the most impermeable pavement, the spatial distribution of air temperature above the surface can be divided into three types : sunrise type, daytime type and evening type.④ In the business district of Monument for Liberation, when the asphalt pavement is selected as the underlying surface, the distribution area of high temperature is significantly greater than the condition of rigid impermeable pavement and cement pavement, and the temperature is relatively high. Thus, because of its high absorption rate and specific heat, asphalt pavement is not suitable as the underling surface in a residential or commercial area compared with cement pavement and rigid impermeable pavement.⑤ For the surface and near-surface air temperature in the business district of Monument for Liberation, the temperature value decreases with increasing of the reflectivity, emission rate, conductivity and specific heat. But the decrease amplitude of temperature with height gradually slows down. The results are as follows: In the sunny noon, reflectivity increasing every 0.1, the surface temperature drops of 0.6℃, and near-surface air temperature drops of 0.16℃ to 0.45℃. For this research project, the effect of reflectivity variation on air temperature at the height range of 0~1.2m is obvious, but for the higher area(more than 1.2m), the improvement is small. In general, by optimizing the reflectivity and specific heat, we can receive greater benefits in improving the urban heat island effect.