The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods. A series of numerical tests were performed, and three factors includi...The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods. A series of numerical tests were performed, and three factors including height-to-width （H/W） ratio, ambient wind speed and ground heating intensity were taken into account. Three types of street canyon with H/W ratios of 0.5, 1.0 and 2.0, respectively, were used in the simulation and seven speed values ranging from 0.0 to 3.0 m s-1 were set for the ambient wind speed. The ground heating intensity, which was defined as the difference b-ween the ground temperature and air temperature, ranged from 10 to 40 K with an increase of 10 K in the tests. The results showed that under calm conditions, ground heating could induce circulation with a wind speed of around 1.0 m s-i, which is enough to disperse pollutants in a street canyon. It was also found that an ambient wind speed threshold may exist for street canyons with a fixed H/W ratio. When ambient wind speed was lower than the threshold identified in this study, the impact of the thermal effect on the flow field was obvious, and there existed a multi-vortex flow pattern in the street canyon. When the ambient wind speed was higher than the threshold, the circulation pattern was basically determined by dynamic effects. The tests on the impact of heating intensity showed that a higher ground heating intensity could strengthen the vortical flow within the street canyon, which would help improve pollutant diffusion capability in street canyons.展开更多
Prevailing ambient wind is the main reason thatcauses inlet flow rate(air mass flow rate)decreasingand air flowing backward to the air-cooled condenserfans upward to the wind,hence a set of wind guidingnets is designe...Prevailing ambient wind is the main reason thatcauses inlet flow rate(air mass flow rate)decreasingand air flowing backward to the air-cooled condenserfans upward to the wind,hence a set of wind guidingnets is designed to improve the detrimental effect.Fig.1 shows four typical units of a 1000MW directair-cooled condenser(DACC)and a set of windguiding nets installed under its edge upward to theambient wind.As shown in Fig.2,the fan inlet flowrate decreases as the prevailing ambient wind velocityincreasing,especially for the first two units upward tothe wind.展开更多
Ambient noise is very important in the prediction system of a sonar performance, because it determines the detection ranges always in a passive sonar and usually in an active sonar. In the uncertainty issue for the so...Ambient noise is very important in the prediction system of a sonar performance, because it determines the detection ranges always in a passive sonar and usually in an active sonar. In the uncertainty issue for the so-nar performance, it is necessary to know this factor＇s statistical characteristics that are only obtained by data processing from the underwater ambient noise measurements. Broad-band ambient noise signals from 16 hydrophones were amplified and recorded for 2 min every 1 h. The results show that the ambient noise is essentially depth independent. The cross correlation of the ambient noise levels （1, 6 and 12 h average） with a wind speed is presented. It was found that the correlation is excellent on the upper frequency band and the noise levels correlate better with high wind speed than with low wind speed.展开更多
基金funded by the National Natural Science Foundation of the People's Republic of China(Grant No.40805004)the R&D foundation of Shenzhen(Basic Research ProjectGrant No. 201006020747A)
文摘The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods. A series of numerical tests were performed, and three factors including height-to-width （H/W） ratio, ambient wind speed and ground heating intensity were taken into account. Three types of street canyon with H/W ratios of 0.5, 1.0 and 2.0, respectively, were used in the simulation and seven speed values ranging from 0.0 to 3.0 m s-1 were set for the ambient wind speed. The ground heating intensity, which was defined as the difference b-ween the ground temperature and air temperature, ranged from 10 to 40 K with an increase of 10 K in the tests. The results showed that under calm conditions, ground heating could induce circulation with a wind speed of around 1.0 m s-i, which is enough to disperse pollutants in a street canyon. It was also found that an ambient wind speed threshold may exist for street canyons with a fixed H/W ratio. When ambient wind speed was lower than the threshold identified in this study, the impact of the thermal effect on the flow field was obvious, and there existed a multi-vortex flow pattern in the street canyon. When the ambient wind speed was higher than the threshold, the circulation pattern was basically determined by dynamic effects. The tests on the impact of heating intensity showed that a higher ground heating intensity could strengthen the vortical flow within the street canyon, which would help improve pollutant diffusion capability in street canyons.
文摘Prevailing ambient wind is the main reason thatcauses inlet flow rate(air mass flow rate)decreasingand air flowing backward to the air-cooled condenserfans upward to the wind,hence a set of wind guidingnets is designed to improve the detrimental effect.Fig.1 shows four typical units of a 1000MW directair-cooled condenser(DACC)and a set of windguiding nets installed under its edge upward to theambient wind.As shown in Fig.2,the fan inlet flowrate decreases as the prevailing ambient wind velocityincreasing,especially for the first two units upward tothe wind.
基金The New Century Excellent Talents in University(NCET Program)of China
文摘Ambient noise is very important in the prediction system of a sonar performance, because it determines the detection ranges always in a passive sonar and usually in an active sonar. In the uncertainty issue for the so-nar performance, it is necessary to know this factor＇s statistical characteristics that are only obtained by data processing from the underwater ambient noise measurements. Broad-band ambient noise signals from 16 hydrophones were amplified and recorded for 2 min every 1 h. The results show that the ambient noise is essentially depth independent. The cross correlation of the ambient noise levels （1, 6 and 12 h average） with a wind speed is presented. It was found that the correlation is excellent on the upper frequency band and the noise levels correlate better with high wind speed than with low wind speed.
